Channel Diplexer Wherein Coupling Apertures Balance And Cancel Out Undesired Modes

Abstract

A channel diplexer composed of a semicircular waveguide and cylindrical cavity resonators is disclosed. The diplexer is characterized in that a plurality of coupling apertures are provided in the common conductor wall between the waveguide and the resonators to couple mutual electromagnetic energies at the conductor wall so that at least one unnecessary resonant mode other than the desired resonant mode in the cavity resonators is prevented. This is accomplished by the mutual positional relationship of the coupling apertures.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a channel diplexer for use in the ultrahigh frequency band, and more particularly to a channel diplexer composed of a semicircular waveguide and cylindrical cavity resonators.

2. Description of the Prior Art

In the ultrahigh frequency multiplex transmission of multiple channel signals by the use of, for example, a circular waveguide, the channel diplexer is employed as means to branch out various channel signals, or conversely, combine them at a terminal office, a repeater equipment and so forth. The semicircular waveguide has hitherto been used in the channel diplexer on the grounds that it is easily connected to the circular waveguide as a transmission line, that it is comparatively less lossy than other forms of waveguides, and that it is easily adapted to the connection with the resonators. As the resonators to be coupled to the semicircular waveguide so as to constitute the channel diplexer device, the use of the cylindrical cavity resonators has heretofore been proposed on the grounds that the cylindrical shape can achieve a higher unloaded Q than other shapes such as rectangular ones and that it is comparatively easy to manufacture.

Since, however, the cylindrical cavity resonator is a multimode resonator, a number of undesired resonant modes are essentially present besides a resonant mode in use. When cylinrical cavity resonators are used in the channel diplexer device, the presence of the undesired resonant modes results in the crosstalk of the other channel components to the particular channel in use and in the attenuation of other channels which are to be subsequently branched thereby causing very adverse effects on the transmission of the various channel guides.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a diplexer of the type composed of a semicircular waveguide and cylindrical cavity resonators wherein crosstalk of other channel components to the particular channl in use and the attenuation of other channels which are to be subsequently branched are avoided.

The foregoing and other objects of the invention are attained by providing within a diplexer composed of a semicircular waveguide and cylindrical cavity resonators a plurality of coupling apertures in the common conductor wall between the waveguide and the resonators to couple mutual electromagnetic energies at the conductor wall so at least one unnecessary resonant mode in the cavity resonators is prevented. This is accomplished by the particular mutual positional relationship of the coupling apertures depending on the resonant mode it is desired to suppress.

BRIEF DESCRIPTION OF THE DRAWINGS

The specific nature of the invention, as well as other objects, aspects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings, in which:

FIGS. 1(a) and 1(b) are a perspective view and a sectional view, respectively, or a part for branching a single channel signal in an example of a prior-art channel branching device.

FIGS. 2(a) and 2(b) are a perspective view and a sectional view, respectively, of a part for branching a single channel signal in an embodiment of the present invention.

FIGS. 3(a) and 3(b) are a perspective view and a sectional view, respectively, of a part for branching a single channel signal in another embodiment of the channel branching device according to the present invention.

FIGS. 4(a), 4(b), 4(c) and 4(d) are a perspective view, a top view, and sectional views, respectively, of a part for branching a single channel signal in a further embodiment of the present invention.

FIGS. 5(a) and 5(b) are a perspective view and a sectional view, respectively, of a part for branching a single channel signal in a still further embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIGS. 1(a) and 1(b) illustrate an example of a prior-art channel diplexer device which functions to branch a single channel signal. It is composed of a TE.sub.01 mode-semicircular waveguide (hereinbelow, simply termed the TE.sub.01 waveguide) and TE.sub.011 mode-cylindrical cavity resonators (hereinafter, simply termed the TE.sub.011 cavities). While the adverse effect of the undesired resonant modes in the example will be described hereunder, it will be understood that a similar adverse effect arises in the combination of the semicircular waveguide and the cylindrical cavity resonators using any different mode. Here, the TE.sub.01 waveguide has the shape of one of two parts obtained by dividing a TE.sub.01 mode-circular waveguide at a diameter thereof, and is comparatively low in loss. The TE.sub.011 cavity has the advantage that the unloaded Q is high owing to the nature of the particular electromagnetic field, and that some structural discontinuities between a cylindrical conductor wall and circular conductor walls does not lead to large loss. The TE.sub.01 waveguide 101 and TE.sub.011 cavities 102 and 103 have mutual electromagnetic energies coupled through coupling apertures 108 and 110 which are respectively provided in common conductor walls 105 and 107 forming parts of a plane conductor wall 104 of the waveguide. The TE.sub.011 cavity 102 has a coupling aperture 109 provided also in a circular conductor wall 106, and the cavity is adapted to be connected to an external output circuit through the coupling aperture. Now, it is assumed that n channel signals having center frequencies f.sub.1, . . . f.sub.i.sub.-1, f.sub.i, f.sub.i.sub.+1, . . . f.sub.n are introduced into the TE.sub.01 waveguide 101, and that the TE.sub.011 cavities 102 and 103 resonate at the frequency f.sub.i. Then, the TE.sub.011 cavity 102 allows only a channel signal of frequency f.sub.i to pass, while the TE.sub.011 cavity 103 stops only the signal of f.sub.i, so that among the n channel signals introduced, only the signal of the center frequency f.sub.i is branched via the coupling aperture 109 to the external circuit.

As illustrated in the sectional view in FIG. 1(b), however, the coupling apertures 108 and 110 are respectively provided on radii of the cavities in the common conductor walls 105 and 107 and in the vicinity of the center line of the plane conductor wall 104, thereby coupling axial magnetic fields at the center of the TE.sub.01 waveguide and radial magnetic fields of the TE.sub.011 cavities. As a consequence, all the unnecessary resonant modes having magnetic field components in the radial direction are excited. For example, the unnecessary resonance of the resonating TE.sub.311 mode existent in the upper side-band of the resonating TE.sub.011 mode is especially conspicuous, and extensively lies within the band of the frequencies f.sub.i.sub.+1, . . . f.sub.n of the higher frequency channels. It branches also the signals within the band through the TE.sub.011 cavity 102, and simultaneously causes heavy losses in the channel signals which are to be subsequently branched for each of the different channels. In this manner, the unnecessary resonance produces such a marked adverse effect that the channel diplexer is not usable for multiplex transmission systems.

It is a matter of course that the adverse effect of the undesired resonant modes is not peculiar to the use of the TE.sub.011 cavities, but that a quite similar result is brought about in the case of employing cavity resonators of any other mode. The prior-art channel diplexer device employing cylindrical cavity resonators has therefore been subject, in spite of many merits of the cylindrical cavity resonators themselves to the limitation, which might be fatal to the channel branching device for multiplex communication systems, that it can be used only in a frequency range where no adverse effect of the undesired resonant modes is seen or in a very narrow frequency range.

The present invention solves this problem fundamentally, and provides a channel diplexing device in which the generation of undesired resonant modes is prevented by the use of a plurality of coupling apertures balanced with respect to electromagnetic fields, whereby an excellent characteristic free from the adverse effect of the undesired resonant modes is exhibited over a wide frequency range. It will now be described in detail with reference to the accompanying drawings.

FIGS. 2(a) and 2(b) illustrate that part in an embodiment of the present invention which branches a single channel signal. TE.sub.011 cavities 202 and 203 are coupled to the TE.sub.01 waveguide 201 through coupling apertures 208, 209 and 211, 212 which are provided in the common conductor walls 205 and 207 forming parts of the plane conductor wall 204, respectively. Since the TE.sub.011 cavities 202 and 203 resonate at the center frequency f.sub.i of an identical channel, only the channel signal of the center frequency f.sub.i among a group of channels conducted to the TE.sub.01 waveguide 201 is stopped by the TE.sub.011 cavity 203 and passes through the TE.sub.011 cavity 202, to be branched to an external output circuit through a coupling aperture 210 provided in a circular conductor plate 206.

Consider the undesired resonating TE.sub.311 mode producing the greatest adverse effect in the example of the prior art shown in FIGS. 1(a) and 1(b). The radial magnetic fields of this unnecessary resonant mode on the common conductor wall 205 exist at every 60.degree. in the circumferneital direction. In addition, the adjacent radial magnetic fields with the interval of 60.degree. are opposite in sense to each other with respect to the center. In contrast, the magnetic fields of the resonating TE.sub.011 mode are radially existent on the common conductor wall 205, under the state where they are uniform in the circumferential direction and where all of them are of the same sense in the radial direction.

On the other hand, the magnetic fields of the TE.sub.01 mode within the TE.sub.01 waveguide 201 as appear on the plane conductor wall 204 are existent in the shape of rings on both sides of, and symmetrically with respect to, the axis of the waveguide. As shown in FIG. 2(b), the two apertures are provided in the common conductor wall 205 radially in a manner to define an angle of 60.degree. about the center of the common conductor wall 205 and at positions symmetric with respect to a plane normal to the longitudinal direction of the TE.sub.01 waveguide 201. The centers of the common conductor walls 205 and 207 are set in the vicinity of a line which is at a distance of D/4 (where D denotes the length of the chordal part of the cross section of the semicircular waveguide) from the center line of the plane conductor wall 204.

The coupling apertures 208, 209, 211 and 212 are provided in sections of the common conductor walls as lie between the center line of the plane conductor wall 204 and the line distant by D/4 therefrom. On the basis of the symmetry of magnetic fields, the coupling apertures may of course be provided radially from the centers of the common conductor walls in sections which lie between an end of the plane conductor wall 204 and the line lying apart by D/4 from the center line of the same wall. The coupling aperture 210 may be provided at any position in the circular conductor wall 206 insofar as the signal of the branched frequency can be coupled to the external circuit in matched condition.

By shaping the coupling apertures 208 and 209 into slots extending radially, those components of the ring-shaped magnetic fields on the plane conductor wall 204 of the TE.sub.01 waveguide 201 which exist along the coupling apertures 208 and 209 can be brought into the state in which they are in the same sense in the radial direction. Therefore, notwithstanding that the resonating TE.sub.011 mode having the magnetic fields of the same radial sense is excited, the resonating TE.sub.311 mode of radially different sense cannot be excited. Of course, quite the same situation applies with respect to the common conductor wall 207 and the coupling apertures 211 and 212.

The undesired resonating TE.sub.311 mode is not excited in either the TE.sub.011 cavities 202 or 203 by balancing the two coupling apertures electromagnetic field-wise in accordance with the present invention. Thus, it will be appreciated that the coupling apertures serve the dual purpose of coupling the TE.sub.011 mode and of balancing and cancelling out the undesired TE.sub.311 mode. The channel branching device according to the present invention can consequently achieve an excellent operating characteristic free from the undesired resonant modes over a wide frequency range.

FIGS. 3(a) and 3(b) illustrate a part for branching a single channel in another embodiment of the present invention. TE.sub.011 cavities 302 and 303 are respectively coupled with the TE.sub.01 waveguide 301 by coupling apertures 308, 309 provided in a common conductor wall 305 and coupling apertures 311, 312 provided in a common conductor wall 307. A channel signal stopped by the resonance of the TE.sub.011 cavity 303 passes through the TE.sub.011 cavity 302, and is branched to an external output circuit through a coupling aperture 310 provided in a circular conductor wall 306.

The two coupling apertures 308 and 309 are provided on a diameter of the cavities in the common conductor wall 305 normal to the longitudinal direction of propagation in the TE.sub.01 waveguide 301 and at positions opposite to each other with respect to the center line of the conductor wall 304. In addition, apertures 308 and 309 have equal degrees of coupling, that is, they are balanced in terms of the electromagnetic fields. The centers of the common conductor walls 305 and 307 are set in the vicinity of the center line of the plane conductor wall 304. As regards the position of the coupling aperture 310, the same as in the coupling aperture 210 in FIG. 2 applies. Here, those radial magnetic fields of the undesired resonating TE.sub.311 mode and all the other undesired resonating TE.sub.(2l .sub.- 1)mn modes (hereinafter, the letters l, m and n denote natural numbers) on the common conductor wall 305 exist at every 180/(2l - 1).degree., and the adjacent magnetic fields with the interval of 180/(2l - 1) are in senses opposite to each other with respect to the center, so that the radial magnetic fields with an interval of 180.degree. are opposite in sense with respect to the center.

On the other hand, the radial components of ring-shaped magnetic fields on the plane conductor wall 304 of the TE.sub.01 waveguide 301 are in the same sense in the radial direction about the axis of the waveguide. Accordingly, by coupling the respective radial components to the TE.sub.011 cavity 302 by the two coupling apertures 308 and 309 in the state where they are balanced in terms of electromagnetic fields, the resonating TE.sub.011 mode whose radial magnetic fields on the common conductor wall 305 are in the same sense is excited, whereas all the unnecessary resonating TE.sub.(2l .sub.- 1)mn modes including the unnecessary resonating TE.sub.311 mode in which they are in the opposite senses are not excited. Needless to say, quite the same relations hold as to the coupling apertures 311 and 312 in the common conductor wall 307. Thus, in accordance with the present invention, any undesired resonating TE.sub.(2l .sub.- 1)mn modes are not excited, and a channel diplexer device can be provided which has the preferable characteristic of being free of the undesired modes over a very wide frequency band.

Although, in the foregoing, both the cavity resonators for passing and stopping have been exemplified as being of one stage, quite the same effect can of course be achieved when a plurality of stages are employed. By way of example, FIGS. 4(a) to 4(d) show a part for branching a single channel signal in an embodiment of the present invention in the case where TE.sub.011 cavities of two stages are employed both for passing and for stopping. In FIGS. 4(b), 4(c) and 4(d), a TE.sub.011 cavity 405 and parts of the TE.sub.01 waveguide 401 close thereto are omitted since the shape is similar to that of a TE.sub.011 cavity 404.

Referring to the figures, the TE.sub.011 cavities for stopping 404 and 405 are respectively coupled with the TE.sub.01 waveguide 401 by coupling apertures 416, 417 provided in a common conductor wall 410 and coupling apertures 418, 419 provided in a common conductor wall 411. A TE.sub.011 cavity for passing 402 is coupled with the TE.sub.01 waveguide 401 by coupling apertures 412 and 413 provided in a common conductor wall 407, and is also coupled with a TE.sub.011 cavity 403, similarly for passing, through a coupling aperture 414 provided in the coupling conductor plate 408. A channel signal stopped twice by the resonance of the TE.sub.011 cavities 404 and 405 passes through the TE.sub.011 cavity 402 to reach the TE.sub.011 cavity 403, and is branched to an external output circuit through a coupling aperture 415 provided in a circular conductor wall 409.

The two coupling apertures which couple each of the TE.sub.011 cavities 402, 404 and 405 to the TE.sub.01 waveguide 401 are provided, as in the case of the embodiment in FIGS. 3(a) and 3(b), on a diameter of the corresponding common conductor wall normal to the longitudinal direction of the TE.sub.01 waveguide 401 and at positions opposite to each other with respect to the center of the circular wall, and under the state where they are balanced in terms of electromagnetic fields. In the respective TE.sub.011 cavities, therefore, any undesired resonating TE.sub.(2l .sub.- 1)mn modes are not excited at all. Consequently, there can be provided a channel branching device which employs TE.sub.011 cavities in two stages and in which the undesired resonant modes are not existent over a very wide frequency band.

Furthermore, in this embodiment, the effects of the undesired resonating TE.sub.2mn mode which has the greatest adverse effect in undesired resonant modes other than the undesired resonating TE.sub.(2l .sub.- 1)mn mode are prevented from becoming crosstalk in the channel. More specifically, since those radial magnetic fields of the undesired resonating TE.sub.2mn mode on the circular conductor wall exist at every 90.degree., the circumferential position of the coupling aperture 414 provided in the coupling conductor plate 408 is set, as shown in FIGS. 4(c) and 4(d), so as to be 45.degree. to the diametrical direction along which the coupling apertures 412 and 413 are provided in the common conductor wall 407. As a result, the resonating TE.sub.011 mode with the radial magnetic fields being uniform in the circumferential direction can pass through the TE.sub.011 cavity 402 at its resonance, whereas the undesired resonating TE.sub.2mn mode cannot pass. Therefore, the crosstalk due to the undesired resonance cannot occur, and the channel branching device has a wider bandwidth.

Furthermore, in accordance with this embodiment, regarding the undesired resonating TE.sub.3mn mode exerting the greatest adverse effect in the undesired resonating TE.sub.(2l .sub.- 1)mn modes the excitation of which is restrained by the present invention, an additional precaution is taken so that when the residual resonant components are slightly existent, their crosstalk into the channel is prevented. More specifically, since the radial magnetic fields of the undesired resonating TE.sub.3mn mode exist at every 60.degree. in the circumferential direction, the circumferential position of the coupling aperture 415 provided in the circular conductor wall 409 is set, as shown in FIGS. 4(b) and 4(c), so as to define an angle of 150.degree. to the position of the coupling aperture 414 in the coupling conductor plate 408. Consequently, the unnecessary resonating TE.sub.3mn mode cannot pass through the TE.sub.011 cavity 403, and the crosstalk is effectively eliminated.

In this embodiment, the crosstalk of the residual resonant components of the undesired resonating TE.sub.2mn and TE.sub.3mn modes is prevented by the circumferential positions of the coupling apertures 414 and 415, respectively. Needless to say, however, the crosstalk of any other undesired resonant modes can be prevented by changing the positions of the coupling apertures 414 and 415 according to a required characteristic. The radial position of the coupling aperture 414 in the coupling conductor plate 408 and that of the coupling aperture 415 in the circular conductor wall 409 are ones at which a distributed signal can be coupled in matched condition. In the case where the number of stages of the cavity resonator for passing is further increased, the crosstalk of more undesired resonant modes or remaining resonant components can be prevented by a similar procedure.

Moreover, in the structural aspect, this embodiment has the feature that it is easy in manufacture. More specifically, with the TE.sub.011 cavity, some structural discontinuity between the cylindrical conductor wall and the circular conductor wall does not lead to a heavy loss in characteristic owing to the nature of electromagnetic fields. It is therefore possible, by way of example, for the coupling conductor plate 408 to be produced so as to be detached from the cylindrical conductor walls. The coupling aperture 414 may then be positioned in the optimum condition by moving the coupling conductor plate 408 and thereafter fixing it by screws or the like. This also applies to the relation between the circular conductor wall 409 and the cylindrical conductor wall of the TE.sub.011 cavity 403, the relation between the plane conductor wall 406 and the cylindrical conductor wall of each of the TE.sub.011 cavities 402, 404 and 405, etc.

Although this embodiment has exemplified the case of employing the TE.sub.011 cavities of two stages both for passing and for stopping, quite the same effect can of course be achieved with an arbitrary number of stages for the cavities of both the uses. As regards the coupling apertures, although circular apertures have been illustrated, it is apparent that the shape is not subject to any restriction.

Although, in the above, the description of the present invention has been made by taking as an example the case of employing the TE.sub.011 cavities as the cavity resonators, it is apparent that a similar effect is achieved in case of using cavity resonators of different modes. Here, the case of using TE.sub.211 mode-cylindrical cavity resonators (hereinafter, simply termed the TE.sub.211 cavities) will be exemplified. FIGS. 5(a) and 5(b) illustrate a part for branching a single channel in an embodiment of the present invention which employs TE.sub.211 cavities. TE.sub.211 cavities 502 and 503 are respectively coupled with the TE.sub.01 waveguide 5 01 by coupling apertures 508, 509 provided in a common conductor wall 505 and by coupling apertures 511, 512 provided in a common conductor wall 507. A channel signal stopped by the resonance of the TE.sub.211 cavity 503 passes through the TE.sub.211 cavity 502, and is branched to an external output circuit through a coupling aperture 510 provided in a circular conductor wall 506.

When the TE.sub.211 cavities are employed, the resonating TE.sub.011 mode exerts an adverse effect as the undesired resonant mode conversely to the foregoing examples. Those radial magnetic fields of the resonating TE.sub.211 mode on the common conductor wall 505 exist at every 90.degree. in the circumferential direction, and the adjacent radial magnetic fields with the interval of 90.degree. are opposite in sense to each other with respect to the center of the wall circle. Therefore, the coupling apertures 508 and 509 are provided along a ring-shaped magnetic field on one side with respect to an axis within the TE.sub.01 waveguide, and as shown in FIG. 5(b), radially in a manner to define an angle of 90.degree. to each other with respect to the central position of the common conductor wall 505 and at equal degrees of coupling, that is, so as to bring coupled electromagnetic fields into a balanced state. In this case, the centers of the common conductor walls 505 and 507 are close to a line which is distant by D/4 from the center line of the plane conductor wall 504, the letter D denoting the length of the chord of the cross section of the semicircular waveguide. Then, radial magnetic fields excited within the TE.sub.211 cavity 502 by magnetic fields within the TE.sub.01 waveguide 501 become opposite in sense to each other in the radial direction with the angle of 90.degree. defined therebetween, since the coupling apertures 508 and 509 are along the ring-shaped magnetic field. As a result, the unnecessary resonating TE.sub.011 mode whose magnetic fields extend radially in the same sense in the radial direction cannot be excited, and only the resonating TE.sub.211 mode whose magnetic fields are of the opposite senses exists. This is also true with the TE.sub.211 cavity 503.

By thus balancing the two coupling apertures coupled in terms of electromagnetic field in accordance with the present invention, a channel branching device having an excellent characteristic free from the unnecessary resonant modes over a wide frequency range can also be provided in the case of using the resonating TE.sub.211 mode. It is apparent that, using other resonant modes than the resonating TE.sub.211 mode, quite equal effects can be similarly attained.

In the foregoing embodiments of the present invention, there have been described the cases of using the same resonant modes for both the passing and stopping cavity resonators. However, the employed resonant modes of both the cavity resonators have no correlation as is apparent from the description, and it will be apparent that they are respectively independent and quite arbitrary. Similarly, it will be apparent that when each cavity resonator includes a plurality of stages, the employed resonant modes of the respective stages are arbitrary. Further, it will be apparent that when an element different from the cylindrical cavity resonator and having an equivalent operation is used for either one of the passing and stopping cavity resonators, quite a similar excellent effect can be achieved by applying the present invention to the other cylindrical cavity resonator.

In the foregoing, the number of the coupling apertures between each cavity resonator and the waveguide has been exemplified as two. However, the number, shape, etc. of the coupling apertures are determined by characteristics required for the channel branching device, such as the half-power width problems, etc. It is needless to say that insofar as a plurality of coupling apertures are balanced in terms of electromagnetic fields, an equal effect can be attained at quite an arbitrary number.

As set forth above, the channel branching device according to the present invention employs cylindrical cavity resonators exhibiting high unloaded Q characteristics and having hitherto brought about undesired resonant modes having adverse influences, and can accomplish an excellent operating characteristic free from the undesired resonant modes over a wide frequency range. It is therefore very advantageous when used in multiplex communication systems in the ultrahigh frequency band, etc.

It will therefore be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

Claims

1. A channel diplexer comprising:

a semi-circular waveguide adapted to receive n channel signals having center frequencies f.sub.1, . . . f.sub.i.sub.-1, f.sub.i, f.sub.i.sub.+1, . . . f.sub.n ;

at least two cylindrical cavity resonators having resonant frequencies f.sub.i attached to the plane conductor wall of said semi-circular waveguide;

the first of said resonators having a coupling aperture in its external circular conductor end wall adapted to couple energy in said resonator to an external output circuit; and

said plane conductor wall common to each of said resonators having a plurality of coupling apertures for coupling and exciting the desired TE.sub.011 mode in said two cylindrical cavity resonators, said apertures being angularly positioned with respect to each other to be balanced with respect to the electro-magnetic fields in said semi-circular waveguide so that at least the TE.sub.311 undesired resonant mode is prevented from

2. The channel diplexer as recited in claim 1 wherein there are two coupling apertures defining an angle of 60.degree. about the center of the plane conductor wall common to each of said resonators and at positions symmetric with respect to a plane normal to the longitudinal direction of

3. A channel diplexer as recited in claim 2 wherein the centers of the plane conductor wall common to said resonators are in the vicinity of a line which is at a distance of one-fourth the diameter of said waveguide

4. A channel diplexer as recited in claim 1 wherein all TE.sub.(2 l.sub.-1)mn undesired mode resonant are prevented from being excited, where l, m, and n denote natural numbers, and wherein there are two coupling apertures defining an angle of 180 degrees about the center of the plane conductor wall common to each of said resonators and at

5. A channel diplexer as recited in claim 4 wherein the centers of the plane conductor wall common to said resonators are on the center line of

6. A channel diplexer as recited in claim 5 further comprising a second stage cylindrical cavity resonator attached to said first resonator and having a coupling aperture in its external circular conductor end wall adapted to couple energy in said second stage resonator to an external output circuit, and wherein said coupling aperture in said first resonator is on a line displaced 45.degree. with respect to a line passing through

7. A channel diplexer as recited in claim 6 wherein the coupling aperture in said second stage resonator is on a line displaced 150.degree. with respect to the line through the coupling aperture in said first resonator.

8. A channel diplexer comprising:

a semi-circular waveguide adapted to receive n channel signals having center frequencies f.sub.1, . . . f.sub.i.sub.-1, f.sub.i, f.sub.i.sub.+1, . . . f.sub.n ;

at least two cylinderical cavity resonators having resonant frequencies f.sub.i attached to the plane conductor wall of said semi-circular waveguide;

the first of said resonators having a coupling aperture in its external circular conductor end wall adapted to couple energy in said resonator to an external output circuit; and

said plane conductor wall common to each of said resonators having two coupling apertures for coupling and exciting the desired TE.sub.211 mode in said two cylindrical cavity resonators and for balancing and cancelling the undesired TE.sub.011 mode, said two coupling apertures defining an angle of 90.degree. about the center of the plane conductor wall common to each of said resonators and at positions symmetric with respect to a plane

9. A channel diplexer as recited on claim 8 wherein the centers of the plane conductor wall common to said resonators are in the vicinity of a line which is at a distance of one-fourth the diameter of said waveguide from the center line of said plane conductor wall.