US2810886A

US2810886A - Duplexer

Info

Publication number: US2810886A
Application number: US393072A
Authority: US
Inventors: Garden Murray
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1953-10-23
Filing date: 1953-10-23
Publication date: 1957-10-22
Anticipated expiration: 1974-10-22

Description

M. GARDEN Oct. 22, 1957 DUPLEXER Filed Oct. 23. 1955 liu-- NNI. 4.

I NI/ E N TOR. Nur/*gy arderz.

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States DUPLEXER Murray Garden, Haddonfield, N. J., assigner to Radio Corporation of America, a corporation of Delaware The present invention is related to duplexers, and particularly to duplexers operative in the microwave frequency region.

Microwave dupiexers are well known. Their function may be described in connection with pulsed radar (radio echo detection and ranging) systems. In these systems, a microwave generator transmits pulses of radio frequency energy under control of a pulse modulator. The energy is applied to an antenna through a transmission line. At a branch point the transmission line leads to a receiver. The duplexer may include a TR (transmitreceive) and ATR (anti-transmit-receive) arrangement. These operate to connect the antenna to the generator under transmit conditions and disconnect the receiver. Under non-transmit conditions, the duplexer connects the antenna to the receiver and disconnects it from the transmitter. This function may be performed by a simple TR switch positioned at the proper distance from the branch point toward the receiver, and the branch point must be properly positioned. Additionally, an ATR (antitransmit-receive) switch may be inserted in the transmission line between the transmitter or microwave generator and the branch point. When an ATR switch is used, the branch point position in relation to the generator (excluding the ATR) is not so important. At high power levels, it is sometimes useful to use a pre-TR switch or tube which aids the TR switch in reiiecting energy which might otherwise pass to the receiver.

The various switches employed as TR, ATR, and pre- TR switches usually take the form of a resonant circuit coupled with a gas discharge tube. Sometimes, these components may be used interchangeably, that is, a component which in one case serves as a TR tube may in another case serve as a pre-TR tube. However, it is not convenient to employ TR switches which are designed for use with hollow pipe waveguide with coaxial line waveguide. On the other hand, it is sometimes inconvenient to use hollow pipe waveguide, because such waveguide is too bulky at the design frequency for the proposed use. Coaxial line is more compact, but does not have the power carrying capacity. However, if standard coaxial line waveguides are to be employed at microwave frequencies with TR components commercially available and of the type suited for hollow pipe waveguide, then a transition must be designed in order to enable the use of the standard component. Such transitions usually are space consuming. On the other hand, coaxial line pre-TR tubes are not available. Therefore, under certain design requirements, it becomes desirable to employ the hollow pipe waveguide pre-TR tube and other TR components with a coaxial line system.

it is an object of the present invention to provide a TR arrangement which is compact and uses standard hollow pipe waveguide components in conjunction with coaxialline waveguide.

Another object of the invention is to Vprovide a TR, pre-TR arrangement employing hollow pipe waveguide components but associated with coaxial line waveguide.

arent @i A further object of the invention is to employ hollow pipe waveguide TR components in conjunction with coaxial line waveguide with a saving of space and a compact arrangement.

In accordance with the invention, at the junction between the receiver transmission line and the coaxial transmission line from transmitter to antenna, a compact transition section from coaxial line to hollow pipe waveguide is inserted. At this junction point, a pre-TR switch is inserted. Notwithstanding that the compact pre-TR arrangement and its transition is mismatched at the high microwave frequency at which it is to operate, a TR cavity arrangement interposed close to the pre-TR switch in the line to the receiver is tuned in such a way that the entire circuit is resonant at the desired operating frequency, and the mismatch of the preTR switch is tuned out by the TR cavity tuning,

The foregoing and other objects, advantages and novel features of the invention will be more fully apparent from the following description when taken in connection with the accompanying drawing, in which like reference numerals refer to like similar parts, and in which The sole figure is a diagram, schematically portraying a radar system in which the invention may be embodied, and showing in cross-section the TR and pre-TR arrangement according to the invention.

Referring to the drawing, the transmitter mayinclude a magnetron transmitter 16 under control of a pulse modulator 12. The transmitter lil is connected to apply energy through an ATR switch le and a transmission line i6 to an antenna 13 which may have directional characteristics and be directed as desired. The transmission line 16 is a coaxial transmission line or coaxial waveguide. it must handle substantial amounts of power, but conservation of space is in this instance very important. The pre-TR, TR arrangement 20 includes a TR switch 22 and a pre-TR switch 24 coupledby a short section of rectangular hollow pipe waveguide 26. The junction A between the pre-TR, TR arrangement 2@ and the coaxial waveguide 16 is made by a transition 28 from coaxial line to hollow pipe waveguide. The hollow cavity resonator 30 of the TR switch 22 is coupled to the receiver 32 by a coupling loop 34 through a coaxial line.

The operation of the system as a whole may be understood from the foregoing. The general operation of such systems is well explained in Radar System Engineering edited by Ridenour, vol. 1 of theV Radiation Laboratory Series published by McGraw-Hill section 11.5, page 407. Reference may also be made to Microwave Receivers edited by Van Voorhis, vol. 23 of the Radiation Laboratory Series, chapter 2 beginning at page 7. When the magnetron il) transmits under control of the pulse modulator 12, the ATR, pre-TR, and TR switches are tired. The transmitter 10 is then connected to the antenna. The branch line to the receiver 32 is blocked because of the short circuit eifectively across this branch line because of the ring of the TR and pre- TR switches. The energy therefore passes to the antenna, and is prevented from passing to the receiver.

The ATR switch ie in this particular equipment is effectively in series with the coaxial waveguide 16, and is spaced effectively three quarters wavelength from the junction A. Therefore, when the magnetron or transmitter 10 is in the non-transmit condition under control of the pulse modulator 12, energy from the antenna 18 passing along the coaxial waveguide 16 is blocked at the junction A looking in the direction of the magnetron 10. In the direction of the receiver, however, neither the pre-TR switch 24 nor the TR switch 22 is tired, and energy passes to the receiver as though the coupling were direct, and the pre-TR and TR arrangement 2t) were not interposedr The function of the pre-TR switch 24 is readily .explained in thatwhen there. shigh Vpowered transmission the TR switch alone and by itself is insufficient to prevent damage to the receiver. Accordingly,

it i'soften desirable lto inserta pre-TRswitch';V VThis pre-V half portion on; one side of a radial planethrough the axi'sofithe' coaxial line;A Thus,V as viewedl in the figure, the enlargement .is made. .in the upper portion of the outerxlconductoraof .the coaxial line 16. The enlarged portionthus has side walls. 36 and continuity with the remaind'erof the outery conductor ismaintained byY including-partial .bottomfwalls 3S to completethe section 26 of rectangular hollow pipeV waveguide, the longitudinal axismof. which is.Y at right angles Vto the longitudinal axis othecoaxial waveguide 16, and having an end opening .contiguous withhalf. of'a cylinder formed by the outer conductor. .of line 16.V The -inner conductor 40 of the coaxialiwvaveguide 16 may alsosbe enlarged at the point Where .the `outerlconductor is enlarged to improve the shofwnlto holdftheportion 54 in place. A pair of metal gaskets 46, and 48 are provided which grasp between them :the metal .platee' of the pre-TR switch 24. A pre-TR ltube 52 is mounted in a resonant aperture in the plate S0. -The 'hollow pipe waveguide section 26Y formed by the .rectangular sidewalls S6-is continued by the gaskets 46 vand48 and by wthefurther portion-54 until it merges into acavity resonator V56. The cavity resonator 56 is part of `the TR switch22which includes the TR tube 58. The TR ytube' -ism'ountedinia standard fashionand `has a tuning .mechanism actuated by rotation of a shaft` 60. It is .contemplated that 4thershaft 60 may be remotely adjusted sbygmeaus ofa llexible rotatable shaft. As understood `in fthe art, 'tlie.shaft `60controlsthe spacing of-a pair fof keepaliye-.electrodes within the tube which in turn vary thetiresonant frequency .of the cavity resonator 56. The` TR- tubef is a standardl type modified by removing its tuning knob and mechanically coupling the rotatable shaftltortheiknob shaft. The-couplingloopi is lo- ;catedi-on theside of the cavity resonator 56 remote from vthe side into .which thewaveguide section 54 leads.

The coupling loop '34 leads toa coaxial transmission line 62 .'which'make'siaright. angle Yturn at Y64 and leadsrto Ya crystal inserted in the transmission line at 66. Only the crystallcartridge 68 is shown, thecrystal and its contact .-Within the holder V(not shown) being Vwell. known in the The coaxialtransmission line 62 has an inner conductor 80.- The inner conductor 84 of a section of coaxial transcoupling VVdisc of 'couplingSZ in relationtoJthe inner conductor S0 may be varied by a nut V88 and locked in place by a c ooperating lock nut 90. .The coaxialltransymission line 86 leads/to an ordinary type caf-coaxialV line jconnector 92 for ready connection to a local oscillator (not shown). Y

In operation, itis well to bear in mindthat the oper- Vating frequency may be 1300 mc. (megacycles per second) 'Becauseof the high transmittedV power in this system, it is Yessential that a pre-TR switch beiemployed. Such a great amount of energy is'fed through to the receiver during transmit periods, if only a TR switch is employed,

zandwith the plate 50provides a substantiallycontinuou's Y -aperturein which is located a low'pressure gasftube,

5. that damage to the receiver, e. g., crystal 'burnout,` results. At the f requency of operation, however, a pre-,TR tube or pre-TR switch is available as a standard component only for hollow pipe waveguide. Moreover, to design a pre-TR tube for coaxial waveguide would require not only considerable engineering skill but would be very'ditficult. However, using the transition section made byenlarging theout'er. conductor of the coaxial line 16 into a rectangular hollowtpipe waveguide section with sidewalls 36, the standard hollow pipe waveguide 1 pre-TR tube 52and1thestandard switch 24 may be insertedV into this section of rectangular hollow pipe vwaveguide, which is then continuedY into the waveguide section 26. Y Unfortunately, this coupling or transition Section 28 does not provide ajgood, match at the operating frequency, during reception, Notwithstanding, a match at the operating frequency during reception may be secured by suitably tuning the tube 58. In transmission, a good receiver protection is. secured by spacing the pre-TR and TR tube theoretically a quarter-wavelength. ln practice, Y

the spacing is made slightly different, in. this case less than a quarter wavelength, in order to secure good results `with .a .matcheducondition during reception. This departure from aquarter wavelength did Vnot causerexcessive leakage to the receiver during transmission. Although the transition 28 into the rectangular waveguide provides Aonly. a poormatch Ato the receiver through the pre-TR resonant.aperture, the tuning of the TR cavity andthe proper spacing'comp'en'sate for the transition Ymis-match, and the unit as a whole give proper and highly desirable operation. The unit 2 0is, in fact, much morek compact .than many. other'. systems which are provided with Va proper .matching section for the'transition selected from .amongthosewhichg are known.

During ,transmit .conditions the pre-TRtube 52 is tired end wall tojthe .enlarged rectangular cavity transition 28.

-Feed throughto, the crystalis further prevented by theV tiring ofithecavity'resonator tube V58 inthe cavity resona- -tor 56.

` The following y tube VVtypes may be employed: For the pre- TRgtube 52,Vv a type WL6260; for the TR tube 58, altype BL25.'v Although the ATR tube is not. shown in (detail it may be anarrangement similar to that illustrated in Fig. 2.5 0a of section 2.10 of chaper 2 of Microwave Duplexers. .edited jby. Smullingand Montgomery, vol. 14 VoftheRadiation Laboratory Series, and also employing a type .BL25 TR tube.

In view of the foregoing, it'will bev apparent that'the `invention `provides .an especially compact pre-TR and TR Varrangement fof microwave frequencies for high power transmission. .outer Yconductrftransition section of coaxial line leading into ashort section of -hollowpipe waveguide in which is inserted a preTR;t`ube in the form of a plate obstructing thewaveguidetransit'ion. section `but having a resonant Y outer conductor havinga portion thereof expanded and j enlarged intotka rectangular hollow pipe waveguide section, and a'transit-r'eceive switchv at the termination of A lsaid hollowpipe Vwaveguide section remote fromsaid outer yconductor and coupled thereto, f a YAY.pre-'transmit-receive `switchin'said'hollowpiper'waveguide section spaced an Y odd multiple, including unity,'"of quarter "wavelengths The Varrangement includes. an enlargedV from said transmit-receive switch, said hollow pipe waveguide section and pre-transmit-receive switch being mismatched to said coaxial line section at the operating frequency, said transmit-receive switch being tuned to compensate for said mismatch.

2. A transmitreceive arrangement comprising a coaxial line waveguide section having an inner conductor and an outer conductor, a section of hollow pipe waveguide, and a cavity resonator, said hollow pipe waveguide section having one end coupied to said coaxial line waveguide through an enlarged outer conductor portion thereof, and the other end coupled to said cavity resonator, said hollow pipe waveguide having at said one end a pre-trausmit-receive switch spaced an odd multiple, including unity, of quarter wavelengths from said cavity resonator, said transition and said pre-transmit-receive being mismatched at the operating frequency, said cavity resonator being tuned to compensate for said mismatch and to match said transition section and said pre-transmit-receive together with said resonator at said operating frequency.

3. The transmit-receive arrangement claimed in claim 2, said pre-transmit-receive switch comprising a metallic plate obstructing said hollow pipe waveguide, and having a resonant aperture with a low pressure gas tube mounted in said aperture.

4. The transmit-receive arrangement claimed in claim 2, said inner conductor having a portion of radius enlarged over the radius of adjacent portions thereof, said enlarged radius portion being substantially coextensive along the length of the line with said enlarged outer conductor portion.

5. The transmit-receive arrangement claimed in claim 2, the coupling of said hollow pipe waveguide section to said cavity resonator comprising the termination of said section in an opening communicating directly with the resonant cavity of said resonator.

6. The transmit-receive arrangement claimed in claim 5, said inner conductor having a portion of radius enlarged over the radius of adjacent portions thereof, said enlarged portion being substantially coextensive along the length of said coaxial waveguide with said enlarged outer conductor portion.

7. A transmit-receive arrangement comprising a coaxial line waveguide for connecting a transmitter and an antenna and having an inner conductor and an outer conductor, a hollow pipe waveguide branching from said coaxial line waveguide outer conductor at a junction, a pre-transmitrece1ve switch in said hollow pipe waveguide at said junction, a transmit-receive switch in said hollow pipe waveguide remote from said junction, said pre-transmit-receive switch alone being mismatched at the operating frequency, said transmit-receive switch being tuned to compensate for said mismatch, a further waveguide for connection to a receiver, said further waveguide by the tuning being coupled with a matched coupling at the operating frequency to said coaxial line waveguide by said hollow pipe waveguide during non-transmit periods of the transmitter.

8. The transmit-receive arrangement claimed in claim 7, said transmit-receive and said pre-transmit-receive switches being spaced apart slightly less than one quarter wavelength measured at said operating frequency.

References Cited in the le of this patent UNITED STATES PATENTS