Abstract: A waveguide bandpass filter includes a fenestrated conductive septum which may be printed on a dielectric circuit board. The center frequency is tuned by a dielectric plate parallel with the septum and contiguous with the fenestrations which is movable in a direction orthogonal to the septum.

Abstract: A double-mode filter having double-mode resonance in each resonator, with at least two dielectric resonators being accommodated within a cut-off waveguide having a given axial length. This double-mode filter is easier to design, easier to manufacture through simplified construction, and also has smaller insertion loss. No metallic bulkhead having a coupling slot is required between each pair of stages, so that lower loss is achieved or the coupling coefficient may be analytically calculated, thus realizing high-precision design.

Abstract: The present invention relates to a waveguide band reject filter employing TEM coaxial type resonators that partially protrude into the top wall of the waveguide in such a way as to produce a predetermined frequency selective discontinuity. By proper choice of location, number of resonators, resonator configuration and protrusion, a spurious free highly efficient frequency selective band reject filter response can be obtained.

Abstract: An improved serpentine feed and method of making same. The invention includes a block of conductive material having a primary microwave waveguide channel and at least one secondary channel. Each secondary channel has at least one broadwall common to the primary channel. A high performance coupler is provided in the common broadwall by which microwave energy communicates from the primary channel to the secondary channel.

Abstract: A microwave filter composed of at least two cavity resonators disposed adjacent one another, and a coupling aperture disposed between the resonators for coupling microwave energy between the resonators, one of the cavity resonators being operative to propagate microwave energy having a TE mode and the other of the cavity resonators being operative to propagate microwave energy having a TM mode, wherein the coupling aperture is constructed for coupling the TE mode in the one cavity resonator with the TM mode in the other cavity resonator.

Abstract: A waveguide filter is provided which comprises a plurality of waveguide resonators arranged in series in the longitudinal direction of the filter with each contacting tightly with adjacent ones, each of the waveguide resonators being composed of a rectangular dielectric having a length and a permittivity complying with the center frequency of a bandpass filter, on the periphery of which a metal film is provided except on the portions of induction windows of its two sides mutually opposed in the longitudinal direction.

Abstract: Circularly polarized radiation is tapped off from an input waveguide through a input iris into an entry cavity, where it is resolved into two orthogonal linearly polarized components. These respectively proceed along two discrete paths to an exit cavity. In each path six independently tunable resonances--traversed by both direct and bridge couplings--provides enough degrees of freedom for quasi-elliptic filter functions. In the exit cavity the resultants from the two paths are combined to resynthesize circularly-polarized radiation, which traverses another iris to the output waveguide. In one layout, four resonant tri-mode cavities form a rectangular array--with entry and exit cavities at diagonally opposite corners and intermediate cavities for the two discrete paths in the two remaining corners.

Abstract: A waveguide filter comprises waveguides with length corresponding to the center frequency of a band pass filter, and shunt plates. Each shunt inductor plate has sufficient size to cover an opening of the wave guide and includes an induction window smaller than the opening, and each opening is opposed to each induction window. The waveguides and the shunt inductor plates are alternately arranged in close contact state, and the center frequency of the filter scarcely deviates.

Abstract: A dual mode circular-type waveguide filter (10) has a cylindrical waveguide body (12) separated by septums (16, 18) into a plurality of resonant waveguide cavities (22, 24, 26). Mutually orthogonal electromagnetic fields (37, 81) in adjacent cavities (24, 26) are electromagnetically coupled with each other by an internal coupling element (60) which is mounted on one of the septums (18) and extends into the adjacent cavities. The coupling element comprises an elongate, conductive wire which includes a first portion (62) extending into one of the cavities and forming a magnetic loop, and a second portion (64) extending into the adjacent cavity and forming an electric probe. The coupling element provides an asymmetrical stopband pole (72a) in the frequency response (70) of the filter.

Abstract: A waveguide filter (43) comprising a series of resonant cavities (45) separated by walls (47) each formed with an iris opening (49) is assembled from two complementary box-like bodies (25) each having an open side (31) and internal partitions forming portions of the walls (47) between the cavities. Each box-like body is manufactured by impact extrusion using an open-topped box-like die (1) in which a slug of material (5) is placed, and a punch (7) which has smaller dimensions than the die and slots (11) for forming the respective partitions. The punch is driven into the die with a force such that the material of the slug is displaced into the slots in the punch and into the space between the punch and the die.

Abstract: A waveguide filter for use in a communication system that treats microwaves or millimetric waves comprises waveguides of a U-shaped cross section and a support on which the waveguides are longitudinally connected in series. Two inductor plates bear on each of the waveguides to form a waveguide resonator. Each inductor plate has first and second planes meeting at right angles. Thus, each inductor plate assumes an L-shaped form. Each first plane covers the corresponding longitudinal U-shaped end of the waveguides. Each second plane covers half of the corresponding open bottom of the waveguides, and has a tongue formed by two notches. This tongue can be bent and inserted into the corresponding waveguide to adjust the center frequency of the passband of the bandpass filter formed by the waveguide filter.

Abstract: An extremely narrow-band bandpass electromagnetic filter comprises a waveguide (1) dimensioned below cutoff and having two or more active sections (30) each containing a dielectric resonator (6). The number of resonators (6) corresponds to the number of poles of filtering. The physical dimensions of the waveguide (1) can advantageously be further reduced by means of passive coupling means (40), where the waveguide (1) cross-section is smaller than in the active sections (30). Each passive coupling means (40) inductively couples adjacent active sections (30). Mode suppression rods (10) electrically connect opposing waveguide walls (2, 3) midway between each pair of adjacent dielectric resonators (6). Preferred embodiments are illustrated, in which the resonators (6) are tranversely oriented within the waveguide (1). Electromagnetic energy travels within the waveguide (1) in a single TE.sub.10 evanescent mode (TE.sub.01.delta. within the resonators (6)).

Abstract: A microwave filter which is optimized to reduce its dimensions, weight, cost, and manufacturabiity includes a filter body which is preferably manufactured by pressure die-casting of an aluminum alloy. In the filter body are formed a plurality of cavities in which resonators as well as tuning and connection screws are located. The cavities are so located with respect to each other that a line which joins the centers thereof appears as the series of connected line segments which are inclined with respect to each other at angles which exceed 90.degree.. To compensate the filter for the relatively larger coefficient of expansion associated with the use of die-castable alloys, the resonators and tuning screws employ materials which are different than that used in the filter body. Electrical losses are minimized by varying, from cavity to cavity, the ratio of the diameter of the cavity to that of the resonator. The weight of the filter is further reduced by cavities or voids which are formed therein.

Abstract: A triple mode dielectric loaded bandpass filter has at least one cavity resonating in three independent orthogonal modes. A triple mode cavity can be mounted adjacent to either single, dual or triple mode cavities. Inter-cavity coupling is achieved through the iris having two separate apertures that together form a T-shape. The cavities can be planar mounted. The filter is designed for use in the satellite communication industry and results in substantial savings in weight and size when compared to previous filters.

Abstract: A waveguide bandpass filter having multiple waveguide sections including alternating ridge waveguide sections and evanescent waveguide sections. The ridge waveguide sections define a resonant cavity and the evanescent waveguide sections reactively load the resonant cavity thus intercoupling the ridge waveguide sections so as to provide a low loss filter having high attenuation, not only at adjacent stop band frequencies, but also at harmonics of the pass band.

Abstract: In a microwave push-pull frequency converter having the form of a waveguide for effecting frequency conversion of a broadband microwave signal, which converter includes a converter module composed of a waveguide section and a pair of semiconductor mixer elements disposed in the waveguide section for effecting frequency conversion between a high frequency microwave signal and a low frequency microwave signal without intermediate frequency conversion, the converter further including a waveguide filter for the low frequency microwave signal connected to one side of the module, the waveguide filter includes a plurality of ridged waveguide sections and a plurality of blocking waveguide sections interposed between, and coupling, the ridged waveguide sections, and the converter module includes fastening devices supporting the semiconductor mixer elements and configured to give the coverter module the form of a ridged waveguide which permits the high and low frequency microwave signals to pass in a single mode.

Abstract: A bandpass filter has a plurality of cascade cavities that operate in a dual-mode and are mounted in a planar relationship to one another. Each cavity contains a dielectric resonator and resonates at its resonant frequency in two HE.sub.11.delta. modes. An iris is located between adjacent cavities and contains an aperture that can independently control inter-cavity coupling. The dielectric resonator is cylindrical in shape and an adjustable metallic plunger is located in a wall of each cavity so that the cavity can be tuned over a relatively broad range. The filter has good mechanical and thermal stability as well as being extremely flexible in the arrangement of cavities.

Abstract: A dual mode filter has a hollow cylindrical longitudinal outer body which is divided by transversely extending disk-like separation walls into a plurality of internal cavities. At least one coupling opening in each separation wall permits coupling of energy from one cavity to another. Said coupling opening being preferably an arcuate opening, in each separation wall, which extends along a constant radius at the outer periphery of the separation wall and over a limited angular span. When the openings are two, they are spaced 180.degree. apart, i.e. opposite one another. Adjacent separation walls are rotatably displaced 90.degree. with respect to each other so that their respective coupling opening(s) is (are) misaligned by 90.degree.. One respective adjustment screw is provided for each separation wall which penetrates through a hole in the outer body into one of the coupling openings in the given separation wall.

Abstract: An odd order bandpass filter has at least one cavity resonating at its resonant frequency in three independent orthogonal modes. The filter has at least one feedback coupling that is made to resonate and change sign at a center frequency. When the filter has two cavities, one being a triple cavity and the other being a dual mode cavity, the filter can be operated to achieve an elliptic function response. Also, the filter of the present invention can achieve a weight and volume reduction when compared to six-pole dual mode filters.

Abstract: A bandpass filter has a plurality of cascade wave-guide cavities each resonating in three independent orthogonal modes. The cavities can be cylindrical or have a square cross-section. Where the cavities are circular, each cavity resonates in TE.sub.111 or TE.sub.010 modes simultaneously. Where the cavities have a square cross-section, each cavity resonates in TE.sub.011 and TM.sub.110 modes simultaneously. Between each triple-mode cavity, there is located an iris having an aperture with four separate radial slots that are offset from a center of the iris. The filter is capable of producing an elliptic function response. In a variation of the invention, an allpass filter has an output that is short circuited and, when used in conjunction with a circulator, it functions as a group delay equalizer. Previous triple-mode filters are not capable of producing an acceptable result relative to dual-mode filters.

Abstract: A multiplexer has a plurality of bandpass filters coupled through E-plane or H-plane T-junctions to a waveguide manifold. Where the multiplexer has four channels and each filter is a six-pole filter, two triple mode cavities make up each filter. Where each filter is a five-pole filter, one triple cavity and one dual mode cavity makes up each filter. Two band edge channel filters are operated to produce an asymmetrical filter function response, thereby causing extra transmission zeros to be created and improving the selectivity of the filter out of the passband. The multiplexer is designed for use in satellite communication systems and can have a reduced volume and weight when compared to previous multiplexers without any sacrifice in electrical performance.

Abstract: In accordance with the present invention there is provided a bandpass T filter and power splitter for electromagnetic energy. It is composed of a plurality of resonant elements serially arranged to form a plurality of forward multi-pole bandpass filters. At least one resonant element is common to both signal paths. The common resonant element transfers energy from the common path to the independent signal paths to effect a power split. The two signal output paths are isolated from one another by a multi-pole bandpass filter. The resonant elements may be composed of either resonant waveguide cavities or dielectric resonators.

Abstract: A waveguide filter particularly well suited for use in the millimeter and submillimeter wavelength range of the spectrum. The filter includes a number of uniformly spaced gratings installed in a waveguide section and having grating strip patterns contoured to conform with a selected waveguide mode, such as the circular TE.sub.11 mode. The gratings are angularly oriented in the manner of a free-space plane-wave quasi-optical filter and provide similar desired frequency characteristics, but without the disadvantages of large size and the need for planewave launchers.

Abstract: Cascaded dual-mode resonance cavities are separated by plates having each a cruciform iris therein, the arms of which have lengths determined by a direct and precise procedure starting from a conventional Butterworth prototype filter. The transfer function parameters are altered to change the filter response and the group delay performance is determined and compared to an ideal flat response for producing a penalty function signal from the difference in order to modify the parameters again in such direction that the penalty function signal is likely to be reduced. The process is repeated until the penalty function signal is minimum, whereby a compact structure is realized which provides an attenuation response having sharp cut-off slopes at the edges of the signal bandwidth together with a close to flat in-band group delay response.

Abstract: A structure comprising a cascade of dual mode resonance cavities wherein each cavity has a pair of tuning screws located at 90.degree. to each other in a sectional plane of the cavity and a coupling screw located at 45.degree. to the tuning screws for coupling the two resonances supported by the cavity. Each cavity is coupled to the adjacent cavity by means of a coupling iris set at a determined angle relative to the angular position of the tuning screws of the cavity and the adjacent cavity is positioned at a determined angle relative to the angular position of the coupling iris which couples said cavity to the former one.

Abstract: A stable electromagnetic oscillator (30) comprises an amplifying element (3) in feedback association with a dual mode resonant cavity (12) that provides a double pole bandpass filter function. Two orthogonal modes (1 and 2) of electromagnetic energy resonate within the cavity (12). An output from the amplifying element (3) excitationally couples into the first mode (1), while the second mode (2) couples into the input of the amplifying element (3). The output (8) of the oscillator (30) is obtained from the first mode (1). Optional injection lock can be used for greater stability by means of coupling a stable a.c. reference (9) into the cavity (12) in alignment with the second mode (2). Optional electronic frequency tuning comprises a phase or frequency comparator (11) and a reference a.c. source (13), producing a d.c. feedback signal fed to varactor diodes (10). Coupling ports (4, 5, 6, 7) of the cavity (12) can be, e.g., irises, capacitive probes, coaxial probes, or any combination thereof.

Abstract: A bandpass filter 8 has a plurality of cascaded wave-guide cavities 11, 12 1N and inter-cavity coupling means 36, 37. One or more of the cavities 12, 1N is rotated relative to an input reference mode 52. The rotation causes quasi-orthogonal coupling structures to be introduced into said cavities 11, 12 1N. The rotation of one or more cavities enables symmetric or asymmetric amplitude and phase responses to be produced as desired.The filter can be used in channel multiplexers for satellite communication systems.

Abstract: A receiver for counterclockwise and clockwise circularly polarized microwave signals of the type comprising a receiving antenna with a feeder system, a polarization converter, a polarization filter and a circuit for converting the microwave signals of both polarization directions from the high frequency to the intermediate frequency plane. A portion of the feeder waveguide belonging to the feeder system of the receiving antenna is designed as a bandpass filter which is effective for both polarization directions. A microstripline substrate, which carries the frequency converting circuit, is connected with the output of the feeder waveguide and is provided with an arrangement for coupling in the energies of the waveguide modes of both polarization directions. The polarization converter is either directly integrated in the feeder waveguide or the polarization conversion is effected by coupling the waveguide modes into the microstripline circuit.

Abstract: A waveguide structure carrying microwaves with two mutually orthogonal planes of polarization and in two different frequency bands, transmitted and received by an associated antenna, comprises two orthomode transducers in the form of coaxial cylindrical guide members of different inner diameters, the smaller-diameter transducer terminating in a short-circuiting end wall while the larger-diameter transducer, adjoining same at an annular shoulder, extends to a feed horn confronting a reflector. Each transducer is formed with two elongate peripheral access slots, opening onto respective rectangular-section branches, which are longitudinally bisected by mutually perpendicular axial planes while being relatively offset in axial direction.

Abstract: An intermediate frequency band-pass filter for providing a pass band, comprising a frame forming a hollow surrounded region, a shield plate mounted in the frame and dividing the hollow surrounded region into two spaces, the shield plate having a coupling window, and two resonators disposed respectively in the spaces and coupled through the coupling window, the shield plate having in an edge thereof a step serving as a trap which provides a frequency suppression capability in the vicinity of the pass band of the filter.

Abstract: A ceramic resonator element having high Q, high dielectric constant, and a low temperature coefficient of resonant frequency is enclosed within a cavity to form a composite microwave resonator having reduced dimensions and weight as compared to a simple cavity resonator. A pair of tuning screws extend into the cavity along orthogonal axes to tune the structure to resonance along these axes at frequencies near the fundamental resonance of the ceramic element. Several such cavities can be formed in a short length of waveguide by the use of transverse partitions at spaced intervals and coupling between cavities can be accomplished by using simple slot, cross or circular irises. In each cavity, a mode-perturbing screw is positioned along an axis 45.degree. from each of the orthogonal tuning screws, such that resonance along either of the orthogonal axes is coupled to excite resonance also along the other.

Abstract: In a selective directional coupler composed of two outer waveguides, the outer waveguides are coupled together by an intermediate waveguide disposed between the two outer waveguides, the intermediate guide being constructed and positioned such that at a selected coupling frequency its coupling mode is in phase synchronism with the transmission modes in the two outer waveguides.

Abstract: A dual mode directionally coupled band reject filter apparatus having coaxially aligned first and second cylindrical cavity members which are asymmetrically mounted to the broadwall of a waveguide. Both cylindrical cavity members include a plurality of tuning screws to establish elliptic-type responses.

Abstract: In a temperature-stabilized microwave filter, each resonant cavity (5) is tuned by means of a tuning rod (10) of a thermally stable material. A first end of each tuning rod (10) extends into the respective cavity (5) without touching its surface. A second end is clamped, remotely of the cavity (5), into the filter body (1-2). At the position of this second end the filter body (1-2) has a bore (13) of substantially the same diameter as the tuning rod (10). The tuning rods (10) are clamped by pairs of retaining screws (15) accommodated in clearance holes in the filter body on one side of a longitudinal groove (21) intersecting the bore (13) and anchored into the filter body (1-2) on the other side of the groove (21).

Abstract: A helical cavity resonator filter utilizes varactor tuning diodes positioned within each helical resonator coil. The diodes are positioned along the longitudinal axes of the coils so as not to interfere with the non-axial electromagnetic fields of the cavities associated with each helical resonator coil.

Abstract: An electromagnetic cavity filter (10) is formed by at least two cavities (12) having electrically conductive walls (40, 15). When more than two cavities (12) are employed, their midpoints do not have to be colinear; rather, it is sufficient that the angle formed by the midpoints of any three successively coupled cavities is an integral multiple of 90.degree.. Thus, a folded "engine block" geometry can be realized such that the filter's input cavity (12) is proximate to the output cavity (12). This allows a canonic filter response. Each cavity (12) is the equivalent to two filter poles because two orthogonal modes of electromagnetic radiation can resonate therewithin. Electrically nonadjacent modes of proximate cavities (12), as well as electrically adjacent modes, can be coupled, permitting elliptic filter functions. Electrically nonadjacent modes are coupled by means of an iris (30) opening between the two cavities (12).

Abstract: A method for designing low loss cylindrical TE.sub.011 mode resonators which permits selective placement of a transmission null at a frequency near the TE.sub.011 resonance frequency. The frequencies of the TE.sub.211 and TE.sub.311 modes, that are naturally excited in the resonator, are controlled by the angular displacement of the resonator input port and output port and by the relative amplitude of the TE.sub.011 mode compared to the TE.sub.211 and TE.sub.311 modes. Proper placement of the transmission nulls improves the selectivity of the TE.sub.011 resonator, and/or can be used to filter out unwanted noise at the frequency of the transmission null. A lumped constant analog circuit model is presented to assist in design of the resonator.

Abstract: A dielectric filter module having an open housing which supports screws for adjusting the characteristics of the dielectric filter. The dielectric filter, which includes an elongated dielectric block having internal cavities and a conductive film extending from the exterior surface of the block into the internal cavities, is mounted in an openended metal housing which surrounds three sides of the dielectric filter. Suitable housings can be inexpensively fabricated to the necessary length from segments cut from commercially available channel members having C-shaped or I-shaped cross-sections. Wires extend through the open ends of the housing to connector elements on the surface of the block adjacent its ends. The connector elements can be adhesively secured metal members or locally deposited regions of metallic film. Either threaded holes on the housing or nut members mounted on the housing can be used for supporting the adjustment screws.

Abstract: A dielectric resonator has a sector shape, and a filter has a signal source for emitting signal to be filtered, signal receiver for receiving the filtered signal and a path defined between the signal source and the signal receiver. At least one sector shaped dielectric resonator is disposed in the path.

Abstract: A band-pass filter comprising a shielded housing having a first and a second chamber. First and second quarter-wave resonators are disposed in the first and second chambers, respectively, for coupling with input energy and delivering output energy. First and second parallel-circuit resonators are disposed in the first and second chambers, respectively, to provide interstage coupling between resonators in the respective chambers. Each of the resonators comprises a multilayered coil structure on a finned bobbin juxtaposed on a common insulative substrate so that its coil portions are separately wound on adjacent fins of the bobbin. Each of the quarter-wave resonators has one end being short-circuited by coupling with the housing and the other end being open-circuited. Each of the parallel-circuit resonators includes a capacitor to form a parallel resonance circuit and has one end coupled to one end of the other parallel-circuit resonator at a point outside of the housing.

Abstract: A dielectric filter in which a plurality of holes are made at predetermined intervals in a dielectric block of small dielectric loss, and a conductor film is formed on the surface of the dielectric block including the interior surfaces of the holes to constitute resonators using the conductor film on the interior surface of each hole as an inner conductor of the resonator and the conductive film on the outer peripheral surface of the dielectric block as an outer conductor, the resonance frequency of the resonators being based on the depth of each hole.

Abstract: The relative positions of the cavities in known single or dual mode multiple coupled cavity waveguide bandpass filters are rotated to achieve new filter structures in which the primary cavity couplings remain intact while the secondary couplings are shifted. The cavity rotation provides design flexibility since the input and output ports can now be taken from the same side of the filter structure. An additional advantage in dual mode filters is that the rotation permits the physical separation of input and output cavities, thereby providing increased isolation and eliminating spurious out-of-band coupling.

Abstract: An electric transmission structure for implementing a transfer function with finite real-frequency transmission zeros, which comprises a main body comprised of a plurality of resonant cavities placed adjacent to each other with inductive coupling irises between adjacent cavities, the resonant cavities being arranged symmetrically relative to a plane of conjugate symmetry, said main body synthesizing the linear phase part of the filter transfer function, and at least one pair of pole resonant cavities arranged symmetrically relative to said plane of conjugate symmetry, each of said resonant cavity pairs synthesizing a pair of finite real-frequency transmission zeros of the filter transfer function, with the respective pole cavities of each pair being connected across the input and output ends of the main body through phase-shift waveguides having defined phase-shift lengths.

Abstract: A microwave filter includes a plurality of resonator cavities which are separated by walls and which have respective resonator rods, and trimming caps made of a dielectric substance are fixed to the respective resonator rods.

Abstract: A hyperfrequency filter comprises a series connection of an inlet length of waveguide (1), a plurality n of resonant cavities (3, 4, 5) and an outlet length of waveguide (2). All these units are of rectangular cross-section and they are interconnected by coupling irises (16, 17, 18, 19). Each resonant cavity includes a dielectric tuning screw (13, 14, 15) for adjusting the resonant frequency of the cavity. Each tuning screw is located in the middle of one of the largest faces of its resonant cavity.The longer dimension a of the cross-section of each cavity is longer than the longer dimension of the cross-section of the waveguide lengths so that the optimum width of the coupling irises is substantially at its minimum possible value for a given set of design conditions on the other filter parameters. This has the effect of broadening the range of frequencies over which a given structure can be tuned without detrimental repercussions on the frequency characteristic of the filter.

Abstract: A folded end-coupled general response TE.sub.011 filter is herein described which achieves all bridge couplings necessary for general bandpass response in a particularly convenient two-tier overlapping structure, where all couplings are made in a single removable iris, and where probe and/or slot couplings are used to achieve coupling of either sign.

Abstract: There are herein described evanescent mode filters each of which include a hollow waveguide, wherein a plurality of resonators are disposed, the resonators including loading structures such as tuning screws, for example, wherein at least one of the loading structures is angularly disposed, relative to the axis of the waveguide, with respect to others of the loading structures to reduce the length of the filter and/or to provide internal bridge couplings.

Abstract: In a microwave filter including a plurality of resonator cavities, at least one of the windows between cavities for coupling them is formed near the end portions of the resonance rods in the cavities, and a part of one of the coupling loops for transmitting signals of microwave frequencies is coplanar with the opening thereby to form an attentuation pole capable of abrupt attenuation of any image frequency.

Abstract: A filter for microwaves includes a plurality of resonator cavities each having a housing formed unitarily with a respective resonance rod. The neighbouring resonator cavities are coupled together by means of a coupling window formed in the wall separating the cavities and a coupling loop, and a hole communicating with the coupling window is formed in the bottom plate of the filter.

Abstract: A compact low loss microwave filter is disclosed which utilizes an angular section of a right circular cylindrical cavity at the resonance structure excited in the circular electric TE.sub.0mn mode. The individual sectors may be electrically or magnetically coupled through common walls to obtain various filter characteristics.