Патент USA US3068424код для вставки
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.