US2699548A

US2699548A - Wave guide structure for microwave radio systems

Info

Publication number: US2699548A
Application number: US136219A
Authority: US
Inventors: Dyke Edwin
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1949-12-31
Filing date: 1949-12-31
Publication date: 1955-01-11
Anticipated expiration: 1972-01-11

Description

E. DYKE Jan. 11, 1955 WAVE GUIDE STRUCTURE FOR MICROWAVE RADIO SYSTEMS Filed D80. 31, 1949 2 Sheets-Sheet 1 INVENTOR. 122w? ,Dyke BY Jan. 11, 1955 WAVE GUIDE STRUCTURE FOR MICROWAVE RADIO SYSTEMS Filed Dec. 51, 1949 E. DYKE 2 Sheets-Sheet 2 Jar. J

Zazzzziz INVENTOR.

United States Patent '0 WAVE GUIDE STRUCTURE FOR MICROWAVE RADIO SYSTEMS Edwin Dyke, Brookfield, Ill., assignor to Motorola, Inc., Chicago, Ill., a corporation of Illinois Application December 31, 1949, Serial No. 136,219

IZ'CIaims. (Cl. 343-180) This invention relates generally to radio communication systems and more particularly to a system for providing simultaneous transmission :and reception at microwave frequencies from a single antenna.

Radio communication systems for providing dependable .communication over long distances have been developed which operate at microwave frequencies. These systems, in most cases, operate on the relay principle with a-plurality of intermediate stations being positioned between the terminal stations and with the signals being relayed from one station to another. Although these systems have the advantage that they are less expensive than wire lines which provide :the same service, it is desired to further simplify and reduce the cost of such equipment while maintaining the dependability thereof. Since radio signals in the microwave range are highly directional, it is necessary that the antennas be carefully located so that they will properly direct andintercept the microwave beam. In many systems it is desired to provide continuous communication in both directions with a transmitter at a first station radiating a signal picked up at a second station, and a transmitter at the second station radiatinga signal to be picked up by a receiver at the first station. It is therefore obviously desirable to use a single antenna ateach station for transmission and reception as this eliminates the cost of one antenna at each terminal station and two .antennas at each relay station, together with the need for carefully orienting the same and for thereafter maintaining the antennas. The antennas at the two stations, which are (properly oriented for providing communication in one direction therebetween, are, at .the same time, inherently oriented to provide communication in the opposite direction therebetween. However, many difficulties are encountered in using a single antenna forboth transmission and reception and a single .antennacan be used only in the event that the strong signal transmitted at each station is prevented from reaching the receiver at that station, and the received signal is not attenuated .by the transmitter so that reception thereof is interfered with. This difficulty is increased .by the fact that available oscillator tubes have construction tolerances which cause substantial variations in their operating characteristics.

It is therefore an object of the present invention to provide .a simple system wherein simultaneous transmission and reception can becarried on with a single antenna.

Another object is to provide a wave guide structure for use with an antenna for separating waves of different frequencies which are handled by the antenna.

A further object of .this invention is to provide wave guide conducting means .including adjustable phase shifting means of simple construction.

A feature of this invention is the provision of a radio communication system includin a plurality of translating devices operating at different frequencies and means coupling the translating devices to a single antenna so that each device reflects waves of the frequency on which the other device operates.

A further feature of this invention is the provision of a microwave communication system including an antenna fed by a waveguide and .a transmitter and a receiver coupledto the antenna by branch wave guides, with the wave guide branch connected to the transmitter including adjustable phase shifting means and. the wave guide branch connected .to the receiver including a spacer for adjusting-thelength thereof so thatreach branch we ice sents a high impedance to the frequency being transmitted through the other branch.

A still further feature of this invention is the provision of a wave guide connected to translating means and forming therewith a reflecting stub, in which the wave guide includes adjustable phase shifting means for compensating for variations in the characteristics of the translating means.

Further objects and features will be apparent from a consideration of the following description when taken in connection with the accompanying drawings in which:

Fig. 1 illustrates the communication system in accordance with the invention;

Fig. 2 is a sectional view through a wave guide illustrating the adjustable phase shifting means;

Fig. 3 is a side view of the structure of Fig. 2;

Fig. 4 illustrates the structure of the cavities formed in a wave guide; and

Fig. 5 illustrates means for adjusting the length of the wave guide.

In practicing the invention there is provided a microwave communicationsystem including an antenna having a horn connected to a wave guide, and a parabolic reflector for directing the waves emanating from the horn. A flat reflector may be .used for changing the direction of the beam. A transmitter and .a receiver are coupled to the wave guide connected to the antenna by branch wave guides through a Y junction. The transmitter and receiver operate at different frequencies and the branch wave guides connecting them are of such construction that the transmitting frequency ,is reflected by the receiver branch and the receiving frequency is reflected by the transmitter branch. To provide reflection at the proper frequency, .a spacer is provided in the branch connected to the receiver which may be changed to provide reflection at the desired frequency. In the transmitter branch an insulating member is adjustably mounted to shift the phase of the wave passing .therethrough with the amount of shift depending upon the position of the insulator. The phase shifter is adjustable .to compensate for the use of transmitting units having different constructions, providing different reflection characteristics for controlling the overall characteristics of the transmitting unit and the wave guide branch connected thereto. The phase shifter is Constructed so that the characteristic impedance of the wave guide with respect to the transmitter output is substantially constant for all adjustments of the phase shifter. I

Referring now to the drawings, in Fig. 1 there is illustrated a communication system including a transmitter and receiver unit 10 contained ina housing .11. The housing 11 is of such size to receive two transmitter-receiver units so that a standby or spare .unit can be housed therein. Connected to the transmitter-receiver unit 10 .by wave guide 12 is an antenna assembly including a horn 13, a parabolic reflector 14 and a flat reflector 15. Suitable connecting means 8 may be provided for alternatively connecting the wave guide 9 to the antenna forconnecting the standby unit thereto. The particular construction of the antenna is not essential to the present: inventionand any satisfactory construction may be used. Connected to' the wave guide 12 is a Y junction including a wave guide portion 16 connected to the wave guide 12 and

branch wave guides

17 and 18 connected to the receiver 19 and the transmitter 20 respectively. The wave guide 17 is connected to the receiver 19 through a spacer 21 which may be changed as will be described more in detail.

The receiver 19 includes a triple cavity composed of

sections

22, 23 and 24 at the input portions thereof. As shown more in detail in Fig. 4, adjusting screws 25 are provided for adjusting the volume of the sections of the cavity so that the frequency response thereof can be controlled. This cavity has a relatively high Q so that the frequency to be received is passed thereby but other frequencies outside the band to be received are very sharply attenuated. A Q of the order of 350 per section has been found highly satisfactory for such a triple cavity filter. The waves which pass through the filter continue to'the mixing portion 26 where they are gplmbined with local oscillations produced by an oscillator 7 made to Figs. 2 and 3.

The oscillator 27 may be any suitable high frequency oscillator such as a klystron or a magnetron. An adjustable attenuating device 28 is provided for controlling the amplitude of the oscillations from the local oscillator. The wave from the local oscillator passes along the wave guide portion 29 with a part of the waves going throu h the directional coupler 31) into the mixing portion 26. The directional coupler includes a pair of openings separated by a barrier, and is effective to allow the local oscillations to enter the mixing portion but prevent the received wave from entering the wave guide portion 29. The mixing is accomplished by crystal unit 31 which is connected to an intermediate frequency amplifier, not shown. An adjustableplunger 32 is provided in the mixmg portion so that this portion can be properly tuned to compensate for variations in individual crystal mixers.

The wave guide portion 29 also includes monitoring provisions including a cavity 33 with an ad usting screw which passes the frequency of the local oscillator. and a crystal 34 coupled to suitable indicating or control means which will indicate to the operator that the oscillator is properly adjusted. A motor 35 is provided and is coupled throu h a drive rod 36 to the oscillator 27 for changing the frequency of the oscillator. The motor 35 can be remotely controlled so that the operator can intake any necessary changes in the frequency of the oscila or.

As previously stated the wave guide branch 18 is connected to a transmitter 20. This transmitter includes a modulated oscillator which may preferably be an oscillator of the type that can be directly or internally modulated such as a klystron or a magnetron. In the wave guide branch 18 there is provided phase shifting means 40 wh1c h may take the form of a polystyrene member extending along the path of the wave guide. An adiustable mounting 41 is provided for the phase sh fting member 4Q for adiustably supporting the phase shifting member within the guide. The amount of phase shift produced by the member 40 depends upon the position thereof within the guide, as will be more fully ex lained. Cou led to the wave guide 18 is a wave guide 42 which includes provisions for monitoring the transmitter. A cavity 43 selects the transmitter frequency and a crystal 44 is connected to suitable indicating or control means at the central station for indicating the frequency of the transmitter to the o erator. Such indicating means may show a maximum indication when the transmitter frequency corresponds to the resonant frequency of the cavity. A wave absorbin member 45 is provided at the other end of the wave uide 42 to absorb waves in this p rtion of the wave guide. The wave absorbing member 45 may be made of any material capable of absorbing waves of the freouencies involved such as a material formed of iron articles separated by insulating material and known as Polyiron. A motor 6 is cou led to the transmitter 20 through control rod 47 for remotely controllin the oscillator in the same manner as previously described with respect to the local oscillator 27. An ad ustable plunger 48 is provided for tunin the wave guide section to which the oscillator is coupled.

For a more complete consi eration of the construction and operation of the phase shifting means 40, reference is The hase shifting means includes an insulating member 49 having slanting ends 5i) which may be offset as shown. The mounting means includes a block 51 secured in a housing 52 extending from the wave guide 18. The block includes opening 53 for guide rods 54 and an opening 55 for a rack 56. In one method of assembly the guide rods 54 and the rack 56 may be secured to the insulating member 49 for supporting the same. The teeth on the rack 56 engage teeth on pinion 57 which is provided in a transverse opening in the block 51. A screwdriver slot 58 may be provided in one end of the pinion 57 which is accessible through an opening 59 in the housing 52 so that the pinion may be turned to adjust the position of the phase shifting member. The insulating member 49 should be made of a material having a relatively high dielectric constant and relatively low losses. Polystyrene has been found to be very suitable for this purpose. The insulating member must be shaped so that the standing wave ratio in the guide observed from the transmitter end is substantially the same for all positions of the phase shifting means so that the impedance of the guide will remain 4 substantially constant. This may be provided by the offset and slanting ends of the insulating member as illustrated and by properly spacing the rack 56 and guide rods 54. In the structure disclosed, it is possible to produce phase shifts of the waves amounting to more than 180 degrees by changing the position of the member 49. However, such a wide variation may not be necessary to compensate for the differences in the construction of the trans-' mitting tubes and phase shifting means providing smaller variations may be suitable in some cases.

In Figs. 2 and 3 there is also illustrated more in detail the configuration of the wave absorbing member 45. This member is of a stepped configuration with a base portion 60 having shoulders 61 bearing against the end of the guide 42 and an intermediate portion 62 which fits snugly within the end of the guide. An end 63 of reduced cross-section extends within the guide in such manner to be engaged by waves in this portion of the transmitter monitoring section.

In Fig. 5 there is illustrated the configuration of the adjustable plungers such as identified at 32 and 48 in Fig. 1. These plungers include movable plates hav ing edges 71 shaped to make sliding contact along the inner surface of the wave guide. The plate 70 is secured to a rack 72 having teeth engaging the teeth of pinion 73. Therack 72 and pinion 73 may be identical to the rack 56 and pinion 57 of Fig. 2. The pinion 73 may also include a slot to be engaged by a screwdriver for adjusting the position of the plate 70.

The attenuating member 28 of Fig. 1 may be mounted in the same manner as the phase shifting means 40 as illustrated in Fig. 2. The attenuating member has a high resistance to the wave and may be constructed of insulating material such as Bakelite with a very thin film of conducting material on one side thereof. Such a conducting film may be made of a carbon or platinum in a very thin film to provide a high resistance.

Considering now the operation of the system, the oscillator 20 produces a wave which is transmitted through wave guide branch 18 to the Y junction and through the wave guide 12 to the horn 13 of the antenna. The wave is reflected and beamed by the parabolic reflector 14 and the direction of the beam then changed by the flat reflector 15. The wave from the transmitter would also tend to be directed through the branch wave guide portion 17 to the receiver which is, in effect, in parallel to the wave guide 12. However, the length of the guide 17 and the spacer 21, and the portion of the guide in the receiver ahead of the iris 38 of the first cavity 22, are of such length that a high impedance is presented to waves of the frequency of the transmitter 20. This has the desirable effect of eliminating waves of this frequency from the receiver and also eliminating the attenuation of the transmitted wave which would be caused by the parallel path through which a portion of the transmitted wave might be diverted. The high impedance of the receiver branch at the transmitting frequencies also eliminates attenuation due to an impedance mismatch at the Y junction which might otherwise occur. When it is desired to change transmitting frequencies, a spacer 21 of a different length can be provided so that the system may be easily converted for operation on different frequencies.

The received waves, which are of different frequency than the transmitted waves, are picked up by the from 13 and pass through wave guide 12 and through the Y junction and branch guide 17 to the receiver 19. The received frequencies are passed by the triple cavity filter and mixed with local oscillations as previously described. The branch guide 18 from the Y junction to the transmitter is of such length that it presents a high impedance at the received frequency and therefore this frequency will not be attenuated by the transmitter branch but will be applied entirely to the receiver. The effective length of the wave guide 18 is adjusted by the phase shifting member 40. The phase shifting member 40 therefore serves an analogous function to the spacer 21 in that the receiving frequency can be changed and the phase shifter can be adjusted to change the angle at which waves are reflected by the wave guide 18 so that the wave guide pre sents a high impedance to the new received frequency.

The phase shifter 41) however has an additional function which is to compensate for different oscillators used in the transmitter. It has been found that various ldystrons and magnetronsavailable have slightly different con:

" structions which impart different reflection characteristics thereto. One reason for this is that tubes such as these may include a short section of transmission line and slight variations in length produce appreciable changes in characteristics. The length of the wave guide 18 therefore has to be particularly adjusted for the different oscillators used. This is obviously undesirable and therefore the phase shifter 40 which is easily adjustable solves a very diificult problem in systems of this type. The settings of the pinion 57 may be adjusted each time the oscillator tube is changed and/or each time the receiving frequency is changed, thereby controlling the effective length of the wave guide 18 so that the reflection of the received wave by the transmitter portion of the system does not substantially attenuate the received wave.

The above system has been found to be highly satisfactory and provides simultaneous transmission and reception from a single antenna without objectionable interference. The system is adaptable for use with transmitters and receivers operating at different frequencies within the same range of frequencies and the frequencies of operation can be changed without substantial changes in the equipment. The simple adjustment of the phase shifter in the transmitter branch of the wave guide permits easy adjustment to compensate for changes in oscillator tubes. A similar arrangement can be used in the receiver but since the length from the junction to the first iris of the cavity in the receiver may be accurately determined, it is easy to compute the size of spacer required for each frequency and a spacer as illustrated is entirely satisfactory. In most systerms the frequencies of operation will not be subject to change.

It is to be pointed out that other devices may be used for changing the characteristics of the wave guides for controlling the impedance thereof, but the ones described have been found to be the most simple and effective for the particular application set forth.

Although one embodiment of the invention which is illustrative thereof is disclosed, it is obvious that various changes and modifications can be made therein without departing from the intended scope of the invention as defined in the appended claims.

I claim:

1. A system for providing simultaneous operation of a plurality of microwave translating units from a single antenna comprising, antenna means, a first translating unit operating at a first frequency, first Wave guide means coupling said first unit to said antenna means, a second translating unit operating at a second frequency, and second wave guide means coupling said second unit to said antenna means, said first translating unit including an electron discharge valve of such construction that the reflection characteristics thereof vary substantially with slight changes in the dimensions thereof, said first wave guide means including a tubular duct, an insulating member positioned therein, and adjustable means for supporting said insulating member in various positions with respect to said tubular duct, said insulating member being so constructed and arranged that the phase of waves passing through said first wave guide means is shifted by an amount depending on the position of said insulating member and that said first wave guide means presents a substantially constant impedance to said first translating unit for all positions of said insulating member, whereby said elongated member compensates for variations in the reflection characteristics of said valve of said transmitter to present a high impedance to waves of said second frequency.

2. A system for providing simultaneous microwave transmission and reception from a single antenna comprising, antenna means, a transmitter operating at a first frequency, first Wave guide means coupling said transmitter to said antenna means, a receiver operating at a second frequency, and second wave guide means coupling said receiver to said antenna means, said transmitter including an electron discharge valve of such construction that the reflection characteristics thereof vary substantially with slight changes in the dimensions thereof, said first wave guide means including a tubular duct, a polystyrene member of elongated shape and having tapered ends positioned longitudinally within said duct, and adjustable means for supporting said elongated member in various positions with respect to a side wall of said tubular duct, said polystyrene member being positioned to shift the phase of waves passing through said duct by an amount such that waves of said second frequency are reflected by said first wave guide means and said transmitter in combination,

said first wave guide means presenting a substantially constant impedance to said transmitter for all positions of said polystyrene member, said second wave guide means and said receiver having such dimensions to reflect waves of said first frequency.

3. A system for providing simultaneous microwave transmission and reception from a single antenna comprising, antenna means, wave guide means including a main portion coupled to said antenna means and first and second branch portions connected to said main portion, transmitter means coupled to said first branch portion for transmitting waves of a first frequency, receiver means coupled to said second branch portion for receiving waves of a second frequency, said receiving means including wave guide structure having first, second, third, and fourth interconnected sections, said first section being connected to said second branch portion and cooperating therewith to reflect waves of said first frequency, said second section including a resonant cavity filter which passes waves of said frequency, said fourth section including means for generating waves having a frequency differing from said second frequency by a predetermined frequency, said third section being coupled intermediate said second and fourth sections and mixing the waves provided thereby to provide waves having said predetermined frequency, said transmitter means including a wave guide section and an electron discharge valve coupled thereto, the reflection characteristics of said transmitter means depending upon the particular construction of said valve, and adjustable phase shifting means coupled to said first branch portion for controlling the over-all reflection characteristics of said first branch portion and said transmitter means so that a high impedance is presented to waves of said second frequency.

4. A system for providing simultaneous microwave transmission and reception from a single antenna comprising, antenna means, Wave guide means including a main portion coupled to said antenna means and first and second branch portions connected to said main portion, transmitter means coupled to said first branch portion for transmitting Waves of a first frequency, receiver means coupled to said second branch portion for receiving waves of a second frequency, said receiving means including a Wave guide structure having first, second, third, and fourth interconnected sections, said first section being connected to said second branch portion and cooperating therewith to present a high in!- pedance to waves of said first frequency, said second section including a resonant cavity filter which passes waves of said second frequency, said fourth section including means for generating waves having a frequency differing from said second frequency by a predetermined frequency, said third section being coupled intermediate said second and fourth sections for mixing the waves provided thereby to provide waves having said predetermined frequency, means for adjusting the effective length of said third section for tuning the same to said predetermined frequency, said transmitter means including a waveguide section and an electron discharge valve coupled thereto, means for adjusting the length of said wave guide section of said transmitter means for tuning the same to said second frequency, the reflection characteristics of said transmitter means depending upon the particular construction of said valve, and adjustable phase shifting means coupled to said first branch portion for controlling the combined reflection characteristics of said first branch portion and said transmitter to present a high impedance to waves of said second frequency.

5. A system for providing simultaneous microwave transmission and reception from a single antenna comprising, antenna means, wave guide means and first and second branch portions connected to said main por tion, transmitter means coupled to said first branch portion for transmitting waves of a first frequency, receiver means coupled to said second branch portion for receiving waves of a second frequency, said receiving means including wave guide structure having first, second, third, and fourth interconnected sections, said first section being connected to said second branch portion and cooperating therewith to present a high impedance to waves of said first frequency, said second section including a resonant cavity filter which passes waves of said second frequency, said fourth section including means for generating waves having a frequency difiering from :said second frequency by :a predetermined frequency, monitoring means rfor :said wave gen- ;erating =means-coupled to said fourth section, said third :section being coupled intermediate said second and fourth sections and mixing the waves provided thereby to provide waves having said predetermined frequency, said transmitter means including a wave guide section and an electron discharge valve coupled thereto, the treflection characteristics of said transmitter means depending =upon the particular construction of said valve, adjustable phase shifting means coupled to said first tbranch portion for controlling the over-all reflection characteristics'of said first branch portion and said transmitter means to present a high impedance to waves of said second frequency, and monitoring means for said transmitter coupled to said first branch portion.

6. A system for providing simultaneous microwave transmission and reception from a single antenna comprising, antenna means, wave guide means and first andsecond branch portions connected to said main por- ;tion, transmitter means coupled to said first branch portion for transmitting waves of a first frequency, receiver means coupled to said second branch portion for receiving waves of a second frequency, said receiving means including wave guide structure having first, second, third, and fourth interconnected sections, said first section being connected to said second branch portion and including a spacer having such length that a high impedance is presented to waves of said first frequency, said second section including a resonant cavity filter which passes waves of said second frequency, said fourth section including means for generating waves having a frequency differing from said second frequency by a predetermined frequency, said thirdsec tion being coupled intermediate said second and fourth sections and mixing the waves provided thereby to provide waves having said predetermined frequency, said transmitter means including a wave guide section and an electron discharge valve coupled thereto, the reflection characteristics of said transmitter means depending upon the particular construction of said valve, and adjustable phase shifting means coupled to said first branch portion for controlling the over-all reflection characteristics of saidtfirst branch portion and said transmitter means so that a high impedance is presented thereby to waves of said second frequency, said phase shifting means including an elongated insulating member extending longitudinally within said first branch portion and means for adjustably positioning said insulating member with respect to the walls of said first branch portion.

7; A communication system including in combination, a transmitter operating at a first frequency, a receiver operating at a second frequency, an antenna, and wave guide means coupling said transmitter and said receiver to said antenna for simultaneous operation therewith, said wave guide means including a main portionand first and second branch portions extending from said main portion, said main portion being connected to said antenna and said first and second branch portions being individually connected respectively to said transmitter and said receiver, said transmitter including wave guide means connected to said first branch portion and having a wave reflecting portion the char- .teristics of which vary with slight changes in the dimensions thereof, said first branch portion including phase shifting means adjustable to change the effective length thereof, said phase shifting means being adjusted so that said first wave guide branch portion and said transmitter wave guide means together form a stub of such effective length that waves of said second frequency are reflected thereby without substantial attenuation, said receiver including a wave guide portion connected to said second branch portion and including high Q band-pass resonant cavity means for selecting waves of said second frequency with said cavity means having an iris at the input thereof, said second branch portion having such length that this portion together with the part of said receiver wave guide portion up to said iris form a stub of such effective length that waves of said second frequency are reflected thereby without substantial attenuation, whereby said transmitter and said receiver are both efliciently coupled to said antenna for simultaneous operation therewith.

"8. A communication system including in combination, a first translating unit operating at a first fre- 8 'quency, 'a se'con'd translating 'unit operating :at a second frequency, an antenna, and wave 'guide' tn'eans for simul- 'taneously coupling Jsaid tfirst and second translating units ;to .said antenna, said wave guide means including a main portion and first and second branch portions "extending from .said main portion, said main portion be- 'ing connected to said antenna and said first and second branch portions being individually connected respectively to said translating units, said first translating unit including wave guide means connected to :said first branch portion and having a wave reflecting portion the characteristics of which vary with slight changes in the dimensions thereof, said first branch portion including phase shifting means adjustable to change the effective length thereof, said phase shifting means being adjusted so that said first wave guide branch portion and said wave guide means of said first unit together form a stub of such effective length to present a high impedance to waves of said second frequency, said second translating unit including a wave guide portion connected to said second branch portion and bandpass resonant cavity :means for selecting waves of said second frequency, said cavity means having an iris at the input thereof connected to said wave guide portion of said second unit, said second branch portion having such length that this portion together with said 'wave guide portion of said second unit form a stub of such effective length to present a high impedance to waves of said second frequency, whereby said first and second translating units are both efficiently coupled to said antenna for simultaneous operation therewith.

9. Microwave radio apparatus including in combination, a transmitter opera-ting at a first frequency, a receiver operating at a second frequency, an antenna for operation with said transmitter and receiver and having a hollow wave guide portion for coupling signals thereto, said transmitter having a hollow waveguide portionconnected to said wave guide portion of said antenna, said receiver having a hollow wave guide portion connected to the junction of said wave guide portions of said transmitter and said antenna, said transmitter including an electron discharge valve having reflection characteristics which may differ with each particular valve, said wave guide portion of said transmitter including adjustable phase shifting means therein, said phase shifting means being adjusted to compensate for the reflection characteristicsof said valve so that said transmitter and said wave guide portion thereof form a stub of such efiective length to present a high impedance to waves of said second frequency, said wave guide portion of said receiver having therein tuned filter means constructed to select said second frequency and reject said first frequency, said filter means including a plurality of irises which define a plurality of high Q cavity filter sections, said iris of said filter means nearest said antenna being so positioned with respect to said wave guide portions of said antenna and saidtransmitter to present a high impedance to waves-of said first frequency applied from said transmitter to said antenna.

10. A system for providing simultaneous microwave transmission and reception from a single antenna includingin combination, antenna means, tra-nsmitter'means for transmitting waves of a first frequency, hollow wave-guide means interconnecting said transmitter means and said antenna means, receiver means coupled to said wave guide means for receiving waves to a second frequency, said receiver means including a hollow wave guide structure having firs-t, second and third interconnected sections, said first section having therein a resonant cavity filter tuned to select waves of said second frequency, said resonant cavity filter being positioned with respect to said wave guide means to reflect waves of said first frequency passing through said waveguide means from said transmitter means to said antenna means without substantially attenuating -the same, said third section including means for generating waves having a frequency differing from said second frequency by a predetermined frequency, said second section being coupled intermediate said first and third sections and mixing the waves provided thereby to produce waves having said predetermined frequency, said transmitter means including a Waveguide section and an electron discharge valve coupled thereto, said transmitter means having reflection characteristics, and adjustable phase shifting means in theportion of said wave guide means intermediate said receiver means and transmitter means, said phase shifting means controlling the overall reflection characteristics of said portion of said Wave guide means and said transmitter means so that a high impedance is presented thereby to waves of said second frequency.

11. Microwave radio apparatus including in combination, 'a transmitter operating at a first frequency, a receiver operating at a second frequency, an antenna for operation with said transmitter and receiver and having a hollow wave guide portion for coupling signals thereto, said transmitter having a hollow wave guide portion connected to said wave guide portion of said antenna, said receiver having a hollow wave guide portion connected to the junction of said wave guide portions of said transmitter and said antenna, said wave guide portion of said transmitter including adjustable phase shifting means, said phase shifting means being adjusted so that said transmitter and said wave guide portion thereof form a stub of such effective length that waves of said second frequency are reflected thereby, so that waves of said second frequency received by said antenna are applied therefrom to said receiver without substantial attenuation, said wave guide portion of said receiver including tuned filter means constructed to select said second frequency and reject said first frequency, said filter means including a plurality of irises which define a plurality of high Q cavity filter sections, said iris of said cavity means nearest said antenna being positioned with respect to wave guide portions of said antenna and said transmitter that waves of said first frequency applied from said transmitter to said antenna are reflected thereby, so that waves of said first frequency from said transmitter are applied to said antenna without substantial attenuation.

12. A compact microwave unit for providing simultaneous microwave transmission and reception from a single antenna including in combination, antenna means, transmitter means for transmitting waves of a first frequency and including an electron discharge valve, hollow single conductor wave guide means interconnecting said transmitter means and said antenna means, receiver means for receiving waves of a second frequency coupled to said wave guide means at an intersection thereon intermediate said transmitter means and said antenna means, the portion of said wave guide means extending between said intersection and said transmitter means together with said transmitter means forming a stub of such effective length to present a high impedance to waves of said second frequency, said receiver means including rigid wave guide structure having first, second and third interconnected sections, said first section having therein a resonant cavity filter tuned to select waves of said second frequency, said resonant cavity filter being positioned with respect to said wave guide means to reflect waves of said first frequency passing through said wave guide means from said transmitter means to said antenna means without substantially attenuating the same, said third section extending substantially parallel to said first section and including means for generating Waves having a frequency differing from said second frequency by a predetermined frequency, said second section being coupled intermediate said first and third sections and mixing the waves provided thereby to produce waves having said predetermined frequency, said portion of said wave guide means extending between said intersection and said transmitter means having a substantial part thereof extending substantially parallel to said first section of said wave guide structure of said receiver means, so that said transmitter means and said receiver means together form a compact unit.

References Cited in the file of this patent UNITED STATES PATENTS 2,258,974 Dagnall Oct. 14, 1941 2,422,190 Fiske June 17, 1947 2,424,156 Espley July 15, 1947 2,433,368 Johnson et a1 Dec. 30, 1947 2,445,896 Tyrrell July 27, 1948 2,484,798 Bradley Oct. 11, 1949 2,510,461 Bruck et al7 June 6, 1950 2,547,539 Ring Apr. 3, 1951 OTHER REFERENCES Journal Inst. of EB, vol. 93, part III A, No. 4, May 1946, pages 633638.