close

Вход

Забыли?

вход по аккаунту

?

Патент USA US3083370

код для вставки
March 26, 1963
c. E. SCHWAB
3,083,361
RADAR TESTING APPARATUS
Filed July 28. 1955
2 Sheets-Sheet 1
T
____
NR
__
RU
6oTN
I. A
D
_
___
R_Us#
l 5 ‘l\|
w
E
___
_M
_
__
R o__L
E ___
__
__O
__
__
__..I
_0|«|o_î
B
__
__
R
EEM_MVAGAl_H nluE1_.
oE
œ
J.__
P:T._WM
JS
_
o
FIG.l
__ __
___
x
h___
n
2 OJ
March 26, 1963
c. E. scHwAB
3,083,361
RADAR TESTING APÉARATUS
Filed July 28. 1955
2 Sheets-Sheet 2
/ ßA/ /
Tl ME--ò
FIG.3
Patented Mar.. 2h, lâh?,
l
2
3,053,361
system is supplied to the “echo box” and causes it to
“ring” or, in other words, to undergo self-oscillation for a
Carl E. Schwab, Fiushing, Nif., assigner to Hazcltine
Research, inc., Chicago, Eil., a corporation of illinois
Fired July ZS, 1955, Ser. No. 525,643
2 Gaines. (Qi. 34E-f7.7)
brief interval after >the nadar pul-se is transmitted. These
self-oscillations are, in turn, supplied back to the receiver
of the system thereby to produce `a signal at the output
terminals of the receiver which is indicative of the “loop
sensitivity” of the radar system. In effect, the echo box
ERADAP. TES'IÈNG A‘ÃBE’AìP-.ATSS
simulates a distant target or, more precisely, la standard
General
target at a standard distance. Also, by adjusting the rate
This invention relates to apparatus for testing the over 10 at which Ithe self-oscillation Áwithin `the “echo box” decays
all performance of a radar system and, while it is of gen
so that such nate of decay corresponds to the desired rate
eral application, it is particularly useful in testing the
of recovery of the receiver, a signal of more or less con
recovery characteristic of the receiver associated with the
stant amplitude is produced at the output of the receiver
radar system sub-sequent to the moment when la radar
over the decay interval provided the receiver recovers at
pulse is transmitted.
the desired rate. Departure of the peal; amplitude of
In a »radar system it is always desirable to know that
this output signal from the desired constant level indicates
the system as a whole is functioning properly. This is
that the receiver units of the radar system are not re
especimly important in many situations where improper
covering properly.
operation of the system may result in the loss of rather
While it appears that such “echo boxes” may be
expensive equipment which is relaying on such radar sys 20 utilized to indicate the over-all performance of the radar
em `for its proper guidance or operation. It is also desir
system, such “echo boxes” have several undesinable fea
able to have means for checking the operating condition
of a radar system which may ìhe readily and reliably
utilized by unskilled operators.
In order to check the over-all performance of a radar
system, it is necessary to decide on some ybas-ic character
istic of the system which is indicative o-f the over-.all
tures which limit their use Aand reliability. In the first
place, the “echo box” is a resonant circuit and «must he
tuned to the same frequency as the operating frequency
of the transmitter. AThe matter is complicated `because
the resonant frequency of the echo box is subject to
change «because of temperature variations. Tuning iad
operating condition of the system. One such characteris
justment of the “echo box” may be made by adjusting
tic is the so-called “loop sensitivity” of the system. By
some physical dimensions thereof but such adjustments
“loop sensitivity” is meant the sensitivity of the signal 30 are time consuming and present an occasion for human
path starting with the transmitter, continuing through re
errors to enter into the results. Also, the rate of decay
flection of the signal olf of a distant target, and ending
of the self-oscillation of the “echo-box” is highly de
with a signal being supplied to the output terminals of
pendent -on the Q of the “echo box.” As is known, the
the receiver of the radar system. The greater the sen
Q of an “echo box” is rather unstable :and quite subject
sitivity of this loop, «the greater is the magnitude of the
to change yas a result of temperature changes `which affect
signal produced in the receiver output in response to a
the dimensions of the box as well as the contact charac
given magnitude of transmitted signal. This “loop sen
terlstics of the metal spring fingers usually ‘associated with
sitivity” is, of course, dependent on the distance of the
the frequency-adjustment mechanism of the “echo box.”
target as lWell as atmospheric propagation conditions and,
As a result, considerable skill is necessary in ëboth the
hence, to afford any indication of the operating condition 40 design and operation of an “echo box” in order to obtain
of the radar system, this “loop sensitivity” must he speci
a reliable indication of the over-all performance of la
fied for a standard target at a standard distance.
Whe
this is done, any departure of the magnitude of the re
ceiver output from the proper value will indicate that
some part of the radar system is not functioning properly.
Another basic characteristic of importance in connec
tion with a radar system is the recovery characteristic of
the receiver subsequent to the moment when a radar pulse
is transmitted. If the receiver fails to recover its
optimum sensitivity rapidly enough, then echo signals
from nearby targets may be lost completely or else evalu
ated improperly. Thus, it would appear that knowledge
of the recovery characteristic as ywell as the “loop sensi
tivity” of :a radar system would afford suilicient complete
information to enable the proper decision as to whether
the radar system is functioning properly and, hence, pre
radar system.
It is an object of the invention, therefore, to provide
new and improved radar testing apparatus which avoids
one or more of the foregoing limitations of such appa
ratus heretofore proposed.
It is another object of the invention to provide new
and improved radar testing apparatus of relatively simple
construction and having highly stable performance char
acteristics to enable checking of the over-all performance
of a radar system.
It is a further object of the invention to provide new
and improved radar testing apparatus which is not fre
quency sensitive and which requires no frequency adjust
ment thereof in order to check the over-all performance
of a radar system.
vent the loss of expensive equipment that may be con
In accordance with the invention, apparatus for test
ing the over-all performance of a radar system including
It has been heretofore proposed to test these character
a pulsed transmitter and a receiver, and especially for
istics of a radar system by means of a resonant cavity or 60 testing the recovery characteristic of the receiver subse
trolled thereby.
a resonant one-quarter wave-length transmission line
which is coupled to the radar system at a point common
to both the transmitter and receiver. Such devices are
commonly referred to as “echo boxes” and each individual
radar pulse transmitted 'by the transmitter of the radar
quent to the moi rent when a radar pulse is transmitted,
comprises a transmission line of length substantially
greater than the operating wave length of the trans
mitter and responsive to a portion of each of the trans
mitted. radar pulses for producing multiple signal reflec
3,088,361
tions of successively decreasing amplitude which are sup
plied to the receiver for determining the operating con
dition thereof, the attenuation factor of the transmission
line being such that the average rate of decrease in am
plitude of the signal rellections produced by the line cor
d.
which the radar system is being put. Where, for exam
ple, the radar system is being utilized for navigation pur
poses to determine the distance of distant targets, the
utilization device 16 may be a suitable oscilloscope for
properly displaying the target echoes to enable determina
responds to the desired rate of recovery of the receiver
tion of the distance
after each radar pulse is transmitted. The apparatus
also includes means for coupling the transmission line
for automatically controlling the direction of liight there
to the radar system at a point common to both the trans
mitter and the receiver.
For a better understanding of the present invention,
together with other and further objects thereof, reference
is had to the following description taken in connection
with the accompanying drawings, and its scope will be
pointed out in the appended claims.
Referring to the drawings:
FIG. l is a circuit diagram, partly schematic, of a com
plete radar system and radar'testing apparatus constructed
in accordance with the present invention;
FIG. 2 is a partially sectional view showing a possible
physical form of the radar testing apparatus of the present
invention, and
FIG. 3 is a graph representing signals developed at
various points of the FIG. l system and used in explain
-ing the operation thereof.
Description and Operation of Radar Syste/n
Referring to FIG. l of the drawings, there is shown
a complete radar system and suitable radar testing appa- .
ratus constructed in accordance with the present inven
tion for testing the radar system. Considering first the
radar system, such system includes a transmitter 1€), of
conventional construction, for developing periodic pulses
or bursts of radio-frequency energy which may be re
ferred to as radar pulses. The transmitter 10 may in
clude, for example, a suitable oscillator circuit or device,
such as magnetron, and suitable pulse circuitry for con
trolling the periodic operation thereof. During normal
operation, the radar pulses produced by ‘the transmitter
10 are supplied by way of a transmission line l1‘1 to van
antenna 12 which is effective to radiate these radar pulses
towards distant targets. The solid line yenclosed by two
dashed lines on adjacent sides thereof, used to denote
the transmission line `11, is intended to represent a co
On the other hand, the radar sys
tem may be utilized aboard an aircraft or a guided missile
of, in which case the utilization device 16 may comprise
suitable relays and control circuits for controlling the di
rection of flight of the aircraft in response to the received
radar signals. Suitable synchronization signals may be
supplied to the utilization device 16 from the transmitter
10 by way of a conductor 17.
There may also be coupled to the output of the receiver
15 a peak detector 18‘ and a meter 19 for indicating the
peak amplitude of the video signal present at the output
terminals of the receiver 15. Such a peak detector and
meter are particularly useful in conjunction With the test
'ing apparatus of the present invention. The necessity of
their presence, however, depends on the nature of the
utilization device 16 and, where such utilization device
is of a type suificient to cooperate with the testing appa
ratus of the present invention, the separate peak detector
1.8 and meter 19 may be omitted unless desired for some
other purpose.
Description of Radar Testing A ppa?atus
Referring further to FIG. 1 of the drawings, there is
shown apparatus 20` for testing the over-all performance
of a radar system such as represented, for example, by
units 10--19 of FIG. 1. The radar testing apparatus 20
comprises a transmission line 21 of length substantially
,greater than the operating Wave length of the transmitter
10 and responsive to a portion of the transmitter signal
`for producing multiple signal reflections of successively
decreasing amplitude which are supplied to the receiver
15 for determining the operating condition thereof. In
practicing the invention, the transmission line 21 may be
rather extensive in length, for example, its length may be
80 feet. It Will be noted, however, that in the FIG. 1
.drawing the transmission line 21 has been broken as in
dicated, and the middle portion thereof not shown, in
order to simplify the drawing. The transmission line 21
vmay be of any conventional type suitable for the signal
axial cable type of transmission line, the outer dashed
frequencies being dealt with and, depending on such sig
lines representing the outer conductor of thecoaxial-cable.
nal frequencies, may be of any of the following types,
It is, of course, not essential that the transmission line
namely, either a rectangular or a circular wave guide, a
11 be a coaxial cable and such transmission line may be
strip-above-ground-plane transmission line, a coaxial cable,
of any other suitable type, for example, it may be of the 50 or a suitable type of two-wire line. It has been found
wave-guide type. As shown in FIG. 1, the transmission
that for the 100G-3000i megacycle range that coaxial cable
line 11 may be connected tothe antenna112 by properly
constitutes a particularly useful type of line for the trans
connecting a pair of couplers 13a and 13b.
mission line 21. By Way of example, the transmission
A T.-R. (transmit-receive) box 14 is coupled to the
line 21 of the FIG. 1 drawing has been shown in the form
transmission line 121 and also to a receiver 15. In this 55 of a coaxial cable.
manner, one antenna may be utilized for both the Vtrans
The length of transmission line 21 is preferably such
mitter and the receiver of the radar system. The T.-R.
that the time required for an electrical signal to travel
box 14 is of conventional construction and includes a
from one end of the line to the other end is at least equal
cavity containing a gaseous discharge tube which rapidly
to one-half the duration `of a radar pulse. This condition
ionizes in response to a high-energy transmitted radar 60 may be met by suitably selecting the length of the transmis
pulse and thereby effectively presents a short-circuit to
sion line 21 and is, of course, dependent on the velocity
the transmission line 11 and, thus, protects the receiver
of propagation characteristics of the particular type of
15 from damage or overloading due to the high-power
`transmission
_line that is used. Also, the parameters of
radar pulses. After an individual radar pulse has been
. the transmission line 21 are preferably such that the av
transmitted, the gaseous discharge tube of the T.-R. box 65 erage yrate of decrease in amplitude of the signal reilections
14 deionizes to readily enable transmission of weak tar
produced by the transmission line 21 corresponds to the
get echo signals from the antenna 12 to the receiver ‘15.
desired rate of recovery of the receiver units 14 and 15
ln this manner, during the intervals between transmission
of the radar system after each radar pulse is transmitted.
of radar pulses, the antenna 12 is effective to intercept .
echo signals from distant targets Aand these echo signals 70 In particular, `the total round-tripl signal attenuation that
results from translation of a signal down the transmission
are, in turn, supplied by way of the T.-R. box 14 to the
line
21 and back again should -be selected to produce this
receiver 15, which may be of conventional construction.
desired rate of decrease in signal amplitude. The total
Coupled to the output terminals of the receiver 15 is
round-trip attenuation of the line 21 is also dependent on
a suitable utilization device 16, the construction and
form of which depend upon the particular purpose to 75 the length thereof and, hence, in determining the proper
5
3,083,361
length for the transmission line 21, this requirement must
be taken into consideration in addition to the requirement
that the one-way transmission time be at least equal to
one-half the duration of a radar pulse. Another way of
6
the reactive type, i.e., should have a minimum resistive
component in order to prevent excessive attenuation of
the signal being translated.
As shown in F'lG. 1, the testing apparatus 2t) is con
saying it is that the attenuation per microsecond of delay 5 nected to the radar system by ñrst disconnecting the ra
factor of the transmission line 21 must be such that a
dar antenna 12 and then directly connecting the coupler
selected length of the line will satisfy both of these re
25 of the testing apparatus to the coupler 13a of the
quirements.
radar system. This is one possible way of coupling the
The two ends of the transmission line 2l are terminated
in such a manner as to produce substantial impedance
apparatus V20 to the radar system and is intended as be
Another alternative is to leave
the radar antenna 12 coupled to the radar system and to
signal supplied to the transmission line 21 to be reilected
couple an auxiliary antenna to the coupler 25 of the
back and forth along the transmission line 21. To this
testing apparatus 20 and then to position this auxiliary
end, the end 22 of the transmission line 21 may be termi
antenna adjacent the radar antenna 12 a predetermined
nated in, for example, a short circuit while the other end
15 ñxed distance therefrom. In this manner, coupling be
23 of the line 21 may be terminated in, for example, an
tween the testing apparatus 20 and the radar system
discontinuities for enabling the portion of the transmitter
open circuit.
The purpose is to produce substantial re
ñection 4of the signal from either end of the transmission
line 21 and any type of termination suitable for this pur
10 ing only representative.
proper is accomplished by Way of the electromagnetic
radiation passing between the main radar antenna 12 and
the auxiliary antenna.
l
pose ¿may be utilized,
The testing apparatus 2li preferably also includes con
Radar testing apparatus 20, constructed in accordance 20 trol means 30 capable of terminating one end of the
with the present invention, also includes means for cou
transmission line 21 in a matched resistive load 31 for
pling the transmission line 21 to the radar system at a
disabling production of multiple signal rellections over
point common to both the transmitter it) and the re
desired intervals to ascertain that the receiver l5 response
ceiver 15. By “common point” is meant a point, region,
is caused primarily by the multiple signal reflections and
or location through which both signals from the trans 25 not by other extraneous signals to be discussed herein
mitter l@ and signals to the receiver 15 must pass. Such
after. The control means 30 may take the form of a
a common point is represented by the point along the
push button, the barrel 32 of which is designed to slide
transmission line 1l at which the coupler 13a is located.
over the end of the transmission line 2l. In this man
The coupling means for the radar testing apparatus Ztl
30 ner, the pressing of the push button engages the resistor
includes means such as a coupler 25 for coupling a sig
31 with end 23 to absorb any signal energy reaching the
nal-translating path to the radar system. The coupling
end 23 of the transmission line 21. The resistor 31 is
means may also include, for example, additional seg
normally maintained in a disengaged position from end
ments of transmission line 25 and 27, the segment 26
23 by means of a suitable spring 33 and accompanying
being connected to the coupler 25' and the further end of 35 retaining rings.
segment 27 being terminated by a reactance coupler 2S
Referring now to FIG. 2 of the drawings, there is
for coupling this signal-translating path to the transmis
'sion line 2l near one end of the line 21. The coupling
means also preferably includes signal-attenuating means
29 inserted at an intermediate point along the signal
translating path represented by transmission-line seg
ments 26 and 27 for minimizing the etfect on the radar
shown a possible physical form of the radar testing ap
paratus 20 of FIG. l. Corresponding elements have
been denoted by the same reference numerals in both
figures. The structure of FIG. 2 is, of course, only rep
resentative but has been found to be useful where a
length of 1/2 inch diameter coaxial cable of the order
of 80 feet is used for the transmission line 21. Such a
ength of coaxial cable Will produce a one-way trans
attenuator 29 may be of a conventional type «suitable
mission time of the order of 0.1 microsecond. The co
45
for use with the type of transmission lines actually used
axial cable is suitably coiled as shown in FIG. 2. The
and may have an attenuation value of, for example, 9
over-all dimensions of the outer case 35 in which the
decibels. In some cases, it may be desirable not to uti
testing apparatus is housed may be, for example, 12" X
lize transmission-line segments 26 and 27 in which case
12” x 8” and the total weight or" the unit is of the order
one end of attenuator 29 may be connected directly to
of 15 pounds. For ease or" transporting the unit, carry
to the coupler 2S while the other end of attenuator 29
ing handles 36 and 37 may be aflìxed to the upper end
is connected directly to the reactance coupler 2S.
of the case 35'.
Where the reactance coupler is coupled as shown in
system of any impedance discontinuity caused by the re
actance coupler `28. This signal attenuating means of
FlG. 1, the loop portion thereof should be positioned
Operation of Radar Testing Apparatus
to coincide with a current node of the standing wave
Considering now the operation of the radar testing
produced on the transmission line 21 in order to afford 55 apparatus just described, the apparatus 20 is connected
as broad a coupling band width as possible so that the
.to the radar system at a point common to both the
coupler will be comparatively insensitive to the operating
transmitter and the receiver. More specifically, in the
frequency. It is not critical, however, that the reactance
case of the FIG. 1 scheme, the radar `antenna 12 is diS
coupler 28 should be coupled to the transmission line 21
-connected and the coupler 25 of the testing apparatus
precisely as shown in FIG. 1 of the drawings as «such 60 2t? is connected to the coupler 13a of the radar system.
reactance coupler may, for example, also be coupled to
The radar system is operated in a normal manner and,
the transmission line 21 by coupling in an endwise fash
fhence, the periodic radar pulses developed by the trans
ion through the end 22 or" the transmission line 2l. In
mitter l@ are supplied directly to the testing apparatus
such case, the short-circuit termination of the end 22 iS
29. Each radar pulse is translated by `the segment of
65
not used and the center conductor of the line 21 is formed
coaxial cable 26, the attenuator 29, and the coaxial cable
into a pickup loop so as to afford suitable electromag
netic coupling to the loop portion of the reactance cou
pler 28. Where the coupler 2E is coupled in this man
ner, the coupling arrangement resembles that of a pis
ton attenuator.
Sullìcient mismatch or impedance dis
continuity is maintained at the end 22 because of the
highly reactive nature of the coupler. Other suitable
coupling arrangements will be apparent to those skilled
in the art. In any event, the coupler 2S should be of
segment 27 to the reactance coupler 2S. The reactance
coupler 28 is effective to couple a portion of each radar
pulse to the reflection-producing transmission line 21.
Because of the impedance discontinuity presented by the
reactance coupler 28, a portion of each pulse is reilected
back towards the radar system and is not coupled to the
transmission line 21. Most of this initially reilected
energy is absorbed by the attenuator 29 so that operation
I:of the transmitter 1t? is not adversely affected. The
3,083,361
7
attenuator 29 is also effective to absorb an appreciable
amount of the energy of each radar pulse during its
initial passage through the attenuator 29 en route to the
directional coupler 28. Thus, the portion of each radar
pulse reaching the transmissio-n line 21 is reduced in mag
nitude relative to the magnitude of such pulses when
developed at the transmitter 10.
The portion of the radar pulse supplied to the trans~
mission line 21 travels towards the far end 23 thereof
and is thence reflected off of the open-circuit termina
tion at this far end. Subsequently, the pulse energy
travels back towards the short-circuit end 22 of the trans
mission line 21 and is then reflected off of this short
circuit end 22. Thus, the signal energy from each radar
pulse is reflected back and forth along the transmission ì
line 21 several times. However, each time the pulse
travel to theA far end >ofthe line andback again is’approx
imately equal to thel duration of the radar pulse, such
time being represented by the dimension T of the FIG. 3
curves. In this manner, a continously decreasing stair
case wave form is produced. The> difference in power
.level of -successive steps of the staircase, as represented
by the dimension P2 of the drawings, is determined
primarily by the round-trip attenuation of the' transmis
sion line 21. In other words, the only cause for difference
in the amplitude of successive reflections is the attenua
tion produced by the transmission line 21. This attenua
tion is, `of course, dependent on the type of transmission
line utilized as well as the length thereof. vIn this manner,
by properly selecting the type and length of transmission.
line a staircase wave form >of desired duration and rate
of decease may be developed.
The rate of decrease of the staircase wave form repre
sented by cure B is a importance in testing the recovery
`characteristic of the units associated with the receiver o_f
the coaxial cable segments 26 and 27 and the attenuator
29. In this manner, multiple -signal reflections of suc 20 the radar system. This becomes apparent in connection
with cure C of FIG. 3 which represents the power re
cessively decreasing amplitude are supplied back to the
quired at the coupler 13a of the radar system in `order to
radar system. The -amplitude of successive signal reflec
produce a constant predetermined signal level at the out
tions decreases because of signal attenuation caused by
put of the receiver 15. It will be noticed `that the power
the distributed resistive component of the -transmission
line 21 and because of the signal energy removed from 2,5 required for this purpose decreases with time subsequent
to transmission of the radar pulse represented by curve
the line 21 each time the signal passes the reactance
A. This, in effect, represents the composite effect >of
coupler 28. In other words, the transmission line 21
the recovery time required by the T.-R. box 14 and the
is not a theoretically ideal transmission line and, hence,
receiver 15 `subsequent to each radar pulse. A finite
a signal suffers some attenuation as it is translated down
recovery
time is required because each radar pulse causes
30
the line. This transmission-line attenuation, which is
the gaseous discharge tube associated with the T.~R. box
normally considered undesirable, 4is utilized in the present
14 to become ionized and, hence, a finite time interval is
invention to obtain the desired successive decreases in
required for the gaseous discharge tube to deionize sub
.signal amplitude. Where the signal energy removed from
sequent to the production of the radar pulse. Also, it is
the transmission line 21 by» way yof .the reactive coupler
28 each time the signal passes the coupler 28 is relatively 35 common practice to afford further protection to the
yreceiver 15 by «gating the initial lamplifier circuits thereof
slight, as will be >the usual case because the coupler 28
tova nonconductive condition during the occurrence of
presents a relatively large impedance discontinuity, the
they radar pulse. A certain finite time is also required for
decrease in amplitude between successive signal reflections
these circuits to become conductive again subsequent to
may be considered as being caused primarily by the
40 each radar pulse. Accordingly, as these circuits and the
`distributed attentuation of the transmission line 2.1.
T.-R. box 14 recover their normal operating state for the
Referring Vnow to FIG. 3 of the drawings, curve A,
reception of echo signals from `distance targets, they
which `is the boundary of the cross-hatched area, repre
become more sensitive and better able toV translate the
sents a radar pulse as developed by the transmitter 10
target echoes. Hence, less input power at coupler 13a
and supplied by way of the transmission line 11 to the
is required to produce the desired constant predetermined
testing apparatus 20. The multiple signal reflections of
signal level at the output of the receiver 15.
successively decreased amplitude which are developed by
Curve D of FIG. 3 shows Athe wave form of the output
the testing apparatus 20 are represented by curve B of
signal produced at the output of the receiver 15 in
FIG. 3 which is in the nature of a staircase wave form.
response to the multiple signalV reflections of the testing
Curve B represents the multiple signal reflections -at the
apparatus 20 where the average rate of decrease of the
50
output of the testing apparatus 20 or, in other Words, at
staircase Wave form a curve B is designed to coincide
the coupler 25. It'should'be vremembered that the trans
with the desired rate of recovery of the receiver 15 cir
mitter 10 is transmitting periodic radar pulses only one
cuits and the T.-R. box k15 after each radar pulse, provided
of which is represented by curve A. Therefore, curve
such circuits and the T.-R. box 14 do recover at the
B- represents the response of the testing apparatus 20` for
desired rate, Thus, the existence of a more or less con
only one -cycle of a recurrent type operation. In other
stant amplitude signal, as represented by curve D, at the
words, curve B is the response of -the testing apparatus
output of the receiver indicates that the receiver circuits
20 to a single one of the periodic radar pulses, a corre
signal passes the reactance coupler 28, a portion of such
signal is coupled back into the radar system by way of
and the T.-R. box 14 are recovering at the desired rate.
spending response being produced by each of the other
In practice, the top portion of the output signal repre
radar pulses developed by the transmitter 10.
The difference in power level of the ñrst step of the 60 sen-ted by curve D will not be perfectly flat because of the
staircase nature of the signal reflections from the testing
Vmulti-ple signal reflections represented by curve B from
apparatus 20 or, in other words, there may be a slight
Ithe _power level of the input radar pulse represented by
ripple along the top portion of this output signal. vFor
curve A, which «difference is represented by the dimen
1simplicity of presentation, however, this signal is shown
sion P1 of FIG. 3, is determined primarily by the at
tenuation of the attenuator 29, the reactance coupler 65 as having a relatively flat top. Also, the average ampli
tude of this output signal represented by curve D is in
28, and the transmission line 21. More precisely, because
dicative of whether the “loop sensitivity” of the radar
each radar pulse must pass through the attenuator 29,
system is of the proper value. In other words, where the
the reactance couplerl 28, and the entire length of the
amplitude of this output signal corresponds to a desired
-transmission line 21 twice before reappearing at the
coupler I25 asa signal reflection, the decrease in power 70 predetermined' value, then it is known that lthe “loop
sensitivity” .of the radar system is also of the proper
represented by P1 is equal to twice 4the attenuation pro
value. Accordingly, if this information is made available
duced by these elements.
For multiple signal reflections as shown by curve B of
FIG. 3, the time delay of the transmission line 21 is
chosen so that the round-trip time for a radar Ipulse to
to a person checking the radar system, he may properly
decide whether the system is operating properly.
There are several alternatives as to how the nature
3,083,361
of the receiver 1S output signal may be presented to the
person checking the radar system. In many applications
the nature of the utilization device 16 is such that the
presence or absence- of the proper type receiver 15 output
is indicated directly to the operator. For example, where
the target echo signals are being displayed on an oscil
loscope, then direct examination of the receiver output
wave form on the oscilloscope display screen will enable
the operator to determine the manner in which the radar
10
defective T.-R. boxes sometimes act like resonant circuits
and, hence, “ring” or undergo self-oscillation in response
to the radar pulses. This means that the T.-R. box itself
would be developing and supplying signals to the receiver
15 subsequent to the transmission of a radar pulse which,
of course, is undesirable. Thus, by disabling the .testing
apparatus 20 momentarily by way of the push termination
'assembly 30, the operator may check the meter 19‘. The
presence of a meter reading under these circumstances
system is performing. Another alternative is where the 10 would, for the example of a defective T.-R. box 14, indi
utilization device 16 comprises various relays and control
cate that the T.-R box 14 is undergoing self-oscillation
circuits for controlling the operation of some further
and, hence, is defective.
equipment associated with the radar system. In this case,
It is thus apparent that radar testing apparatus con
proper operation of the radar system may be directly
structed in accordance with the present invention repre
indicated by determining whether the relays associated
sents a useful and reliable piece of test yapparatus of
with the utilization device 16 are operating properly. A
relatively simple construction. All the operator need do
third alternative, as illustrated in FIG. 1 of the drawings,
is bring the testing apparatus, which may take the form
is to utilize as separa-te peak detector 18 and meter 19
as shown in FIG. 2 of the drawings, to the location of
for developing a visual indication of the peak amplitude
the radar equipment to be tested and then connect it to
of the signal present at the receiver 15 output. By proper 20 the radar system by way of a suitable connecting cable
ly selecting the time constants of the components »associ
or coupler and then observe the reading on the meter 19;
ated with the peak detector 18 and meter 19, the meter
If the reading equals or exceeds the desired predetermined
19 may be made to give a desired predetermined indica
value, then the operator knows that the radar system is
tion only when both the recovery characteristic and the
functioning properly. Otherwise, he is apprised of the
“loop sensitivity” of the radar system are of the desired 25 fact that some part of the system is not operating proper
value. Assume, for example, that the recovery character
ly. In this manner, a radar system may be quickly
istic of, say, »the T.-R. box 14 should change due to either
checked by a relatively unskilled person. In addition,
aging or else leakage of the gaseous discharge tube associ
it will be noted that the testing apparatus will furnish
ated therewith. Then, the recovery curve for the T.-R.
accurate and reliable indications over a long period of
box 14 and receiver 15 does not fall as rapidly as the 30 time without need for any adjustment of the apparatus.
ideal curve represented by curve C of FIG. 3 and, hence,
The performance of testing apparatus constructed in
the signal present at the output of the receiver 15 for a
accordance with the present invention is highly stable
single cycle of operation assumes a shape as represented,
because such performance is determined by stable circuit
for example, by curve E of FIG. 3. This nature of out
elements of a passive nature which are not readily ‘sus
put signal as represented by curve E would cause the 35 ceptible to changes in temperatures, etc.
meter 19 to read less than the desired Value, hence indicat
While there has been described what is at present con
ing improper operation of the radar system.
As mentioned, the length of the transmission line 21
sidered to be the preferred embodiment of this invention,
it will be obvious to those skilled in the art that various
of the testing apparatus 20 should be selected so that the
changes and modifications may be made therein without
time required for an electrical signal to travel one way 40 departing from the invention, and it is, therefore, aimed
from one to the other end of the .transmission line 21 is
to cover all such changes and modifications as fall within
at least equal to one-half the duration of the radar pulse,
the true spirit and scope of the invention.
which is the same thing as saying that the round-trip time
What is claimed is:
relay of the transmission line 21 is at least equal to the
1. Apparatus for testing the over-all performance of
duration of a single radar pulse. Where the transmission
a radar system including a pulsed transmitter and a re
line 21 is of greater length than this minimum, there
ceiver, and especially for testing the recovery character
will be time in-tervals between successive steps in the
istic of the receiver subsequent to the moment when a
signal reilections during which no signal energy is being
radar pulse is transmitted, the apparatus comprising: a
supplied back to the radar system. Thus, instead of a
transmission line of length substantially greater than the
staircase wave form, a series of pulses of successively
operating wave llength of the transmitter and responsive
decreasing amplitude would be produced. This type of 50 to
a portion of each of the transmitted -radar pulses
signal is entirely suitable for testing the radar system
for producing multiple signal reflections of successively
provided the rate of decrease of the envelope of this
decreasing amplitude which are supplied to the receiver
series of pulses is properly adjusted so that this envelope
for
determining the operating condition thereof, the at
decreases at the same rate at which the T.-R. box 14 and
tenuation factor of the transmission line being such that
receiver 15 recover after a radar pulse. Of course, in
the average rate of decrease in amplitude of »the signal
order to keep the weight and size of the testing apparatus
reflections produced by the line corresponds to the de
at a minimum, it will generally be >desirable to usel the
sired rate of recovery of the receiver after each radar
shortest possible length of transmission line 21. The
is transmitted; and means for coupling the trans
length of the transmission line 21, however, should not be 60 pulse
mission line to the radar system at a point common to
made so short that the time required for -a radar pulse to
make a round trip down the transmission Iline 21 and
back again is less than the duration of the radar pulse.
If this should be permitted to occur, then phase addition
both the transmitter and the receiver.
2. Apparatus for testing the over-all performance of a
radar system including a pulsed transmitter and a re
ceiver, and especially for testing the recovery character
and cancellation of the radio-frequency carrier signal
65
istic
of the receiver subsequent to the moment when a
forming the radar pulse will result in undesirable ampli
radar pulse is transmitted, the apparatus comprising: a
tude variations in the resulting signal supplied back to
transmission line of length substantially greater than the
the radar system which may result in an improper evalua
operating wave length of the transmitter and responsive
tion of the operating performance of the radar system.
Also included in the testing apparatus 2t) is the push 70 to a portion of each of the transmitted radar pulses, the
two ends of the transmission line being terminated in such
termination assembly 30 for enabling the operator to
a manner as to produce substantial impedance discon
suppress signal retlections within the transmission line 21
tinuities thereat for enabling the portion of each of the
and thereby prevent any appreciable amount of reflected
transmitted radar pulses supplied to the transmission line
signal energy being supplied back to the radar system.
to be retlected back and forth along the transmission line
A provision of this type is desirable because, of one thing, 75 for producing multiple signal reflections of successively
3,083,361
decreasing amplitude which are supplied to .the -receiver
for determining the operating condition thereof, the at
tenuation factor of the transmission line being such that
the average rate of` decrease in amplitude of the signal
reflections produced by the line corresponds to the de
sired rate of recovery of the receiver «aftereach radar
pulse is transmitted; and means for coupling the trans
mission line to the radar »system at a point common to
both the transmitter -and the receiver.
12
References Cited in the file of this patent
UNITED STATES PATENTS
2,217,957
2,429,632
2,532,539
2,549,131
2,602,922
Lewis ________________ _.. Oct. 15, 1940
Lair __.__f_ ____________ __ Oct. 28, 1947
2,658,998
Hyman ______________ __ Nov. 10, 1953
Counter _et 4al ___________ __ Dec. 5, 1950
Rideout ______________ _.. Apr. 17, 1951
Maynard ______________ „_ July 8, 1952
Документ
Категория
Без категории
Просмотров
0
Размер файла
1 080 Кб
Теги
1/--страниц
Пожаловаться на содержимое документа