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Патент USA US3089115

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May 7, 1963 _
3,089,105
A. ALFORD
COAXIAL CHOKE COUPLER
Original Filed July 28, 1951
2 Sheets-Sheet 1
‘a’
INVENTOR.
B
Y
Arm/raw Alford
W ‘W
May 7, 1963
A. ALFORD
'
COAXIAL CHOKE COUPLER
3,089,105
Original Filed July 28, 1951
2 Sheets-Sheet 2
FIG. 5
INVENTOR.
Andrew
A I Ford
W%%%
BY
'
94/
United States Patent 0 "ice
_
3,089,105
Patented May 7, 1963
2
1
modi?cations of the invention the outer conductor is pro—
vided with a so called disc line coupling, in which an
3,089,105
COAXIAL CHOKE COUPLER
Andrew Alford, 299 Atlantic Ave., Winchester, Mass.
Continuation of application Ser. No. 239,046, July 28,
1951. This application July 10, 1956, Ser. No. 596,930
1 Claim. (Cl. 333—73)
improved coupling effect is obtained over those previously
known which utilize the sleeve coupling type of unit. In
this disc type joint there is less power radiation than
from the sleeve type of joint. In one modi?cation (see
FIGURE 3), in addition to the disc line elements set
forth above, there is also provided a sleeve type of inn
The present invention which is a continuation of my
pedance and a cavity type of impedance, thus waves
copending application Serial No. 239,046, ?led July 28,
1951, now abandoned, relates to a coupler for trans 10 radiating from the joint of the outer conductor sections
will successively meet a low impedance in the sleeve joint,
mitting high, ultra high, or very high frequencies through
a high impedance in the cavity, and a low impedance in
a structure operated at a lower frequency and maintained
the disc line, which impedance is lower than that en
above a ground potential without introducing excessive
countered in .the sleeve type of joint. These successive
re?ections or radiation at the coupler while at the same
time not interfering or grounding the structure or radiator 15 impedances which are mismatched one with the other,
when coupled together with the signi?cant difference in
operated at the lower ‘frequency. More particularly the
characteristic impedance of air with the disc line imped
device of the present invention may be called a coaxial
ance, cooperate to effectively reduce the amount of power
choke coupler, but the use of the words “coaxia ” and
radiation. This reduction of power radiation is quite
“choke” are both taken in a more general sense than
usually applied to coaxial lines or choke coils. The de 20 noticeably larger than that obtained with conventional
and known joints as exempli?ed.
vice of the present invention‘may have many uses, as for
The invention will be more readily understood from
instance in mounting a high, ultra high, or super high
the speci?cation set forth below when taken in connection
frequency transmitter on top of a low frequency insu
with the drawings illustrating an embodiment of the same,
lated radio tower. In this case the problem is to trans
mit these very high frequencies through the tower which 25 in which:
FIGURE 1 shows a section through .a coaxial choke
is insulated and maintained at potential above the ground
coupler of the present invention.
without disturbing the existing electric system. In this
FIGURE 2 shows a plan view of the arrangement of
case the so called coaxial choke coupler at the bottom
FIGURE 1.
of the tower will be ‘designated to pass the high fre
30
cycles to 5000 megacycles and higher, so that the antenna
FIGURE 3 shows a modi?cation of the arrangement
of FIGURE 1 in which a three step coaxial choke cou
on top of the ‘tower may transmit such short waves.
pler is shown.
quencies, as for instance of an order from 100 mega
FIGURE 3a shows a top view of the modi?cation of
FIGURE 3, and
high frequencies on planes. In such cases whole sec
FIGURES 4 and 5 show application of the present
tions of the stabilizer may act as an antenna for lower 35
This problem also arises in transmitting both lower and
frequencies, such sections being insulated from the rest
gof the plane.
Mounted on top of the stabilizer will be the high fre
invention to an antenna tower and a stabilizer on a plane
acting as an antenna.
In the arrangement shown in FIGURE 1, the coupling
unit comprises an outer conductor 1 and an inner con
40 ductor 2. The outer conductor 1 is formed of two ele
pler between the insulated section of the stabilizer and
ments 3 and 4 which are insulated from each other in a
the rest of the plane. The range of frequencies usually
quency antenna which will be fed through a choke cou
central section 5. The section 3 of the outer conductor
de?ned for very high frequency, ultra high frequency and
is provided with a ?at outwardly extending ?ange 6 while
super high frequency, namely from 100 megacycles to
5000 megacycles and higher ‘are readily transmitted 45 the section 4 is also provided with an outwardly extended
flange 7 which ?anges are positioned opposed to one
through the coaxial choke coupler system of the present
another and separated by an insulator 8‘ which may also
invention most advantageously. While the range is prin
serve as a dielectric. The two sections of the outer con
cipally applied to frequencies over 100 megacycles, the
same principle herein set forth may be applied to lower
frequencies within the allowable physical dimensions of
the choke coupler and the statement of range should not
apply as a limit of the scope of the invention.
ductor are held together by means of an insulating ring 9
which ?ts over the shoulder of the ?ange 7 of the section
4 and through which bolts or screws 10 are passed ex
tending through the ?ange 6, capped by nuts 11 or other
suitable means to clamp together the outer conductor
The advantage of this arrangement of the present in'_
sections about the insulating element 8. The inner con
vention is that it introduces a low value of capacitance
and further that the radiation leakage is comparatively 55 doctor 2 is also formed of two sections 12 and 13 insu
lated ‘from one another and separated by a space 14
small. It is also possible by proper design to maintain a
which may be ?lled with an‘ insulator as indicated in
substantially low standing wave ratio. Further the pres
FIGURE 1. Section ‘1'2 terminates in a small end 15
ent invention may be readily adapted to any low fre
quency transmission structure for use with it of a very
which extends into a recess in the end of the conductor
high frequency antenna within the range of frequencies 60 13. The recess within the end 13 and the terminal end
15 of the conductor 12 may all be coaxial with one an
covered by the present invention.
other, and the insulator ?lling the space 14 should also
This invention further relates to and provides a so
extend outwardly to come between the shoulder 16 on
called choke coupler in which a frequency range is trans
the inner section 12 and the end of the inner section 13*
mitted through a line in such a way as to minimize radia
tion eifects at the coupling unit. In accomplishing this, 65 so that sections 12 and 13 of the inner conductor are
insulated from one another.
the impedance between successive sections of the inner
The inner conductor is supported and centered co—
axially within the outer conductor by means of a central
cylindrical tube 17 of insulated material upon either end
conductor joint so as to attenuate any high frequency
waves which may otherwise radiate from the joint and 70 of which rests insulators 18 and 19 which may be in the
shape of a frustrum of a cone. By such an arrangement
thereby interfere with the low frequency transmission in
and outer conductors are minimized, while at the same
time substantial mismatching is provided in the outer
the ?eld in which the coupler is located. In the several
except for the impedance sections, the impedance along
3,089,105
3
4
the line will be uniform throughout. The outer con
ductor may be terminated at its ends by conductive ?t
tings 20 and 21 which thread into the ends of sections
4 and 3 respectively coaxially with the inner conductive
ends 22 and 23‘ respectively, which may be spaced and
ance line. When properly proportioned this arrangement
supported coaxially by cylindrical insulators 24 and 25
respectively.
The choke coupler in this case provides a complete
results in a very moderate low frequency capacitance and
a high value of leakage index, that is a very small leakage.
The coupler constructed in accordance with FIGURE
3 may have a low frequency capacitance of 25 micro
microfarads and a leakage figure of over 44 db. The
good performance of the three stage coupler is due to
the fact that a three stage choke is effective even when
the gap spacings described above are comparatively
coupling unit with coupling receptors at each end to
large.
which coaxial lines may fit, one going up to the high
The performance of the three stage coupler may be
frequency antenna and the other going to the power sup
compared to that of a single stage coupler of FIGURE 1,
ply which may be on the ground side of the system.
which with a gap of .032.” had a low frequency capaci
In the choke coupler shown in FIGURE 1, two im
pedances are introduced in the coupler, one which may be
tance CT=42.=1 micro-microfarads and a leakage ?gure
called Z, the impedance of the inner conductor in the 15 around 30 db.
This capacitance C;- consists of two parts in the single
section where the space v14 is situated which may be
stage coupler, the capacitance between the inner conduc
?lled with an insulator as stated, and two, Z2, the plate
or disc section in the outer conductor separated by the
tors CI and the capacitance between the outer conduc
insulator 8. The effective wave length of the section of
tors'CQ, the total capacitance CT being CI plus Co.
the inner conductor along the insulating or spacing ele 20
In the arrangement of FIGURE 3, the inner conduc
ment 14, should be equal to approximately a physical
tor 26 is made with a low impedance section 27 in which
quarter wave length at the center or mean frequency or
portions of the inner conductor 28 and 29 are separated
by the insulating element 30 similarly as described in
some frequency within the band to be transmitted pro
viding such length is substantially less than oneJhalf the
connection with FIGURE ‘1. This comprises a low im~
wave length of any frequency in the normal band. Even 25 pedance at high frequencies and a high impedance at low
if the quarter wave length corresponded to a frequency
frequencies. Between two coaxial conductive elements
31 and 32 there is provided a low impedance at high fre_
well within the transmission band, it would provide im
quencies and a high impedance is provided because of
proved results, although the nearer to the mean fre
quency, the more effective will be the improvement.
the element 31 and the cavity 50 with the gap adjacent
With regard to the so called disc impedance Z2, the 30 the lower section of the outer conductor, which imped
ance form a part of the coaxial line together with
reactance component of this impedance should be zero
at the mean frequency and the disc line or section is
the low capacitive plates in the outer conductor which
preferably designed to provide this result.
will presently be mentioned. The combination of these
For this purpose the diameter of the plate sections is
impedances provides over the high frequency band of
35
chosen at approximately one-half wave length as cor
operation a very moderate low capacitance and a high
rected for the value of the dielectric serving as an insula
value of leakage index. At no frequency in the operat
ing range will the combined impedance be a hindrance
for.
I have found that the diameter should be approximately
to ef?cient transmission. The sleeve 3-2 within the sleeve
equal to
40 31 is provided with a shoulder 33' opposite the end of
the sleeve 31. .The shoulder 33- is the end of a coaxial
section 33' which is joined to the coaxial outer conductor
section 34 in the solid section 34'. The section 33', 34
and the cavity 511 form a high impedance which is sub
stantially symmetrically positioned with the high im
where K is the value of the dielectric constant. For 500
may
megacycles, for instance, L124”. 11/2). would be equal 45 pedance just mentioned.
The outwardly and smaller inwardly extending ?ange
to 12" and if some insulator is used which has a di
electric constant of 4, the diameter of the disc should
be in the neighborhood of 6''.
35 in the outer conductor forms part of the low frequency
capacitance element with its opopsing ?ange 36 connected
to the bottom section of the outer conductor 37, as seen
The effect on the propagation of waves through the
v
coaxial line depends upon the sum of the two impedances 50 in FIGURE 3.
The general construction of the elements follows along
Z1 and Z2. When Z1+Z2 is known, the standing wave
the same pattern as described in connection with FIG
ratio introduced by the coaxial choke coupler can be
URES t1 and 2, with the exception of the additional im
calculated. In the present invention the choke coupler
pedance section formed by the coaxial elements 32 and
has a high reactive impedance at low frequencies and a
low reactance at the frequency of the high frequency 55 31, 31 and 37, ‘and 33' and 34. The sections 34 and
37 together with the top section 38 as viewed in FIG
source. By low reactance is meant, low in comparison
URE 3, complete the outer conducting coaxial sleeve
with 50 ohms in the range from 100: megacycles to 5000,
element which is coaxial with the inner conductor 26 to
and by high impedance is meant an impedance of sub- >
complete the three stage choke coupler.
stantially 1000 ohms or more at the low frequency trans
mission. A low impedance for the high frequency will so, FIGURE 4 shows the application of the invention to
the installation of very high frequency antenna 39 on the
permit transmission at high frequencies without re?ec
top of a lower frequency radio tower 40. A coaxial
tion and the construction of the choke coupler in accord
cable 41 may carry transmitting current to the antenna
ance with the present invention will effect this transmis
39 and this may be supplied through a coaxial choke
sion through the choke coupler without radiation.
65
coupler 42, one end of which is at ground potential and
The low impedance at high frequencies is in the outer
connect to the input transmission line 43. In this case
'21s well as in the inner conductor with the structure as set
the tower is insulated from the ground by suitable in
- orth.
sulators 44, 44.
The arrangement described in FIGURES 1 and 2 is
FIGURE 5 shows the arrangement as applied to a very
known as a single stage coupler. In the sketch shown 70
high frequency antenna 45 mounted on the top of a sta
in FIGURE 3, a three stage coupler is shown. In this
bilizer 46 of a plane 47. The stabilizer 46 acts as a lower
structure the power radiated through the gap between
the plates 35 and 36 separated by the insulator must ?rst ' frequency radiator and the unit 45 has a very high fre
quency radiator. In this case the stabilizer 46 is insulated
pass through a low impedance line, then through a high
impedance line, and finally through another low imped 75 from the rest of the plane by an insulator 48 and current
3,089,105
5
is supplied to the very high frequency radiator 45 through
a transmission line 49 which has coaxial choke coupler
50 at the position of the insulator 48 so that the stabilizer
may be maintained above ground potential for its low
frequency transmission without interference.
6
Having now described my invention, I claim:
A coaxial choke coupler for transmitting high frequency
energy over a band in the range from 100 megacycles
to 5000 megacycles about a mean frequency, said coupler
comprising, coaxial inner and outer conductors, inner and
outer insulating sections in said inner and outer conduc
tors respectively, said sections dividing each conductor
in the arrangement of both the single stage and the three
into ?rst and second portions, said inner conductor in
stage coupler is very satisfactory and has been measured
sulating section being coextensive with the ?rst and second
above 30 db in the case of the single stage coupler and
10 portions of said inner conductor along the axis common
above 42 db in the three stage coupler.
As has been previously mentioned, the leakage ?gure
At low radio frequencies, such as in the normal radio
broadcast band and in the range generally called low
radio frequency as compared with the short wave bands,
the choke coupler presents an impedance of 1000‘ ohms
to said conductors for a distance substantially equal to
a quarter wavelength for energy in said center conductor
insulating section of said mean frequency, said outer con
ductor having a pair of opposed spaced ?anges at adja
or more, preferably 5000‘ ohms or more, while at the 15 cent ends of said ?rst and second portions thereof extend
ing radially outward from and orthogonal to said com
short wave band wherein the coupler is used to transmit
mon axis, said outer conductor insulating section being
power the impedance is low in comparison to 50 ohms.
a thin annular disk orthogonal to said common axis with
Consideration of the structure will show that ordinarily
opposite sides in contact with both opposed faces of said
within the operating band the reactance in the inner con
20 spaced ?anges for a radial distance substantially equal to
ductor of FIGURE 1, when it is approximately
)\
4
a quarter wavelength for energy in said outer conductor
insulating section at said mean frequency, wherein said
outer conductor first portion includes an inner annular
section coaxial about said common axis formed with a
will be practically zero and slightly inductive while the 25 sleeve end section extending radially inward from a shoul
reactance in the outer conductor will be low and slightly
der portion of said ?rst inner annular section, said outer
capacitive within the operating band.
What is meant by applicant’s previous reference to the
conductor second portion includes an inner annular sec
tion coaxial about said sleeve end section for nearly the
entire axial length of said sleeve end section, the end
diameter of the plate sections is that the common or
rather coextensive sections of the plate should be approxi 30 of said second portion inner annular section facing said
shoulder portion across a gap which is substantially bi
mately one-half wave length in diameter. Normally the
sected by the plane of said thin annular ‘disk, said outer
inner diameter of these plates is fairly small. This being
conductor ?rst and second portions also including an
the case the overall width of the plates, that is the outer
radius minus the inner radius, is substantially a quarter 35 outer annular section from which said ?anges extend, said
of a wave length in width. A quarter of a wave length
is desirable because such a width will present an extremely
low characteristic impedance at the inner edges of these
rings or plates. The speci?c explanation of this phe
nomena involved an elaborate explanation utilizing Bessel 40
functions. It may also be noted that as this is a coupling
device for transmission over a wide band, there is a fairly
large leeway in the selection of the speci?c size utilized.
This feature would explain the apparent divergence of the 45
drawings as shown in FIGURE 1 from this previously
made explanation.
?rst and second outer conductor portions being coaxial
about only one of said inner conductor portions.
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,401,344
2,451,876
2,465,922
Espley _______________ __. June 4, 1946
Salisbury ____________ __ Oct. 19, 1948
Peterson ____________ _._ Mar. 29, 1949
595,352
598,375
Great Britain _________ __ Dec. 3, 1947
Great Britain _________ __ Feb. 17, 1948
FOREIGN PATENTS
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