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Dec. 11, i962
R. w. PETER
RADAR WITH TRAVELINGMAVE TUBE DUPLEXER
Filed June 12, 1958
2 Sheets-Sheet 1
Dec. l1, 1962
3,068,4M
R. w. PETER
RADAR WITH TRAvELING-wAvE TUBE DUPLEXER
Filed June 12. 1958
2 Sheets-Sheet 2
ä
è
rNVENToR.
HULP W. PETER
BY
ßf
United States
3,068,414
CCL
-Patented Dec. 11, 1962
-2
1
`
3,068,414
v
to the radar receiver. A separate TR tube is not needed.
The invention will be described in greater detail by
'
RADAR WITH TRAVELING-WAVE TUBE
"
‘
`
‘
Y
DUPLEXER
reference to the following description taken in connection
with the accompanying drawing in which:
-
Rolf W. Peter, Princeton Junction, NJ., assignor to Radio
Corporation of America, a corporation of Delaware
Filed June 12, 1958, Ser. No. 741,484
FIG. 1 is a block circuit diagram of an embodiment of
a radar system according to the present invention;
, ,
,. FIG. 2 is a section through one form of a traveling,
6 Claims. (Cl. S25-_23)
wave` tube which may be used in the circuit of FIG. vl;
FIG. 3 is a section through another type of traveling
The present invention relates, in general, to radar and,
more> particularly, to improved duplexing circuits for 10 wave _tube which may be used in the circuit of P_IG. l;
radar-»systems
‘
„
'
‘
and
'
`
`
-
,
.
FIGS. 4 and 5 are block circuit diagrams of systems ac
y Conventional pulsed radar systemshemployïa single
antenna both for reception and transmission. The con
cording tothe invention showing the admittances at dif
nection between the antenna, transmitter, and receiver
ferent branches of the circuit.
normally includes a gas-ñlled tube known as a TR (trans 15
mit-receive) tube or switch. »During transmission, the tube
fires (conducts) -and the transmitter energy is prevented,
or `substantially prevented, from reaching the receiver.
.
`
_
l
Throughout the ñgures similar yreference numerals are
_ „ applied. to similar elements.
The timing circuits 10 shown in FIG. 1 produce'syn;
chronizing pulses at leads 12> and 14. ’Transmitter `16 is
conventional and may include a high power modulator
Duringv reception, the-.gas in the tubedeionizes andthe
received echoes passto the receiver.> Transmission line 20 triggered by the pulses at lead 12 and a magnetron, klys
_lengths are such _that littlefpower passes to the transmitter „___ tron, traveling-wave tube or the like driven by the modula
tor._ The pulse-modulated radio-frequency signal output
_of transmitter 16 is applied via lead `18 to the rotatable
»_ Unfortunately,.'TR tubes are not perfect switches. Dur
antenna 20. . Lead 18 is a schematic representation for Aa
ing -transmission, a portion'of the transmitted power,
waveguide, coaxial line or the‘like. __A portion of the
known as leakage power, passes through the TR `tube to
during reception._
_,
»
__
_
._
_
._
y
~
_
Íthereceiver and. may damage the latter’s delicate input .... energy on line 18 attempts to travel down lead_22 and into
the input section 24 of traveling-wave tube 26. However,
stage (usually a crystal). l'The arc formed when the TR
for reasons which willbe explained _in greater» detaillater,
_tube Íìresdeteriorates .the TR -tube and causes the tube
_eventually to fail. Finally, the TR1tube suffers rfrom
slow- deionization and this prevents thede'tection of echoes
fat shortranges. „ -„
"
‘
'
'
`
‘
this is prevented since- looking -from junction 28ytoward
30 the traveling-wave tube, the latter appears to a high
'
_
power'signal like an open circuit. _ '
'
object ofthe presentrinvention is to provide anirn'- 1”.' `Echoes received by ¿antenna 20 pass down transmis'
~sion line 18 ~to junction 28».4 _ The line length betweenjunc
proved'form' of duplexer which has none of the disadvan
_tion 28- and transmitter A16 is _such that the transmitter
tages outlined above. "
f `
..
. - Ä
.
Another object of"_the'invent_ion is to provide a simpli 35 looksto the echoes like an open circuit and no,- or sub
stantially no, received power is lost. However, .a low
power» signal looking from junction 28 toward the travel
_fied radar system -which’ doesV not require a conventional _
ing-wave tube 26 'sees a matched load and the signal is
` 'Yetsanother object of the invention is to provide an im
«therefore substantially completely passed to the traveling
proved'radar system which is useful at short ranges and
which can employ short pulses.
‘ ' '
40
'
useful for duplexing functions.
'
wave
tube.
_
'
_
'
_
‘ The traveling-wave tube ampliñes the received echo and
Still another object of the invention'is to provide-an im
proved type of Ytraveling-wave tube which _is especially
applies it to receiver 30. The receiver further amplifies
the signal, detects the video components thereof, andA ap
ï
plies the latter to display 32. ` The display> may comprise a
` According to? the present invention, a traveling-wave
4tube acts as the duplexer'for a radar system. The_travel 45 PPI indicator, in which case the video‘ pulses areapplied
to intensity modulate the electron beam thereof.
ing-wave tube, which is- itself new, includes an input sec
»tion which looks -to a low power signal like a matched f '.
termination and tov a high power signal likel a-reactive
load-upreferably an open circuit. The input section in'
`
The sweep voltage is generated in stage 34 and applied
to the deflection means of the indicator. The deflection
means may include a rotatable deflection coil which is
Ycludes a slow-wave structure, which is mis-matched 'at 50 driven synchronously with-the lrotation of antenna 20.
The means for doing this is indicated schematically as
tube parameters including the interaction factor, the beam .3 -including'the antennadrive .motor 36 .and servo link 38
between the drive 'motor or antenna and the deñection
current, the slow-wavev structure length, and the like are
sochosen that a low-power input-signal at the radio-fre
The operation of the circuit of FIG. l may be vbetter
quency is matched to the electron beam over a reasonably 55
understood by referring 'to FIG. 2 which illustrates one
large frequency band. However, when the input signal is
form of traveling-wave tube which may be used` in the
ata high level, such as the case when a transmitted pulse
its far end, through which the electron beam passes. _The
coil.
is _applied to the input section, the slow-wave structure
looks to the input signal like a reactive load and substan
tially no transmitter power is lost to the tube.
t
' v
_- , `In a preferred form of the invention, a second reactance
is placed in circuit with 'the line leading to the input sec
tion of the traveling-wave tube and a portion of the
,
.
.
‘
.
Y
v
'
«
.
circuit.v This traveling-wave tube includes a low-noise
gun shown schematically at 40, an input waveguide 42
60 leading to the antenna and transmitter, and an input vslow
wave structure shown in the drawing as a helix 44.l The
helix is terminated at its input endv in a metallic cylinder
46 through which the electron beam 48 passes and at it's
output end in'a metallic shield 50. The shield is folded
'transmitted power is reñected by it. Thus, the full amount
of transmitted power need not be reilected by the input 65 back over the helix and effectively Áserves as the outer
>section of the traveling-.wave tube and it can be of lower
conductor of a coaxial' transmission line, the inner con
power handling capability than would `otherwise be nec- 1 ' ductor of which `is the helix. Since one end'of the helix
essary.
is connected directly to the shield, the coaxial line -is
,The traveling-wave tube also includes a second slow
effectively short-circuíted at this end. Beyond the shield
wave structure coupled by the electron beam to the first 70 50 and spaced therefrom is a second helix 52. _ Thishelix
slow-wave structure for amplifying a received signal. The
is terminated _at itsinput end in a matched termination
'output of the traveling-wáve'tubefmay be applied directly
54 and at itsout-put end in a metallic cyliii'der 56. Iso
3,068,414
_
_
3
~
e
4
lation between the two helices is provided by the shield
57 (effectively a waveguide dimensioned to be below cut
off at the input radio-frequency). . The output waveguide
structure is shown at S8 and the collector is shown as
slow-wave structure is short-circuited. However, the in
vention is not limited to this specific structure. All that
is necessary is that the end of the slow-wave structure
be terminated in an impedance which is widely different
60. The 'beam-focusing means is> ex'empliñed by a mag
net coil 62. ’ yOther rmeans of -beam-focusing maybe used,
put slow-wave structure maybe open circuited provided
like periodic'magnetic'or electrostatic focusing.
from its characteristic impedance. For example, the in
-
that the distance from the T vjunction (FIG. l) to the
_ The tubeparameters are'such thatv an input signal of
en__d of the slow-wavestructure is equal. _t_o_~„-. -_: _. -
low amplitude is matched to the electron beam; `In this
specific form of tube the maximum arnount‘ofj-_povver -10
which can` «be transferred by the beam maybe ‘on the
'
'
`
y
n)
-
'
-
‘
'
where n is an integer.
order of 0.1 watt. Accordingly, an input“_signal of> low
amplitude isi ain-pliñcd. by the first and. second slow-wave
In the Aforms of»v thefinvention describedabove,v during
structures 44 and 52 .and is applied via output waveguide
transmission the- full amount of .transmitted powerl fis
15 reflected from the input section of the traveling-.wave
58. ,to the receiver.
.
. _
o
tube. Since .the peak transmitted power maybe high
-` In the- case of an input signal'of large amplitude (which
the input section ofv the traveling~wave tube should pref».
may be on the order of tensor hundreds of kilowatts
era-bly be of lhigh-po\'ver'- handling capability. However,
in. 'the >case of a radar signal). the, input section >of the.
traveling-wave tube looks like a highk impedance. The
with slight circuit modiñcation, the fulla‘mo'unt ofïtrans
input. section. is a transmission line which is. lshort circuitcd 20 mitted power need not Ibe retle'cted‘from the slowwave
structure itself. A portion of the power can he reßected
at-'its far end. »Its length plus. »that of the transmission
from a »reactance 80 which may- be placed, for example,
liuc 22 (HG1 l) ÍS
_
I
~
in shunt with the» receiving arm. An` arr-angementfof this
Y' "
nit
k
type is illustrated schematically in FIG. 4_. ' Instead of a
_
“isi-Ã
.
25 single reactanee $0, two or more reactances may be placed
where n. is an integer.. so, that looking from. :function 2,8
between the. T junction and the traveling-wave tube.. 1 .Ai
(FIG. l) toward the traveling-wave tube. a- high~power
ternately, one (or several) pieces of line of different line
impedance. and'appropriate length may ¿bc substituted and
vseries connected into the traveling~wave tube input line.
signal sees an open circuit. Since there is verylittle
transmitted power lost tothe traveling-wave tube and
furthermore, since the travelingfwave tube. itself does not 30 These modifications are discussed; info general. Way later
'produce at its saturation level> au. output signal havinglari
.in Cßnuectî‘ollwìêh FIG- .5»
’
. - j
f "
' Íï
amplitude sufñciently large to f_lturxagcv the delicate. input
The basic properties ot thc prcscnt'iuvcntiou ‘are satis'
_stage to the receiver,4 the TR tube may be completely
eliminated. Instead,V the output. waveguide 5.8 may bc '
fied, if the antenna is matched. to the rccciviuglarfu (trav -
connected.. directly to the receiver.v
.
3.5
' While the. arrangement shown in PIG.. 2 lis suitable'for
use. with radar transmitters of lowv to moderate amounts
eipower. itis desirable, in the case ofv higher amcuntsof:
.input power to employl an input. section to the, traveling
wave tube having higher power handling ability. One
of. a'iarge number of. Suitable tube structures is shown
in FIG.. 3. Here,l the input section. to the travelingfwave
ing-wave tube ïplus receiver) during' reception (low put
signal-power level.)- aoti. the transmitter .is matched. tothe.
antenna- ciuriris transmission. (irish ihput; sîsoairower
level). F1""he above'conditions may AÍntost., easily beje'x
pressed. terms of admittances. Dorine receptionthe
admittance Ya .Sleen by the. antenna must @tuttiv the admit.’l
-40
tance Y1 of the receiving arm. During transmission,Y the
admittance Yfmseeu by the. transmitter .must equaithe
admittance Yr ofthe antenna. which, .in turn. should be a
tube comprises a folded waveguide rather than a helix.
conductance G4.
f
~
_
._ -_
The folded. waveguide. essentially consists 0f interleaving,
In thel embodiment of theÍ invention shown in FIG., 4,
metallic plates 64, each formed with an aperture through 45 a reactance 80 is placed at or close to the T junction
which the electron 'beam -66 passes. The waveguide is
effectively in parallel with the receiver arm. The react
short-circuited at its far end by plate 70. The path fol
lowed by the slow-wave is indicated by arrow VV68. As
ance may be a lumped reactance such as a capacitance
or a distributed reactancc. `such as. a piece of transmission
in the embodiment of FIG. 2, the path length along arrow
line with movable plunger or snorting bar- .Looking from
68 plus the length of transmission line 22 (see FIG. l) 50 the T iurictiou toward the. receiving arm. one secsy tbc
areequalto>
"
c
admit-tance Y2=Yr+¥a where Ysrèißz. and .Y1 equals s
'
'
nk
h
îlot
where n. is an integer, and t is the wavelength ofthe radar 55
pure. conductance .G1 during . reception (thc sisnsl is
matched tothe beam),y and a pure susceptance- jB1v during
transmission (the high-'power signal sees a reactive termi~
nation).
signal. Accordingly, a high-.power signal at junction 28
looking toward the input section to the traveling-wave
The remainder of the traveling~wave turbe is similar
are applied to similar parts. The focusing magnet is not
shown. The helix is shown supported by' ceramic rods
`69 and the latter in turn are supported by ceramic disks
71. The output means is a coaxial line 72 to which the
-end of the second helix is capacítively connected. Other 65
output means are possible.
`
'
`In the embodiments of the invention illustrated', the
Second slow-wave structure, in iboth cases, is shown as
a forward-wave amplifier. It is to be understood that in
each case it can be va backwardfwaver~ amplifier instead. 70
The choice will depend upon whether. the ‘broad-band
characteristics of the forward-wave amplifier or the volt
age tunable characteristics of the backward-wave amplifier
are
desired.
-
«
,
.
'
.I_n the traveling-wave tubes illustrated sabQvc, the input 75
^
-
_
YR; Yz-iîYa
Substituting Y1+jB2 for Y2 gives I
tube sees an open circuit.
to the one shown in `FIG. 2 and similar reference numerals 60
'
f
'
`
From FIG. 4 the Áfollowing can be seen: ’
_
` (i)
YR=ÍB2+YL+Y3
(2.)
However, at I_ow signal levels Y1=.=G1
Therefore,
_
f `
`
'
Yn=ÍB2+Gi+Ys
(3)
l
`
(4.)
At Ilow signal levels the admittance YR seen by the antenna
must equal G1.. .Substituting this in the equationÁ above
ajos/¿414
5
input scction'of the'travelinglwave; the'lower'` therefore,
Therefore,
YTR=ÍB1+ÍB2+G4
the open end voltage (in the case of an open-circuited
traveling-wave tube input section) or the short-circuited
Vcurrent (in the case of aV'short-circuited traveling-wave
(8)
During transmission, the kadmittance YTR seen by the
transmitter should equal aconductance and this conduct
ance should. `be equal..to ._the. antenna conductance G4.
tube input section) at this point.
A' '
-
l.A more »general aspect'of the -invention is'shown in
Substituting G4 for YTR in Equation 8 ,gives
FIG. >5. Here the circuit which reñects a portion of the
transmitted power is illustrated as a block 90. This block
‘represents one or more reactive elements which may be
in'series, in parallel, or in series and parallel with the
arm leading' to ‘the- `traveling-wave tube. fit may repre
sent lumped or series elements, or both, or there lmay >be
In the -forms of the invention discussed previously there
one> or several such elements. The reactance 90 may be
was no reactance placed in parallel across the receiving
inductive or capacitive or may include inductive. and
arm.k Accordingly, this may -be treated as the special case 15 capacitive components. The only conditions which must
in which
be satisfied in all of these cases are:
Ysäißz=0
(11)
(a) During reception;
In this special case, the admittance Y2 is 0 during trans
mission under the following conditions:
YRÉ Ya’i“ Ya
(1)
(a) The input section-'T10 the traveling-wave tube is 20 where Y2=1`BR-|-GR (12)- ~*(-for low signal level)
short-circuited and the electrical length -from the T junc
GR being the conductance of the matched input to the
tion to the end of the input section is
traveling-wave tube at low signal levels, and jBR being
the susceptance contributed by the reactance of block
25
(b) The input section to the traveling-wave tube is open
circuited and the electrical length from the T junction to
the end of the section is
i):
90, and Y3=--iBR
,
so> that
e
YR=GR
30
2
(c) The input sectionl of the traveling-wave tube` is
reactively terminated and its length is intermediate a and
(b) During transmission:
( 14)
_
YTR: Yri" Y2
(6)
where Y4=G4 (given)
Y2=jBR---jBTR (15 ) (for high signal level)
b above and is such that the input signal sees an open 35 jBTR being the susceptance contributed by the traveling
wave tube at high signal levels
circuit looking from the junction toward the traveling
wa-ve tube.
and
In the more general case, the reactance iB, is iinite,
say capacitive (positive susceptance) , and relatively small.
In this case, we see from' Equation l0
40
whereby
‘
J'BR=J`BTR
( 16)
Y2=0
( 17)
S0 that YTR: G4.
What is claimed is:
l. In combination, a transmission line structure having
that since jB2 is positive, the line »between the junction
and the transmitter must have a length such that it is
slightly inductive (Y3 is negative); the same holds for the 45 three branches leading from a common junction; a signal
receiving channel connected to the first of said branches
line between the junction` and the end of the input section
which is matched to said iirst branch at a relatively low
to the traveling-wave tube (1'B1 is negative when jBz is
positive). If jB2 is positive (capacitive), and the input
input signal level and mis-matched thereto at a relatively
high input signal level, whereby looking from said junc
section to the traveling-wave tube is:
(a) Short-circuited at its end, then the line between 50 tion toward said signal receiving channel one sees a con
ductance G1 at low signal level and a susceptance iB1 at
the junction and the end of the input section of the travel
high signal level; a reactance connected in shunt >with
ing-wave tube is slightly less than
said ñrst branch and having an admittance 1‘B2 looking
11X
from the junction into said reactance; antenna means
55 connected to the second of said branches; and transmitter
means connected to the third of said branches and having
(b) Open-circuited at its end, then the line between the
an admittance Y3 looking from said junction toward said
junction and the end of the input section to the traveling
transmitter means, where Y3=iB1=--}'B2.
Y
wave tube is somewhat longer than
2. In combination, a transmission line structure hav
60 ing three branches leading from a common junction; a
mt
traveling-wave tube having an input slow-wave structure
y
2
connected to the first of said branches which is matched
The susceptance 1‘B2 may be inductive (negative) rather
to said first branch at a >relatively low input signal level
than capacitive. In thisrcase, the line lengths under a and
and mis-matched thereto at a relatively high signal level,
a+?
b above are slightly more than
j
Ä nÃ
a+?
(capacitive)`and slightly less than
65
whereby looking from said junction toward said traveling
wave tube one sees a conductance G1 at low signal level
and a susceptance ÍB1 at high signal level; a reactance
connected in shunt with said first branch which, looking
from the junction into said reactance, has an admittance
70 J'B2; antenna means connected to the second of said
nk
branches which, looking from said junction toward y."said
2
antenna means, has an admittance G4; and transmitter
(capacitive), respectively. The larger jB2, whether posi
ing from said junction toward said transmitter, has an
means connected to the third of said branches which, look
tive or negative, the .less power «will be retiected kfrom the 75 admittance Y3, where Y3=jB1= -jB2.
:www
_ 3,-. In -the QQmbination as Set forth in claim '2,A said act
8
References Cited in ihe ñle of this patent j
mittançe i132- being equal. to 0-
UNITED STATES’PATENTS
, 4. In t’hecomhingtionäas set forth in claim 2, said re
actance being- one of the type which, looking from the
2,361,295l
junction into said reactance, appears inductive.
2,603,743
Lawson _____________ _- July4 15., 195,2
...2,753,481
Ettenberg- _,__,__,..-..__,___.. July 3„> 195.6
5.. In the. combination asl set; forth in claim 2, 'said re- `
ac_tance being' one Qffthe _type which," looking frQm the
_ìiinct‘g-ion- i?l‘toÍ saidV regci'ance, appears capacitive..
.pill 'slpwëwàvgstr-ucìúiëe being terminate@ ät ‘ifs far €1.41@
@1.1. impedancéiwhim differs widely .from its @masten
-Lieweuyn _K_____' _____ __, Jan. 16, 1945
'
OTHER REFÈRÈNC'E'S " Y
Y
y `- Microwave Theory and Techniques by Reich et al., Van
_10 Nostrand Co. Inc., 1953, pp. 834-8w3éfrêliec1gm.l
v.RÁCA Magnetrons and Traveling Wave Tubes, RCA
Tube Div., copyright 4'195 6, pp. 25, 26 relied on.
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