close

Вход

Забыли?

вход по аккаунту

?

Study of scintillation and fadings of microwave signals with respect to tropospheric irregularities

код для вставкиСкачать
STUDY OF SCINTILLATION AND FADINGS
OF MICROWAVE SIGNALS WITH
RESPECT TO TROPOSPHERIC
IRREG U LA RITIES
A THESIS SUBMITTED TO THE FACULTY OF SCIENCE
GAUHATI UNIVERSITY
FOR THE AWARD OF THE DEGREE OF
DOCTOR OF PHILOSOPHY
IN PHYSICS
DEPARTMENT OF PHYSICS
1993
ProQuest Number: 10117458
All rights reserved
INFORMATION TO ALL USERS
The quality of this reproduction is dependent upon the quality of the copy submitted.
In the unlikely event that the author did not send a complete manuscript
and there are missing pages, these will be noted. Also, if material had to be removed,
a note will indicate the deletion.
ProQuest 10117458
Published by ProQuest LLC (2016). Copyright of the Dissertation is held by the Author.
All rights reserved.
This work is protected against unauthorized copying under Title 17, United States Code
Microform Edition © ProQuest LLC.
ProQuest LLC.
789 East Eisenhower Parkway
P.O. Box 1346
Ann Arbor, MI 48106 - 1346
CERTIFICATE
This is to cerfify that
this thesis is the result of 2-esearch
work pox-fox-mod. by MR. SANJAY SHARMA
supervision.
under
my
guidance
and
This thesis, as a whole or a part thereof, is not
published or submitted to any other University for the award of
any degree. The thesis fulfils all t?ie requirements as per the
rules and regulations of Gauhati University for
the award of
Degree of DOCTOR OF PHILQSOPHY and I recommend i £.
Date .
PLACE:
27 12 93
.
,
G ,U ,
.
(MINAKSHI DEVI)
RESEARCH GUIDE
Department of Physics ,
Gauhati University ,
Guwahati 781 014- ■
ABSTRACT:
The
basic
aim
character
of
the
information
terrains
of
Assam
atmospheric
and
matter
and
environmental
The
is
microwave
recevied.in
(atmospheric)
propagation.
subject
of
work
valley
fade/scinti11ation so
system
present
is
included
signal
the
over
to
fade
selected
analyse
the
association with different
parameters
to
understand
towards
presented
in
receive
then
responses
work
to
each
in
the
six
chapter
the
microwave
chapters.
is
discussed
The
very
briefly in the following sections.
Chapter
1
:
"
Introduction
And
Scope
Of
The
Present
Investigation
Starting with a brief
microwave frequencies
troposphere
towards
introduction on the need of utilising
in communications and
propagation,
this
the role of
chapter
the
presents
a
review of
work done by different workers of the globe towards
fading
microwave
in
communication
and
propagating
media
scintillation.
The chapter also highlights
such
studies
over
in
signal
north
generation
eastern
the
of
region
fading
the
of
role
of
and
importance of
the
Indian
sub­
continent.
Chpter 2 : "Theoretical Aspects Of The Microwave Propagation
And Physics
Of
physics
radio wave
of
The
Medium
This
chapter
propagation with
properties of the propagating medium.
respect
to
the
varying
Models associated with
the scattering
of microwaves
discussed here.
The system gain parameters needed for reliable
communication
conditions
theoretical
durations
for
are
presented
models
are
specified
for
turbulent
medium
fade margin over
in
fade
discussed
in
encompasses
this
depth,
for
normal
probability ) and strong fade conditions.
CO
varied
chapter.
fade
rate
(10
are
The
also
terrain
existing
and
dB/decade
fade
of
Chapter 3 : "Experimental Arrengment And Circuit Developement"
The technical details such as radio receiving parameters and
system
informations
like
frequency,radiating
margin, antenna height etc of the four
power,fade
links operating at 6/7
GHz are presented. The path profile for each link is drawn for
K=4/3 and 2/3 conditions.
links
are
examined
for
The fresnel
different
zone clearance for the
earth
radius
factors.The
experimental arrangements to record data from the above links
at
the
microwave
receiving
sites
are
presented
chapter.lt also presents techniques of receiving
temperature, wind velocity and direction,
in
this
dry and wet
rain fall
rate from
conventional systems and from the systems developed by us. The
merits of our systems are also highlighted.
Chapter 4
Here
s
"Observation On fades In The LOS Microwave Links".
the fade character analyses are made for
the microwave
links.The basic approach for the analyses are as follows.
[1] . Fade pattern !
The fade pattern of each link is examined in relation to the
fade depth and
terms
of
rate.
fade depth
The fade
and
fade
types are
rate.After
then classified
receiving
the
in
fade
pattern information over each link, the quantative analysis of
fade depth,fade rate and fade duration are made.
[2] .FADE DEPTH :
a.
The
occurrence
probability
examined by analysing
of
fades
the diurnal
and
over
each
seasonal
link
is
variation of
fadings.
b.
Probability
distributions
of
fade
depth
over
different
links have been made and equations and slopes are found out
for
each
case.
Each
link
is
then
defined
equation and slope of the distribution curve.
in
terms
of
the
C33. FADE RATE
The following analyses are made in relation to the fade rate
for
each
link
probability
Diurnal
and
seasonal
variation.
Occurrence
and Cummulative distribution of fade rate [43.
AVERAGE FADE DURATION !
Probability distribution of average fade duration at specified
fade depth level is drawn for each link. The eqation and slope
of the fade distribution curve are also found
C5 3
COMPARATIVE
STUDY
: The
fading
out.
characterstic
microwave signal over all the links, under study,
with other stations of varied geographical
of
the
are compared
locations for the
comprehensive study of the microwave propagation characterstic
over different terrains and enveronmental situations.
Chapter 5 : "Probing Of The Troposphere Through Remote Sensors
And
Effect
Of
climatology
The
of
humidity,radio
Medium
this
On
Microwave
region
refractive
in
Fades".
terms
index,and
of
rain
fall
The
radio
temperature,
is
described
The probability occurrence of different gradient level in the
RRI, during
probability
various observational
occurrence
of
periods
effective
earth
also found out for each gradient condition.
fading
with
inversion,
atmospheric
parameters^
superrefraction,
is evaluated.
radius
The
factor
is
The correlation of
such
as
temperature
and subrefraction condition
is
found out. A few case studies have been conducted associating
sodar
returns
with
fadings
over
the
Milmilia
path.
The
microwave fadings are associated with hot and cold fronts,
elevated layers as observed from sodar echograms.
This chapter also inclueds the spectrum analysis of the fading
events
over
the
three
links
and
the
structure
parameter is evaluated over Milmilia link path.
any
constant
Chapter
following
6
:*Results, Discussions
aspect
have
been
And
described
Conclusions
in
detail
The
in
this
chapter.
1. Fading variation of each link in terms of terrain features
&
atmospheric
variabilities.
medium associating
The
relevant
physics
of
the
fadings has been discussed.
2. Reliability of each link is defined in terms of link cutoff
and based on that result, favourable communication periods are
def ined.
3. Suggestions are put forward for the improvement of LaopaniHabaipur link.
C l v J>
PREFACE :
The radio communication through the near earth environment is
dependent on various factors that govern the system dynamics.
This is more so in the case of microwave line of sight
(LOS)
links.
The transmission and reception of microwave signal
such
links
are
characteristics
always
and
associated
with
meteorological
the
parameters
in
terrain
such
as
temperature, water vapour contents, pressure and wind profile.
These factors play a significant role because the RR1
propagating
medium
is
largely affected
by
these
which are prone to undergo severe variations
of the
parameters,
from region
to
region.
The
microwave
LOS
links
maintenance of vital
But
there
has
propagation
been
have
communication
little
and
terrains
in
in
big
links
systematic
characteristics
variabilities
come
study
The
to
For this purpose,
on
the
region.
microwave
meteorological
basic
present work is to study these aspects over the
the North Eastern Region.
for
in the N.E.
relation
features.
way
aim
of
the
LOS 1inks of
we have selected
four microwave links of P8»T and Railways, operating in the 6
- 7 GHz range.
The selection of the links are made in such a
way as to represent the different terrain features of the
north eastern region. The experimental data generation is
organised by
(1) . Making fade records of these links.
(2) . Taking
wind
records
velocity
of
etc,
temperature, humidity, pressure
along
with
radisonde data are collected
a tower
from the
measurment.
and
The
India Meteorological
Department.
(3) . Remote sensing of the atmosphere through sodar at Gauhati
University
and
Mirza.
Mi 1mi 1ia-Durgasarovar
Both
link.
the
All
the data
round the clock basis for three years.
< Tu J>
stations
lie
on
are collected
the
on
The
analyses
of
the
data
have
thrown
the
following
largely
affected
information on microwave propagation:
Cl]
The
atmospheric
Laopani-Habaipur
situation
link
when
because the first fresnel
has
K =2/3
zone
situation
over
is
the
generated
the Laopani-Habaipur
is
obstructed at the midpoint of the path during this situation
of
the
atmosphere,
resulting
frequent
short
lived
link
cutoffs.
[2]. Multipath type of fading
night
hours
with
the
is generated basically during
preferential
time
of
post midnight to early morning hours from
development
from
layered structures
of atmosphere.
C3], Scintillation Type of fading, with shallow fades usually
develops after a couple of hours of local sunrise due to the
turbulent
conditions
of
the
atmosphere
(specially
when
convection is poor).
[4]. Multipath occurrence factor for each link is found out.
This shows that Laopani-Habaipur link has large occurrence of
this type of fading.
[53. Large occurrence of scintillation type of fading
summer prenoon time
during
is attributed to the incoherent mode of
scattering from bubble like structures of atmosphere
(when PBL
breaks up ).
[63. The links over Kamrup district of Assam valley follow the
characteristic of low latitude costal
regions stations,
Laopani-Habaipur
characteristic
link
follows
the
of
while
low
latitude interior region indicating landlock staions may bear
costal region features depending on terrain situation.
< Tu O
Based
on
the above
results
we
have
made
the
following
modelling and predictions.
Cl] The fade duration characterstic will
of
fading
mechanism.
It
is
possible
tell
to
about the mode
predict
the
fade
mechanism through fade duration analysis.
C2]
It is possible
to predict
the
fade character
(shallow,
deep and scintillation type) through examination of PBL height
and microstructures inside the PBL received through SODAR (two
sodars in a path is sufficient for our analysis)
The
thesis
aspects.
presents
a
comprehensive
report
Some of the results presented here,
on
the
above
have also been
published in the journal etc.
The outcome of this work is the development of some systems and
instruments which can be used as import substitutes.
I believe that this study has generated a very valuable pool of
data as well as wealth of information so that it will provide
a guideline for system engineers and scientists associated with
microwave communications for future link set up.
C x)t.
iLy
ACKNOWLEDGEMENTS
I would
like
to
express
Minakshi
Devi
for
her
to
overcome
many
my
profound
gratitude
me
to
my
extreme
guidance,
hurdles
affection,
during
to
fascinating
constant
care
a nd
encouragement.
1
to
Frof.P.Dutta
J c i s , Prof.
also
from
J.Das
c a r r v out
Physic.-,
p.
"T
!
this
t:
r t r e ng
3 01
r.j s'. HO ... r c j
1
—
,,
1’* '• *L.. 3
\ d1 ■ ^
: . - o pe
: a.
enabled
study.
who
to
has
Dr.
Dr.
me
I extend
introduced
for
his
S . C .M a z u m d a r ,
Govind,
Prof.
the i r
many
Sankar
valuable
discussions.
financial
'lie
'
, n s .o ->
fn.a In Ien.--i.o- 1
*•
and
irdhury,
support
received
Government
of
Head
department
for
ui, 1■;ei s
he i i
fo
-I r..' e
u p p c ; 1 l.ng
W1. £ 1i
the
Electronics,
to Prof. P .K .'
».o i!: w i '.h
>.
of
for
sr.d f r u i t f u l
which
guide
electronics,
Dr.
Rao
my
India,
to
work.
Gauhat i
Uo ' u r e
G.Gwarup,
acknowledge
of
of
thanks
D: . N’a r a y a n
Department
Mi oi cwa ve
i,-r
Dr.
encouragement
1 an grateful
1 fif . a n
and
gratefully
the
sincere
Macumadar,
s u g g e s lions,
:
m>
course
world
to
care
A .K .B a r b a r a ,
very
express
the
Prof.
the
wish,
gratitude
:nI ;
r .*»
+■
•
]
of
the
providing
. ......r k ^ . I am a l s o
1n...a r t m e a t ,
.;
'ink
n
to
for
collect
• t I r.g In c a l i b r a t i n g
'1 >.
necessary
than k f u l
Guwahati
director,
‘ ... the
allowing
the
the
IMD,
of
fie'd
recording
Guwahati,
fo.
•J 3 . 3 .
tl Cflk
* i. »
dp
e r. c o u r a o
■ ; ■;
-Ad
dI 3 c u s s i c e s
’ ’ jjije
I
Mr .K. I. T i m o t h y
rendered
: .„
thankful
. ..•nd e . ed
j
and
by
f.lends
-1i.r i
Mohan
.. m e i ts
for
to
for
1h e
cons tn;;t 1 ; j
Mr.
Deepkama',
them.
Sarat,
and
Drons,
Basant
throughout
this
for
Muhin,
‘•he I >
period.
ie thanks
to my pa/
brother in ;aw Fiat:
er»t which
inspire
m
CONTENTS -
ay
Ab s t r a c t
Pr e fa c e
<Tu.>
Cviip
Ac k n o w le d g e m e n t
CHAPTER 1
INTRODUCTION AND
SCOPE OF
PRESENT INVESTIGATION
l. 1
General
l. 2
LOS Links
1. 3
Effects Of The Propagati,ng Medium On
l. 4
Introduction
cty
C3>
Microwave Medium
C41>
T roposphere
C4J
1 . 5. Radio Refractive index
C5y
1. 6
cey
Effective Earth’s Radius; factor
1 . 7. Free Space Loss (FSL)
csy
l. 8. Fresnel Zone
C9y
1 . 9. Microwave Fadings
CQy
1 . 10. Microwave Propagation ! A review
a iy
i. 11. Scope Of The Study
a ay
CHAPTER 2
THEORTICAL A SPEC T OF MICROWAVE PROPAGATION AND
PHYSICS O f THE MEDIUM
Ci4>
2.1.
Introduction
2.2. Tropospheric Propagation Model(Two Ray Optics Theory ) C i 4 >
2.3. Radio Climeteology
Ct7y
2.4. Bending Of The Radio Wave
Ct92
2.5. Multipath Fadings
C22>
2.6. Generalised Theory Of Scattering OfRadio Wave
C24y
2.7. System Gain And The Reliability
C2Qy
2.8. Amplitude Distribution
C3t y
. 2.9.
Number Of Fades And Average FadeDuration
2. 10. Concl usion
C322
C33J*
CHAPTER 3
3.1.
EXPERIMENTAL ARRANGMENTS AND CIRCUIT DEVELOPEMENT
Introduction
3.2. Terrain Features And Fresnel ZoneClearance
C345
C342
1. Mi1mi 1ia-Durgaarovar Link
C355
2. Maopet-Durgasarovar Link
C35j>
3. Motapahar-Durgasarovar Link
4. Laopani-Habaipur Link
3.3. Microwave Link Information
C'36->
C4G2>
3.4. Fade Measurment And Calibration of The Fade Recording
System
C475
3.5. Measurment Of Associated Weather Parameter
C&22
3.6. System / Circuits Developed Under ThisScheme
C53J
1. Sound Detection And Ranging (SODAR)
<535
2. Facsimile Recorder
C595
3. Fast Response Dry And Wet Temperature sensing
System
4. Telemetric Anemometer
<T<36J>
5. Fast Response Rain Gauge
c'73J>
3.7. Conclusion
CHAPTER 4-
4.1.
C775
OBSERVATION ON FA D ES IN THE LO S MICROWAVE LINKS
Introduction
4.2. Types Of Fading
4.3. Fade Depth Distribution And Multipath Occurrence
Factor
1. Mi 1mi 1ia-Durgasarovar Link
C7SO
C&OJ
C8 2 >
C825
a. Probability Of Fade Distribution
b. Diurnal And Seasonal Variation of Fade
Occurrence
2. Maopet-Durgasarovar Link
<335
C83^
a. Probability Of Fade Distribution
<833
b. Diurnal And Seasonal Variation Of Fade
Occurrence
<873
3. Laopan i-Haba ipur Link
<873
a. Probability Of Fade Distribution
<873
b. Diurnal And Seasonal Variation Of Fade
Occurrence
<873
4.4. Fade Rate Characterstic
<923
1. Maopet-Durgasarovar Link
c'925
2. Mi 1mi 1ia-Durgasaovar Link
<933
3. Laopani-Habaipur Link
<933
4.5. Fade Duration
<1033
4.6. Comparetive Study Of Microwave Fades Observation With
Other Stations
<1083
1. Fade Depth
<1083
2. Fade Rate
<1193
4.7. Conclusion
C H A P T E R -5
<1223
PROBING O F T H E TR O POSPH ER E THROUGH REM OTE SENSO RS AND
E F F E C T OF THIS MEDIUM ON MICROWAVE F A D E S
5.1.
Introduction
5.2. Radioc1imateo1ogy Over The Link Path
<1253
{1263
1. Surface Temperature
{1263
2. Temperature Inversion
<1283
3. Water Vapour Content
<1283
4. Radio Refractive Index At Surface it At 950 mb
Pressure Level
<1303
5. Radio Refractive Index Gradient
<1353
6. Effective Earth Radius Factor
<1353
C133J
5.3. Sodar Observation And Microwave Propagation
5.4. Microwave Fadings And Atmospheric Conditions
As Received
ByThe Sodar
(1 3 9 5
5.5. Case Study
(1 4 7 5
5.6. Spectral Analysis And Determination of Structure
2
Parameter Cn C1555
2
5.7. Method of Receiving the Structure Parameter Cn
2
5.8. Observation Of Cn
Parameter At Different
AtmosphericConditions OverLink Path.
5.9.
Conclusion
CHAPTER-6
C1575
RESULTS. DISCUSSIONS
C1595
C l 642
AND CONCLUSIONS
6.1. Selection Of The Links
C16G5
6.2. Path profile And Fresnel ZoneClearance
C1665
6.3. System Development
(1 6 7 5
6.4. Fade Characteristics Of Microwave Signal
C1G75
1. Fade Distribution
C IS 75
2. Diurnal And Seasonal Variation of Fades Over
The Link And Comparetive Study
C1685
3. Fade Rate
C1695
4
C1695
Fade Duration
6.5. Fades And Atmospheric Conditions
C1705
6.6. Structure Constant Parameter
C1715
6.7. Future Scope of Study
C1715
6.8. Suggestion
C l 725
References -
C1735
CHAPTER 1.
INTRODUCTION AND
SCOPE OF PRESENT INVESTIGATION
1 1.13 GENERAL INTRODUCTION
The theoretical foundation for the
was
laid by James Clarck
radio
Maxwell
in
communication could be possible only
first
transmitted
Newfoundland.
a
wireless
1854.
in
But
practically
when
from
Marconi
mainland
The earlier communication systems were of
transmission of
voice
by
by
means
on
in 1904 when the vacuum tube
oscillators were
invented.
Communications by radio waves
is
made
bands for use in different purposes.
frequency band designation
off
of
carried out only
typical
communication
1897,
message
gap type where the message was sent
actual
wave
But
wave
was
amplifiers
and
at various
Table 1.1
that are in common
spark
pulses.
radio
to
frequency
summarises
use along
the
with
services provided.
Table -1.1
Frequency Band
Designation
Typical
3-30 kHz
Very
Navigation,
30-300kHz
Low frequency
Radio Beacons
300-3000 kHz
Medium frequency
AM brodcasting.
low frequency
Service
Sonar
Direction Finding
3-30 MHz
High f requency
Telephone,
Telegraph.
&
Facs im i1e
30-300 MHz
Very high frequency
Television,
FM brodcast
Air Traffic Control
300-3000 MHz
Ultrahigh frequency
Television,
Satellite
Commu., Radiosonde
3-30 GHz
Superhigh frequency
(M ic row av e)
Microwave
links,
R a da r , Sa tel 1i t e
1
Communication.
30-300 GHz
Extreme high Freq.
Any specific communication
with
a
particular
Radar,
channel
frequency
is
range
typically
called
process of modulation
in which amplitude,
of the carrier signal
is varied
to be transmitted,
etc.
bandwidth.
frequency
in accordance with
requires a specific bandwidth.
of the human voice require a bandwidth of 4 KHz
fidelity
music
demands
at
associated
least
15
transmission of colour picture requires
or
Transmission
whereas
high
Television
MHz
bandwidth.
This requirment has put a limitation on the number
of channels
that can be transmitted over
a
7
phase
information
KHz.
a
The
specified
carrier
frequency
domai n.
To overcome this problem,
techniques
which transmission of more
carrier have
multiplexing
been
than
developed.
techniques
one
There
like
signal
are
like frequency
(FDM) and
time
division
individual
voice signals which are
over
a
various
division
multiplexing
have their own frequency content
multiplexing.
(TDM)
shifted
single
types
of
multiplexing
etc.
overlaping
in
In
FDM.
in
frequency,
through
sinusoidal
amplitude modulation so that spectra of modulated
signals
longer
transmitted
overlap
and
these
signals
can
be
simultaneously over a single wide band channel.
FDM provides
channel
sharing
of
or sub channels,
the
frequency
whereas
in TDM,
channels are assigned a specified
amplitude modulation
and C o o l
Because of
l
n
l 9 yy/
by
the
In other words
the
individual
individual
time slot by means of
(f&-xjkL0S 1931 ,
no
a n d Wi 11 s h y
sub
pulse
19 9 7 .
.
large channel
now become very popular
capacity,
and
satellite - ground and ground
is
microwave communication has
very
widely
- ground LOS
o
used
links.
both
in
These systems
provide the needed transmission bandwidth and
allow
reliability
to
transmission of many thousands of telephone channels as
well as several TV channels over the same route and using
same facilities. The transmitted power
for
these
the
system
very low (less than one watt) because highly directional
is
high
gain antenna are used.
[ 1.23 LOS LINKS :
There are two types of Line of sight (LOS) links
1. Terrestrial LOS Link.
2. Satel1ite LOS Link.
Terrestrial
radio
relay
systems,
employing
many
stations and operating at frequencies above 1 GHz
repeater
were
first
introduced in 1947 by the BELL SYSTEM in the United States.
was a 240
channel
telephone
system
between
New
York
It
and
Boston. Subsequently one video channel for television was also
provided. By 1962 most of the city
distance
telephone
circuits
video
in
the
circuits
and
were
carried
USA
microwave frequencies. Such radio relay systems
are
long
on
commoniy
known as microwave links.
In India, the first microwave link was set up in 1966
Calcutta and Asansol.
between
In the first phase of microwave links in
the north eastern region,
there were both wide band and narrow
band systems. A wide band system linked Calcutta
and
while a narrow band system connected Asansol, Kathihar,
Asansol
Tiger
hill, Cooch Behar, Shillong, Jorhat, Dibrugarh and T insukis.
But for the intercontinental
the
terrestrial
or
microwave
transoceanic
links
are
economic point of view as these links
stations to overcome
terrains
people
now
need
feasible
many
from
repeater
earth's curvature. Over the inaccessible
it is difficult
are
not
communications
shifting
to
install
towards
3
microwave
satellite
links.
so
communication
systems.
The
success of
microwave
transmissions
encouraged
engineers to use satellite as a space communication
Nevertheless,
very well
1 1.3]
the ground
to ground microwave
within the continental
EFFECTS
OF
COMMUNICATION :
In the satellite
THE
to
MEDIUM
communication
signals have to pass through the upper
media while
travel
in ground to ground LOS
(Ionosphere),
below 40 MHz
is
is well
transparent
qualities
frequencies
control
at
VHF
irregularities
towards
and
in
situations
current systems are proved
suffer
through
small
magnitude of
comparison
scale
Ksllsy
with
role
and
or
and
(scintillation)
But
the
in various
electric
Even
while
GHz
passing
But
suffered
the
by
is much
the
low
in tropospheric and near
A brief description
of
the
troposphere
i O / / k Ws7 s-i-s l' a £ . a L . 1Qiycz , a s r a &£ . aL
along
i
t
Bas
the mechanism of mode of
medium
towards
microwave
4
affected
by
features c W K s s l s r M. S.
in this medium and also to realise
the
a nd
is therefore presented below.
tropospheric variabilities and terrain
To understand
in
earth
(Aax-oris 1 9 S 7 , Fz-ank arid L i u l 9 8 4 , S u n a n d a Ba.su
its variabilities
response of
has
reception
irregularities.
in the ionospheric medium
to that experienced
1Q777.
radio waves
and
different
attenuation
upper
signals
that
[1 .4 ] TROPOSPHERE :
Microwave propagation characterstics are largely
stc.7.
of
to
the ionosphere
than
by
has
of
frequencies.
ionospheric
fluctuations
environments
The
to be a nuisance at VHF.
fluctuations
microwave signals
atmospheric
signal
transmission
microwave
microwave
the ionospheric medium generated
geomagnetic
signals
lower
situation,
higher
MICROWAVE
links.
communication
In ideal
zones.
ON
links the
towards
known.
to
practically no
solar,
to
only through the lower atmosphere.
atmosphere
links have served
and sub continental
PROPAGATING
ground
platform.
2y uu
s £. a L .
propagation
the
of
dynamical
signal,
it
is
necessary
these
to
have
aspects.
the state of
Troposphere
This
indepth
theoretical
section attempts
is the region of
earth
up
to
the
a
height
In the
content
conditions and
which
sharply
decreses
is
which
8-10
km
from
at
of
remaining
polar
the
dependent
with
This
a
The
water
is
average
known
is
as
cai led
uniform
above which the temperature
gas
weather
troposphere
is characterised by
is
on
height.
6^c/km.
km
practically
The only exception
The upper boundary of the
temperature zone,
[ 1.5]
review of
extending
percentage
strongly
temperature gradient
the tropopause,
height
is
of
height,
the same as it is on the surface.
lapse rate.
a
in
latitudes and up to 16
troposphere,
components does not vary with
vertical
to give
atmosphere
10 to 12 Km at moderate
at the equator.
vapour
background
art of this subject.
surface of
lattitudes,
an
minimum
increases
with
for some altitude.
RADIO REFRACTIVE INDEX :
Key characterstic parameters of the troposphere
are
temperature,
an
and humidity.
The RRI N
which
parameter to describe the troposphere
N = (n — 1 )* 10 N units
....
The derivation of this equation
radio frequencies
....
given
the radio refractive
in
index
C'simth €rt al 1953 and Bean and duttan 1953
N = (77.7P/T)
(1.1)
chapter
T = Absolute temperature
e = Water vapour pressure
in m bar
in °K
in m bar
5
2.
At
(R R I ) is given by
)
+ (3.73*105 e)/T2 ....................
Where P = Atmospheric pressure
important
is given by .
....
is
is
pressure,
(1.2)
The first term of equation
(1.2)
is referred as dry
and second term as the wet component.
point
in
The
refractivity
at
a
space thus varies primarily because of variations
in
temperature and water vapour concentration.
the R R 1 may occur
The vertical
in short term as a
The
variation
turbulent
in
fluctuations.
variation of refractivity for an average standard
atmosphere can be described by its exponential
height
component
decrease
with
G O ^ —l 3 .
I C C IP. P v p o r - t
[ 1.61 EFFECTIVE EARTH RADIUS FACTOR :
In 1933 Burrows,
method,
to
Shelling
and
Ferrel
introduced a simple
where radius of curvature of the radio ray r,
the radius of earth r,. may be expressed
relative
in terms of
refractivity gradient as
r/r0 = K = Cl + SdN / dH )/ 157 ]~ 1 .......................(1.3)
Where K is normally referred as
factor and dN/dH
(1.1a)
shows
equation
factor
variation
This
in K
indicates
Km.
for
dN/dH
effective
earth radius
K takes -ve values for
further
increase
conditions.
radius
This
factor
to
in
a
-200
can be seen
that
when
effective
varies
from
-ve
to
+ve
obstruct
the
in
terrain
shows
it may
units-
of dN/dH beyond
particular
in some situations or extend the radio
super
N
clearly
different dN/dH conditions,
other situations.
200
The effects of this variation
iQ81j>
from
It is also seen that K becomes
-157
C'£t~ph&ns&n,
Fig.
dN/dH as given by the
between
fig. (1.2)
and
that
radius
in N unit /km.
varying
-200 N units/Km,
path
with
earth
increases exponentially when dN/dH decreases
Nunit /Km to -157 N units / Km.
large
effective
is refractivity gradient
the
(1.3).
the
earth
values
at
propagation
horizon
in
some
These conditions are known as sub refraction
refraction
refractivity gradient
respectively.
near
the
earth
unit/Kra.
6
The
mean
surface
value
is
of
-40
N
dN/dH
(
* -
N Unit / Km
Effective Earth Radius Factor )
F iq.C1.1a ) E f f e c t iv e Ea r t h Ra d iu s F a c t o r A s A F u n c t io n
of
F iq C1.1 b ): Ben d in g O f Ra d io Ra v s F o r C o n s t a n t L in e a r Re f r c t iv it v
G r a d ie n t C F rom S t e p h e n s e n 1980
7
corresponding
to a K value of 4/3
For dN/dH
-40
>
units/km
subrefracted corresponding
unit/km,
the ray
(B&a.ri
the
arid.
ray
dutton l9£>8 J
is
to 0<K < 4/3.
said
If
to
dN/dH
be
<
-40
N
is said to be super refracted corresponding
K >4/3 or K < 0. For negative K
values,
ray
paths
are
to
bent
sufficiently downward so that trapping or ducting
is possible.
At the critical
the rays are
parallel
value of dN/dH
= -157 N units/km
to the earth surface.
Information on radio refractivity and refractivity
averaged over 50 or 100 meters of the atmosphere
world wide as well
as
IQ & O ,
I
i977, Vanh.atsw cti'Ti e£ ctl
These
meteorological
observations by radiosonde.
data
originated
limitations with respect to
meteorology.
For example,
only twice a day and they
small
scale structures.
the
from
available
data
are
lack the
However,
many
These
large body of the historical
towards
possibility
of
such
-j.1
years
data
normally
despite
Betz r-i rig t oyi
Bctr-h.ctz'-
application
corrections can often be estimated from
the
a rid
1 Q 7 £,
1978,
some
as
in more detailed form for specific areas
(C C IR 1 9 7 8 i' a £>C)r t Bo B —i , BrzctYi e*t a l
1Q 7 7 , Dt1s7ip a n d a
is
gradient
of
carryradio
collected
revealing
disadvantages
additional
data are still
data,
so
applicable.
C1.73 FREE SPACE LOSS :
Communication
systems
operating
at
microwave
follow the principle of free space propagaton.
lost in space primarily because of
wave front as it travels
the inverse square
law.
through
frequencies
The radio energy
spreading of energy
space
The free space
in
accordance
loss
primarily
upon the carrier freqency and the distance between
and
receiver.
The
free space
loss
in
(FSL)
is
with
depends
transmitter
given by the
following expression.
FSL
(In dB)
= 32.44 + 20
log d +
20
Where d is in km f is in MHz
8
log
f
the
.... C 1.4i>
is
[1.83 FRESNEL ZONE :
The free space propagation occurs between two antenna situated
well away from the surface of
absorbing
objects.
The
described in terms of
earth and other
amount
fresnel
of
reflecting
clearance
is
Fresnel
zone
zone.
or
generally
forms
a
series of concentric circles around the direct path. The first
fresnel zone is defined as
the surface of
the
ellipsoid
of
revolution, with the transmitting and receiving antenna at the
focal points, at which a reflected wave has an indirect
half a wave length longer than the direct path.
of the zones are
wave
length
The
path,
position
dependent. The cross-section
through the fresnel ellipsoid orthogonal to the
propagation is the first fresnel zone.
direction
of
It is calculated by the
following expression.
H = 17.3{d4dz/f(dA+ d2))1/2
.....................(1.5)
Where f is the frequency in
GHz dt d2 are distances
from transmitter and receiver
to
a
particular
in
kms.
point
where
fresnel zone radius is to be evaluated.Measurments have
shown
that, to achieve the free space loss,
should be clear from
the
transmission
obstruction by a distance
0.6 times the first fresnel zone. Generally,
of
at
path
least
the full clearance
of first fresnel zone is preferable during normal
atmospheric
conditions.
[ 1.9] MICROWAVE FADINGS :
Fadings of microwave signals
are caused basically by the
following factors and theoretical aspects of these factors
are
described in chapter 2.
1 Absorption,
that causes a direct attenuation of the signal.
2 Refraction, a
abnormal
process
when
bending
of
waves
caused
by
changes in mean value of the dielectric constant of
the medium.
3 Random Scattering,
where
due
to
9
random
fluctuations
in
dielectric constant of the medium,
phase,
angle of
arrival
Fadings generated
varitions
and polarization of
due to the above mentioned
classified in the following categories
Ca!)
Ground
Reflection
C Constant
refractivity gradient of
constant component
component is
in amplitude,
the
waves
occur.
causes
can
be
:
Component) : As
medium
varies,
the
phase
of
the
also varies and when phase of the constant
opposite
to
the
direct
wave,
it
generates
fadings. This type of fading may last for several hours.
CB!) Ground Ref lection CVariable
Component!) :The
scattered field from the ground or from low
diffusively
level atmospheric
irregularities interfering with the direct field causes
rapid
fluctuation.
When
the scattered
components
very
interfere
with the direct wave we may have a very deep fading.
CO
Reflection From Inversion Layer
caused due to
i This type of
fading
is
changes in atmospheric refraction or changes
inversion layer height.
in
Inversion layers are fairly stable and
last for several hours specially during night time.
CD!) Atmospheric Refraction : The direct
wave
refracted by an inversion layer located
at
height
between
transmitter
and
may
the
receiver.
be
total 1v
intermediate
This
occurs
frequently over watery paths. These are selective in space
but
not in frequency and fadings due to this cause last for several
hours.
CE!> Turbulent Layer Scattering : Received field in this cases
fluctuates rapidly but fluctuations have small amplitudes. This
feature is usually observed over long paths.
CF!)
Diffraction
By
Earth
:
refraction the line of sight may
With
abnormal
atmospheric
be
temporarily
interrupted
10
and diffraction fading
effective for
long
will
set
above
This
link path with small
CG9 Absorption By Precipiation,
frequency
in.
11GHz
are
is
particularly
clearance.
Oxygen And Water
generally
Vapour
affected
:
by
The
these
parameters.
[1.101 MICROWAVE PROPAGATION
In the global
scenerio
started since
installed.
1948,
A model
was of particular
anomalous
systems.
research work on microwave
when
microwave
links
were
first
behaviour
importance for an evalution of the effect of
A general
condition
on
analysis of the
and theoretical
in details.
the
propagtion
for an estimation of statistical
propagation
of fading
: A REVIEW
Statistical
works
radio
of
communication
distribution
is given by
S..H.
distribution of signal
function
Lin Cl 9713
received
under
multipath propagation have been studied from numerous experiments
&g.
CCIR C 19789R&poi-t 3 3 8 ~ 3 , Raylcn-- C 1953,3,
C 19703,
Bui l ington Cl 9709,
C 19719,
Rumml&r-C i 9739 , R u m Lert 19323 etc.
Vi gnats- C19703 , Lin C 1 9 7 1 3 , R.uthroff
The effect of atmospheric conditions
also
extensively
studied
were carried out by many
1985,
F t-i is 1948,
Rise C 195 7,7 Cf'i&n
all
on
over
microwave
the
workers eg.
Craw fox-el
1953,
world.
signal
Experiments
Dur-fcee 1 948,
fie L l
1967,
Pearson
Bax-net
1970.
ichiaucjAe 1983 Sc h tauone 1983, IveOs ier 1983, Gossax-dL 1934,
1989.
The
effect
of
meteorological
parameters
vapour pressure on microwave prpagation
is
by
comparing
different
distribution of microwave
fading. The
report on
boundary
control of
Schiauone,
1983
layers and
while
the
AEL on microwave propagation
is well
1 9 4 8 » Toe 19890
11
well
is
like
See
water
demonstrated
world
wide
effect
of
diurnal evoluation
of
received
(Gilnuan et al
In India, work on radio meteorology started
the measurment of radio refractivity
1 966-67,
C h a tts rjs s
S i-iv a s ta v a
Refractivity profiles as well
profile
1968,
as
in
1966-67
with
(K u l s h s r s t h a
V s n k s t s h 'w a r a n
refractivity
&
19789
gradient
and
water vapour content were mapped by various NPL group ( S a r k .a r
st.al
1988,
Ma.jxmid.ax-
st.al
by
19779
taking
16
radiosonde
stations over the Indian sub continent. Microwave
propagation
with
atmospheric
respect
to
radio
meteorology
boundary layer have been taken up
1937,
Gse-a & iz-arh-ar- 1 9 8 0 ,
Bets s t
al
1989,
Metjwiudcup
Bvtta
and
by
with
several
s t al
1934,
e£, e t l . 1 9 7 4 ,
Report on rain attenuation measurment
groups
o. I
iySi
s t. ctl.
19759-
Rac>
st
Metjxuftvdetx-
over
( R sd d y
different
Indian
stations have also been received {R e tin a 1 9 8 4 , S s n s t a l . 1 9 8 5 .
Tiwetx-i
st
al
Studies
1 98 6 9 .
on
been carried out over inland
and
subcontinent C S ix th v m a r s t a l
199 0
st
al
Milimeter
waves
costal
regions
,
have
of
also
Indian
Sar-ketr s t . a l . 1 9 9 0
, M ai tr-a
19939.
Even with all these studies and analyses there are good scopes
for understanding
fadings
as
the
media
are
dependent
which
are
highly
out
the
temporal
point
microwave
of
fadings
variabilities
may here
physics
signals
seen
towards
on
the
localised
microwave
atmospheric
nature.
We
differences in fading
of
through
in
experiments
conducted
simultaneously and at the same frequency range. C B a r n s t t
The present study
of
microwave
propagation,
in
the
1 97 0 9 .
north
eastern regions of the India is the first of its kind.
11.11] SCOPE OF THE STUDY :
The
topography
different
of
the
North
Eastern
from the rest of the country.
region
This
of
area
India
is
therefore
stands as a good candidate for studying the aspects of microwave
propagation
at
different
terrains
and
situations. The localised nature of atmospheric
12
environmental
variabilities
along
with
towards
selected
different
flora
may
contribute
microwave propagation. The
that they
cover
significantly
microwave
1inks
are
different terrain conditions.
so
The
links so selected are as follows.
1.
r->
^.
Milmiiia - Durgasarovar links
6 GHz (Marshy)
Maopet -Durgasarovar links
6GH z (Hilly)
3. Motapahar - Durgasarovar link
6GH z (Bui 1t up area)
4,
7GHz (Plain)
Laopani - Haba ipur links
The fade character information
collected
over
these
links
will be utilised for the present study.
To receive atmospheric irregularities
any, which may affect the
and layer structures,
microwave signals,
two
SODAR
are placed along the Milmiiia Durgasarovar link. One
units
unit
installed at Mirza 17 km south west of Guwahati and the
it
is
other
unit at the Gauhati university campus.
Further,
to
examine
meteorological
the
parameters
response electronic
effects
on
of
microwave
thermohygrograph,
and fast response rain gauge are
the
associated
propagation
telematric
fast
anemometer
developed and placed at
the
field stations.
This study will also help to understand the
complex
dynamics
of the lower atmosphere which has immense
importance
meteorological study and
weather
Further,
it
installation
will
of
prediction
create
the
a
data
microwave
of
base
links,
for
as
in
phenomena.
the
future
microwave
communication is coming in a big way in the N.E. region.
#
13
the
CHAPTER 2 - TH EOR ETICAL A S P E C TS
O F MICROWAVE
PROPAGATION
AND PHYSICS OF TH E MEDIUM
t2.1l INTRODUCTION :
Microwave propagation
tropospheric
et.al.
characters
variabilities
and
i952> Clifford et.al i970
are
largely
terrain
affected
features
by
(Crawford,
Boithias i979, Inoum*
et.al.
i97£f, Dougherty and Hartt97) . To understand the mechanisms
of
mode of propagation of radio waves in this medium and also
to
realise the dynamical response of the system towards microwave
signal,
it
is
necessary
to
have
an
indepth
theoretical
background in these aspects. This chapter attempts
to
give
a
theoretical review of the state of art of this subject.
[2.21 TROPOSPHERIC PROPAGATION MODEL CTWO RAYS O P TIC -TH EO R Y ):
The troposphere is the region of the earth’s atmosphere
immediatly adjacent
upward
for
to
the
earth’s
some tens of Kilometer.
space conditions are modified by
surface
In
and
extending
troposphere, the
free
two factors.
1. Surface of the earth
2. Atmospheric medium
A simplified propagation model can be conceived by considering
a flat earth surface and that the space wave that reaches
recevier has two components, the direct wave
reflected wave as shown in the
fig.(2.la).
and
The
the
ground
direct
follows the ray path Sd and the ground reflected wave
the
wave
follows
the ray path St. The reflected wave travels a greater distance
than the direct wave and introduces a phase difference.
be the path difference,
then the phase angle corresponding to
AS is given by.
4>a = 2n/X. * AS
If AS
...................
14
(2.1)
F ig.C2.1a ) : A Model Dia g r a m F or T r o po sph er ic Pr o p a g a t io n
Ra v P a t h
F ig .(2.1b ) : T he F ield S tr en g th Ph a s o r Dia g r a m A t T he Receiver
15
VS is expressed
in
terms
of
transmitting
/receiving
antenna
heights as
AS
-
2ht h r7 d
...
....
....
(2.2)
Where ht is the height of the transmiting antenna
.
hr is the height of the receving antenna.
d
is
distance
the
between
transmitter
the
and
the
receiver.
Therefore,
distance
the
phase
terms
antenna
of
height
a nd
not
.......................(2.3)
This
is
this
process.
nature
in
is given by.
Pa = 4rchthj,/ d
affects
angle,
the
the
only
The
phase
reflection
amplitude
of
and
reflection
constitution
of
change
the
that
at
phase
of
depends
reflecting
the
in
might
earth’s
the
a
take
surface
reflected
complicated
surface,
place
angle
also
wave.
way
of
in
The
on
the
incidence
and on the polarisation of the wave.
Let
be
the electric
represented
reflected
field coefficient at the
by
wave.
r =
receiving point will
of the direct wave.
to the direct
strength
at
the
a
wide
reflection
i
point
of
coefficient
the equation
(2.4)
,2
is
is
for
in
wave
at
relative
the
field
fig. (2. lb).
T.ne
{p-p-)l, The cosine rule
is
field strength ER .
,
,
terrain
t
shown
the
the amplitude
the reflected wave
1 + It | + 2 |r j cos
range
reflection
reflected
|r| Ed> where Ed is
to receive resultant
/
the
(p -'Pa'1' Phaser diagram
is
receiving
/
For
then be
of
& is equal to [150^-
phase angle
applied
amplitude
The phase of
wave
of
p, where p is the phase of
It !
The
point
!p
-
p.-)
conditions
equal
to
reduces to.
16
-1.
.... i2.4)
it
For
is
this
found
that
condition
After expanding this equation and putting
equation
(2.3),
the value of
we get
E h = <2E0 / d!* Sin(2rr hT hR /X d)....
The approximate form of equation
....
(2.5)
(2.5)
is.
2
ER " E q
This
<4n h T h R
equation
from
/
(2 . 6 )
>
shows
the
importance
of
antenna
height
towards
resultant field strengths at the receiving ends.
[ 23] RADIO CLIMATOLOGY :
The
radio
refractive
parameters
for
propagation
Dutton,
The
the horizontally
conditions,
But
the
curvature
some sort
under
unusual
out of
to this,
of
antenna
For derivation of
an
impressed
both
The
nonpolar
polarisation
influence
of
high
of
atmosphere
causes
a downward
nearly
1/4
meteorological
of
ana
curvature
or
atmospheric
the
earth's
conditions,
radio
layers near the earth’s surface.
a part of
field
upon
is always
radio energy
the
molecules
the
frequency
embeded
with
is scattered
is
polar
c <" T j
or
constant
of
field
molucules
is
1 + i10T /
17
effect
to be considered
fluid
radio
on the
dielectric
r~4
3
wave
C Boon
in normal
i9757.
P (.10)
radio
lobe CTcttarski 19617.
polar
P
fundamental
on
the R R 1, D e by e ’s treatment
electric
and
the
theory
as the atmosphere
turbulences,
normal
of
earth
is
energy may be confined to the
In addition
any
near
atmosphere
one
launched radio wave and
this
curvature.
is
establishing
through
iQ&Sj.
index
given
first.
under
by
the
cMitna
where
s = dielectric constant.
M = molecular weight.
p = density of the fluid.
Nn = Avogadro’s
number.
= the average p o 1 arisabi 1 ity of the molecules
<n0
liquid assuming no interaction between the
in
th
m o l e c u l e s
p = permanent dipole moment.
return to
the removal of
/ <100 GHz
ICO
+
o r i e n t s
land
3.1
=(K14 Pa/T)
the
field,
CM It -
£■ - 1
for
random distribution after
<i>t <<1 , £
CO
Ilf
for
external
required
(K21
—9 1CO
to
time
lT J
relaxation
H
molecules
=
K5
I
t
* e/T
*
(A +B)/
T)
+
<K12
..................................(
2. 8
Pc ■'T
)
Where A & B are constants and P is the atmospheric pressure.
The refractive index n is given by
n = (fj'e)
1/2
Where p'
n = { l + ( u ’ t - l ) }
is the permibility of the medium
l/:
n - 1 =( p ’ &- 1 )/2
(2.9)
The term radio refractive index
N = (n
- 1
( R R I ) is then defined as
1! 10b = Kj Pd / T + K2 e /T + K3 e / T2 +
..... (2.10!
Where e = water vapour pressure
Kt = 77.G07 - 0.13 °K/m bar
K2 = 71.6 +8.5°K/ m bar
K' = (3.747 +0.031)
105 ( °K)2 /m bar
18
F,.
N = 77.6 Pd/ T + 72 e/ T +( 3.75)
N = 77.6 P/T
where
N =
-
5.6 e/T
3.75 * 105 (e / T2 )
Pd = P-e
77.6/T
(P + 4810 e/ T ) ....
N = 77.6 P /T
This
+
equation
t 2 .4]
.......
3.73 * 105 ( e/T2 )
shows
the
vapour pressure towards
.... <
......(2.12)
significant
control
the variation of RRI
of
water
values.
BENDING O F RADIO WAVE :
The
relation
and
change
follows.
and
+
105e/ T2
v
between
of
Let
the
radius
refractive
p be
velocity
earth surface.
the
the
index
radius
of
of curvature
with
of
height
can
curvature
propagation
Then from the figure
at
a
(2 2),
of
of
the
be
the
height
H
we have
p ti& =v dt
60/tit - v/p
v =1/
U r£vuv >A-"'2= k4 £-r-1'-'2
At a height H+dH = H +dp,
(v + d v ) =(p+dH)
..
........ (2.13)
the velocity
d&/ dt
Therefore dv/dH = d£/dt = v/p
p = v/dv
dH
..
........ (2. 14 )
Now from equation n o . (2.13)
and
(2.14)
p = 2/dtj,
......
we have
......
dH
19
ray
path
derived
radio
above
as
path
the
v-kdv
Fig.(2.2) : Geomatry For A Spherical Earth.
Fig.(2.3 a,b) : Simplified Model Of Effective Earth Radius.
20
Thus the radius of curvature of a path is a function of rate
of
change
almost
of
dielectric
continuous
course with
constant.
change
with
seasons. However,
p is assumed to be four times
purpose
of
gross
B a I ffia i n
19903
This
parameter
height,
time,
suffers
day and
of
in practice an average value of
the
estimation
earth’s
of
radius
for
the
LOS horizon {Jordan and
.
In working with propagation problems,
it is often convenient
to consider
lines
curved
as
the ray path as straight
they
actually
are and
then
curvature by using a large value of
the earth which
depends
instead
of being
to compensate
the effective
for
the
radius
of
on the variation patterns of the RRI .
To establish this relation,
let us consider figs. (2.3 a,b ). In
fig.(a) the actual ray path is shown above an earth of radius a
and fig.(b)
same.
shows the equivalent
In order for
straight
the straight line
line path of
path
of fig.(2.3bi to
be the equivalent of that shown in fig.(2.3a),
that a change in height dH be the same
the
it is necessary
in the two cases
for
the same horizontal D. Now from the fig (2.3b) we have.
dH =B0 - AO = (K a +H) {1/(cos9a )- 1>
For small angles
l/cos«s=l + e?^2/2
dH = ( K a
But
Where H is small compared to K a
= sint?* =D /(K a + H) = D/K a
Therefore
dH = D2/2 K a
.....
.....
(2.16'
On the other hand in fig 2.3b
dH = D2/2 a-D2/2 p
.....
.....
(2.17:
After solving the equation no (2.16) and (2.17), we get
.....
K = l/(l-a_.,p)
For a radius of
.....
(2.18)
curvature p equal to four times the radius a
of the earth, the effective radius of earth is A/3 times the
actual radius. By using this effective radius, curvature of
the earth’s
surface is taken care of by a straight path.
21
[2 .5 1 MULTIPATH FADING :
Under normal atmospheric conditions
exists
sight
between
path.
the
two
However,
antenna
changes
and
of
in
such a
the
direct
layered
and
receiving
10&Q,J
Celtfford
Each
path and
antenna
and
reflection
designed
variations
the
in
component
by
line
of
scattering
different
its
arrives
and
from
Fadings
from
is resultant
follows
amplitudes
10700,
refraction
path
refractive
from
thus generally
different
possibly
the
received signal
signal
Strofcbehn
/
well
propagation
may cause multipath propagation
the signal
with
or
a
one
the reflected components
structures.
propagation
&t . a. l .
situation
on
or
index structure of the medium
only
own
at
the
c'Mon
phase.
inhomogen it ies
due
atmospheric
to
the
layers
are
generally known as multipath fading.
The
diurnal
and
are
closely
related
conditions
to
causing
distribution
propagation
function
seasonal
of
can
variations
the
be
occurrence
multipath
the
separated
the
multipath
of
received
into
a
and
occurrence
C'Morl La.
theoretical
probability
1370,107$,
of multipath
Ekxrn&t
107$,
The
statistical
under
propagation
relations
propagation
meteorological
statistical
probability of occurrence of such events.
methods
the
propagation.
signal
characterising
of
multipath
distribution
phenomeinon
and
the
Various experimental
for
fading
Bhoauquisi
an
have
estimation
been
proposed
arid Norbur-y
I y7o',
e tc .j .
A
general
fading
relation
for
estimating
probability
of
is given by
F (R < Li = K Q f® dc Fr,x L 2
Where P
the
......
- Probability of occurrence
L
- Amplitudes
in linear measure
K
- Factor for climatic conditions
o otL -i
......
of
(2.19 s
Fig.(2.40 : Sample Record Of T he Mu ltipa th T ype Of F ading .
23
£}
- Factor for terrain conditions
f
- Frequency in GHz
d
- Path length in Km
Fn - Path clearance factor
B,C,X, - Constants
Multipath fading may occur due to interference between direct
wave and different wave components like,
1. Specular component of ground reflected wave .
2. Non specular component of ground reflected wave .
3. Partial reflection from atmospheric sheet or elevated
layers.
4. Additional direct (non reflected) wave.
These additional wave paths occur either due to surface layers
of
strong
positive
refractive
horizontally distributed changes
developed
because of
index
gradient
or
of RRI . The fadings
these multipath
phenomena
can
to
that are
be quite
severe, depending upon the effective reflection cofficients or
on
relative
interference
amplitudes
of
of
the direct
the
component
wave with
partial reflectd waves from layers,
last
for
specular
couple
ground
interference
duration
of
multipath
of
minutes.
reflected
resulting
order
fading
of
During
deeper
seconds.
is presented
of
The
specular
and
generates fadings that may
component
even
those
waves.
such
can
and
A
fades,
cause
rapid
sample
in fig.
the
additional
fades
record
(2.4).
non
of
Fadings
with
the
result
from multipath reflection can be avoided at the receving site
by adopting frequency or space diversity system.
[2 .6 ] GENERALISED THEORY OF SCATTERING OF RADIO WAVE FROM
REGULAR AND IRREGULAR TIME VARYING REFRACTIVE INDEX STRUCTURE
When
a
medium,
19620.
radiowave
propagates
through
it is distored by a number
The
distortion
can
be
24
ionized
of mechanisms C£tx-obh~ffi
characterised
groups.
non
into
three
1. Absorption : This causes direct attenuation of the wave.
2. Refraction : Here a general bending of the wave
by the
change of mean
value
of
the
is caused
dielectric constant
with height.
3.
Random scattering
: Here
scattering
occur
due
to
random
fluctuation in the dielectric constant, which causes variation
in the amplitude,
of
phase, angle of arrival and polarisation
the wave.
To analyse problems on scattering of radio waves from regular
and
irregular
surfaces
the
following
theoretical
approaches
are generally adopted. These are,
1. Theories based on turbulences (Booh&r & Gordon i960)
2. Mode theories ( Eullinostion )
3. Reflection theory ( Firis. Crawford., Hogg 1957)
Each
theory
gives
experimental
agreement
observations. An
problems has also been
necessary
to treat
the
as
well
unified
received
as
deviations
treatment of
(Gjossing 1968).
scattering
turbulent irregularities and for
problem
with
scatter
It
is not
separately
for
reflection from layers.
The
treatment given by Gjossing C 19689 in terms of three dimensions
spectra
can be discussed in this case and can be
by
(2.6).
fig.
scattering
Here dV
structure.
is an
elemental
If K0 = Wave
volume
number of the
illustrated
inside
incident
field
Ka = Wave number of the scattered field
Then
K0 = Ka
=
2f ]
/'K
K = K0- Ka
K =
(4rr / M S i n
Where &
K
8/2
............
............ ( 2 . 2 0 )
= Angle between K0 and Ka
= position vector of the scattering volume .
25
a
F ig .C2.5) : F u n d a m e n t a l G e o m a t r y O e S c a t t e r e d F ie l d .
26
The scattered
E_M =
field is then given by
K.^ /4 jt R /E.-U. f( rt ) e ''*<r d^ r....
Where E0 is the magnitude of
....(2.21)
electric field and f(r,t) is the
space time function of the normalised permittivity. The angular
spectrum of scattered field strength is the Fourier
Transform
of the product E(r), and f^(r).
The
angular
power
spectrum
of the
scattered
product of Ea and its complex conjugate,
wave
is the
giving the scattering
cross section by the following expression.
(S) = (rr K4 /2 ) <p (K)
Where
.....
......
4* (K ) is the spatial power
index field such that <p
(2. 22!
spectrum of the
(k) is the
refractive
Fourier Transform
of the
spatial autocorrelation. Here the incident wave is a plane one
and the linear extension of the scattering volume V1"'3 is very
small compared to the distance between the transmitter and the
scattering volume.
The scattering
cross-section is
defined
above as the power
density of the scattered wave in the direction of Ka (per unit
solid angle per unit scattering volume per unit power density
of
the
incident
scattering
wave on
cross- section
difference between
turbulent
index
scattering
varies
as
volume).
fourth
power
Thus,
of the
incident and scattered wave number besides
being a function of
refractive
the
the
field.
conditions.
In
spatial
It also
the
power spectrum of the
varies with
following
expression is deduced for turbulent,
reflected conditions etc.
27
the different,
sections
the
streamline and layers
€13
Scattering
irregularities
From
to
a
Turbulence
large
extent
:
The
are
tropospheric
contributed
variations in the radio refractive index, so it
to
discuss
the
of RRI spectra.
fluctutions
takes
1
_
=
.03
Cn1
2
X
the
essential
the troposphere in terms
In the K range corresponding to the inertial
subrange for the refractive
crossection
in
is
by
/
the
index
spectrum,
the
scattering
form
^
-
1 1
/
^
(sina/2)
----------(2.23)
Where Cn2is the Tatarski structure function,
2
“
_ o / -a
= 5.3 <* £)
1 ^ °
2
{&£)
is the standard deviation of permittivity fluctuations
and & is the scattering angle.
C2) Scattering From Single Layer : Let us consider a layer
where refractive index varies according to a function (say)
fi(h) with height. The scattering cross section can than be
written as
=
C33
f] k2/2 K
f£ ih) e~jkh dh |2 --------------(2.24)
Scattering
From
Turbulent
Layers
-
Let
us
consider
a
medium where the turbulence is confined to one or more layers
of limited vertical extent .In such layers we may expect that
the mean temperature and humidity (and hence
vary differently at the two layers.
refractivity) to
In such a situation,
the
refractivity profile will consist of two parts.
1. A gradient layer of normal refractivity gradient
(dN/dH =
-40N ).
2. Random fluctuations superimposed on this mean profile,
caused by the turbulence. The resultant scattering
cross-section.
28
—.— _ 2 ^ -1/3, . A .11/3
j.2
I- .. . ~ jkh ,, ,2
.03 Cn X
(sin&/2)
+ n K /2 |f^(h) e
dh |
------- (2.25)
[ 2.71
SYSTEM GAIN AND THE RELIABILITY :
System
gain
is
a
useful
measure
of
performance
of
a
communication set up, because it incorporates many parameters
of interest to the system designers of the microwave system.
In
its
simplest
transmitted
sensitivity
form,
it
is
output power
for
a given
the
and
difference
the
signal.
The
between
receiver
receiver
the
threshold
gain
must
be
greater than or at least equal to the sum of gains and losses
in the equipment. Mathematically,
this can be expressed by the
following
Barnett-Vigants
equation
known
as
a
reliability
equation CFeH&r,iQQt5
G a = P t " C min - F m
..... (2 . 2 6 )
+ L p + L f+ Lb~ G t“ G r.....
Where Gfl is the gain of the system.
Pt is the transmitter output power.
Cmin is the recover threshold value.
Lp =92.4 +20 log d +20 log f, is the free space loss ...(2.27)
Lf is the feeder loss.
Lb is the branching loss (in the protected system ).
Gt
Grare
gain
of
transmitter,
receiver
antenna
respectively over isotropic radiators.
Fm is the fade margin of a non diversity communication system.
Fade Margin Requirment For A Specified System Relibilty :
The
Barnett-Vignant
previous
allowable
receiving
reliability
section
may
fade
margin
the worst
be
applied
for
month
equation
a
to
mentioned
determine
communication
information
over
in
maximum
system
that
the
link.
after
This
fade margin can be calculated from equation (2.26) in the form
of the following equation.
29
Fr„ = 30
Where
A,
iogd +10 log
(1-R)
is
the
(6 A B f) - 10 log
is the reliability
roughness
factor
for very smooth terrain
(1-R1-70-----(2.28)
factor for a 400 km route.
of
the
terrain,and
is
equal
to
4
including over water.
1, for terrain with some average roughness and
is equal
to 1 ' A
for mountainous /very rough terrains.
B
is the factor
probability,
to convert worst
which
fade margin
of a highly
99.99%
will
service
to annual
1/4 for average
or very dry areas.
is available
for worst month period
case
probability
is 1/2 for very humid area,
inland area and 1/8 for
This
month
on an annual
can be
reliable
reliability
basis.
received by
system
per
the
value
putting B = 1.
(without
hop,
The
diversity)
fade
margin
In
with
needed
be.
Fm = 30
log d + 10 log
(6 A f ) - 30 dB---------- (2.29)
Where f is the operating frequency.
It is to be noted
that a 10 dB
an
order of magnitude
Now
from equation
increase
improvement
(2.26)
and
in fade margin
gives
in relibility.
(2.29)
the
required
system
gain
can be calculated as
Ga = 50
log d +30
log f + 10 log
(6 A)
+62.4 +Lf + Lb -Gt -
Gr
............ (2.30 )
From this equation
it is obvious that
increased with
increase of path
the
30
the system gain
length.
For
an
is to be
unproteote
carrier system a 5dB increase in the system gain allows 25 %
longer hop with the same relibility.
C2.81 AMPLITUDE DISTRIBUTION :
From the analysis of
observation
fading
large number of fade data
is that the probability
> (10 dB )
is low
compared
F*h&r i981j and this probability
of signal
attenuation.
of
the genera!
occurrence
of
to shallow fades
deep
(Kamilo
decreases with the increase
The cumulative amplitude distribution
of most non diversity fading signal
can be represented by a straight
10 dB/decade of probability.
in the deep fade
region
line with a inverse slope of
This typical distribution can be
defined by the equation c Lin 1Q71J,
P (V < L ) = £
.....
..... (2.31)
Where V is the enevelop voltage
of
the random fading
normalised to its non faded signal
signal
level
and
£
is
the
level,
signal
L is any specified
multipath
occurrence
factor
depending upon the fading environment.
However,
water
there are
rad io
observed
to
probability
and
links
be
some
exceptional
where
strong
the
and
fad e
in
these
by a inverse
probability. On the other hand,
short
decreases
depths
detected
are
type
of
over
generally
cases
the
occurrence of fades P (VI L) decreases very slowly
is characterised
very
cases
distances,
very
rapidly
the
with
slope
of 20 dB/decade
of
in certain radio links like tor
probability
L
and
is
of
fade
occurrence
characterised
by
an
inverse slope of 5 dB/decade of probability.
The
R ay leigh
P ro b ab ility
D ensity
Function
The propagation of the radio signals
-
through a medium can be
described by an Rayleigh probability density
signal
undergoes
incident
on
the
multipath
medium
and
fadings.
this
If
medium
31
a
function
radio
produces
if the
carrier
is
scattered
beams
then
converted
density
the
transmitted
into
a
function
randomly
of
this
constant
varying
envelope
amplitude
signal.
is
signal
The
described
is
probability
by
Rayleigh
density and is defined by the following expression.
_
P (v ) = v/ot2
= 0
,
(
, .
e
(v
2 / 0
--*2
}
(
q<
v <
------------------ (2.31)
}
< 0)
Where v is the amplitude.
So
by examining
the
mechanism
average
mean
the Rayleigh
responsible
value
of
density
for
the
function
one
generation
the Rayleigh
density
can
of
assume
fades.
function
is
The
given
by
E (v ) = (n/2 )1 "20( ---------------------- (2. 34)
Where the rms ac component
[ 2.9]
is 0.655oi
NUMBER O F F A D E S AND A V ER A G E FA D E DURATION :
The multipath propagation conditions are also characterized by
other
aspects
durations,
signal
the
signal
number
arid
iy 7 cc,
Bar-risr t1
ca t-
variations,
of
level. <1Mo g&nsen.
Tat t e r s a l l
otc. J
of
fades
1Q7Q*
1utx-i g h l
Vigam s
and
signal
as
level
dynamic
example,
l y ’77,
or
in
of
l Q 7 i , Sul Li rig t o n
fade
change
coxd
acrid.
Sctscthi
1Q71 ,
a
fades
fades.
how
long
a signal
P(v< L)
will
L. However P(v < L) does
aspect
large
may
communication
long
rate
the
of
the
Mog&ris&ri
1979,
Afc-iycirtici
t yr7 ,
Dos
st.ol
iQQcf
.
information
long
example
'St&phezris&ri
The amplitude distribution of signal
the
for
of
the
number
have
systems
of
fades
same
may
tolerate
in
of an AGC
fades should be well
short
the
unit,
and
amplitude
short
design
these
known.
32
below
not tell
character
the
Furthermore,
the design
fade
be
give us only
of
of
a
specified
anything
the
about
signal.
a small
but
a diversity
dynamical
For
number
distribution.
fades
the
or
Some
not
the
system
behavior
of
In the study of duration of fades
for
the
different
parameters
fade
are
depth
t(L), the experimental data
plotted
levels
on
The
a
log
scale
distribution
along
can
with
be
well
represented by a straight line for fade depth deeper than -10 dB.
The slope of this straight
of fade depth,
line shows that with the increase
the fade duration does not decrease gradually
but follows a power law.
[2 .1 0 ] CONCLUSION :
This chapter presents
physics of the
the
basic
and
the
related
to
propagating medium associated for with
of different types and magnitudes.
RRI
theories
effective
earth
For
radius
the
fade
this purpose effect of
factor
at
different
environmental situations have been presented. The basic system
parameters such as system gain and reliability with respect to
fade
margin
distribution
are
pattern
discussed
at
along
different
s ituat ions.
#
33
with
possible
environmental
and
fade
terrain
CHAPTER - 3 EXPERIMENTAL ARRANGMENTS AND CIRCUIT DEVELOPMENT.
[ 3.1] INTRODUCTION :
Microwave communications are comming in a big way in the north
eastern
region of
covered
by
features.
the
widely
Indian subcontinent.
different
topographic
comprehensive
weather
terrains
and
are
botanical
So, to examine the association of microwave fading/
attenuation with these environments,
a
The
or
picture
tropospheric
of
it is essential
terrain
and
features
meteorological
at
to have
different
situations.
With
that aim in mind, a number of microwave links over this region
are
selected.
The
selection
aspects can be addressed
is
so
made
that
propagation
to different terrain conditions. The
selected links are as follows
1. Milmilia - Durgasarovar
(Indian P&T Link, Marshy)
2. Maopet - Durgasarovar
(Indian P&T Link, Hilly)
3. Motapahar - Durgasarovar
4. Laopani - Habaipur
(Indian P&T Link, Built up)
(Indian Railway Link, Plain, wet)
The sites of microwave links for the proposed study are shown
in the figure (3.1), This
shows that the P&T microwave
links
are in the Kamrup district while the Railway link falls in the
Nagaon district of Assam valley.
[ 3 .2 ] TERRAIN FEATURES AND FRESNEL ZONE CLEARANCE :
The terrain features of
microwave links have been collected
from
various
data
sources.
The
basic
path
height
have
been
obtained from the survey data made at the time of establishing
the
links.
seasons
The
data
on
vegetations
have been obtained
imagery survey data.
from
and
their
the botanical
From these data,
and
characterstic
of each terrain are summarised as follows.
34
changes
with
satellite
features
It is to be noted
that here all
the heights
are measured
with
respect
to sea
level unless the base level is specified.
C l 'J
Mil mill a - Durgasarovar Link :
The terrain profile over this link is shown in the fig.(3.2a!.
The main receiving station Durgasarovar is at a height of 228
meters and Milmilia
is at
height of
105 meters.
This
link
falls in Guwahati- Calcutta LOS Microwave communication
and
is basically covered with marshy agricultral
and forested plain
meters at 5-6
land
(20 km).
A small
km from Durgasarovar
hill
also
land
path
(10km)
of height 220
falls
at
this
link
path. The link passes over the major swamps of Deepor Bill and
as well as over Kukurmara Bill system which lies further south
to the link. Also it runs along the river Brahmaputra towards
the
north
as
well
as
along
river
reserved
forest
summer,
most of he belt is covered with
The
fresnel
using
is populated
Kulsi
zone
with
ellopsoid
the equation
for
sal
this
of
Fresnal
different
conditions
zone
of
over
this
viz.
4/3
K
and
the
south.
sagoon
The
trees.
In
paddy fields.
link
(1.5) as described
clearance
to
is
calculated
in the chapter
link
and
is
by
1.
The
examined
for
2/3.
The
fresnel
ellopsoids for both the values of K are plotted and are shown
in
figs. (3.2a)
ellopsoid
meters
and
(3.2b).
Fig. (3.2a)
shows
that
fresnel
is cleared from the highest peak of the hill
for
situation
K = 4/3
of
K,
condition,
the
fresnel
and
zone
even
for
clearence
by 24
the extreme
is
22
meters
fig. (3.2b) .
CeD Maopet - Durgasarovar Link : Fig.(3.3a)
profile over
Durgasarovar.
this link
meters
forming
this
This
link.
terrain
is at 1660
above
a
that
step
This
is
The
runs
to the south
from
hilly. The heighest point of
meters and
peak.
like
link
shows the terrain
antenna height is about 70
path
structure.
35
covers
The
two
plateaues
first step is 30
km long and average height of it is 550 meters.
point,
there
situated
is a steep
at an average
rise
to
height
the
of
900
distance of 50 km. Beyond that point,
increase
in height
up
next
to Maopet.
At the 32 km
plateau
meters
and
which
runs
is
to a
there is a steady steep
This
link
is covered
with
evergreen forest as well as with desidious forests.
Over this
link,
PINE
the
major
trees
are
SAL,
SHAGUN
and
the
and
abundant foliage like bamboo.
Fresnel zone ellopsoid over this link for K = 4/3 and 2/3 are
plotted as shown in
fresnel
zone
figs.(3.3a) and (3.3b). Fig.
clearance
for
K
=
4/3
value.
(3.3a) shows
Fresnel
zone
clearance is 195 meters for K = 4/3 (at the hill point) while
for the extreme K situation
meters
fig-(3.3b).
uninterrupted
LOS
The
the clearance
clearance
communication
is
even
is reduced
adequate
for
worst
to 120
for
an
atmospheric
situation.
C
3j
M o tap ah ar
-D u rg a s a ro v a r
This
link goes
part
is hilly,
are two peaks
towards
L in k
:
east of
Durgasarovar
covered with built
in the path,
and
its west
up area and shurbs.
There
one is of height 200 meters at 10
km and another of 180 meters at 13 km from Durgasarovar.
terrain
between
these
two
peaks
is
a
plateau
with
The
average
height of 160 meters. The eastern end of the lane extending 5
km
is a plain covered
by cultivated
land.
The
hill
and
plateau are mainly covered by planted forest of Sagoon,
the
Sal,
and Sisso trees.
Plot for fresnel ellipsoid is shown in figs.(3.4a) and
for values of K = 4/3 and 2/3 respectively.
clearance
(3.4b)
The fresnel
is 40 and 23 meters for K =4/3 and 2/3
zone
situations
over this link.
C
40
Laopani
-
H abai pur
L In k
:
The Laopani Habaipur link lies in Nagaon district and covers a
36
37
93*0'
F ig.C3.1) : S ites Of T he Mic ro w ave L inks And Other F ield
S tatio n s Used F or P resen t S tu d y .
LOCATION OF THE MICROWAVE LINKS AND THE OTHER FIELD
STATIONS USED FOR RECENT STUDY
cc
LO
I L M
( R
X
m
M
X
O
38
E C
A
0
E N
T
P A
T
U
- D
E R
N
H
R
S A
A
G
R
O
H
E
V
T
I S T
S A
S I T
D
A
A
)
T
A
R
R
N
O
F ig (3.2 a )
E I V
D U R G A
N
I L I A
X
C
V
:
5
R
0
M
E T E R
K m
I C R O
L l ' 2
M
W
K
C E
2 1 5
L I N
D I S T A N
A V E
G
IN
6
H
K M
2
^ T
R
A
N
S M
m
i l
T E R
i l
I T
m
Path Profile Of Milmilia - Du r g asaro var L ink
4 /3 . E arth ' s Radius F ac to r .
F or K » 4-/3.
E
A
i a
S I T
E )
0
S
y 3 1
39
3 W
N l
1 H 9 1 3 H
H T
R X
T X
5 0
0
M
M
2 1 5
E T E R
E T E R
D I S T A N C E
: 5
IN
K M
^ T R A N S M
I T T E R
M I L M I L I A
F ig.C3.2b ) : Path Profile Of Milm ilia - Du r g a s a r o v a r L ink
F or K - 2 /3 , Ea r t h ' s Rad iu s F a c t o r .
)
A
K m
in
S I T E
N
A T 2
cP
( R E C E I V E R
S A R O V A R
T E N
D I S T A N C E
=
D U R G A
A N
P A T H
K= 2/3
MILMILIA-DURGASAROVAR MICROWAVE LINK 6GH2
rv .
S I T E )
40
A
T H
L E
I S
N
G
H
T
T A N
C
6
E
H E I G H T
F or k - 4-/3,
FIG C3 3 - 0 : PA TH PROFILE
D
ANTENNA
P
K
m
3 2
OF
IN
K M
T X : 7 0
M
T R S
M A O P ET - D U R G A S A R O V A R LIN K
E a r t h ' s R a d iu s F a c t o r .
^
MAOPE T-DURGASAROVAR LINK 6 GH2
R E C E I V E R
S I T E
D U R G A S A R O V A R
O'
in
CD
O
C\J
in
o
iO
o
O'
in
in
----- 1----CM
<-n
O
i£>
LT
y31 3H Nl 1H9I3H
41
transm itterssite
o
)
FlG.C3.3B)
: PATH PROFILE OF MAOPET - DURGASAROVAR L in k
p OR k . 2 /3 , E a r t h ' s R a d iu s F a c t o r .
DISTANCE IN KM
32
------ •-----------‘
------------ 1-----------
PATH DISTANCE: ^ Km
a n t e n n a height t x : 70 m e t e r s
MAOPET-DURGASAROVAR MICROWAVE LINK
k=73
6A
DURGASAROVAR
^RECEIVER SITE)
■ 228
-r
S8313W Nl 1H9I3H
CM
id
—
42
distance
16
in k m
2A
RX '■ 80 M E TE R S
TX: IOO M E T E R S
33'5 Km
F ig.C3.4-a ) : Path Profile Of Mo t a p a h a r
F or k . 4 /3 , Ea r t h ' s Rad iu s
( RE CE I V E R SITE )
ANTENNA HEIGHT
PATH DISTANCE
D U R G A S A R O V A R LIN K
Fac to r .
[TRANSMITTERj
32
MOTAPAHAR
MOTAPAHAR DURGASAROVAR MICROWAVE LINK
DURGASAROVAR
cO
saaiaw
43
n i
i h q i
SITE
D IS TA N C E
H E IG H T
D IS TA N C E
ANTENNA
PATH
IN
Km.
KM
R x:
80 M ETER
T X ! IOO M E T E R
33-5
motapahar - durgasarovar link
K-2/3
TR A N S M IT T E R
M OTARAHAR
F ig.(3.4 b ) : Path Profile Of Mo t a p a h a r Du r g a s a r o v a r L ink
F or k - 2 /3 , Ea r th ' s Radius F a c to r .
R E C E IV E R
OURGASAROBR
3h
44
X
\ -
X
LU
o
T X
0
K « V 3
X
X
:
3 0
B 0
B O
D I S T A N C E
2 0
R
IN
M E
M E
E
H
T ’
K M
T E R S
4 0
K M
T E R S
I G
5 5
R
5 0
X
( H A B A I P U R )
5 5
Fig.(3.5 a ) : Path Profile of L a o p a n i - Ha b a ip u r L ink
F or « * 4 /3 - E a r t h ' s Radius F a c to r .
( L A O P A N j )
10
T
H
D I S T A N C E
A N T E N N A
P A T H
LA0PAN1 HABAIPUR MICROWAVE LINK 7GH2
F O R
2 S
X
CD
io o
CP
< *I— Xa .
•saaiaw ni i h q i s h
45
K
-
2 / 3 -
2 £
III
HABAIPUR
( r e c e iv e r site)
Fig. ( 3 . 5 ) •. Path Profile Of Laopani - HabaiPur Link
For
Earth' s Radius Factor.
b
X
o
DISTANCE IN KM
U J
J-
[(TRANSMITTER S I T E )
D I S T A N C E 55 KM
7GH2
CD
LAOPANI
PATH
LAOPANI HABAIPUR MICROWAVE LINK
.O O
path of 55
km.
This
river K o p i 1i which
The altitude
of
91
The
meters.
cultivated
in
situation
from
over
a plain
is crossing
this
link path at three points.
Laopani
is 54
terrain
ellopsoids
fig. (3.5a)
meters
over
over
and
this
and
this
terrain
that
link
of
is
along
the
Habaipur
covered
is
with
of
the
44
the
respectively.
fresnel
meters.
atmosphere,
at the mid path of
obstruction
by
link for K = 4/3 and 2/3 are
(3.5b)
of the atmosphere,
obustruct ion
condition
runs
land and forests.
The fresnel
showns
link
ellopsoid
But
fresnel
For
resulting
=
is fully
interestingly,
ellopsoid
link by e arth’s bulging.
type of fading
K
is
4/3
clear
for
2/3
obstructed
This
leads
to
in a complete fade out of
signals Fig.(3.5b).
t 3.31
MICROWAVE LINK INFORMATION :
The information on the various
mentioned
link
is given
in
link parameters of the above
the table 3.1
T a b le-3,1
Information On Link Parameters
Link
M i 1m i 1 ia
Maopet
Motapahar
Laopan i
Parameter
D.sarovar
D.sarovar
D.sarovar
H a b .Pu r
1.D is tance
40.2 Km
64.4 Km
33.5 Km
55 . 0 Km
2.F requency
6.4 GHz
6.0 GHz
6.0 GHz
7 . 13 GH
3.Antenna T x
50 mtrs.
70 mtrs.
100 mtrs.
80 m t r s
Height Rx
50 mtrs.
70 mtrs
80 mtrs.
80 m t r
43.3 db
44.8 db
45.5 db
39 .5 d b
43.2 db
44.8 db
45.5 db
35 .5 db
5.HASL Tx
105 mtrs
1660 mtrs
54 mtrs
Rx
228 mtrs
228 mtrs
228 mtrs
91 mtrs
40 db
40 db
40 db
30 d bm
4.Antenna Tx
Ga inRx
6.Power
* - With respect to lpv signal
level.
46
s
[ 3.4-3 FADF MEASURMENT & CALIBRATION
SYSTEM :
Scheamatic
diagram
fig. (3.65.
The
for
set
recording
up
consists
stage along with differential
To study
fade
of
character
RF,
IF,
AGC
receivers
differential
amplifier
amplifier and chart
depending
the
signal
on
level
the
placed
are
fed
voltage
type of
is
level
are
or
to
zero
with
the
detector
through
converter
The
of
a
system
normal
Fluctuations
help
in
links, the AGC
f i g . (3.7).
volt.
shown
recorder.
recorders
to current
recorder
at
measured
is
and
fade character of the above mentioned
outputs of the
this
OF THE FADE RECORDING
over
calibration
chart.
F i g . (3.8)
the
describes
system
sections
used
technique
the
Indian
consisting
disconnected
signal
in
the
from
generator
of
the
rest
is used
is
IF
after
the
proper
dynamical
is
output
of
Here,
RF
The
and
the
a
are
standard
source.
As
the
'F
from this generator
goes
detector
caliberated.
calibration
amplifier
circuit
a calibration
through
then
and
the
Its
for
link.
a 70 MHz signal
section.
processing
range
of
as
is 70 MHz,
to
railway
antenna
of the receiver
fed
adopted
and
to
the
recorder
amplifier.
calibration
of
The
the
system is done on a regular basis.
However,
P&T
for calibrating
links,
the antenna
section
is
then
attenuator
pad
schematic
(3.9).
the calibration
intact
with
the
is inserted between
for
this
the fade depth
rest
of
the RF and
arrengment
variation
the dynamical
Habaipur
is also
made
to act as a source and F:F
is allowed
corresponding
Here
registering
Further,
itself
kept
diagram
The
recorder.
range of the setup for *he
the above procedure as adopted for Laopani
link has been followed.
where
dynamical
range
is
is
information.
47
is
the
IF section.
shown
then
system.
in
detected
adjusted
for
the
in
An
The
fig.
the
suitably
F ig .
(3 .
):
B lo ck
D iag ra m
Of
M ic ro w a v e
45
S ig n a l
R e c e iv in g
Set
Up
Fig (3.7) : Circuit Diagram
Of Differential
49
Amplifier
ANTENNA
P F
STAGE
l
A G C
I F
S'TA G E
CHART
RECORDER
7T
SIGNAL
GENERATOR
Fig.C3.8I>
Technique
: Block
Adopted
Diagram O f S i g n a l C a l i b r a t i o n
At
The N.F R a i l w a y Receivers
50
Fig.
(13.93 : Block
Diagram
Of Signal Calibration Set Up Adopted
At P&T L i n k .
51
r 3.53 MEASURMENT OF ASSOCIATED WEATHER PARAMETERS:
To
realise
the effect
of medium
on
microwave
propagtion
the
following tropospheric parameters have been measured:
(a) Ground based temprature, humidity, pressure and wind speed
(b)
Dry
of 25
<c )
and wet
temperatures
at different
heights
by
a
tower
meters height from the ground.
Dry
temperature,
direction
at
humidity,
different
pressure,
heights
wind
(up to 2 km!
speed
with
and
the
help
of rad iosonde.
!d) Elevated structure,
thermal
plumes,
cold and hot fronts
bv
sodar.
The data on temperature and humidity
the help of
the system
0.5°C
time
conventional
is poor
could
be
and
thermohygrograph.
fluctuations
measured
resolution
for a meaningful
which
with
is
study
observation.
To
15
of
limited
level
overcome
been
collected
But
temperature
is
also
not
is detected with
only
of
upto
Moreover,
to microwave
this
with
sensitivity
accuracy.
minutes,
in relation
a change of 30 dB signal
of
have
the
acceptable
fadings
where
in 2-3 minutes
limitation,
four
sets
of
electronic dry and wet temperature systems along with recorder
have been developed.
Details of the circuits are described
in
section 13.61.
The data on wind speed are also collected by aconventiona 1 typ
of
anemometer.
necessity
sensor.
limitation
of making a physical
This
proximity
But
of
limits
the
receving
of
this
connection
placing
stations.
of
To
the
anemometer
of
the
to
this
te 1erne trie optoelectronical Sy control led anemometer
solar
cell
parameters
is
developed.
through
frequency
details of the circuits
This
system
modulated
is given
a
in section 3.6.
and
close
drawback
a
powered by-
transmits
radio
the
recorder
sensor
overcome
is
signals.
w _n g
.he
For
monitoring
troposphere,
both
remote sensing techniques are used.
direct
or
insitu
The radiosonde
and
is one of
the insitu techniques where the associated data at different
heights
can
be
sensors.
By this
received
through
technique,
we
a
baloon
receive
the
equipped
with
temperature,
dew
point,wind speed and wind direction information. But the major
disadvantage of the radiosonde technique is height resolution.
Furthermore,
period
the measurments are available only for a limited
of
information
time.
on
However,
temperature
radiosonde
inversion,
technique
subrefraction,
gives
super
refraction and ducting conditions very effectively during the
flight time. So this information can be correlated with fading
of microwave signals observed during the period.
t 3.6] SYSTEM AND CIRCUITS DEVELOPED DURING THE RESEARCH PERIOD
CiD Sodar-
Among
the
ranging
remote sensing
techniques
techniques,the
(SODAR)
can very
sonic
detection
effectively
be used
and
for
continuously monitoring of the tropospheric conditions.
In
an
effort
microwaves,two
to
identify
SODAR units
the
cause
are installed.
of
fadings
in
One in the midpath
between Milmilia -Durgasarovar microwave link and the other at
the Gauhati university,
diagram
of
the
device
C B a rb cu ra .
is
et.ctL.iQ Q l
shown
in
T R -1 5 .
fig(3.10).
The block
The
system
consists of following units
1. Antenna
2. Transmitter
3. Receiver
4. Recorder and monitor
The photograph of antenna and sodar are shown in fig.3.11a, b.
System Description
The antenna is a parabolic dish of 6 feet in diameter
focus
is at the
on
suitable
a
. The
height of 160 cm. The dish system is mounted
base
for
damping
unwanted
53
vibrations
while
transmitting high power acoustic pulses.
serves as a receiver of the echoes.
by
a
carefully
designed
The same
dish also
It is therefore surrounded
acoustic
shield
of
double
wall
hexagonal structure. Shield height is 8 feet and is internally
lined with thick foam to prevent reverberation and the space
between the walls is filled with saw dust, which keeps out the
external
noise.
The transducer
is a high power
unit with flat response in the frequency range
This
unit
horn,
and
is
filled
with
a
specially
is mounted at the focus
activated by
(80 Watt)
1.5 - 2.2 KHz.
designed
exponential
of the dish.
the tone burst generator.
PA
The unit
is
The frequency of the
tone burst is adjustable from 1.2 KHz to 4 KHz and 2 KHz is
the frequency selected by us for probing the atmosphere.
tone
signal
is
then
sufficiently
amplified
by
the
The
power
amplifier to generate an electrical output power of 140 watt.
The duration of the tone burst is also adjustable from 20 to
100 m sec.
external
The
triggering
circuit and
control
is fed
pulse
to the
is generated
transmitting
by an
as well
as
receiving system to maintain the proper synchronisation.
The same
transducer
signal from
is used
for
receiving
the backscattered
atmosphere and is routed to the receiver system
through a preamplifier. A T/R switch is introduced between the
preamplifier and
transducer
highly
preamplifier
sensitive
probing signal
and
the
is brought
is
circuits
placed
to the
received
signal
is
bandpass
active
filter
switch
from
isolate and
the
burst
designed
is further
used
through
are
a
passed
of
power
optoelectronic
this
purpose.
An
to blank the receiver
in
a
The output
quality
of
a
the
T/R switch
site.
with
thick
noise.
The
biquad
narrow
control
device
optoelectronic
input
period of 200m sec, so that the strong echoes from
54
high
assembled
good
through
protect
The
losses and pick up
then
for
which
.
at the antenna
receiver
shielded cable to avoid
specially
to
sent from the transmitter
preamplifier
single setup
unit
for a
the nearby
OSCILLATOR
T/R SWITCH
POWER AMP.
gate
&
tbg
gate
PRE AMP
CON T R O L
RANGE
COMP.
ACTIVE
FILTER
BUFFER
AMPL.
P O W E R AMP.
UNIT
DETECTOR
A/'D
RECORDER
MARKER
C L OCK
3 . 10 :
Block
D i a g r a m Of The Sodas
Unit
Fig. (3.11a ) : Photograph Of T he Antenna Unit
Fig. C3.11b ) : Photograph Of T he Sodar Un it .
56
structure
do
not
interfere
signal. The echo signal
with
the
received
backscattered
is then detected and amplified to an
adequate output level. The detected output is then fed to the
log amplifier such that the slope of the
lograthmic transfer
function
the
output
is
of
controlled
the
log
by
the
amplifier
gain
is
of
then
amplifier.
suitably
The
boosted
for
are shown
in
recording in a recorder.
Some
sample
fig. (3. 12
based
records of the
a.b.c,).
inversion
Where
layer
which
not
Fig. (3, 12c)
so
well
shows
developed
due
to
developed
structure
radiative
ground
after
also
occurs
a representative
thermal
plumes
cooling
a
fig.(3.12b) shows the elevated layer recorded on Sodar
type of
set
generally
the
earth,,
hours.
sun
is
represents
of
This
of
fig. (3. 12a)
couple
echogram.
hours
sodar echogram
during
Sodar
of
night
echogram
characterising
of
poor
convective state of the atmosphere.
Table-3.2
Characters tic Of Gauhati University Sodar
System
----
Transmitting Frequency
2 KHz
Pulse Width
50 msec
Transmitted Power
140W
Antenna System
parabolie dish
Pre Amplifier Sensitivity
1 uV
Pre Amplifier Gain
80 dB
Band Width Of Filter
20 Hz
Display
Facsimile
Modi float lull Incorporated In The System -
In
the
basic
design
of
the
unit
57
there
is
not
much
of
a
F ig .C3.12 a ,e$,c ) : Photograph O f S ample Record
Echogram
58
O f S odar
difference
from
modifications
the
introduced
its reliability.
Replacement
the
pre
of
scattered
the high
cum
signal
transmissions,
developed
given
present
which
more
the
system
unit.
system
The
are
received
a
facsimile
of
the
to study
of
signal
In
sodar
variations
of
height
Basic
P rin ciple
before
through
to
being
avoid
power,
the
As
with
the
to
the output
sensitive
on
fed
bar.
paper
frequency
the
echogram
is
the
The
of
The
is
a
three
a recorder
structures
and
filtered
and
which
is
stylus
is
ie on
of
received
frequency
burns
frequency,
a
to
al lowed
intensity
as
pass
of
the
varying
59
is
the
to
converted
through
frequency
fed
the paper
the
to
to
converted
properly
devices,
al lowed
voltage
so that
increase
is
signal
optoelectronic
signal
loading.
conducting
that
the
such
of
so
-
backseat ter
The
in
system,
intensity as a function of time.
frequency.
is
is to have a
signal
variation
their
processed
recorder
.
(x,y,t!
can be received.
received
the
description
any
The
in
:
picture
view
during
shown
the project and a brief
back-
from the high
three
dimensional
of
periods
signal
echogram
on
end
weak
receiving
recorder
is necessary
increased
front
the
The basic aim of using a of a facsimile
parameters
some
optoelectronic
is protected
sodar
in the following section
Recorder
an
transmitting
signal.
c)
by
than 60 dB during
strong
as a part of
comprehensive
But
has
the
amplifies
so that the receiver
b,
Facsim ile
up
transformer at
switch
by
transmited
f i g . (3.12a,
the
gain
amplifier
attenuating
power
in
built
The modifications are:
amplifier
attenuator
and
generally
buffer
converter
is
stylus
move
shades
over
a
a
heat
depending
gets
of
for
through
received
burning
■
'VFC i
amplified
to a degree
the
a
to
signal.
deeper,
grey.
The
F ig .C 3.13) : P h o t o g r a p h
Of
F a c s im il e
60
Re c o r d e r .
recorder that generate a triggering pulse at the beginning of
each
scan,
synchronises
backscattered
high power
master
echoes.
recorder
is
pulse
pulse.
shown
receiver
The blanking
transmitting
trigger
the
The
in
the
of
for
the
receving
receiver
from
the
the
is also synchronised with this
photograph
f ig (3. 13 1.
of
The
the
facsimile
system
basically
consists of the following units:
1. System synchronising unit.
2. Electronic unit consisting of VFC, amplifier and associated
circuits like system protecting device, matching unit.
3
Mechanical
unit
consisting
of
paper
intake
and
driving
sys tern.
4. Writing unit.
M e rits
1.
of
The
The
S ystem
system
—
has
been
materials and know how,
developed
withall
indigenous
its parts are easily available an
re pa ir ab1e.
2.
The echogram can be received on
C3D
E le c tro n ic
D ry
And
W et
ordinary wax coated paper
T em perature
S e n sin g
System
:
The conventional thermohygrograph used for routine temperature
/humidity
enough
measurment
to
humidity.
record
There
temperature
the
are
recorder
overcome this
wet
is found
to be
quick
cases
changes
when
results
not
fast
in
inadequate
to
loss
of
and
sensitive
temperature
response
and
of the
information.
To
limitations a fast response electronic dry and
temperature
1QQ2 TR-2J. The
sensing
system
is designed
circuit diagram is shown
circuit is based on
in
<iBa.rb<j.ra. e i a l.
fig. (3. 14). The
LM 335 and associated amplifier circuit.
The output of the temperature sensor
!Vc, =R Iaal) is fed to a
summing amplifier to get an amplified output of the temperatur
controlled signal. This output is fed to the
The
output
voltage
is
calibrated
to
the
chart
recorder.
corresponding
1
1
1 0
-----
GND
+
!
/
2
------- ------------------ !
1
!
k
----h
h
:
:
i
i
i
i
!
: \ ! 7
!
!
\
--i--- +-3
\ 6
-(+
4 H +
t
:
1
1
------------------------------------------------
h-----------
;
:
:
:
!
1
1
:
i
!
1
1
+
:
1
1
+
l
+
i
1
!
+
—
+
1
i
1
1
+
i
+
100 k
■+----------- b
•+•+ +
I!!
I
il
l1
i
4.7k
1
+
1
10k
H— ---- j_
+++
i
-- H------ +
•+ •+ •+ •
!+ +
1
i
:!!230 ohm
!
i
— +■+•+ !
1
!
•+••+••+•
1
10k
1
:
+ -----------:
!
+ ----- — ----+ ------ — + -----------L.M 3 3 5
1
j
i
i
-h
+
1
1
+
+
<c
— o
0 +V
1
i
l
I
•+•+ +
! !
! + ----------+
i
■
i i
i
!
!
------------------------------
--- +
1
1
/
/
!
1
1
4
1
:
i
1
1
1
1
1
1
!
1
1
1
1
+
--- h
1
1
15k
.01m f
— + +
GND
C i r c u. i t D i a g r a m 0 f The
Fast R e s p o n s e
T e m p e r a t u r e S e n s ing Unit.
62
--------- +
i
i
i
:
GND
F ig .C3.15a ) : P h o t o g r a p h O f T h e T e m p e r a t u r e
S e n s i n g C ir c u i t ,
F ig .(3.15b ) : P h o t o g r a p h O f T o w e r T o Me a s u r e T h e T e m p e r a t u r e
A t D if f e r e n t
h e ig h t s .
63
V
o
l t a
Calibration Curve For Temp. Measurment
T e m
0
W
e t
T e m
p e r a t u
r e
In
O c
p ,
+
D r y
T e m
p
Fio.C3.16) : Ca l ib r a t io n Cu r v e F or Dry An d Wet T e m p e r a t u r e
Me a s u r e m e n t .
64
Fio.C3.17
a &b )
: S a m p le Re c o r d O f We t A n d Dr y T e m p e r a tu r e
F l u c t u a t io n s
65
temperature. For wet temperature measurments the same circuit
is
used.
measure
The
the
photograph
temperature
of
at
the
circuit
different
and
the
tower
to
heights
are
shown
in
and
wet
f ig. (3.15 a & b).
The
calibration
curve
are
drawn
systems and are shown in fig.
for
both
(3.16).
dry
bulb
The sample records of
wet and dry temperature variations during afternoon period are
shown
in
fig-
(3.16
a,b).
Fig. (3.17a)
shows
temperature
variation of the wet sensor, where temperature shows variation
from
19°c
to
24°c.
Fig.
(3.17b)
shows
the
temperature
variation of dry bulb from 25 °C to 30 °C, during this period.
From the temperature records it can be clearly seen that the
temperature fluctuations up to 0.1°C can be detected with a
time resolution of less than a minutes.
This
resolution for the micro structure study
of
is a convineant
the
temperature
parameter.
C4.3 Telematric Anemometer :
The
design
conversion
philosophy
of
corresponding
optoelectronic
that
are
the
system
mechanical
rotations
train
electrical
of
of
frequency-modulated
obtained
are
calibrated
instant.
The
block
on
to
diagram
give
of
wind
92
on
vane
MHz
wind
The
to
a
is
an
pulses
carrier,
are
pulses
velocity
system
the
through
The number of
the
the
a
based
1092 T R -3 y .
a
transmitter.
is
pulses
device CBetrbax-a. &t.ctl.
transmitted by a small
fig.(3.16).
of
at
presented
so
that
in
It consists of
1. Cup and cone wind vane
2. Transmitter
3. Receiver with recording system.
The cup and cone wind vane has three conical
of
diameter
10 cm and
arm
length
66
of
22
cm
cups and cones
each
which
are
placed
at
the
corner
system
rotates with speed
gives one electrical
then
an
equilateral
in proportion
triangle.
to
and
then
The transmitted signal
Output pulses are detected,
recorded
on
a
heat
the
thermal
sensitive
snsitive
paper.
condition we get a continuous
ten
duration
marks.
of
Here
two
the
pulses
So
vane
wind.
It
These pulses are
is received by a
paper.
a
charger
recording
or
transmitter
long
remains
quiescent
wind
in between
on
for
unit
over a tower
without
the
wires.
for
the
cell.
or at
necessity
The
Thus
any
of
the
place
battery
photograph
this
of
system is
(3,19a & b)
is
miles/hour. The
on
This system requires a power
unit and the recorder unit of
speed
ten
next
connecting
shown in the figs.
The wind
setup,
for
the
complete setup can be arranged
the
power
strong
gap
12 volts which can be provided by a solar
near
So,
very
line with small
remains
for
get one dot mark
in
transmitter
and
eight sequence of pulses.
of
of
amplified
rotation of cup and cone system we will
two
This
transmitted by a FM transmitter of range 150-200 meters
receiver.
the
that
pulse at each rotation.
operating at 92 MHz.
FM
of
calibrated
wind
speed
in
can
terms
be
of
speed
calculated
from
in
the
fig.(3.20) both in terms of length of dot marks and in terms
of gap between two marks.
Figs
10th
(3.21 a,
Nov.
b)
s hows
and
1992
sample records it
speed
is changing
Oct.
the
wind
the sample
31st
Oct,
can be seen that
from
is
0-15
moderate
records
1992
on
67
it
speed
respectively.
10 th
mi 1es/hour,
and
of wind
From
Nov. ,
wind
wh i 1e on 31
i
b l o wi n g w:
on
i-
U ,
st
ELECTRONIC
COUPLER
RECEIVER
Fig.
1 3. i8'J : B l o c k
D ia g r a m
Of
The
63
T e le m a tr ic
A n e m o m e te r.
F i g C3.19a ) : P h o t o g r a p h O f A n e m o m e t e r T r a n s m it t e r Un it .
F ig .C3.19b ) : P h o t o g r a p h O f Re c o r d e r Un it .
69
wind calibration chart
1-mark length ; 2-time interval
wine
bo0
9
G ( m ii b
e /
h r!
15 i~
TV
!
\
5
10
15
20
m ark !e n q t h ( m m ) /t im e interval (se c )
mark length
time interval
Fiu.C3.20) : C a l ib r a t io n C u r v e F o r Wind S p e e d Me a s u r m e n t .
70
Fio.C3.21 a
& b) : Sample Record Of Wind Speed.
71
variable
speed
of 0-10
miles/hour.
The
output
of
the
has not been used for the present study but would
be used
for
further
analysis
that
is
going
on
system
effectively
in association
with sodar echogram.
C5i>. FAST RESPONSE RAIN GAUGE:
Accurate
very
data
on
total
essential
to
microwave signal
rainfall
understand
inherent
rainfall
But
it has
mm/hr
been
generally
attenuation
that period.
capable of
principle
rain
So,
of
that
this
pass
the drops
drop
then
through
VFC
of
sens i t ive
paper
heavy
a
Thus,
when
the
two
and
a
two
blanks.
ten
conditions
lmm/minute and
timer.
be
The
very
the
each
TP. -43.
and
is
expected
is
The
rain
fed
of
form
applied
heavy
we
chart
for
set
get
economic
device
90 sec
a
at
is marked
through
a
eight
use
so
of
recorder
on
h
rain
is
v
eight
paper
black
a
very
on
the chart
the
are
space
So
dot
chart
a
dro
drops.
in
marks
paper
an
During no
slow
may
rain
dot
incorporated.
correlatig
nozzle
receive
the
ten
the system
72
on
fhe
is
we get a blank
of
is also
move
each
of
Each
then
the
basic
water
the
a black
marks
identification,
the
We
after
and
a
size.
to
recorder. When
is
The
number
to
during
instrument
the
fed
the
in
rain collected
essential
count
time.
appreciable
in rain rate.
to
of
to 25 0
of 200
to have an
unit.
drops,
For
be
amplifier
signifying
automatic speed control
rain
is
funnel
is very
traces
of
may
essential
1993
the
in
rain
changes
and
which
individual
set
seconds
pulse
pulse
rain
rates
it are of equal
drop
used
blanking
a
power
of
integration
out of
a
a rain
too close for
between
through
and
rain
cutoff
gauge
falling
s ignature
between
rain
attenuation
fast
large
to fast changes
produces
a
link
CBa.rba.ra. et.al.
to
their
few
is a very
responding
drops
allowed
it
of
for
to
are
The conventional
recording
that heavy
last
leading
10 GHz.
in
because
observed
rain
intensity
tilting bucket or tripping buckets
limitations
intensity,
rainfall
the
generally above
gauges such as syphon type,
have
and
speed
paper
not
of
by a
norma 1 1y
microwave fading
FIg {3 .22 .) B L O C K
D IA G R A M
OF F A S T
73
RESPONSE
R A IN O A U G E
F ig .C3.23) : Ph o t o g r a p h O f C ir c u it Dia g r a m O f F a s t Re s p o n s e
Ra in Ga u g e S y s t e m .
74
Calibration curve
fast response rain gauge
300
rainfall rate fmm/hr)
L.
200
'
150b
100 r
500
10
20
SO
40
Number of drops (in 10 sec,}
00
a e rie s A
F ig .C3.24-) :
C alibration C u r v e F o r Me a s u r in g T he Ra in F a l l
In t e n s it y
75
FlG.C3.25
A
& EO : SAMPLE RECORDS OF RAIN FALL INTENSITY
Me a s u r m e n t .
76
at 6/7 GHz. However this is developed to examine the effect of
fast changes in rain rate on microwave fades because of
large
rainfall rate situation over this region.
The block diagram of the system is shown in the fig
(3.22!
The system consists of the following units
1
Collector and sensor
2. Counter
3. Recorder
4. Marker
5. Automatic speed control
(The photograph of the system is shown in fig. 3.23!
To find out the rainfall
rate,
a calibration
associating the number of drops
chart
in ten seconds with
is drawn
rainfall
rate mm/hr and is shown in fig.(3.24). This chart is drawn to
find the rain fall rate up to 250 mm/hour.
The sample records of different rainfall
in the figs(3.25a,b). Fig.
intensity are shown
(a) represents the rain falIrate of
moderate intensity varying from 14 mm/hour
to 28 mm/hour and
fig.(b) shows variation of rainfall rate up to 65mm/hr.
it is
seen from the plot, that any changes in rainfall rate within
seconds ( or even in mili-second) can be easily resolved.
E 3.71 CONCLUSION :
This chapter describes the different terrain features over the
four
links
fadings.
Fresnel
for
observation
of
6/7
GHz
microwave
The path profile analyses point to the fact
zone clearance
and Milmilia
Laopani-
used
links,
Habaipur
is though
the first
link
for
well
fresnel
K
= 2/3
maintaned
zone
that the
over
Maopet
is obstructed
condition.
in
Relatively
small clearance is noted over Jorhat link for both, K = 4/3 aid
K = 2/3 conditions. The microwave setup and calibration
77
procedure
is described.
Facsimile
recorder,
The system and circuits
Fast
response
recorder, Telemetric anemometer,
dry
and
wet
like Sodar,
temperature
and Fast response rain gauge
etc. that have been developed are discussed
and sample record
are
of
presented
systems over
for
each
case.
The
merits
the
developed
the commercially available ones are highlighted
The system calibration curves are shown along with the circuit
b 1ocks.
CHAPTER - 4
OBSERVATION ON FADES IN THE LOS MICROWAVE LINKS.
[ 4 .1 ]. INTRODUCTION :
Information on fade
signals
is
depth,
necessary
fade
for
rate,
and
fade
duration
designing of a reliable microwave
link. So test runs are made over a link to receive these
so
that
modifications
of
in
the
after receiving the dynamical
system
can
variations
data
be introduced
of these parameters
or in case of estabilished links, the fade character data help
in
the designing
environmental
The
fade
different
LOS
situations
1 9 7 9 ,M a s \ im d a r- & t
is made by
of
a l,
(
1
are
9
over
4
7
a similar
terrains
> S t & p h a r is & n
and
and
M og& ns& n
An extensive review on these aspect
19745
S te p h e n s o n
data
links
C l9315.
therefore
collected
terrain conditions
over
as mentioned
four
links
of
in the chapter
3.
The relevant parameters for such a study are the probability
(P <L )
that
signal
level
the
L,
amplitude
v(t!
the expected
below a specified signal
will
number
be
of
below
fades
a
per
To
characterise
the
unit
time
level and the average duration t(L)
of the fades below L. These parameters are all
the specified signal
specified
functions
of
links,
the
level L.
fades
occurred
over
these
amplitude data are recorded in recorders with appropriate time
constants so that the fast fading over a particular
recognised.
So,
the
time
constant
of
the
link
recorders
is
are
appropriatly selected after a few test run and these are set
at
100 m sec.
for
grouped at hourly
this interval
all
interval
the four
but when
links.
The fade data are
the fade
rate
is high,
is reduced accordingly. The fade depth is coded
at intervals of 10 dB level and the duration the signal
79
level
remains below a specified level is found out. Also determined
is the number of times the signal enevelope crosses the median
level
in the upward direction.
is known
The
as number of fades and
number
of
intersections
this fade number
per unit
time is called the fade rate. The average fade duration at any
fade depth is obtained from the ratio of the total time at or
below
the fade depth
level
to
the
number
of
fades
of
this
depth.
[ 4,2] TYPES OF FADING :
The fade character analyses over these links indicate presence
of
different
Milmilia,
fade
Maopet,
figs.(4.1
types.
Representative
Laopani
:a,b,c,d,e).
and
The
Motapahar
fade
fade
links
characters
patterns
are
are
of
shown
in
basically
classified in terms of fade depth and fade rate as shallow and
deep, or slow and fast fadings as discussed below.
1.
Fig. (4. la)
fading.
This
represents
type
Milmilia, Maopet
fading, the
of
and
the
fast
fading
or
scintilation
is observed
type of
The preferable
is always
time of developement of
less
this
fading lies in the post sunrise hours within 9 to 10
hours and fading continues
hours).
In this type of
to 160 fades per hour.
The depth of fades are generally shallow and
than 6 to 7 dB.
of
generally over
Laopani- Habaipur link.
fade rate varies from 20
type
to post
midday
hours
(13 to 14
The probability of occurrence of this type of fading
varies with season and will be discussed in the next section.
2. Fig.
(4.1b) portrays
a slow and shallow
This type of fading is observed
depth
in all the four links and the
varies from 2dB to lOdB. The pattern is independent of
season but is
3. Fig.
type of fading.
usually seen during
(4.1c) shows
pre midnight hours.
rapid and deep fades.
80
In this type of
F ig.(4.1:a , b , c . d , e O
:
Ph t o g r a p h
Of
Sa m p le
Rec o r d s
Different T ype Of F a d in g s Ov e r T he Mic r o w ave L in ks Under
Study.
81
Of
fading,
the
depth
varies
from 5 to 40 dB and
the signal
crosses the median level 4 to 15 times
per hour. Fades of this
type are detected
links and the preferred
in
all the first
time of occurrence is early morning hours.
4. Fig.14.Id)
shows
slow and deep
fades.
In
this type
of
fading the fade depth varies from 5 to 20 db and the signal
crosses
the
median level 1 to 3
times
this type are detected in Milmilia,
and
preferable
time
per
hour. Fades of
Maopet and Laopani
of occurrence
links
is pre or post midnight
hours depending on the terrain situations.
5.
Fig.
(4.1e)
shows
a
typical
fade
pattern
where
fast
fades are modulated over slow fadings. Such pattern is seen in
Milmilia,
Maopet and
Laopani links.
[ 4.3] FADE DEPTH DISTRIBUTION AND MULTIPATH OCCURRENCE FACTOR
In the study of signal
fades due to multipath
interference,
the cumulative amplitude distribution P(V<L) of
to be determined.
Here,
deep fade is
fade depths are expressed
probability of fade is expressed on a log scale.
which
describes
the
typical
distribution
is
in dB and
The equation
P(V<L)
= a L
2
where V is the envelope voltage of the randomly fading signal
normalised to its non faded signal, L is any specified signal
level and a is the parameter depending upon fade environment.
The result of
fade depth distribution analyses
probability distribution,
diurnal
and seasonal
in terms
character
all the three links are described in the following section.
is
observed
that
signal
over
Motapahar
practically no fades and therefore this
link
of
for
It
suffers
link is normally not
taken in to account for indepth studies.
C13 Milmilia -Durgasarovar Link A .Probabi1itv Of Fade Distribution !
For this analyses,
the fade depth distribution
82
is plotted by
taking
all
the data
probability
depth
collected
distribution
level
is
shown
in
follows the log normal
The value of
is
then
£
fig.
study
obtained
(4.2)
and
periods.
at
The
various
the
fade
distribution
fig-
(4.2).
(the multipath occurrence factor) for this link
determined
slope of
so
the
pattern as is seen from
and
fade
2
link can be defined by P = 0.609 L .
distribution over this
The
plot
over
this
line
fixed
at
is found
out
0.609.
to be
So
the
11 dB/decade
of
occurrence of fades.
B. Diurnal And Seasonal Variation Of Fade Occurrence:
The temporal
variation pattern of fade depth occurrence
then determined by making a morphological
is
study of the same.
For this purpose fades of depth within 1 to 45 db have been
taken.
Fig. (4.3)
shows
that
the
probability
of
fade
occurrence
is
maximum during winter season where fadings are detected over
30% of winter periods.
It is followed by summer months where
20% of the total summer data show fadings. The fading is less
in other seasons.
Fades over this link show a clear diurnal
character (fig 4.4) and the fade patterns too are different at
different times of the day.
the early morning hours
Deep fades are detected more
(type c & d as shown
during all the seasons except for summer when
abundant in premidnight hours and when
seen.
in fig.
in
(4.1),
fades are more
midday fades are often
It is also to be noted that midday fades are fast with
low depth whereas the early morning fades are rapid and deep.
C2D. Maopet-Durgasarovar Link :
This
by
link runs over hilly terrain and this terrain
ever green as well
probability
pattern
distribution fig.
factor
as by the desidious forest.
over
(4.5).
this
To receive
(ie. <?), the procedure
mentioned above,
link
follows
£
adopted
value follows
83
The fade
log
normal
the multipath occurrence
in
Milmilia
is followed on this link too. The
received by using the
is covered
2
link as
curve then
P =0.714 L . The slope of
MILMILIA-DURGASAROVAR LINK
PC OF TIME FADE DEPTH IS > ABCISSA.
EQUATION OF B E S T FITTING CURVE . P - 0.609
F IG .C 4-.2) . P R O B A B IL IT Y
OCCURRENCE
OF
FADE
DEPTH
Milm ilia - Du r g a s a r o v a r Mic r o w ave L ink
84
OVER
S e a s o n a l V a r i a t i o n Of Fade O c c u r r e n c e .
c
o
4i
h
3
O
O
0
o
■D
O
CL
F ig .C
4.3) : Seasonal variation Of PC Or Fade Occurrence Over
Milmilia , Maopet And L aopani L inks .
85
Diurnal Variation Of Fade Occurrence
PC Of F ad e
Milmilio Durgoearc?/ar Link
sum m er
+■
Tim e (in H o u rs)
0
Poet M on soon
W inter
&
P re M onooon
F ig .(4.4) : Diu r n a l V a r ia t io n Of PC Of F a d e Oc c u r r e n c e A t
Differ e n t
Se a s o n s
Ov e r
Mil m il ia - Du r g a s a r o v a r L in k .
86
this curve
(4.5).
This
factor indicates that attenuaion decrease rate though is
same
over
a
is 11 dB/decade of probability
marshy
probability
much
of
higher
variation
winter
) and
receiving
fadings
than
of
fig.(4.3).
(Milmilia
fade
It
that
months
of
that
with
34
hilly
over
over
the
of
(Maopet),
hilly
The
link
is
fades
occour
occurrence,
the
terrain
link.
this
maximum
%
link
Milmilia
occurrence
shows
a
fig.
is
seasonal
shown
in
during
followed
the
by
the
premonsoon months.
The diurnal variation of fading at different seasons over this
link
is shown in fig. (4.6). Here too, we have taken fades of
depths ranging between 2 to 45 db. A clear diurnal
in the occurrence
that the fading
preferential
hours
more
(3 )
The
of
is
has
generally
period
except
fades
of
been
received.
a nocturnal
occurrence
variation
Figure
shows
phenominon with
during
early morning
for summer months when the fades
are
seen
often in premidnight hours.
Laopani
-
H a b a ip u r
probability
shown
in fig.
follows
the
of
:
ocurrence
(4.7).
log
L in k
of
Here also,
normal
fades
over
pattern.
Similarly,
to be .774 and then the equation of the
slope
of
the
using this
curve
is
is
link and
multipath
is found
distribution curve
as P = .774 L . The
dB/decade
occurrence as shown in the fig.(4.7).
the
2
parameter
10
link
the fade distribution curve
occurrence factor £ is calculated for this
is received by
this
of
probability
The seasonal
of fadings over this link is shown in fig.
of
variation
(4.3) which gives
that the probability of occurrence is heighest during summer
months.
While computing this figure.
all fades up to -45 dB
have been considered.
The diurnal variation of occurrence probability of fadings
shown
in
the
fig.
(4.5),
which
indicates
that
is
nocturnal
fadings are more often detected over this link. Well developed
fadings, with fade depth
> 45 dB, are present during midnight
87
MAOPET-DURGASAROVAR LINK
i i
i
o
j ___i i i
O
q
o
o
o
d
PC OF TIME FADE DEPTH IS > ABCISSA.
EQUATION OF BEST FITTING CURVE : P - 0.714 L 2
i i i i i i i i i I it t r rn
]
20.00
i i | i ii i i i m i
40.00
FADE DEPTH IN DB
60.00
Fig.(4.5) . Probability Occurrence Of Fade Depth Over
Maopet - Du r gasar o var Microwave L ink.
88
Diurna! variatio n Of Fade O c cu rren c e
% Of Fade O ccurren ce
Maopet — Durgasarovar Link
— I------ 1-------- 1-------
7
:
i
—r~
—T~
11
13
15
" I —
17
19
i
I
21
23
Time fin Hours)
Post Monsoon
0
Winter
Pne Monsoon
F ig.(4.6) : Diurnal V ariation Of F ade Occurrence At Different
Seasons Over Ma o pet - Du r g a sa r o va r L ink .
89
LAOPANI-HABAIPUR LINK
EQUATION OF BEST FITTING CURVE : P - 0.774- L 2
<
01
01
F ig .(4-.7) : Pr o b a b il it y Oc c u r r en c e O f F ad e Depth o ver
L a o p a n i - Ha b a ip u r L ink
90
Diurnal Variation Of Fade Occurrence
O ve r L o a p a n i— H a b a ip u r link.
‘u m m e r
+■
Seasons
Poet M oncoan
v
Winter
&
F ig .C4-.8) : D iu r n a l V a r ia t i o n O f F a d e O c c c u r r e n c e A t D if f e r e n t
Se a s o n s Ov e r L a o p a n i-
91
Ha b a i p u r L in k .
Pne Monsrinn
hours and we detect only few cases of day time
fadings
as
can
be
seen
from
the
fig.
development of
(4.8).
In
diurnal
variations, there is a marked difference between the P&T links
and the railway link. Here
premidnight occurrence of fading
is more than the early morning fade events.
[4.4] FADE RATE CHARACTERSTIC :
Fade rate of a signal
is as important a parameter as the fade
depth.
analyses
Comprehensive
of
such
parameters
help
understanding the dynamical behaviour of the system.
rate
of
microwave
fades/hour
seasonal
. The
signal
fade
variation.
may
rate
The
vary
also
fade
from
has
The fade
1 fade/hour
a
diurnal
rate distribution
in
as
to
120
well
as
pattern
with
respect to these aspects for the three links are described in
the following section.
MAOPET - DURGASAROVAR LINK
s
Fig.
(4.9) shows the probability of occurrence of
fade
rate
levels
for
a
complete
season.
This
different
shows
that
probability of occurrence of fades of rate 5-10 fades/hour
is
maximum.
in
The
fade
rate
as
high
as
120
fades/hour
shown
fig.(4.la) has also been observed during summer with afairly
low occurrence probability (.5% only).
The cumulative distribution of average fade rate also reflects
this
pattern
fig. (4.10).
of
seasonal
Here,
we
see
dependence
that
for
of
50%
fade
rate
probability
value
level,
winter favours 5 fades/hour while during summer it goes to 10
fades/ hour.
Fig. (4 11)
represents
the average
diurnal
variation
of
fade
rate. This shows that fade rate is maximum during daytime and
minimum during night hours.
in summer
winter
months
months
with
with
8
18
The average fade rate
fades/hour
fades/hour.
and
During
is
is highest
minimum
post
monsoon
pre-monsoon periods, average fade rate is 15 fades/hour.
92
during
and
MILMILIA - DURGASAROVAR LINK I
The analyses on fade rate for this
link have also been done
following the procedure adopted for Maopet
represents
the probability
of
occurrence
link.
of
Fig.
fade
(4.12)
rate
of
a
particular level over Milmilia Durgasarovar path. Here too, we
note that the fade rate varies with season and probability of
occurrence is highest during winter months with 5 fades/hour
which is detected 34% of the total winter period.
However the
maximum fade rate is observed in summer when 80 fades/hour is
noted
with
.1%
occurrence
of
probability.
The
maximum
fade
rate for pre/ post monsoon and winter season is limited at 40
fades/hour.
Fig (4.13) shows the cumulative distribution of the fade rate
on the seasonal basis. At
is 5 fades/hour
in
50% probability level, fade rate
winter and
and postmonsoon months while
10 fades/hour
in
summer
in
premonsoon
for 50% probability
level, the fade rate is 12 fades/hour.
Fig (4.14) gives the diurnal
It shows
during
that
midday
the
fade
in summer
rate
variation of average fade rate.
with
22
fades/hour
is
maximum
months.
LAOPANI HABAIPUR LINK !
The fade rate analyses over this link have been carried out in
a similar way as described for other two links and the maximum
fade rate is observed during summer as we have seen for
other
two
occurrence
links.
of
fade
months of the year.
Fig.
present
shows
the
probability
levels
at
different
The fades with
160 fades/hour
are more
summer.
But
and
of
rate at various
often detected during
less during winter,
(4.15)
the
these fast fades are very
while fade rate up to 140 fades/hour are
during pre / post monsoon period.
93
PROB. OF OCCURRENCE OF FADE RATE
FADE RATE (FADES/HOUR)
Fig.C4.9) : Probability occurrence of F ade Rate At Different Seasons
Over Milmilia - Durgasarovar L ink.
94
FADE RATE (FADES/HOUR).
PC. OF TIME ORDINATE EXCEEDED.
F ig .C4-.10)
: Cu m u la tive Distribution Or F ade rate At Different Seasons
Over Ma o pet - Du r g a sa r o va r L ink .
95
Diurnai Variation Of Average Fade Rate
Maooet— Durm*nmwo.r i :_i.
1 9
*
Z &
w
3
oc.
vi
c" a
A v e r a g e F ade Rate ( F a d e s / H o u r )
18
17
*
3
-
lum m er
Post Monsoon
Pro Monsoon
F ig .C4-.11)
Di u r n a l
V a r ia t i o n
Of
Aver ag e
S e a s o n s O v e r Ma o p e t -
96
Fade
Ra t e
D u r g a s a r o v a r L in k .
At
D if f e r e n t
R A TE .
F A D E
O F
O C C U R R E N C E
O F
P R O B .
Fig
( 4 .1 2 )
. Probability Occurrence Of Fade Rate A t Different Seasons
Over Milmilia - Du rgasarovar L ink.
97
FADE RATE (FADES/HOUR).
0 .1
1
10
1 0 0
PC. OF TIME ORDINATE EXCEEDED.
Fig.C4.13) : Cumulative Distribution Of Fade Rate At Different Seasons
Over Milmilika -D urgasarovar L ink .
98
D iu r n a l V a r ia t io n
O f A v e ra g e
Fade
R a te
Average
Fade
Rate ( F a d e s / H o u r )
Milmilia — D u rg a s a ra v a r Link
Seasons
lum m er
+■
Winter
Post Monsoon
&
Pro M onsoon
F ig .C4.14) : D i u r n a l V a r ia t io n O f A v e r a g e F a d e Ra t e A t
D if f e r e n t
Se a s o n
O v e r Mil m il ia - D u r g a s a r o v a r L in k .
99
PROB. OF OCCURRENCE OF FADE RATE.
FADE RATE (EADES/HOUR)
FiG.C4.15y : P r o b a b i l i t y O c c u r r e n c e O f F a d e Ra t e A t D if f e r e n t
Sea so n s
over
L a o p a n i - H a b a i p u r L in k .
100
FADE RATE (FADES/HOUR).
151.00
101.00
51.00
1.00
n
i—
i— i— i i i i | ------------------ r~
i— i— i i i 111
PC. OF TIME ORDINATE EXCEEDED.
1
10
100
F ig .(4.16) : Cum ulative Distribution Of Fade Rate At Different
Seasons Over L aopa n i -H abaipur L ink.
101
Diurnai Variation Of Average Fade Rate
L a o p a n i— Hofcoipur Link
O
CD
Cb
-P-
TO
O
®
C*
A v e r a g e F a d e Rate ( F a d e s / H o u r )
N)
4*
26
4
-t
C
2
0
■
11
13
15
i
i
i
17
i
i
21
23
Seasons
P ost M onsoon
F ig.C4-.17)
Diu r n a l
V a r ia t io n
Winter
Of
F ade
Pro
Ra t e
S e a s o n s Ove r L a o p a n i -H a b a ip u r L in k .
102
At
Monsoon
Different
This picture is also reflected in the cumulative distribution
of fade rate
(fig 4.16).
The fade rate which
is high during
summer with 20 fades/hour at 50% probability level,
goes down
to 8 fades/hour during winter.
We then examine the presence of diurnal variation,
the fade values.
A clear preferential
if any,
of
deve1opementa1 time of
fast fade is noted. The fast fades start developing after 3/4
hoursof
local
sun rise and
hours, f ig. (4. 17),
the
fade rate
average
fade
increases
rate
goes
till
up
prenoon
to
12/14
fades/hour during summer and premonsoon pre midday hours,
[ 4- 5] FADE DURATION :
The average fade duration at any fade depth level
from the ratio of
total time at or below the fade depth to
the number of fades
average
fade
at that fade level
duration
for
Milmilia-
shown in fig.(4.18). The curve
From this observations an
fade
For
the
Durgasarovar
level
average fade
is defined by t= 550 L and
region.
{Viga.ri.ts 1Q70). The
link
is
represents the plot of average
fade duration against each fade depth
curve
is obtained
Maopet
for
duration
this
link.
distribution
is best fitted for the deep
-
Durgasarovar
distribution curve for the average fade duration
Link
the
is shown
in
fig.(4.19), For this link too an equation for best fitting of
the curve is found out and isdefined by
t = 514 L. Similarly
the average fade distribution plot for Laopani- Habaipur
is shown in fig.4.20.
link
The best fitted equation for this case
is t = 246 L
This
analysis
experince
shows
fades
of
that
large
Milmilia
durations
and
with
Maopet
the
links
cofficient
factors 550 and 514 respectively, while the Laopani - Habaipur
link suffers fades of small
246.
This study
durations with cofficient factor
indicates that fading mechanisms
districts of Assam valley may not be the same.
103
over
two
FADE DURATION (IN SECS.)
1
| i i i i r n r r " f i 'i r i " n
0.00
20.00
i i i] i m
m
i i i i |
40.00
FADF DEPTH IN DB
60.00
F ig .C4-.18) : Dis t r ib u t io n C u r v e F o r A v e r a g e F a d e Du r a t io n
Ov e r Mil m il ia - D u r g a s a r o v a r L in k .
104
I 1 I I I I I_________
I
I
I I I I I 11
o_________
I
I
o
o
FADE DURATION (IN SECS.)
1“j- —
"I l"Tr I I I I I
0.00
|
I I I I I I I I I JTTTTTTl I' I
20.00
40.00
FADF DEPTH IN DB
|
60.00
Fig.C4-.19) : Distribution Curve For Average Fade Duration
Over Maopet - Durgasarovar L ink .
105
FADE DURATION (IN SECS.)
FADF DEPTH IN DB
u
ir . r a
I I O A M - .L .V
J
n » f - » T r .i r i i
i T i » '\ k
L y io i K i d u i i w i n
i
r*i
ir»i
ti~
U U I \ V tL
r,~
OR
A » / r n
r-\
a
4
v L.r^AV
Ov e r L a o p a n i - Ha b a ip u r L ink .
106
C
I
a r*»—
/\L 7 C _
r%
.
Tirtt
1 7 V j r \ A 1 IW IN
in
a
i
The results are presented
in the following table
TABLE-4.1
Summary of characterstic features of fade depth, fade rate
and fade duration as observed over the microwave links.
Parameter to be
studied
l.Type of
Link 1
Milmilia
Link 2
Maopet
link 3
Laopani
1.
Fast S h a l 1ow 1.Fast,shal1ow
1.
F a s t , s h a 11ow
2. S 1ow,shal1ow *
2.SIow,shal1ow 2 . s 1o w ,s h a 11ow
3.Rapi d ,deep
3.Rapid,deep
3.Rapid,
deep *
4.Slow,deep #
4 Slow,deep *
4 . S 1ow,deep
5.Fast fading
5.Fast fading
5.Fast fading
modulated
m o d u 1ated
modulated over
over siow
over slow
fading
fading
slow fading
f ades
* indicates
the dominating feature of the fading.
2.FADE DEPTH
Equation for P =.609 L2
the probabi1ity distribu­
tion of fade
depth
Slope for
equation of
of the best
fit for the
11
of
of
P = .714 L2
dB/decade
probability
occurrence
11 dB/decade of
probabi1ity of
occurrence
P = ,714 L2
10 dB/decade of
prob a b i 1i ty of
occurrence
fade dist­
ribution curve.
Link cutoff
003
Seasonal
Winter
variation
of fade occurrence
Diurnal
of
variation
fade
005
%
Winter
maximum
Summer
maximum
Early morning
occurrence
.009 %
%
Early morning
maxima
maxima
107
max imum
Premidnight
maxima
3.FADE RATE
At 50% probabil
ity level
Seasonal
10 Fades/hour,
variation
Diurnal variation
15 Fades/hour,
20 Fades/hour
Summer Maximum. Summer maximum.
Summer maximum
Pro Midday
Pre Midday
Pre Midday
maximum
maximum
maximum
t =550 L
t =514 L
t =248 L
Equation for
Ind icat ing
Indicating
Ind icates
the best fitted
Presence of
Presence of
Presence of
straight 1ine
Slow Fades.
Slow Fades.
Fast fades.
FADE DURATION
[ 4.63 COMPARETIVE STUDY ON MICROWAVE FADINGS WITH OTHER
STATIONS :
Results of seasonal and diurnal variations of fade depth /fade
rate observed over the above mentioned links are compared with
those
reported
from
some
other
stations.
The
geographical
configuration of the stations are given below
1.
Low
latitude
interior
region
of
American
Continents
American
continents
(Palmetto, Ottawa and Omaha).
2. Low
latitude
costal
region
of
(Jacksonv i1 1e ).
3. Low latitude tropical
(1) FADE DEPTH
Seasonal
region
of India
(Delhi, Tirupati).
:
Variations
:
From
the
earlier
discussions
and
analyses it is clear that fade occurrence over Milmilia and
Maopet
and
the
links
fade
reaches
maximum
occurrence
over
during
winter
Laopani
108
link
months
reaches
fig. (4.2)
maximum
during
summer.
reported by
We
now
compare
these
patterns
with
those
other groups.
It is to be noted that while analysing these features as shown
in table 4.1
(and also in our figures) we take in to account
fades of all depth
Palmetto
link,
threshold
level
(- ve excursion
fades
up
to only
of
fading
defined.
variation
over
represents
links.
The
occurrence
the
fading
winter
of
Summer
fades
for
over
Fig. (4.21)
and
overe
Jacksonville
shows
Jacksonville
character
But over
-20 dB are considered.
considered
Ottawa are not well
pattern
) up to -45 db.
Palmetto
fig, (4.22)
and
Ottawa
variations
Jacksonville,
and
the seasonal
while
Equinoxial
The
Ottawa,
in
%
Palmetto,
Milmilia, Maopet, Laopani are shown in the table 4.2
Table 4 2
Seasonal Variation Of Fade Occurrence Over Different S tat ions
Stat ions
Summer
1.Jacksonv i11e
2.Ottawa
3.Pa 1metto
4.Mi 1mi 1ia
5.Maopet
09»
14»
20*
Z6t
26$
05S
10
27
6 Laopani
40*
26
Post monsoon
07
06
Winter
°2*
01t
34*
33
$
19
Pre Monsoon
4.6
05
05
16
29
$
26
# - Maximum Occurrence
$ - Minimum Occurrence
It is clear from the table C4.23 that over
Jacksonville the
maximum occurrence of fading is observed during winter months
like that observed over Milmilia and Maopet links. However the
109
fade events are more or
less evenly distributed over Maopet
link for the whole season.
On the other hand the fade occurrence character over LaopaniHabaipur
is
more
akin
to
those
detected
over
interior
continental stations like Ottawa and Palmetto as shown in the
fig.(4.22). The similarity in all
maximum
in
fade
occurrenceis
these three links a summer
clearly
detected.
This
is
a
significant observation because we generally do not expect to
receive
stations.
costal
But
region
we
must
effect
point
over
out
these
here
two
that
land
these
links
located very near to the mighty river Brahamputra fig.
Where the river width may go up to 8 km
locked
are
(3.1).
at places.
B. Diurnal variation Of Fade Depth:
In this
section
an
attempt
has
been
made
to
compare
the
diurnal variation pattern of fade occurrence of the links over
Assam valley with different stations as given in the table 4.3
Table : 4.3
Stat ions
Path Length
1.Omaha-Pal metto
2.Palmetto
3.De1h i-Meerut
4,Tiruttani-T irupati
5.Milmi1ia-Durgasarovar
6.Maopet-Durgasarovar
7.Laopani-Durgasarovar
57 Km
31 Km
63.5 Km
60 Km
41 Km
64 Km
55 Km
Hilly
Hilly
Plain Terrain
Hilly Terrain
Marshy
Hilly & forest
Marshy & Foresty
Our earlier observation on diurnal
shows
that all
the study
links
maximum
occurrence
of
fades
morning
hours
to
prenoon
(up
Geographical Location
fade occurrence character
follow
during
period
post
in
the same
midnight
many
pattern
and
cases)
of
early
except
during summer months when more events are detected during pre
110
Seasonal
V a ria tio n
Of fa d e
O ccurrence.
P e rcenta ge O f Annual
F a d e T im e
O v e r C o s t a l R e g io n (J a c k s o n v ille )
M o n th s
F iq.C4.21) : S e a s o n a l V a r ia t io n O f PC Of F ad e O c c u r r e n c e
Lo w L a t it u d e s C o s t a l Re g io n S t a t io n s ( J a c k s o n v il l e ).
ill
Ov e r
Seasonal Variation Of Fade Occurrence.
P e r c e n t a g e 'O f A n n u a l F a d e T fm e
P a lm e tto & O tta w a (In t e r io r R e g io n )
M o n th s
□
P a lm e tto
+
O tta w a
Fio.C4.22) : S e a s o n a l V a r ia t io n O f PC O f F a d e O c c u r r e n c e
O v e r L o w L a t it u d e In t e r io r Re g io n S t a t io n s CPa l m e t t o & O t t a w a )
112
midnight hours.
It is to be noted that though Laopani-Hbaipur
experiences
totally
patterns,
a
different
seasonal
fade
occurrence
the diurnal variation features are same as observed
for the other two links. We will now examine the diurnal
occurrence
character
those observed
over
by us.
some
other
It is seen from
links
in
fade
relation
the fig.
(4.23)
to
that
probability of fade occurrence over Omaha- Palmetto link (path
length 57 Km) shows the pattern similar to that observed over
Assam valley. They have also received a
midnight
links.
occurrence
in fade
The Palmetto Link
as
(path
shown
summer time high pre
by
Milmilia
length 31 Km)
& Maopet
also shows
the
same pattern, fig.(4.24).
Fig.(4.25)
over
shows
Delhi-
the diurnal
Meerut
link
variation
(Prasad
of
hourly
et.aL,t990).
fade depth
This
figure
however does not speak the occurrence character of fades.
may bring here
We
our figure on diurnal variation of fade depth
fig.(4.26) over Milmilia link.
this picture on fade depth
It is however to be noted that
is true for other
1inks
too.
We
note from the figure that the fade depth is always high during
night to morning hours and reaches the heighest
5- 6 hours in the morning. We also
value within
note a similar feature on
fade depth variation over Delhi- Meerut
link fig.(4.25) where
average fade depth varies between 2 db in midday
the
early
morning
hours.
The
fade
depth
to 13 db in
variation
patterns
over this link and also those over our links show that average
fade depth is always low during daytime and high during
post
mid night and early morning hours.
However, for some links where cutoff or fade out conditions are
very
often
character
generated,
in terms of
it
is worthwhile
link cut off events.
fade out time over TirupatiKm)
to analyse
Tirutanni
link
the
Fig. (4.27)
(path
(2.27)
shows
that
113
link
cut
shows
length 60
where fade out conditions are very often detected.
st. al. t9932>. Fig.
fade
off
(Rao
events
D iu rn a l V a r ia t io n Of F a d e O c cu rren ce *
Time Beyond Level(10*3 Sec)
Over Omaha— Palmetto Link (57 km Path)
Time (EST)
0
Summer
+■
Winter
Fig. (4.23): Diurnal V ariation Of F ade Occurrence
Over Omaha - Palm etto L ink.
114
D iurn al V a r ia t io n Of F a d e O c c u r r e n c e
k m ).
Time Bay end Leve»l( 10 * 5 Sec.)
O ver P a lm e tto L in k P a th (31
T lm e(E S T )
□
Sum m er
1-
W in te r
F ig .C4.24) : D iu r n a l V a r ia t io n O f F a d e O c c u r r e n c e
O v e r P a l m e t t o L in k C31 KM).
115
Diurnal Variation of Fade Depths
Delhi— Meerut Link (63.5 Km)
13
12
'H ------------h
11
A v e r a g e F a d e D e p th ,(In d b )
10
9
5
h—er"
7
6
5
4
4
JET’
1
-
--e— b—ef
o
~T ~
12
u
i
16
I—
'20
24
T im e ,H ra LT
□
Winter
F ig . (4 .2 5 ) : D i u r n a l
+
Pre Monsoon
v a r ia t io n
O f A v e r a g e F a d e De p t h
O v e r D e l h i - Me e r l jt L in k .
116
Ave ra g e f a d e d ep th
Diurnal V ariatio n Of Fade Depth
F ig .C4.26) : Diu r n a l V a r ia t io n O f A v e r a g e F a d e De p t h
O v e r Mil m ilia -D u r g a s a r o v a r L in k .
117
Diurnal Variation Of Fade Out
No o f Fade out
Tiruttani— Tirupati Link (6 0 K m )
Tim * 1ST
□
Winter
+-
Pro Monsoon
F ig . (4,27) . Diu r n a l V a r ia t io n O f F a d e O u t
O v e r T ir u t a n n i - T ir u p a t i L ink C 60 Km )
lie
are highest during early morning hours of pre monsoon period
and
fade out condition is
This
compartive
study
lowest
indicates
character with large fade
basically
well
during
that
events
maintained
post monsoon period
the
diurnal
fade
during night to prenoon is
over
different
link
paths
irrespective of the frequency and path lengths. However, season
to season variation in fade events may be different depending
on the local environment and terrain situations.
C23.Fade Rate :
In the above article we have described the fade occurrence and
fade depth variation at different seasons
and at different
hours of the day. Another important associated parameter that
needs analysis is the fade rate variations.
So this parameter
will now be examined over different link paths.
It is seen from our earlier discussion in this regard that the
fade
rate
various
varies
hours
of
from
the
2
day
fades/hour
to
25
depending
upon
fades
/hour
seasons.
While
during this analysis we have taken into consideration of
types of fading including the multipath types.
be
noted
that
corresponds
However
figs.
to
there
fades/hour
fade
average
are
during
(4.11)
rate
pattern
fade
rate
instances
summer
(4.14)
that
for
of
have
a
Fig. 14.2a).
(4.17)
that
It
fades
start developing in the morning hour,
with
of
local
noon.
described
seen
high
period.
than
100
from
the
fade
rate
generally after 3 - 4
hours of sun rise. This fade with fast
2-3 hour
been
more
is
all
It is also to
particular
getting
at
rate continues up to
This type of fading
is very rarely
detected during night hours, when multipath fadings are often
developed.
developed
It
is
during
to
late
be
mentioned
night
or
that
early
deep
fades
are
morning
hours
and
these features are maintained at different seasons.
Fig.(4,28)
that gives a diurnal fade rate variation pattern over Delhi Sonepat path carries the same
119
Diurnal Variation Of Average Fade Rate
Fades
Per Hour
D elhi—So nip e t L in k
lu m m e r
F iq .C4-.28)
+■
P o st Monr-oon
Tim e (Hns, 1ST)
v
W inter
&
Pre Monsoon
Diurnal V ariation Of Average F ade Ra te
Different Seasons Over Delhi - Sonepet L ink .
120
At
PC
OF
T IM E
FADE
DEPTH
MlLMILIA - DURGASAROVAR LINK
0.00 0.00
r r rr~T r n T y m m
20.00
FADE
DEPTH
rrryn^rr tn~ri T'i
40.00
(IN
60.00
DB)
Occurrence Of Fade During T he Worst
Month Period Of No v .
F ig .C4.29) : Probability
121
features of the fade rate variations over the links studied
by us.
[ 4.71 C O N C L U S O N :
Microwave propagation
character'stics
in terms
of
fade
depth
distrubution, fade occurrence, fade rate and fade duration are
extensively studied over the three LOS
and
the
observations
presented
analyses
in
of
this
the
related
chapter
features
links of Assam valley
to
these
along
with
with
those
aspects
a
few
have
been
comparetive
received
from
various
workers of the globe.
The
fading
patterns
are
first
classified
into
five
major
groups after defining the pattern on the basis of fade
rate
and fade depth. The analyses indicates that terrains features
though
have
pattern,
a
role
to
play
towards
controlling
the
fade
these are to a large extent dependent on the Fresnel
zone clearance factor and atmospheric situations. This we have
clearly seen
in Laopni
- Habaipur
link,
where first fresnel
zone is 50* obustructed in K = 2/3 condition leading to link
cutoff
events
with
probability
of
.008
occurrence factor is also high as 0.774.
the
same
breath
receiving
the
event with
that
large
this
fade
large fresnel
can
not
events
be
The
%.
multipath
I must add here,
the
because
sole
we
zone clearance,
factor
for
seen
that
have
Maopet
at
link shows
the probability of black-out to be appriciably high (0.005 *).
Here we may considers the experimental
C 1Q 7 2 5
observation by
, where it is shown that coefficients
B a r-rL & t
in probability of
multipath fading increases by a factor of 1.2 when
operating
frequency changes from 6 to 7 GHz. This will no doubt increase
the fade events at 7 GHz compared
to what will
GHz.
or
However,
there
may
be
two
three
be seen at 6
factors
working
simu1tenious1y ( like multipath fading / scattered signal from
small
scale
irregularities)
for
generating
fades
links. Because we have seen that when short duration,
number of black- out events dominate in the Laopani -
122
in
these
large
Habaipur link, The maopet and Milmilia links shows only a few
events with relatively large black-out periods.
It
is
worth
mentioning
here
that
fresnel zone clearance though
in
Motapahar
is 24 meters,
the
link,
the
link suffers
practically no fading. This is a hilly cum builtup area and it
is not
passing over a big water expouse. So in such a terrain
we don't expect the atmosphere to generate a conditions
that
may
zone
result,
to
large
fadings.
clearance is very low
fadings
we
So
even
if
the
fresnel
have not observed any significant
over this link
Further,
the
occurrence
seasonal
over
Kamrup
those Nagaon districts
and
diurnal
Links
variations
(Milmilia
( Laopani
Maopet
lk
link),
in
fade
Links)
and
are to be noted with
interest, because when Maopet and Milmilia link suffer maximum
fades during winter and early morning hours,
the Laopani Link
experince maximum fades during summer and pre midnight hours.
We
may
here
point
winter over Maopet
out
the
generation
of
thick
link because of height factor.
fogs
during
Similar
is
the situation over Milmilia where fog condition during winter
is
The
generated by river Brahamputra.
large winter
inversion
(as
observation
invesion,
time fades can be explained
dealt
and
in
sodar
chapter
5)
echogram.
seen
The
by temperature
through
effect
of
radiosonde
temperature
thunderstorm or font wave on micrqwave fadings are
discussed by many workers
1QS3,
Schivone 1 Q 8 3 5 .
The
effect of temperature inversions on microwave fadings during
winter night have been received
et.nl.
But
from Indian stations too CDcts
i Q8Q5.
we
do
not
have
sodar
observation
over
Laopani
link
to
relate these events with temperature structures. However large
fade
events
(R u th ro ff
during
i9715,
summer
night
have
also
when R R 1 gradient is negetive.
123
been
reported
This
factor have been
that
Milmilia
costal
and
further
Maopet
examined
links
where we
behave
region stations whearas
like
Laopani
a
have
seen
low latitude
link shows the fade
character of the low latitudes interior regions of American
continents.
occurrence
So
the
are mostly
But so far the diurnal
large
scale
variations in
by the
local
environments.
variation is concerned,
the fades are
controlled
basically night time events,
preferential
fade
time of development
varying between pre midnight to early morning hours.
It is also seen that the mode of
from
irregular
medium
that
scattering
results
to
fade
of
the signals
occurrence
at
different hours of the day. We have seen that after 2/3 hours
of sunrise to pre midday hours,
fast
fades
with
average
the signal
10to
15
suffers relatively
fades/hour
(
Instant
fade/ratemay go up to 160 fades/hour) and this type of fading
is seen in all links irrespective of their terrain situations.
However,the
magnitude
of
fluctuations
vary from a place to another.
The
and
number
large rapid
of
events
variations
of
the RRI in the atmosphere and its association with fast fades
have been reported by Tuhuji Ci£*575, Trol&s&lg C1QG55 Sar-hazst.a.1. CiQ825etc. The analysis of such fades with respect to
boundary layer structures has been dealt in chapter 5.
The
whole
exercise
leads
to a
result
that
probability
of
development of fades over the Kamrup links are high during the
winter early morning periods.
But the significant part to be
highlighted is the worst period for
the communication is not
the winter months but is during the post monsoon period.
The
worst month statistics, during the month of November over the
Milmilia link is shown in
0.007 % of
higher
than
the
the
total
fig.(4.29) where the link cutoff is
data
average
of the month, which is 0.004 %
value
of
the
year.
This
large
occurrence of fade black out events can be correlated
with
large occurrence of ducting conditio during the post monsoon
months.
124
CHAPTER - 5 PROBING OF THE TROPOSPHERE THROUGH REMOTE SENSORS
AND EFFECT OF THIS MEDIUM ON MICROWAVE FADES.
[ 5.1] .INTRODUCTION I
The quality of signal
reception
and
probability
of
failure etc in a microwave communication systems are
controlled by radio refractive
tropospheric
humidity.
parameters
A
knowledge
index which
viz
on
largely
is a function of
temperature,
initial
link
pressure
refractivity
and
gradient
and
total
refractivity profile in the form of monthly average is
very
essential
system.
So,
for
designing
of
a
reliable
communication
the practice of mapping RRI at different seasons
over a station is followed by the system designers for
last
four decades CBean & Meancy 1955, Bean. & Thayer- 1959,etc. J>,
Such
studies
stations
on
the
RRI
C Venha teshwar-an
have
&
also
Nara.yna.rt
been
1977,
made
at
Indian
Deshpande
1977,
Km lsftrestha & Sr-iMaetaua, 1990, etc. J>, Also an extensive study
on the radioc1imeteo1ogy over 18 Indian stations has been made
by
the
NPL
groups
,Sarkar- et.al 19825.
microwave
large
propagation
number
of
(Majumdax-
e t.al.1977, Sarhar-
et.al
197Q
The effect of RRI and its gradient over
have
workers
also
CLee
been
1989,
well
Dae
dealt
with
et.al. 1989,
by
a
Raa
et.al. 1993 ,Gera et al 19802.
In this chapter the temporal
vapour content,
variation of temperature,
water
temperature inversion, RRI and its gradient,and
the effective earth radius factor will first be analysed over
the link path and then microwave fading characteristic will be
associated with the above mentioned parameters along with the
sodar observations.
125
[ 5.2] RADIOCLIMATOLOGY OVER THE LINK PATH
The
radioclimatology
temperature,
the
vapour
link
path
content,
radio
gradient and effective earth radius
factor
analysing
water
over
the data
research
work
department.
from
the systems
and
The
also
variation
occurrence probability,
of
index
is determined
as a part
Indian
these
terms
refractive
developed
from
of
in
by
of
Meteorological
parameters
in
terms
of
seasonal dependence etc are described
in the following section.
C15SURFACE TEMPERATUREA knowledge on temperature variations with time ( both in long
and
short
term)
is very
essential
to understand
dynamical
aspects of the atmosphere such as transfer of heat flux and
momentum etc.
These parameters play a very significant role
in controlling the radioclimatology of the atmosphere.
first will present the average picture of temp
different months
So we
variation at
over the Milmilia link path where two sodar
units and other meteorological
sensors have been placed,
for
this purpose the maximum and minimum temperatures recorded for
each day are noted by an electronic thermometer from which the
average
maximum
evaluated.
As
and
minimum
year
temperatures
to year
variability
during the observation period
present in the fig. (5.1),
for
of
a
months
these
parameter
is not significantly
the Tmajc
and
Tmin
are
large,
we
for each month
averaged over a year 1990 only. The monthly variation of average
maximum
coldest
tmperature
month
temperatures
month
of
average
The
with
fig.(5.1)
the
is
temperatures
the
temperature
temperatures
during
and
in
as
monsoon
August
when
that
and
10.5 °C
hottest,
of 32
atmospheric
expected
maximum
of 22,5 °C and
August
shows
minimum
with
maximum
rain
are
fall
temperature shoots up to as high as 32 ^C.
126
not
goes
by
as
the
average
and
and
rain,
high
down,
the
minimum
C respectively.
controlled
periods
is
respectively,
and 22.5
is
January
The
the
as
is
average
S e a s o n a l V a r ia t io n Of S u r f a c e T e m p ,
Tem p.
In
Milmilia— Durgasaravar Link
M o n th s
□
Max Average Temp,
+"
Min. Average Temp,
F ig . (5.1) S e a s o n a l V a r ia t io n O f S u r f a c e
127
tem perature
C2}.TEMPERATURE INVERSION !
In
chapter
1,
where
the
physics
of
the
troposphere
was
introduced, we have discussed the changes in the RRI gradient
with temperature and humidiy
the
important
above
parameters
context
section,
is
we
inversion.
the
will
To
that
need
temperature
present
find
variations
out
the
the
to
with height.
One of
be
in
explained
inversion.
occurrence
probability
Here,
of
of
in
the
this
temperature
occurrence
of
inversions, the temperature at three different heights ( up to
300
meters)
examined.
are
For
measured
and
this study,
IMD are more often used.
conditions
of
radiosonde data
inversions
received
from
are
the
It is also to be mentioned that as
these temperature data (both IMD and tower) are received over
Mi 1mi 1ia-Durgasarovar path,
these inversions are examined for
this
shows
link
inversions
only.
Fig.5.2
(average of the
the
inversions
%
o f
received
occurrence
of
fro both
IMD
and tower! at different seasons. During this analysis we have
not oberserved a year
to year
variability of probability of
occurrence of inversions, the histogram shown in fig (5.2) are
therefore average of all these years. A clear seasonal peak in
the occurrence of early morning
winter
and
probability
during summer.
not generate
of
inversion is observed during
generation
of
such
events
is
low
It is also to be noted that the sunset hours do
inversions as often as the early morning
hours
except for the summer months.
3. WATER VAPOUR CONTENT:
The water vapour content has a positive role to play towards
changing the atmospheric situations.
chapter
1,
the
significance
changing the value of RRI.
of
So,
We have already seen in
water
vapour
pressure
we present the variations
in
of
water vapour concentration over a season. The maximum value of
water vapour concentration for each day is found out and from
these values the monthly mean of the maximum of water vapour
concentration
is
evaluated.
The
seasonal
128
variatio
of
water
Of days
Occurrence of Temperature inversion
6
z
Seasons
jT T H
00,00 GMT Hours
Fig (5.2)
Oc c u r e n c e
1\
OF
\|
12.00 GMT Hours
T e m p e r a t u r e In v e r s io n s Ov e r
Mil m il ia - D u r g a s a r o v a r l in k p a t h
129
vapour content is shown in fig.
(5.35, which portrays that the
winter is the dryest season of the year average vapour content
is maintained at 12 gm/meter3. During the months
of
summer,
when we have the monsoon, the valueof this parameter reaches a
maximum
of
23
gm/meter3. The
water
vapour
concentration
fairly large during post monsoon periods which is equal
is
to 18
gm/meter3.
RADIO REFRACTIVE INDEX!
For
this
pressure,
analysis^ the
water
vapour
parameters
like
surface
pressure,
that
have
temperature,
been
collected
for
different
1
during
the
observation
period
are
analysed
seasons. The morning and evening values for for each parameter
are averaged while computing RRI from equation 2.5. Fig(5.4)
shows the surface RRI variations
over a year.
Here
too,
the
average values of all the years under study have been shown.
The surface 'RRI
reaches
maximum,
around
400
N unit,
during
summer as expected. This feature can be more clearly seen from
fig.(5.5) where probability of occurrence of different values
of RRI
(950 m bar pressure
level) is shown.
It is seen from
i
this
figure'
that
the
probable value of RRI
probability
of
obtaining
the
i.e 360 N units during summer
most
is 46%,
when the mosjt probablie value of RRi during winter lies within
310-320 N units with only 30% ocurrence probabilty.
In post
monsoon peiods, the expected RRI value is 360 N units.
I
Now, to see ithe distribution of RRI at 50% probability level,
!
the cumulative distribution of this parameter
i
seasons are plotted and is shown in fig. (5.6).
note that RRI
months.
at
different
Here too,
we
is high during summer as minimum during winter
During summer at 50% probablity
level,
the value of
RRI is 350 N' units while in winter it is 320 N units.
130
Seasonal Variation Of Water Vapour Cone
W a t e r V a p o u r C o n e . ( g m / ’m e t e r *
Over M ilm ilia D u rg a sa rcw a r L in k
m onths
F ig (5 .3 ) S e a s o n a l
v a r ia t io n
OF Wa t e r V a p o u r C o n c e n t r a t io n
O v e r Mi l m i l a - D u r g a s a r o v a r
131
l in k
Seasonal
V a ria tio n
Of
S u rface
RRi
FRI <N U n it)
O v e r M ilm ilia d u r g a s a r o v a r L in k
M o n th s
Fig (5.40 Seasonal var iation of S urface Radio Refractive
index
132
P C o f O c c u rre n c e
O f RRI
RRI At 950 m b a r Level
RRI N U n its
•umrrwr
Post M onsoon
F ig
(5.5)
Pr o b a b il it y
Winter
OF
Oc c u r r en c e
Pre M onsoon
Of RRI At 950
Ove r Mil m il ia -D u r g a s a r o v a r L in k .
133
m bar
Cumulative PC Of .Occurrence of R R!
M ilm ilia D u rg a o a ro v a r L in k Path
C u r n m u la liv e
P C C T .O c e u tr e n c e O f RRI
100
----- 1------ 1
400
■320
2 t3 U
RRI In N Unit
■ \rrw r
Winter
Pact Moncaon
F ig (5.6) Cu m u l a t iv e PC Of RRI At 950 m b a r
Over Mil m il ia -D u r g a s a r o v a r Pa t h
134
Pre Mancaan
Once the RRI at antenna height
is known we examined
gradient at different seasons as discussed
in the
the RRI
following
section.
5. RRI
gradient:
The RRI gradient from surface to 200 meters above antenna
is
evaluated
is
then
for
measured
each
season.
The
for
different
probability
RRI
gradient
distribution
levels.
Fig(5.7)
shows that though RRI is high during summer, the gradients are
relatively more during postmonsoon periods.
The most probable value of RRI
period
is
-60
occurrence.
probability
to
The
-120
maximum
occurrence
of
N
gradient during
units/km
value
2*
of
is
with
-200
also
post monsoon
average
N
20*
units/km
observed
during
of
with
this
period. The ducting conditions are more favourable during post
monsoon season when dN/dH becomes < -157.
6. EFFECTIVE EARTH RADIUS FACTOR : The effecive earth radius
factor K depends upon the refractivity gradient.
The value of
K is the prime parameter used
engineers
by communication
optimizing the terminal equipment characterstics.
sight system,
K factor determines
in
In a line of
the radio horizon distance
for a given set of transmitting and receiving antenna height.
We
will
here
examine
the
variation
of
K
factor
over
two
seasons namely post monsoon and winter. These two periods have
been
selected
reaches
the
by
considering
highest
value
the
during
fact
post
that
RRI
monsoon
and
gradient
minimum
during winter months. For this analysis one year data have been
considered.
The K value between
1 to 157 are grouped
over these seasons. Here,
detected
and
therfore
not
in number
of days
the extreme sub refraction are not
considered.
135
Fig
(5.8)
shows
this
RRI
G r a d ie n t
U p
To
9 5 0
m b a r
Le ve l
P C Of O c c u r r e n c e ( d N / d H )
C V er Milrnilia— O u rg a s a ro v a r Link P ath,
Sum m er
F
ig
+
(5.7)
P
r o
950
RR! G ra d ie n t
0
W inter
P ost Mon,
b a b il it y
m
b
o
Of
v e r
M
O
c c u
il m
r r e n
il ia
-D
u
c e
r g
136
a
A
Of RRI
G
s a
r
r o
v a
r a d ie n
L
in k
.
Pre M on soon
t
u
p
t o
OCCURRENCE IN NUMBER OE DAYS.
F ig . ( 5.8) Pe r c en tag e Of Oc c u r r en c e Of K V a l u e s
F o r Different S e a s o n s Ov e r Mil m il a -D u r g a s a r o v a r L ink
137
parameter along with the number of days a particular value of
K is received. This shows that K factor takes a wide range of
values from
1 to 157 during
post monsoon
periods.
While
in
winter the excursion of this factor is limited within 1 to 10.
The ducting condition during post monson is expected atleast
in 8 days with in 3 months.
[ 5.4] SOD AR O BSER VATION AND MICROWAVE PROPAGATION SODAR is one of the remote sensing devices which can monitor
the atmosphere up to 1 km height giving continuous information
on tempeature inversions and micrometeoro1ogical parameters of
lower atmosphere CMcAl list&r 1968, Little 19690.
To receive the information of the lower atmospheric situations
due to changes of temperature,
are
installed
microwave
over
fadings
humidity etc.,
two SODAR units
Mi1mi1ia-Durgasarivar
over
this
link
are
link
then
and
the
examined
in
association with inversions, elevated layers, rising inversion
layers
etc.
A
few
typical
characteristic
features
of
SODAR
echogram as seen over this link are presented. These are:
1. Development of nocturnal inversion of depth rangingfrom 50
to 180 meters
2. Breaking of inversions after 2/3 hours of local sunrise .
3.
Absence
of
well
premonsoon/monsoon
developed
( even
convective
post mosoon
plumes
days)
in
many
because
of
rainy or cloudy situations over this valley.
These features are outlined briefly in the following sections:
C JO NOCTURNAL INVERSIONS -
Two types of inversions in the study of near earth environment
are often detected either through SODAR echograms or through
radiosonde
measurment
{Gilman.
st.al.1946 ,Sin.gal
st.al.1977
Gera et.al.1980 ,Wychoff et al.Oct. 1973, Das at. al 1990 ,Rao
st al 19930
Gossax-d. 1977,810. These are:
1.Ground based inversions
2.Elevated inversions
136
The
ground
based
sodar echogram
cooling
of
nocturnal
nocturnal
inversions
) developed due
the
earth’s
ground based
(as
recevied
on
the
to the consequent effects
surface.
inversion
A
typical
of
echogram
of
is shown in fig. (5.9a).
The
depth of this inversion layer does not remain constant and we
observe the depth to vary between 50 to 150 meters,
on
the
atmospheric
generally
conditions.
developed
after
Ground
couple
of
based
depending
inversions
hours
of
sunset
are
when
ground temperature reaches a steady low value. This feature of
temperature
is detected
in all
the events
and
fig.
(5.9 b)
shows a typical such case. Here the temperature is recorded by
an
electronic
thermograph
and
the
sensitivity
is
kept
at
0. 33.C/mm. The temperature reaches a steady state at 1800 Hrs
The inversion layer is also developed during such hours.
Fig(5.10 a) shows a typical
long
lasting
low elevated
layer
observed over this link. This type of layer is often detected
during night except for daytime cloudy conditions.
The height
of
There
such
layers
varies
from
100
to
250
meters.
alsocases when instead of a well developed nocturnal
layer,
sodar
echogram shows
clean
stratified
are
elevated
structures. Fig
(5.10b) shows such a stratified structure with in a PBL.
inversion
layer
geneally
dissipate
after
sun
rise.
with interest that plume strucures are not well
many days of the year because of
and
the
rising
inversion
We
The
note
developed
in
rainy or cloudy conditions
layer
maintains
a
high
level
fadings
with
depending on the ground heating conditions.
[ 5.4-1 MICROWAVE FADINGS AND ATMOSPHERIC CONDITIONS
AS RECEIVED BY THE SODAR:
Before examining the association
sodar
returns
features
let
me
first
of
microwave
highlight
some
characterstic
of the fadings over this link. These are:
1. Large nocturnal fading with high fade depth
2.
The
favourable
time
for
development
139
of
fadings
is
post
~Sr
06
1900
19 00
13(0
16 06
15-06
I
IV
t'
F ig .C5.9a ) De v e lo p m e n t Of T he Gr o un d Based In ver s io n
b ) Record Of T he Dry T em p er a tu r e During T h a t T ime
140
1 I
7 8 92
9'r :
' !
'
,
;ri.. ■
:
i j f h:
r "
,
tHHiVBieivjjti,
.... • .
GIQO':
5200
/~N
(X
I
.
y.V.jfcr
Bf«
■ L c .
*
u*
X
il
til
*W T :
<y
1
i - i / 1
i
: 1 !K l± i M i - - 1 Li:
i
1
fgo
■Sb-’i ' i
l
i<
, 'H M I
- ^ . a' ';:iii f ■
P fH
'
'-i*
■
cm;
: ' ■
0^0
cH-CO
r
' • •
'i-'
02-00
OICO
,0800
^06
?30<
CB)
Fie. (5.10 a ) S a m p l e Re c o r d Of T he No c t u r n a l Ba s e d E l e v a t e d
Layer
Cb) Sample Record Of The Stratified Layer
141
midnight to early morning hours.
3. The nocturnal high level fades disappears after sun rise
and
fast
or
scintillation
type
with
low
fade depths
develops after couple of hour of sunrise and that may
continue up to post mid-day hours
4. Fadings are mostly absent during 14 to 16 hours .
To examine the associations
of fading with near earth
structure
atmospheric
as
well
as
with
conditions
layer
received
through SODAR, we present here the path profile of this
for K = 4/3 conditions fig
(5.11).
link
As seen from the figure,
the transmitting and receiving sites are
105 meters and 228
meters respectively from the mean sea level. The positions of
two sodars are also marked in the figure.Sodar (1) is at 4 Km
from the receiving sites and sodar
the
We
is situated almost
in
mid path of the link.
have
seen
nocturnal
are
(2)
that
during
inversions
often
detected.
the
situations
when
(150-180 mts) are present,
Fig(5.12)
shows
a
high
level
deep fadings
representative
sodar
echogram when 30 dB fades are detected over this link. Now we
consider the presence of high level PBL upto 200 meters over
the link path as detected by two sodars and then assume that
this situation prevails beyound the sites from the Sodar 2 up
to the transmitter point. The horizontal extension of the PBL
can
probably
be
justified
because
of
the
same
terrain
situation of this link beyound Sodar 2 to transmitter point.
The
figure
elevated
figure
shows
the
structure
that
the
at
path
the
ellipsoid
profile
of
atmosphere.
of
fresnel
effected by high level nocturnal
this
It
is
zone
link
clear
of
and
the
from
interest
the
is
inversions. So in a situation
when first fresnel zone clearance at the mid path is effected
by a boundary
PBL will
layer, a signal
energy that passes through the
propagate with a differential
resulting fading and attenuation.
But
142
propagation velocity,
in a situation when
143
215
DISTANCE IN KM
MILMILIA
^TRANSMITTER SITE)
Fio.C 5.11)
S chematic Diagram O F T he L ayer S tructure With
Respect T o Microwave F adings Over Milmilia Du r g asaro var link
0
DURGA SAROVAR
(RECEIVER SITE )
X
LU
X
o
Z
LU
f—
LU
o r
LD
MILMILIA- DURGASAROVAR MICROWAVE LINK 6GH2
PATH DISTANCE L1‘2 Km
ANTENNA H T T X I 5 0 METER
RX*. 50 METER
F ig ( 5 .12) Re p r e s e n t a t iv e S o d a r Ec h o g r am Co r r e s p o n d in g T o
Mic r o w a ve F ad in g Ove r Mil m il ia -D u r g a s a r o v a r L ink
144
2 - ( lO
\
ft?
A. f f D
3-dt.
'M
& -< ? 2.
^ ^ * * * ^ f:
rJO__ ^ q& -2300 ^-00
Z-<*>
U 0T>
%
s 0 t>
F
g
C5.13) S a m p l e Re c o r d
O
f
T h e S h a l l o w M ic r o w a v e F a d in g
C o r r e s p o n d in g T o L o w L e v e l In v e r s io n L a y e r
145
F ig C5.14-) De v e l o p m e n t O f F a s t FA ding C o r r e s p o n d in g T o T he
Rising
in v e r s io n
Laver
146
the inversion layer goes low as marked by the sodar echogram
and
a
fresnel
zone
clearance
is
well
maintained,
the
consequent effect of PBL on microwave fade is expected to be
low.
We have seen
signal
undergoes
that
for
low
level
nocturnal
only shallow fades as shown
inversions,
in fig
(5.13).
After sunrise, with fast increase in temperature, a transition
in the height of
the PBL
(5.14). The PBL height
be
formed
processes.
PBL
if
ground
in sodar
often
observed
echogram
fig
increases and plume structures are to
heating
is
significant
In such a transition situation,
is dissipating,
have
is observed
a turbulant
fast
and
medium
for
convective
when the nocturnal
is generated
scintillation
type
and
of
we
fading
during this transition periods. The absence of daytime plumes
is clearly seen from fig. (5.15)
However,
we have
noted
that even
in the absence
of
thermal
plumes, the signal is relatively less affected in the day time
because of low level mixing is present. The depth of microwave
fading during this period is low.
5.5 CASE STUDIES A few case studies associating
microwave
fading
in the
Links with atmospheric variabilities are presented below
Case 1: Fades In Mi1imi1a Link And Atmosphere Through Sodar:
On April 17,1992 low depth fades develope in this link at 9.00
hrs continuing to 11.30 hrs, when fade level soots up rapidly
and
crosses
20
db
the
in
a
fairly
recorder.
range
reveals
rain signature at 9.30 hours and
is associated with rain.
layer disappears and a mass
about
300
meters.
structure causing
This
sonic
air
Sodar
short
dynamic
fading
of
level
time
echogram
crossing
Fig
the onset
(5.16)
of
slow
Then the prevailing boundary
of
reflecting
mass
returns.
formed
Strong
caused by this reflecting structure.
147
front
an
is seen at
ill
multipath
The signal
defined
fading
level
is
returns
to normal
level,
soon after the structure disappears
(marked
in the figure 5.16)
Case 2: Elevated Layer Structure And Microwave Fades: On April
3,1993 at 17 hrs an hour after
local
sunset,
Milmilia
link
shows fades of depth near to 20 db .During this period sodar
return shows a well developed elevated
180 meters Fig.
layer at a height of
(5.17). A large change in the wet temperature
corresponding to a gradient of 0.5 degree/ meter is registered
at this hour. On the other hand ,in contrast with the normal
pattern,
the
temperature
dry
bulb
gradient
sensor
of
-
structure and corresponding
has
0.03
registered
a
degree/meter.
fadings
record
The
disappear
when
low
elevated
the
two
gradients reach their normal conditions at 19.00 hrs . It is
to
be
mentioned
that
this
elevated
layer
lies
within
the
antenna height.
Case 3:.- Undulation In Microwave Signal In Laopani-Habaipur
and Lumdimg-Habaipur links: Extraction of Wave Structure:
Here a special fading pattern over two links Laopani-Habaipur
and Lumding-Habaipur (fig (5.18) is presented.
The fades over
Lumding link have not been dealt with earlier as no signiicant
fades have been detected over this link .This microwave
link
is also falls over Nagaaaon district.
To
realise
pattern,
the
periodic
component,
if
any,
in
the
fading
the fade data are filtered out to remove relatively
slow fades over which wave structures are seen to undulate.
The filtered data are then processed through auto correlation
series to examine the periodic component.
The auto corelation
parameters of Laopani link Fig.(5.19) are seen to undulate about
the mean,
suggesting presence of wavy structure
in the time
series. We note that the fastest component is 0.7 milli hertz.
The time series is then processed through Maximum entropy to
find
out
frequency
components
if
148
any
present
in
the
F ig . (5.15) A b s e n c e OF T he DA y T ime Plu m e S t r u c t u r e
149
F ig . ( 5 .16) F a d e s In T he Mil m il a - D u r g a s a r o v a t L ink An d
A tm o sph er e T hro ug h S o d a r
150
F ig (5.17) Elev a ted L ayer S tr u c tu r e And Microwave F ades
151
Fig (5.18) Simulteneous Sample Records Of T he F ading
Observed Over L ao pa n i -H abaipur and L umding -H abaipur L inks
152
OCj
Fig. C5.19a ) Au to Correlation Parameter
L aopani -H abaipur L ink
153
1.2C
T3
j
1
'Zs'
i
c
3 0.30
■<
-*
i
<
<-
>v
O
-i
33
1—
Z
t
S0A 0
0)
5
O
CL
4
3
i
V
< ■
k
l
0.00
0.00
Fr'3quency(m H z)
200.00
:
F ig. ( 5.20 ) Power Spectrum Of F ade Character
a ) L ao pa n i -H abaipur L ink
b ) L umding -H abaipur L ink
154
variable (fig.(5.20 a and b) The analysis indicate presence of
short
periodic
similarities
the
two
wave
of
minutes
.We
note
the
striking
in the Maximum Entropy spectrum of the data of
stations
structures
few
at
suggesting
both
the
presence
stations.
This
of
study
same
periodic
also
indicates
presence of a short periodic wave with fastest frequencies of
7/6 millihertz
in Laopani/Lumding
link.
We note the striking
similarities in the maximum entropy spectrum of the data o the
two
stations
suggesting
presence
of
the
same
periodic
structures at both the stations.
This
study
probably
indicates
over
development
Habaipur
which
are
of
wave
reflected
like
structure
in both
Laopani
and Lumding stations.
(5.6) SPECTRAL ANALYSES AND DETERMINATION OF STRUCTURE
PARAMETER Cn 2Tropospgere
rise
to
is in continuous
local
atmosphere.
variations
in
the
of
discussion
turbulence.
discussed
(For
and hydrometeor
here,
only
this
to
purpose
in chapter
-2).
So,
turbulence
refractive
Random fluctuation of RR1
presence of aerosol
our
state
index
give
of
the
is also caused by the
.However we will confine
the
effects
relevant
when
which
caused
theories
by
have
a electromagnetic
the
been
wave
passes through such a medium it suffer fading or attenuation
because of scattering of the wave in the turbulent medium .
It is well
when wave
accepted
length
and
seen
from
is large compared
the turbulent medium,
various
to the
experiments
that
irregularities
in
the wave get scattered in all direction
but in case of a wave length smaller than the turbulent eddies
the
scattering
direction
of
confine
the wave
to
a
narrow
propagation.
So
zone
in
in a
real
the
forward
situation,
microwaves within 3 to 10 GHz are found to be affected largely
by this type of medium.
155
Diffrent
types of fading patterns are observed over
line of
sight microwave links Because of scattering of the wave in the
such media. Broadly, two types of fadings are relevent for our
interest. One type is caused by incoherent scattering of the
wave while other
.Incoherent
is due
to coherent
scattering
is
scattering
caused
due
of
to
the wave
atmospheric
fluctuations of the refractive index while coherent scattering
is due to coherent reflection from stratified layers. A scale
size is associated with scattering from layered structure.
Therefore
it
scientists
is a common
and
practice
enginners
to
adopted
evaluate
the
by
communication
structure
of
the
irregularities. This type of analysis on wave propagation and
scattering in a random medium are well dealt with
workers ( M a n n in g 1 9 93 ; I s h im a r u ,
1978;
Reddy,
by various
19875.
To receive the structure information of the irregularities one
has
to
consider
atmospheric
transiion
the
random
velocity
from
field.
laminar
and
The
flow
turbulent
velocity
to
nature
field
turbulent
of
the
undergoes
flow,
which
a
is
characterize by the Reynold number R. The condition that fluid
flow becomes a turbulent
is that R should exceed a critical
value Rcr. The Reynolds number depends on the velocity v and
kinematic
viscosity
of
the
fluid
and
characterstic
scale
length L0 of the particular fluid flow ( R = L0 v/v). When the
flow is turbulent, one can define local Reynold number R which
determine
the
stability
of
the
inhomogeneity.
The
inhomogeneity is marked by a random velocity fluctuation with
a characterstic length having a smallest value l0 (this ranges
from .05 cm to .1 cm with a nominal value of .1 cm).As long as
R
is
greater
fragment
into
than
unity,
smaller
and
inhomogeneity
smaller
will
continue
inhomogenities
point is reached where the energy of inhomogeneity
until
to
the
is of the
order of that disipated into heat by viscosity! M a th x ir, 19935.
When this stage is reached inhomogeneity ceases to exist . The
1oca 11y
156
homogenious and isotropic turbulent field exist in the scale
range of L0 <r<
10 which is called the inertial
subrange and
is determined by the energy dissipated per unit mass per unit
time
with
in
inhomogeneity
.This
is
called
the
Kolmogrove
second hypothesis.
The
above
formulation
leads
to
the
spectrum
of
the
refractivity fluctuations called Kolmogrove spectrum as which
determine
the
propagation
statistical
characterstic
in a turbulent atmosphere.
For
of
the
radiowave
refractivity
fluctuation field N the spectral density function is given by
o
<£n <K) = .033 C„ K
2
where Cn
_ 1 i / -a
AA
is the structure constant parameter
and K is the
wave number This shape of the spectrum hold for the inertial
subrange
2jt/L0 < K< 2n/l0 . For value of K < K0 < (2n/L0 ) a
range called the input range,
the spectral densities saturate
at the value <£n (K0 ). Also for value of K. > 2n/l0 called
the
dissipation
an
subrange,
the
spectrum fall much faster
2 2
exponential factor exp (- a K ). Where a - .169 10
by
p
C5.7) Method Of Receiving T he Str uctur e Parameter Cn There
are
number
of
techniques
to
determine
the
structure
parameter of the medium . These are:
1. From the radio sonde measurment
2. From the power spectra analyses
3. From the scintillation measurment
A
model
microwave
irregularities
was
scattering
conceived
with
respect
to
medium
by Eklund and Wicker-1,1968
for
microwave propagation where both scattering and reflection of
the
wave
in
the
medium
are
considered.
In
this
model
a
relationship is assumed between the change of refractive index
AN
through
refractive
sharp
index
boundaries
and
fluctuations.
spectral
This
157
intensity
relation
2
Cn
of
is given as
r>
in
An = .6 Cr,t'#10
Based
on
continent
developed
transmission
loss,
measured
over
the
for
transhorizon path, a relationship
2
between Cn and
refractivity
gradient
Indian
sub
has
been
AN.
The
relationship is given by
Log Cri2 = -17 + .023 (-47 -AN )
(2) From power spectrum analysis:
2
Cn can also be computed from the power spectral
the signal
From
analysis of
records using the Fast Fourier Transform algorithm
this
the
structure
constant
parameter
can
be
calculated by using the formula
2
-1
- ( 5 - • m • )‘
( 1 + ! m ! >/2
cr, = Pi'fc’ <2rr * .033) * v K
* [n/ 4T {3+!m !)/2* sin { (rc/4)(5-!m !)J]-1
* t(!m!+l)/2 * T2 {(!m!+1)/2/T(*m!+1))3"1
where v denote the mean drift speed of the medium, L the path
length
in
Km,
K
gives
the
wave
number
and
m
denote
from
the
the
spectral slope.
(3). From scintillation measurement:
2
The Cn parameter can also be calculated
following relation by using the scintillation data
2 - .31 C 2 K 7/6 L 11/6
where o>n
is the variance of the
logrithm of the
intensity,
is given as
2
2
<yn
= In
( 1 +S^ ) ■
,
where the S* is the scintillation index
It is important to note that diurnal
computed
only
predominent.
from
the
data
2
variation of Cn can be
where
the
In case of layers during nighttime,
at the receiving end
scattering
is
if the signal
is predominantly due to the reflection
from the inversion layers and the scattering
158
portion
is
low,
computation
then
has
under
no meaning
such
and
during night are fictitious.
containing
only
the severe
circumstances
as
such
the
2
Cn
the
derived
To solve this problem
scintillation activity
values
the data
with
high
fading rate have to be utilized.
CS. 85 OBSERVATION
OF
CN2
PARAMETER
AT
DIFFERENT
ATMOSPHERIC CONDITIONS OVER LINK PATH 2
The different techniques of finding out the Cn
parameter have
2
been discussed in earlier section. Here we presenting the Cn
parameter
calculated
out
by
adopting
the
technique
(1)
and
(3) .
2
Before going for measurment of Cn parameter we first allow our
time series to under go few statistical
test to examine the
presence of any regular structure in a particular time series.
Also
we
present
examined
in the
receive
Maximum
the
the
prominent
irregularities
frequency
Entropy
frequency
spectrum
component
technique
have
for
present
been
component
this
in
adopted
if
any
purpose.
the
To
spectra,
after
the
time
series is checked for the presence of a periodic component by
autocorelation
sec.interval
function.
of
time.
Each
The
series
is
structure
sampled
at
parameter
the
is
1
then
evaluated by using the technique3.
Fig (5.2ia) shows the presence of low periodic structure with
a
frequency
of
about
.01Hz
during
a
typical
pre
monsoon
morning time fades over Milmilia. The smallar structure are not
well developed .Fig (21 b) shows the autocorrelation parameter
for
the
same
structure
link.
Now
present
in
are
morning
not
well
to receive
the
hours
over
defined
Maopet.
as
in the
the significant
respective
sample
each
through Maximum Entropy analyses.
159
The
undulating
case
frequency
series
of
milmilia
component
is
processed
o
o
_TER
Ocn
o
o
AUTOCORRELATION
o
m
d
c
c
I
I
I
I
10.00
20.00
30.00
TIME LAG (15 SECS.)
I
1
I
I
I
T
I
I
I
I
I
I
I
I
|
I
I
I
I
I
I
I
I
I
|
o
o
0.00
o
111111
o
o
i i p n i T r i i i i |i i i r i T 'm
I
o
o
O
in
l
d
AUTOCORRELATION
1111111 m
o
m
o
1 • ^
v
0.00
M
M
I I
I
10.00 20.00 30.00
TIME LAG (15 SEC.)
I I
I
| 1 1
I T
r
n
T T
|
I
I
I
I
Fig. (5.21 A&b ) Autocorrelation
a ) Milmilia-D uragsarovar
b ) Maopet -D urgasarovar
160
I
I
I
I
|
I' I
I
I
I
40.00
1 1 M
)
parameter
link
link
Maximum entropy can give a very high resolution and correct
frequency
information as demonstrated by the power spectrum.
Therefore
in
this
analyses
maximum
entropy
is
adopted
to
recognise the most likely frequency component sustained by the
system. Relatively large power component present in 0.01 Hz and
0.02 Hz
in Milmilia and Maopet
clearly
seen
in
time
series
fig.(5.22.a&b) through
the
respectively
Maximum
are
Entropy
analyses. Once we are convienced that series contains periodic
undulating components, we calculate the structure parameter
2
Cn by using relation (3). This is the general procedure we
2
are adopting before evaluating Cn parameter for each case.
A
typical
value
of
C
2
at 6 GHz Mi 1mi 1a-Durgasarovar link
-13
-2/3
2
found to be 5.6 xlO
meter
. The values of C
as
n
observed by ohter groups is shown in table 5.1.
Table 5.1
>ii
„ _ 2 . , -2/3.
Value of C n (meter
)
Name of the Worker
Tatarski i (1971)
Gj ess ing (1968)
1.4»10~13 to 4.4*10”16
-14
2.2#10
Clifford & strohbehn(1970)
4*10_14
Majumdar
10“13to 10~14
-12
3.18*10
Dutta (1984)
Now we attempet to measure
2
the Cn through
index
as
gradient
seasonal
measurment
variation
plot
of
given
the
(5.23)
161
2
Cn
by
radio
equation
is
given
refractive
1).
in
The
fig.
3 200.00
<
a:<
150.00
QC
I
cn
or.
<
100.00
_I
<
>
_J
50.00
<
a'.
i
o
fl.
U)
0.00 '~i-T-r'7-r_r-inr-r-pi-|-i-ri~r i | .....
0.00
10.00
20.00
Li J
i
i~t—|—i— |
50.00
t REQUENCY ( n Hz )
lj
3
.. l
<
>
>~
Lb
<
or.
i—
CD
QZ
<
Lb
ZD
_I
<
>
<
CY
I
U
Lb
Q.
(/)
FREQUENCY Cm Hz )
F ig . (5 .2 2 ) F r eq u e n c y Co m p o n e n t Pr esen t In T he F a d in g Eve n t
T hrough Maxim u m En t r o p y Method
A)
O v e r Mil m ie ia - D u r g a s a r v a r L ink
E) Ma o p e t - D u r g a s a r o v a r L ink
162
S e a s o n a l V a r ia tio n Of C n * 2
S tru ctums C o n s ta n t P ara rr ietc
1C-*
Milmilia— D u rg a c -a rw a r Link
Months
Fio. C5.23) S e a s o n a l V a r ia t io n O f
Du r o a s a r o v a r link a s o b s e r v e d
163
over
Mu mil ia
Ra d io s o n d e
2
where it shows that maximum value of Cn lies in the months of
"“16
2/3
summer with the value of 1# 10
m
. This is followed by
”
the post monsoon months where it has the value of
9*10 ^
and
-1 7
and the minimum value is observed during the months
-2/3
m
of winter with a value of 2.5*0 ^
5*10
(5.9) CONCLUSIONS:
This chapter gives the detailed radioclimatology over the link
path Mi 1mi 1ia-Durgasarovar by analysing seasonal variation of
temperature,
pressure,
water
vapour concentration,
RR1,
RRI
gradients, effective earth radius factor. The study shows that
average temperature reaches maximum during early post monsoon
period
while
seasons.
The
water
RR!
Units,in summer
monsoon
level.
with
vapour
though
-120
The worst month
RRI
goes
peaks
to a value
as
at
high
monsoon
as
390
N
the gradients reach the maximum during post
period(-60to
large
concentration
N
units/km)
link cutoff
gradients
leading
at
events
20
%
can
to ducting
probability
be
explained
conditions
(at
least 8 days within 3 months) during post monsoon period.
The ground based inversions seen through the tower installed at
the
link
path
and
also
through
Radiosonde
are
found
to be
responsible or winter post midnight/ear 1y morning fades.
A simple model
in which the height and variations
received
the
from
two
sodar
units
in
the
link
in PBL as
path
are
associated with the type of fading seen during night and
in
post sunrise transition period.
A few case studies associating microwave fadings with elevated
structures
(at antenna heigh)
and with humidity
through sodar returns are presented
164
fronts
seen
The
structure
from power
2
scintillation measurements and also through RRI. The C obtain
the value of 10
received
constant
—
1 0
M
—
2/3
parameter
type
of
evaluated
^
during summer is much higher than that
in other months.
scintillation
is
This
indicates that development of
fluctuations
summer.
*
165
in
the
signal
during
CHAPTER-6 RESULTS. DISCUSSION AND CONCLUSION OF THE PRESENT
STUDY
[ 6.1] SELECTION OF THE LINKS -
Microwave
propagation
terrestrial
valley.
studies
have
been
carried
links with different terrain features
The
three
P&T
links
taken
for
this
out
over
over Assam
study
fall
in
Kamrup district .while fourth is railway link and is situated
in Nagaon district,
(kindly refer table 3.1 and fig.3.1).
terrains are so selected
that they cover marshy,
The
hilly and
bui1tup areas.
[ 6 .2 ] PATH PROFILE AND FRESNEL ZONE CLEARANCE -
Path
profiles
over
these
links
are
drawn
for
different
atmospheric conditions leading to various values of effective
earth radius factor K. Fresnel zone clearance is examined over
each
link
fresnel
for
all
zone
these
links
as
Laopani-Habaipur
2/3
condition
multipath
conditions.lt
clearance
Mi1mi 1ia-Durgasarovar
(hilly)
K
(a marshy
expected.
link,
(fig
fadings
is
fresnel
3.5b)
over
observed
that
maintained
for
and Maopet-Durgasrovar
over
a
plain
wet
land
of
zone is 50* obstructed for K=
and
this
well
land)
But,
is
we
have
link with such
associated
large
situations.
We
also note that fresnel zone clearance is relatively low over a
bui1tup area (Durgasarovar- Motapahar) and in extreme case of
K =2/3,
the clearance is maintained only by 24 meters.
or elevated
within
A duct
layer of width 30 to 50 meters which comes well
the width
of
a
normal
elevated
layers
if
generated
should have a significant control on the propagation character
over this link. And we therefore expect more fades over this
region compared
with Durgasarovar-Mi1imi1a and Durgasarovar-
Maopet links where fresnel
fact of
interest
is that
zone clearance is very
this
builtup area does
166
large.
not
The
favour
generation of a situation
valus
of
2/3
and
Laopani-Habaipur
presented
hence
links)
a sample
fades of depth
in the atmosphere where K takes a
of
multipath
fades
(as
observed
are
seen.
We
have
not
fade character
over
this
over
already
link,
where
up to only 5 dB is detected (chapter 4). This
observation points out to the fact that atmospheric situation
over a terrain if lead to a worst condition (with respect to
K), appropriate fresnel zone clearance must be maintained. So,
the
atmospheric
conditions
must
be
examined
systematically
before designing of a microwave link.
[ 6 3 1 . SYSTEM DEVELOPMENT :
Important outcome of the present work
some
major !instruments
recorder,
fast
such
response
as
rain
is the development of
fast
gauge,
response
temperature
telematric
anemometer,
facsimile recorder and sodar. These systems will help to study
the
microstructure
of
the
tropospheric
parameter
for
the
indepth studjy of the subject.
[ 6 .4 3 . FADE CHARACTERISTICS OF MICROWAVE SIGNALS :
CD. F ade Distribution
The fadings so observed over these
per
their
phenomenon
atmospheric
morphological
is
realised
variations.
links are then grouped as
character
by
and
the
associating
Basically
Physics
these
five
of
events
different
type
the
with
of
fading pattern are observed over the above mentioned
links as
shown
are
in the fig, (3,2 a,b,c,d,e).
These characters
then
grouped in to two as a) multipath and b) scintillation type of
fading
in terms of their fade rate.
The multipath
type of
fading occurred during night time scintillation type of fading
developed more often during pre noon hours.
The
multipath
occurrence
factor
167
for
each
link
is
then
evaluated through fade depth pattern and these are summerised
as follows for different paths.
1. P = 0.609L2 (Milmi1ia)
2. P =0.714L2
3. P =0.774L
2
(Maopet)
(Laopani)
Where P is the probability distribution and L gives the value
of
the
specified
signal
level.
The
distributions
clearly
indicate that multipath occurrence probability is highest over
Laopani-Habaipur
significantly
link.
The
high over
link
this
cutoff
figure
link and we
note
is
also
short
lived
blackout once in two days.
C2) Diurnal And Seasonal Variation Of Fades Over T he Link
And Comparative Stud y The fading is observed to be basically a nocturnal
phenomenon
as reported by other workers. The depth as well as occurrence
percentage is observed to be significantly high
links
during
night
hours
though
the
over all
preferential
the
time
of
development of fades may vary from pre to early morning hours
depending
early
on
morning
seasons.
The
winter
fades
occurrence
can
be
of
post
coupled
midnight
with
the
and
high
occurrence of surface based inversion layers.
In
terms
Milmilia
of
seasonal
and
Maopet
variations
links
of
follow
occurrence
the
of
character
fades,
of
low
lattitude costal region (American continental) where the fade
occurrence is maximum during winter months. On the other hand,
Laopani
link shows the character of a low latitudes
interior
region (Palmetto and Ottawa ) where the maximum occurrence of
fade is detected during the months of summer (chapter 4). The
significance of this observation is that even a LOS hop over
interior landlocked area may behave like a costal
depending
on
the
terrrain and
environmental
region link
situations.
The
presence of the mighty river Brahmaputra near/over these links
168
and
play
prolonged
rainy/cloudy
towards controlling
conditions
the fade
have
pattern
a major
over
role
to
Milmilia and
Maopet 1inks.
C3). F a d e Ra t e :
Another important parameter to study the dynamic aspect of the
propagation data is the fade rate. We have detected a distinct
diurnal variation in fade rate over all these links. Nocturnal
fades are slow and deep. The shallow and fast fades develops
after two or three hours of local sun rise and continue up to
1 or 2 hours of local noon. The fades over all these links are
predominent1y
due
to
the
coherent
mode
of
scattering
or
reflection f.rora the layered structures Cdiscused in chapters 4
and
5).
These
fast
fadings
are
attributed
to
turbulent
conditions of the atmosphere when inversion layers move up and
i
process of breaking of layer starts. This type of fast fading
is more often detected during summer day hours. Such) fades are
associated with the poor mixing of atmosphere (because of many
cloudy
days')
and
non
generation
of
well
structured
leading to incoherent scattering from relatively short
bubble
like
structures.
This
mode
of
scattering
is
plumes
lived
rarely
observed dufing night hours.
C4>. F a d e Du r a t io n :
Fade duration is another important parameter which requires a
considerable
attention
for
design
of
reliable
link and
the
probability of occurrence of a particular fade duration can be
i
examined thjrough the distribution curves of fade duration. The
probability' of occurrence of fade duration
over
three
links
follow the power law with the equation t = a L.with different
value of a. The corresponding
equation for fade duration
the three links are shown below
1. t = 550L (Mi 1mi 1ia-Durgasarovar link)
2. t = 514L (Maopet-Durgasarovar link)
3. t = 246L (Laopani-Habaipur link)
169
for
This
shows
that
fades
are
fast
and
short
1ived
over
Laopani-Habaipur link. This feature is associated with the non
specular
ground
reflection
component
that
is
reflected
from
the earth bulge during K=2/3 condition.
t 6.51 FADES AND ATMOSPHERIC CONDITIONS :
This study is basically done over M i 1mi1ia-Durgasarovar path
as
two
sodar
unit
and
all
other
parameters have been monitored
associated
over
this path.
meteorological
The RRI,
RR1
Gradient and effective earth radius factor have been examined
for
different
situations.
It
is
found
that
RR I is
though
maximum during summer months, the gradient reaches the highest
value during post monsoon period
and minimum during
winter.
The worst month statistics (chapter 4) indicating large number
of blackout events in post monsoon periods have been explained
with the development of ducting conditions during this period.
The blackout
monsoon
events
periods,
the
though are
overall
more often
development
favourable during winter
pre sunrise hours
this
with
has
been
coupled
large
detected
in
post
situation
is
more
(chapter A&5) and
temperature
inversions
detected through temperature profiles.
The contribution of the PBL
(or inversions)
fadings
through
taking
has
been
average
examined
thickness
and
a
height
towards microwave
simplified
of
PBL
for
model,
by
different
seasons as revealed by two SODAR units over the link path. The
effect
of
these
layers
towards
the
obstruction
of
first
fresnel zone ellipse has been traced. The PBL conditions have
been defined from this model for generating different types of
fades.
This model
however,
need modification as phase change
in the microwave signal has not been introduced.
A few case studies associating different types of fadings with
elevated layers, hot and humid fronts have been presented.
170
[ 6.63. Structure Cost ant Parameter
:
2
Structure constant paraameter
(C^ ) is realised through radio
sonde measurements and from the microwave scintillation data
through
power
spectral
analysis. This parameter reaches a
,,„-16
, -2/3,
, . .
summer
(10
meter
) and minimum
maximum
value
during
-
1 8
during the months of winter which is found to be 10
~2/3
meter
. This observation supports the fact of development
of
summer
scinti11 at ion
type
of
fadings
from
the
turbulent
structures of the atmosphere.
6.7 FUTURE SCOPE OF STUDY:
The relatively high link cutoff events and multipath ocurrence
factor
in ;the
through 50%i
bulge
at
Laopani-Habaipur
link
has
been
explained
obustruction of the first fresnel zone by earth’s
the
worst
atmospheric
occurrence factor predicts
communicatiion will
be
situation.
The
multipath
that this type of interruption
present
in
the existing
hops
in
passing
i
over a region where K=2/3 situation can be generated easily.
This
prediction
has
been
degree of dink cut off
supported
in many of
by
the
fact
the railway
that
links
high
in the
N.E. is a common feature.
It is
therefore necessary
to
carried
be
out
Habaipur a!long with
over
that more measurement on fades are
terrains
like
the
one
probing of the atmosphere
of
Laopani-
throgh sodar
l
and other meteorological sensors for a more clear apprisal of
system dynamics.
It is seen from the sodar returns that many dynamical
aspects
of the system received from such echograms can be associated
with
various aspects of fades seen in the 6-7 GHz links. So,
by examining sodar echogram,
a fairly good idea on microwave
fades pattern can be obtained. Because of the localised nature
of the PBL, microwave fading characters would also be affected
171
differently
over
different
terrains.
We have here
presented
such a study over a single terrain only . So it will be useful
to extend this work over varied terrains by mapping the PBL
received through a mobile sodar.
SUGGESTIONS :
It
is
suggested
at
least up
and
communications.
increase
and
When
such
operational
were
put
height
to make
thereby
the dynamical
suggestion
antenna
to 100 meters
obustruction
technical
that
a
measure
forward
of
be
the fresnel
avoiding
factors
range
should
is
zone
to user
free
interruption
not
possible
an alternative
the
increased
receiving
agency
way
setup.
like
the
due
is
of
in
to
to
These
Indian
Railways, who has welcomed it and has offered infrastructural
facilities if such a scheme is drawn up.
#
172
REFERENCES :
Aarons J.
IEEE Trans. On Antenna
And Propagation, 1977
Vo 1. AP-25, PP 729
Banerjee P.K,Majumdar S C.
Bhattacharya Sumana and Reddy B.M.
Proc. Of ICOMM -90
PP 700-704
DEC.19-21
Barbara A.K., Devi M.
Instrumentation on MV Link
Sharma S.,Timothy K.I.
Link Monitoring And On
Probing Of The PBL
TR-1, Jan.1991.
Barbara A.K., Devi M.,
Sharma S..Timothy K.I.
IGARSS-93 Publication
Aug-18 to 21, PP 263-266
Barbara A.K,.Devi. M,
Sharma. S. ,Timothy K.I.
A Few Aspects On Microwave
Propagation Character
Over Assam Valley
TR-II, July 1991
Barbara A.K, Devi M.,
Sharma S.,Timothy K.I
Development Of Facsimile
Recorder
TR-3 ,1992
Barabara A.K, Devi M.,
Sharma S., Timothy K.I
Raindrop Size Measurement
And Distribution.
TR-4, 1993
Barbara A.K, Devi M.,
Sharma S., Timothy K. I
Fast Response Rain Gauge
TR-5 ,1993
Barnett U.T.
The Bell System Technical Journal
Vo 1. 51 No.-2, Feb. 1972
PP 321-361
Barnett W .T .
The Bell System Technical Journal
Oct. 1970, PP 1827- 1871
Basu S,, Kelley M.C.
JATP. 1979
Vo 1.39 PP 1229-1242
B*, PP :180,
(1-3)
173
Bean B.R.,Thayer G.D.
Proc. of IRE, May 1959
PP 1827-1871
Bean B.R.,Meancy F.M.
Proc. of IRE, Oct.
PP 1419-1436
Bean B.R.,Dutton E.J.
Radio Meteorology
Dover PubIication,1968
Birnbaum George,Bussey H.,E.
Proc. of IRE Oct 1955
PP 1412-1418
Bui 1ington K.
The Bell System Technical Journal
July-Aug.1971 PP 2039-2049
Chanda A.,De A.K.,Das J.
Proc. Of ICAPRDT-93
1955
28-31 Dec.,PP 555-560
The Bell System Technical
Chen W.Y.S.
Journal
Vol. 50, No. 4, April
PP 1455-1485
1971
Collin R.E.
Antenna and Radio Wave
Propagation
Mc-graw Hill International
Edition
Crawford A.B.,Jakes M C. Jr
B .S .T .J .
Jan. 1952
Das J ., De A.K.
Majumdar D. D.
International Journal of Remote
Sensing Vol. 11,No 6, !990
PP 1033-1045
Deb N .C . ,Das J ,
Proc. Of ICAPRDT-93
28- 31 Dec.,PP 589-596
Deshpande D.U.
Journal Electronic and Telecom
Engineers, Vol. 23, No. 9, 1977
PP 563-569
Devi M. ,Timothy K.I,
Sharma S.,Barbara A.K.
Raindrop, Rainrate And
Microwave Attenuation
Proc. Of 3rd International
Conf. On Advances in
Pattern Recognition and
Digital TechniquesDec 1993
PP 539-544.
Dolukhanov M.
Mir Publisher,Moscow 1971
174
Durkee A.L.
Proc. of IRE
Feb. 1948, PP 197-205
Dutta H.N.,SarkarS.K.,Reddy B.M.
Sen Gupta Nandini
I.J.R.S.P.,Vol
PP 1-12, t98«
Fri is H .T .
B.S.T.J., Vol 27, No 2
April 1948, PP 183-233
Feher Kami 1o
Digital Communication Microwave
Application, PHI Private Limited
Gossard E.E.
Radio Science,Vol 12,No-1
Jan.-Feb. 1977,PP-89-105
Gossard E.E.,Neff U.D.
2amora R.J.,Gaynor J.F.
Radio Science,Vol 19,No-6
Nov.-Dec.,1984,PP 1523-1533
Griffiths J.,McGeehan J.P.
IEE Proc.,Vol 129,No-6
Dec.,PP 411-417.
Gurm H.S.,Somal H.S.
1. J.R.S.P. ,Vol 10
Singh Darshan,Dhi11 on.G.S.
Aug 1981, PP 131-136.
Hil1 R. J.
Radio Science,Vol
13, Feb.
13,No-6
PP: 953-961
Hogg D.C.
Proc. Of ICAP -83
Conference Publication No.-219
Part-2 Propagation,PP 1-3
lonoue, T & Akiyama T.
IEEE Trans. AP 22,557-565
Kay lor R.L.
B.S.T.J.,Sep 1953
PP 1187-1201
Kishor P.,Kumar T.R.V.
Rao D.N.
Proc.Of IGARSS-93
IEEE Catalog No: 93CH3294-6
PP 323-325
Kulshrestha S.M.,Srivastava S.K.
1.J.R.S.P.,Vol 19,
Oct.-Dec.1990,PP 319-325.
Kuriharo Yoshitaba
Proc.IRE, Oct 1955
PP 1362-1368
175
Lakshmi D . R . fSarkar S.K.
Ionospheric and Tropospheric
Radio Propagation
"A Review on the lectures at the
workeshopon HF/VHF and microwave
propagation"
Lai D.S.
C 1imeto1o g y , Chaitanya Publishing
House ,A 11ahbad
Lee J i in Lang
Radio Science, Vol 24,No 2
PP133-146,March-Apri1 1989
Lin S . H .
B.S.T.J., V o l -50, No-10
Dec 1971 PP 3211-3270
Mitra A.P. ,Reddy B.M.
Aggarwal S.
"Tropospheric Propagation and
Antenna Measurment"
First advanced cource,NPL I97F
Majumdar D.Dutta,Das J .,De A.K.,
Sinha Roy P.K.,Basu S. Mai lick,
Sen A.K.
Technical report on Project
"Statistical studies on he tropo­
spheric propagation for UHF/VHF
and microwave 1 inks*
Mathur N.C.
Proc.
of
ICAPRDT 93
28-31 Dec,PP- 545-554
Mitra A, Marina Dan.Bera R.
Sen A.K,
Proc.Of ICAPDT_93
PP 525-531
Muchmore R.B.,Wheelon A.D.
Proc. of IRE,Oct 1955
PP 1437-1449
Openhiem A.V.
Signals and System
PH I Publication
& Willsky A.S
Pari Steen A.
IEEE Transactions on antenna
and propagation ,Vol AP-31,No-6
PP 938-948
Pickering L.W.,Joseph K. De Rosa
IEEE Transaction on communication
Vol-com-27,No-8, A u g . 1979
Pearson K.W.
Proc. IEE, Vol
176
112,
No-7 Julyl965
Prasad M.V.S.N.,Sarkar S.K.,
Dutta H.N..Reddy B.M.,Rao D.Narayan
I.J.R.S.P.Vol-19 Feb 1990
PP 17-24
Rao D.Narayana,Ravi K.S.,
Reddy K.Krishna,Murthy M.J.K.
Dutta H.N.,Sarkar S.K.
Proc.Of
ICOMM -90
Dec.19-21, 1990
PP 696-699
Rao D.Narayan,Rao S.V.B.,
Ravi K.S.,Kumar T.R.Vijay
Murthy M.J.K.
Proc.Of ICOMM -90
Dec 19-21 1990
PP-692 -695
Rao M.P.,Kumar Raghu
Murthy J.Sree Ram
I.J.R.S.P.,Vo 1-10,Oct 1981
PP-176-181
Rao D.N., Reddy K.K.
Proc.Of IGARSS -93
IEEE Catalog No: 93CH 3294-6
PP 323-325
Rice S.0.
B.S.T.J. ,Vol-38,No-3,May 1958
PP 581-633
Roddy Dennis,Coolen John
Electronic Communications
PHI Private Limited
Rummler W .D.
B.S.T.J.,Vol-58,No-5,
May-June 1976,PP 1037-1071
Rummler W.D.
B.S.T.J.,Vol-61, No-9,Nov
1982,
PP 2185-2219
Ruthroff C.L.
B.S.T.J., Vol-50,No-7
Sep. 1971
Sandberg J.
IEEE Transaction on antenna and
propagation Vo 1-AP-28,No-6
Nov.1980
Sarkar S.K.,Dutta H.N.
Reddy B.M.
Proc. Of ICAP-83
Conference Publication No.-219
Part-2 Propagation, PP 294-297
Sarkar S.K.,Dutta H.N.
Reddy B.M.
Proc. Of ICAP-83
Conference Publication No.-219
Part-2 Propagation,PP 229-232
Sarkar S.K.,Prasad MVSN,
Dutta H.N., Reddy B.M.
Proc. Of ICOMM -90
Dec, 19-21
PP 599-602
Schiavone J.A.
Radio Science,Vol 18,No-3
PP 369-380,May-June 1983
177
Schiavone J.A
Radio science,Vol 17,No 5
PP 1301-1312,Sep.-Oct 1982
Schivone J.A.
B.S.T.J.,V01-16,No -6
PP 803-822,J u 1y-Aug. 1981
SenGupta Nandini,DasGupta M.K.
and
IEEE Transaction on antenna
propagation ,Vol AP 32,No-2
Feb 1984
Singal S .P.,Aggarwa1 S.K.
and Gera B.S.
I.J.R.S.P.,Vol-9,PP 52-54
April 1980
Singh Darshan,Soma 1 H.S,
Dhillon G.S,,Gurm H.S.
I.J.R.S.P.,Vol 11,
PP 23-28, Feb 1982
Sivkumar K., Sehgal, Tiwari R.K.
Proc.Of 1COMM - 90
Dec. 19-21
PP 599-602
Smyth J .B.,Tro1ese L.G.
Proc. IRE ,Nov 1947
PP 1198-1202
Somal H.S.,Singh Darshan
Dhillon G.S.,H .S.Gurm
I.J.R.S.P.,Vol 10,Aug.1981
PP 137-143
Stephenson E.t, Mogenson
IEE Trans. Antenn And Prop.
Vol.AP-30 No.3
Stephansen E.T.
Radio Science ,Vol 16, No 5
PP 609-629, Sep-Oct 1981
Tukigi, 0
IRE Transaction, AP 130-136
Vigants A
B.S.T.J., Sep.1970
PP 1513-1529
Vigants A.
B.S.T.J.,Vol 50,No 3
March 1971,PP 815-841
Webster A.R.
IEEE Transaction on antenna and
propagation ,Vol AP 30,NO-4
July 1982, PP 796-802
Webster A.R.
IEEE Transaction on antenna and
propagation ,Vol AP 30,No 4
July 1982, PP 800-802
178
Uesely M.L.
Journal of Applied Heterology
Jan. 1976, PP43-48
Wheelon A.D.,Much More R.B.
Proc. IRE, Oct 1955
PP 1450-
Uheelon A.D.
Proc. IRE, Oct 1955
PP 1459-1466
Uyckoff R.J.,Beran D.W.
Hall F.F. Jr.
Journal of Applied Meteorology
Vo 1 12,Oct. 1973, PP 1196-1204
B. S.T.J. - THE BELL SYSTEM TECHNICAL JOURNAL.
J.A.T. P. - JOURNAL OF ATMOSPHERE AND TERESTRIAL PHYSICS.
ICAP ICAPRDT -
ITERNATIONAL CONFERENCE ON ANTENNA AND PROPAGATION
INTERNATIONAL CONFERENCE ON ADVANCE IN PATTERN
RECOGNITION & DIGITAL TECHNIQUE
ICOMM -
INTERNATIONAL CONFERENCE ON MILIMETER ft MICROWAVE
IEEE -
INSTITUTE OF ELECTRICAL ft ELECTRONIC ENGINEERS
IGARSS -
INTERNATIONAL GEOSCINCE AND REMOTE SENSING SYMPOSIUM
IJRSP -
INDIAN JOURNAL OF RADIO AND SPACE PHYSICS.
IRE -
INTERNATIONAL RADIO ENGINEERS
179
(1) . B 1omquist A., NorburyJ.R. : EUROCOP-COST Final Rep.
On Project 25/4PP 141-173, 1978.
(2). Boithias L. : Electronic Lett. 15(7), 209-210.,
(3). Booker H.G., Gorden W.E.
: Proc.
1979.
IRE, V. 38, PP 401-402.
(4) . Clifford S.E.,
Strohbehn J.W.
: Trans. IEEE
Propagation, V AP-18, PP-264 -274, 1970.
Ant.
&
(5) . Das J., De A.K.,
Majumdar D.D.,
Sen
A.K.,
Basu
Mai lick S.K.: Indian Journal Of physics, 63B-(2), 149-160
1989.
(6 ). De A.K., Tripathy S.K., Deb N.C. &
ICAPRDT - 93, PP 589-596, 1993.
Das
J.
'
(7 ). Dougherty H.T., Hart B.A.
: IEEE T rans.
Propagation, AP - 27 (4), PP 542-548, 1979.
(8) . Eklund F, Wickert S.W.
(9) . Frank S.J., Liu C. H.: Radio Science, Vol 30,
1985
(11) .GeraB.S., Sarkar S.K.
:
BSTJ
: IJRSP, Vol. 9,
PP
(12) .Gilman G.U., Coxhead H.B. & Willis F.H.
Amer., V 18, PP-274
1968.
403- 415
PP
,Vol .36,
86-96,
System,
Ch-7,
PP
(15) .Ishimaru A, : Wave Propagation And Scattering
Academic Press, New York, Ch 17 And 20, 1978.
1980.
1,
(18) .Majumdar S.C.
&
Sen
A.K.
In
:
PP
364-407,
Media,
(16) .Jordan E.C.,
BalmainK.G.
: Electromagnetic Waves
Radiating System,
PHI Pvt, Ltd.,PP: 657-664, 1990.
(17!.Maitra A., Marina Dan, Bera R.
ICAPRDT -93 PP 531-538, 1993.
PP
: J.Acoustic Soc.
(13) .Gjessing D.T. : AGARD Conference Proc. No37, Part
15-1 to 15-17, 1968.
(14) .Haykin Simon: Communication
1989
Of
Antennas
: Radio Science, 3, 1066,
(10) •FriisA.S., Crawford A.B.,Hogg D.C.
627-644, 1957.
Proc
proc
And
Of
: Electronic Engg., V 44, PP-63, 1974.
(19) .Majumdar S.C., Sarkar S.K.,
Chaddha Ranjan
: Journal
Inst. Electro. Telecom Engrs., V 21, PP 597-604.1975.
180
(20).Manning
R.M.
:
Stochastic
Electromagnetic
propagation, McGraw Hill Inc. New York, Ch 2, 1993.
(21) .Mogensen G.
; Rep. LD 30, 203 PP 1977.
(22) .Mon J.P.,
Weill A., MartinL.
commission F Symposium URSI, 1980.
: paper
Presented
(23) Morita K. : Rev. Elect, commun. Lab, 25(11-12),
822, 1970.
(24) . MoritaK.
1972.
image
: Rev. Elect. Commun.
Lab.20(7-8),PP
PP
At
810-
589-598,
(25) . Raina M.K.,
Uppal G.S.
: IEEE Trans.
Propagation, Vol. AP-32,PP 185-187, 1984.
Antenna
(26) .Reddy B.M.
: Physics Of The Troposphere (
Radio Propagation
for
Tropical
And
Countries), PP 59-77, 1987.
Handbook for
Subtropical
(27) .Sarkar S.K.
: P hDThesis,
And
1978, Delhi Uni.
(28) .Sarkar S.K., Dutta H.N., Pashricha S.H.,
Reddy B.M.
:
Atlas Of Tropospheric Water Vapour Over The
Indian Sub
continent. 1982
(29).Sasaki 0., Akiyama
25(3-4), PP 315-323.
T.,
:
Rev.
(30) .Segal B, & Barrington : CRC Rep.
Rec. Center, Ottawa
Elect.
1315,
169
Commun.
PP,
Lab.
Commu.
(31) ,Sen A.K., Mitra A.K., Tarafdar, Ghosh S.N., Sehra J. S.
Proc.Of
International
Symposium
On
Antenna
And
Propagation Held During Aug.20-22, 1985, At Kyoto Japan.
(32) .Stephansen E. T., MogensonG.E.
- 27(3), PP 643 - 647, 1979.
(33) .Strohbehn J.W.
:
; IEEE Trans. Commun., COM
: Proc.Of IEEE, Vol. 56, No 8,Aug.1968.
(34) .Tatarski V.I. : Wave Propagation In A Turbulent
McGraw Hill Book Comp. Inc. New York, 1961.
Medium,
(35) .Tatarski V.I. : The Effect Of The Turbulent Atmosphere On
Wave Propagation, Nauka 1971.
(36).Tattersa11 R.L.O., CartwrightN.E .
Res.Dep. British P. 0 , England.
:
Rep.
(37).Tiwari R.K., Kumar K.S., Bahuguna C . : IETE,
1985
181
594,
PP
105
PP
130-133,
(38) .Venketeshwaran S.P. & NarayananV.S.:NPL
No-2, 1974
(39) .Wheeler M.S.
269-273.
: IEEE Trans.
Antennas
182
,RTRC Monograph
Propag.,
AP-25(2),
Документ
Категория
Без категории
Просмотров
0
Размер файла
10 535 Кб
Теги
sdewsdweddes
1/--страниц
Пожаловаться на содержимое документа