# Patent

## Title
Dielectric waveguide filter with direct coupling and alternative cross-coupling

## Abstract

A waveguide filter comprising a base block of dielectric material defining at least first and second resonators and a bridge block seated on top of the base block and defining at least a third resonator. In one embodiment, the base block comprises first and second base blocks that have been coupled together in an end to end relationship. An external transmission line or an interior RF signal transmission window or an RF signal transmission bridge provides a cross-coupling RF signal transmission path between the first and second resonators. At least first and second interior RF signal transmission windows provide a direct RF signal transmission path between the first and third resonators and the second and third resonators respectively.

## Background
CROSS REFERENCE TO RELATED AND CO-PENDING APPLICATIONS
This patent application is a continuation-in-part application of, and claims the benefit of the filing date and disclosure of, U.S. patent application Ser. No. 14/088,471 filed on Nov. 25, 2013 and titled “Dielectric Waveguide Filter with Direct Coupling and Alternative Cross-Coupling” and also claims the benefit of the filing date and disclosure of U.S. Provisional Patent Application Ser. No. 61/881,138 filed on Sep. 23, 2013 and titled “Dielectric Waveguide Filter with Direct Coupling and Alternative Cross-Coupling”, the contents of which are entirely incorporated herein by reference as well as all references cited therein.


FIELD OF THE INVENTION
The invention relates generally to dielectric waveguide filters and, more specifically, to a dielectric waveguide filter with direct coupling and alternative cross-coupling.
BACKGROUND OF THE INVENTION
This invention is related to a dielectric waveguide filter of the type disclosed in U.S. Pat. No. 5,926,079 to Heine at al. In which a plurality of resonators are spaced longitudinally along the length of a monoblock and in which a plurality of slots/notches are spaced longitudinally along the length of the monoblock and define a plurality of bridges between the plurality of resonators which provide a direct inductive/capacitive coupling between the plurality of resonators.
The attenuation characteristics of a waveguide filter of the type disclosed in U.S. Pat. No. 5,926,079 to Heine et al. can be increased through the incorporation of zeros in the form of additional resonators located at one or both ends of the waveguide filter. A disadvantage associated with the incorporation of additional resonators, however, is that it also increases the length of the filter which, in some applications, may not be desirable or possible due to, for example, space limitations on a customer's motherboard.
The attenuation characteristics of a filter can also be increased by both direct and cross-coupling the resonators as disclosed in, for example, U.S. Pat. No. 7,714,680 to Vangala et al. which discloses a monoblock filter with both inductive direct coupling and quadruplet cross-coupling of resonators created in part by respective metallization patterns which are defined on the top surface of the filter and extend between selected ones of the resonator through-holes to provide the disclosed direct and cross-coupling of the resonators.
Direct and cross-coupling of the type disclosed in U.S. Pat. No. 7,714,680 to Vangala et al. and comprised of top surface metallization patterns is not applicable in waveguide filters of the type disclosed in U.S. Pat. No. 5,926,079 to Heine et al. which includes only slots and no top surface metallization patterns.
The present invention is thus directed to a dielectric waveguide filter with both direct and optional cross-coupled resonators which allow for an increase in the attenuation characteristics of the waveguide filter without an increase in the length of the waveguide filter or the use of metallization patterns on the top surface of the filter.
SUMMARY OF THE INVENTION
The present invention is directed to a waveguide filter adapted for the transmission of an RF signal and comprising a base block of dielectric material covered with a layer of conductive material and defining at least first and second resonators, a bridge block of dielectric material covered with a layer of conductive material and defining a third resonator, the base block and the bridge block being coupled to each other in a relationship wherein the bridge block bridges the first and second resonators, a first RF signal transmission window defined between the base block and the bridge block and defining a first path for the transmission of the RF signal between the first and third resonators, and a second RF signal transmission window defined between the base block and the bridge block and defining a second path for the transmission of the RF signal between the third resonator and the second resonator.
In one embodiment, the base block defines a longitudinal axis and the first and second RF signal transmission windows are positioned on opposite sides of the longitudinal axis in a relationship spaced and parallel to each other and the longitudinal axis.
In one embodiment, the base block defines a longitudinal axis and the first and second RF signal transmission windows are positioned in a relationship spaced and parallel to each other and normal to the longitudinal axis.
In one embodiment, the base block defines a longitudinal axis and further comprising a third RF signal transmission window defined between the base block and the bridge block and defining a third path for the transmission of the RF signal between the first resonator and the third resonator, the first and third RF signal transmission windows being positioned on opposite sides of the longitudinal axis in a relationship parallel to each other and the longitudinal axis and in a relationship normal to the second RF signal transmission window.
In one embodiment, the base block is comprised of first and second base blocks each covered with a layer of conductive material and joined together in an end to end co-linear relationship and the bridge block bridges the joined ends of the first and second base blocks, the first and second resonators being defined on the first and second base blocks respectively.
The present invention is also directed to a waveguide filter adapted for the transmission of an RF signal and comprising a first block of dielectric material covered with a layer of conductive material and defining at least a first resonator, a second block of dielectric material covered with a layer of conductive material and defining at least a second resonator, a third block of dielectric material covered with a layer of conductive material and defining at least a third resonator, the third block of dielectric material being coupled to and bridging the first and second blocks of dielectric material, a first RF signal transmission window defined between the first block and the third block and defining a first path for the transmission of the RF signal between the first resonator and the third resonator, and a second RF signal transmission window defined between the second block and the third block and defining a second path for the transmission of the RF signal between the third resonator and the second resonator.
In one embodiment, the first and second blocks are joined together in an end to end co-linear relationship and the third block bridges the coupled ends of the first and second base blocks.
In one embodiment, the waveguide filter further comprises an RF signal input/output electrode at one end of each of the first and second blocks, a step defined at the one end of each of the first and second blocks, the RF signal input/output electrode extending through the step, and a slit defined in each of the first and second blocks, the slit in the first block defining the first resonator and a fourth resonator in the first block, and the slit in the second block defining the second resonator and a fifth resonator in the second block, the RF signal input/output electrode and the step being defined in the fourth and fifth resonators respectively, and the third block is located between and spaced from the slits defined in the first and second blocks.
The present invention is further directed to a waveguide filter adapted for transmission of an RF signal and comprising a base block of dielectric material covered with a layer of conductive material and defining at least first and second resonators, a bridge block of dielectric material covered with a layer of conductive material and defining at least a third resonator, the bridge block being stacked on top of the base block in a relationship wherein the bridge block bridges the first and second resonators of the base block, a first interior direct coupling RF signal transmission window defined between the base block and the bridge block and defining a first direct path for the transmission of the RF signal between the first and third resonators, a second interior direct RF signal transmission window defined between the base block and the bridge block and defining a second direct path for the transmission of the RF signal between the second and third resonators, and a first cross-coupling RF signal transmission means defining a first cross-coupling path for the transmission of the RF signal between the first and second resonators.
In one embodiment, the base block is comprised of first and second base blocks each covered with a layer of conductive material and joined together in an end to end and co-linear relationship, the first and second resonators being defined on the first and second base blocks respectively, the first cross-coupling RF signal transmission means comprising a capacitive cross-coupling external transmission line extending between the first and second resonators, the first and second interior direct coupling transmission windows defining first and second capacitive direct coupling RF signal transmission paths.
In one embodiment, the base block is comprised of first and second base blocks each covered with a layer of conductive material and joined together in an end to end and co-linear relationship, the first and second resonators being defined on the first and second base blocks respectively, the first cross-coupling RF signal transmission means comprising a third RF signal transmission window defined between the first and second base blocks and defining a first inductive cross-coupling RF signal transmission path between the first and second resonators, the first and second interior direct coupling transmission windows defining first and second capacitive direct coupling RF signal transmission paths.
In one embodiment, the first cross-coupling RF signal transmission means comprises an RF signal transmission bridge defined in the base block between the first and second resonators and defining a first inductive cross-coupling RF signal transmission path between the first and second resonators, the first and second interior direct coupling transmission windows defining first and second inductive direct coupling RF signal transmission paths.
In one embodiment, the waveguide filter further comprises a third interior direct coupling transmission window defined between the base block and the bridge block and defining a third direct path for the transmission of the RF signal between the first resonator and the third resonator, the first and third interior direct coupling transmission windows defining first and third capacitive direct coupling RF signal transmission paths between the first and second resonators.
Other advantages and features of the present invention will be more readily apparent from the following detailed description of the preferred embodiments of the invention, the accompanying drawings, and the appended claims.



BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the invention can best be understood by the following description of the accompanying FIGURES as follows:
FIG. 1 is an enlarged top perspective view of a dielectric waveguide filter according to the present invention;
FIG. 2 is an enlarged bottom perspective view of the dielectric waveguide filter shown in FIG. 1;
FIG. 3 is an enlarged top perspective view of another embodiment of a dielectric waveguide filter according to the present invention;
FIG. 4 is an enlarged bottom perspective view of the dielectric waveguide filter shown in FIG. 3;
FIG. 5 is an enlarged top perspective view of a further embodiment of a dielectric waveguide filter according to the present invention;
FIG. 6 is an enlarged bottom perspective view of the dielectric waveguide filter shown in FIG. 5;
FIG. 7 is an enlarged top perspective view of yet a further embodiment of a dielectric waveguide filter according to the present invention;
FIG. 8 is an enlarged bottom perspective view of the dielectric waveguide filter according to the present invention;
FIG. 9 is a graph depicting the performance of the dielectric waveguide filter shown in FIGS. 1 and 5; and
FIG. 10 is a graph depicting the performance of the dielectric waveguide filter shown in FIGS. 2 and 7.



DETAILED DESCRIPTION OF THE EMBODIMENTS
FIGS. 1 and 2 depict a five pole embodiment of a waveguide filter 1100 incorporating both direct and alternate cross-coupling/indirect coupling elements in accordance with the present invention.
In the embodiment shown, the waveguide filter 1100 is made from three separate monoblocks or blocks 1101, 1103, and 1105 (i.e., two base blocks 1101 and 1103 and a bridge block 1105) of dielectric material that have been coupled and stacked together in a relationship with the base blocks 1101 and 1103 positioned in an end to end relationship and the block 1105 seated over and bridging and interconnecting the ends and end resonators of the base blocks 1101 and 1103 as described in more detail below.
The monoblock 1101 which, in the embodiment shown is generally parallelepiped-shaped, is comprised of a solid elongate block of suitable dielectric material, such as for example ceramic, and includes opposed longitudinal horizontal surfaces or exterior faces 1102a and 1104a, opposed longitudinal side vertical surfaces or exterior faces 1106a and 1108a, and opposed transverse side vertical end surfaces or exterior end faces or ends 1110a and 1112a. 
The monoblock 1103 which, in the embodiment shown is also generally parallelepiped-shaped, is also comprised of a solid elongate block of suitable dielectric material, such as for example ceramic, and includes opposed longitudinal horizontal surfaces or exterior faces 1102b and 1104b, opposed longitudinal side vertical surfaces or exterior faces 1106b and 1108b, and opposed transverse side vertical surfaces or exterior end faces or ends 1100b and 1112b. 
In the embodiment shown, each of the monoblocks 1101 and 1103 are of the same length, width, and height and each include a pair of resonant sections (also referred to as cavities or cells or resonators or poles) 1114 and 1116 and 1120 and 1122 respectively which are spaced longitudinally and horizontally co-planarly along the length of the respective monoblocks 1101 and 1103. The resonators 1114 and 1116 in the monoblock 1101 are separated from each other by a vertical slit or slot 1124a that is cut into the vertical exterior surface 1106a and, more specifically, is cut into the surfaces 1102a, 1104a, and 1106a of the monoblock 1101. The resonators 1120 and 1122 in the monoblock 1103 are separated from each other by a vertical slit or slot 1124b in the monoblock 1103 that is cut into the vertical exterior surface 1106b and, more specifically, is cut into the surfaces 1102b, 1104b, and 1106b of the monoblock 1103.
The slit 1124a in the monoblock 1101 defines a through-way or pass or bridge 1128 of dielectric material on the monoblock 1101 for the direct coupling and transmission of an RF signal between the resonator 1114 and the resonator 1116. Similarly, the slit 1124b in the monoblock 1103 defines a through-way or pass or bridge 1134 of dielectric material on the monoblock 1103 for the direct coupling and transmission of an RF signal between the resonator 1120 and the resonator 1122.
The monoblock 1101 additionally comprises and defines an end step 1136a comprising, in the embodiment shown, a generally L-shaped recessed or grooved or shouldered or notched region or section of the longitudinal surface 1104a, opposed side surfaces 1106a and 1108a, and end surface or face 1112a of the monoblock 110.
The monoblock 1103 similarly additionally comprises and defines an end step 1136b comprising, in the embodiment shown, a generally L-shaped recessed or grooved or shouldered or notched region or section of the longitudinal surface 1104b, opposed side surfaces 1106b and 1108b, and end surface or face 1112b of the monoblock 1103.
Thus, in the embodiment shown, the respective steps 1136a and 1136b are defined in and by respective end sections or regions 1112a and 1112b of the respective monoblocks 1101 and 1103 having a height less than the height of the remainder of the respective monoblocks 1101 and 1103.
In the embodiment shown, the respective steps 1136a and 1136b each comprise a generally L-shaped recessed or notched portion of the respective end resonators 1114 and 1122 defined on the respective monoblocks 1101 and 1103 which include respective first generally horizontal surfaces 1140a and 1140b located or directed inwardly of, spaced from, and parallel to the surfaces 1104a and 1104b of the respective monoblocks 1101 and 1103 and respective second generally vertical surfaces or walls 1142a and 1142b located or directed inwardly of, spaced from, and parallel to, the respective end faces 1112a and 1112b of the respective monoblocks 1101 and 1103.
Further, and although not shown or described herein in any detail, it is understood that the end steps 1136a and 1136b could also be defined by an outwardly extending end section or region the respective monoblocks 1101 and 1103 having a height greater than the height of the remainder of the respective monoblocks 1101 and 1103.
The monoblocks 1101 and 1103 additionally each comprise an electrical RF signal input/output electrode in the form of respective through-holes 1146a and 1146b which extend through the body of the respective monoblocks 1101 and 1103 and, more specifically, extend through the respective steps 1136a and 1136b thereof and, still more specifically, through the body of the respective end resonators 1114 and 1122 defined in the respective monoblocks 1101 and 1103 between, and in relationship generally normal to, the respective surfaces 1140a and 1140b of the respective steps 1136a and 1136b and the respective surfaces 1102a and 1102b of the respective monoblocks 1101 and 1103.
Still more specifically, respective input/output through-holes 1146a and 1146b are spaced from and generally parallel to the respective transverse end faces 1112a and 1112b of the respective monoblocks 1101 and 1103 and define respective generally circular openings located and terminating in the respective step surfaces 1140a and 1140b and the respective monoblock surfaces 1102a and 1102b respectively.
The respective RF signal input/output through-holes 1146a and 1146b are also located and positioned in and extend through the interior of the respective monoblocks 1101 and 1103 in a relationship generally spaced from and parallel to the respective step wall or surfaces 1142a and 1142b. 
Thus, in the embodiment shown, the through-hole 1146a is positioned between the end face 1112a and the step surface 1142a of the block 1101 and the through hole 1146b is positioned between the end face 1112b and the step surface 1142b of the block 1103. Still further, in the embodiment shown, the steps 1136a and 1136b terminate at a point spaced from and short of the respective slits 1124a and 1124b of the respective blocks 1101 and 1103.
All of the external surfaces 1102a, 1104a, 1106a, 1108a, 1110a, and 1112a of the monoblock 1101, the internal surfaces of the monoblock 1101 defining the slit 1124a, and the internal surface of the monoblock 1101 defining the RF signal input/output through-hole 1146a are covered with a suitable conductive material, such as for example silver, with the exception of the regions described in more detail below.
Similarly, all of the exterior surfaces 1102b, 1104b, 1106b, 1110b, and 1112b of the monoblock 1103, the internal surfaces of the monoblock 1103 defining the slit 1124b, and the internal surface of the monoblock 1103 defining the RF signal input/output through-hole 1146b are covered with a suitable conductive material, such as for example silver, with the exception of the regions described in more detail below.
The monoblocks 1101 and 1103 still further comprise respective RF signal input/output connectors 1400a and 1400b protruding outwardly from the respective openings defined in the respective surfaces 102a and 1102b by the respective through-holes 1146a and 1146b. 
The monoblock or bridge block 1105 which, in the embodiment shown is also generally rectangular in shape, is of the same width and height as the base blocks 1101 and 1103 but has a length that is less than one half the length of each of the blocks 1101 and 1103, is comprised of a suitable solid block of dielectric material, such as for example ceramic, and includes opposed longitudinal horizontal surfaces or exterior faces 1102c and 1104c, opposed longitudinal side vertical surfaces or exterior faces 1106c and 1108c, and opposed transverse side vertical end surfaces or exterior end faces 1110c and 1112c. 
The monoblock 1105 defines a resonant section 1118 (also referred to as a cavity or cell or resonator or pole).
The separate monoblocks 1101 and 1103 are positioned relative to each in an end to end horizontally co-linear and co-planar relationship with the respective end faces or ends 1110a and 1110b thereof located opposite each other and, in the embodiment shown, in a relationship with the respective end faces or ends 1110a and 1110b abutted and coupled/joined to each other; the respective horizontal longitudinal bottom exterior surfaces 1102a and 1102b of the monoblocks 1101 and 1103 are disposed in a horizontal co-planar relationship; the respective horizontal longitudinal top exterior surfaces 1104a and 1104b of the respective monoblocks 1101 and 1103 are disposed in a horizontal co-planar relationship; the respective vertical longitudinal side exterior surfaces 1106a and 1106b of the respective monoblocks 1101 and 1103 are disposed in a vertical co-planar relationship; and the respective vertical longitudinal side exterior surfaces 1108a and 1108b of the respective monoblocks 1101 and 1103 are disposed in a vertical co-planar relationship.
The monoblock 1105 is positioned relative to the blocks 1101 and 1103 in a bridging or overlapping or offset or raised or stacked relationship relative to the base blocks 1101 and 1105 wherein opposed ends of the block 1105 bridge or straddle the ends or faces 1110a and 1110b of the respective blocks 1101 and 1103 and, more specifically, in the embodiment shown, in a relationship wherein the ends of the block 1105 straddle the joined ends of the blocks 1101 and 1103 with one end of the block 1105 overlapping and seated on a portion of the end resonator 1120 of the block 1103 and an opposite end of the block 1105 overlapping and seated on a portion of the end resonator 1116 of the block 1101. Thus, in the embodiment shown, the bottom exterior surface 1102c of the block 1105 is seated against the respective joined end portions of the respective top surfaces 1104a and 1104b of the respective monoblocks 1101 and 1103.
Thus, in the embodiment shown, the blocks 1101 and 1103 comprise base blocks which when coupled together define an elongate parallepiped shaped base block 1500 of dielectric material defining a longitudinal axis L and including opposed, spaced-apart, and parallel horizontal top and bottom exterior faces 1102 (defined by the exterior faces 1102a and 1102b of the respective blocks 1101 and 1103) and 1104 (defined by the exterior faces 1104a and 1104b of the respective monoblocks 1101 and 1103) and extending in the direction of the longitudinal axis L; opposed, spaced-apart, and parallel vertical side exterior surfaces 1106 (defined by the exterior faces 1106a and 1106b of the respective blocks 1101 and 1103) and 1108 (defined by the exterior faces 1108a and 1108b) and extending in the direction of the longitudinal axis L; opposed transverse vertical side end faces 1112a and 1112b (defined by the exterior end faces 1112a and 1112b of the respective blocks 1101 and 1103) extending in a direction normal to and intersecting the longitudinal axis L; opposed end steps 1136a and 1136b (defined by the end steps 1136a and 1136b of the respective blocks 1101 and 1103); slits or slots 1124a and 1124b (defined by the slits or slots 1124a and 1124b of the respective blocks 1101 and 1103) and extending along the length of the base block 1500 in a spaced-apart and parallel relationship relative to each and in a direction and orientation normal to the longitudinal axis L with the slit 1124a located adjacent and spaced from the end face 1112a and the slit 1124b located adjacent and spaced from the opposed end face 1112b; and a centrally located interior layer of conductive material 1520 (defined by the layer of conductive material covering the respective exterior faces 1110a and 1110b of the respective blocks 1101 and 1103) and extending in a direction normal to the longitudinal axis L of the base block 1500.
The combination of the dielectric material of the base block 1500, the slits or slots 1124a and 1124b, and the central interior layer of conductive material define the plurality of resonators 1114, 1116, 1120 and 1122 in the base block 1500 that extend generally co-linearly in the direction of the longitudinal axis L and in which the resonators 1114 and 1116 are coupled by the bridge of dielectric material 1128 therebetween and the resonators 1120 and 1122 are coupled by the bridge of dielectric material 1134 therebetween. The bridges 1128 and 1134 extend in a direction normal to the longitudinal axis L. The interior layer of conductive material 1520 separates the resonators 1114 and of the base block 1101 from the resonators 1120 and 1122 of the base block 1103 and is located between and in a relationship parallel to the respective resonators 1114, 1116, 1120, 1122 and the respective slits or slots 1124a and 1124b. 
In the embodiment shown, the bridge or bridging block 1105 is centrally located on the base block 1500 in a relationship wherein the bridge block 1105 bridges and interconnects the resonator 1116 of the base block 1103 to the resonator of the base block 1101. Specifically, in the embodiment shown, the bridge block 1105 is located centrally over the portion of the base block 1500 including the interior layer of conductive material 1520 in a bridging or overlapping relationship wherein a first half portion of the block 1105 is located on one side of the interior layer of conductive material 1520 and is seated against the exterior surface 1104a of the base block 1101 and the other half portion of the base block 1105 is located on the other side of the Interior layer of conductive material 1520 and is seated against the exterior surface 1104b of the base block 1103.
Further, in the embodiment shown, the vertical exterior side surface 1106c of the bridge block 1105 is vertically co-planar with the vertical exterior side surface 1106 of the base block 1500 (i.e., vertically co-planar with the vertical exterior side surfaces 1106a and 1106b of the respective base blocks 1101 and 1103) and the opposed vertical exterior side surface 1108c of the platform block 1105 is vertically co-planar with the vertical exterior side surface of the base block 1500 (i.e., vertically co-planar with the vertical exterior side surfaces 1108a and 1108b of the respective base blocks 1101 and 1103.
Still further, in the embodiment shown, the bridge block 1105 is centrally located and seated against the top surface 1104 of the base block 1500 between and spaced from the respective slits 1124a and 1124b that are defined in the base block 1500.
Still further, in the embodiment shown, the external transmission line 1700 is seated on the bottom surface 1102 of the base block 1500 (i.e., is seated on and extends between the respective bottom surfaces 1102a and 1102b of the respective joined base blocks 1101 and 1103) in a relationship and position opposed to the bridge block 1105 on the top surface 1104.
In the embodiment shown, the waveguide filter 1100 includes another interior layer of conductive material 1560 located between the base block 1500 and the bridge block 1105 and, more specifically, an interior layer of conductive material 1560 that separates the dielectric material comprising the base block 1500 from the dielectric material comprising the bridge block 1105 and, still more specifically, an interior layer of conductive material 1560 that separates the respective resonators 1116 and 1120 of the respective base blocks 1101 and 1103 from the resonator 1118 of the bridge block 1105.
Thus, in the embodiment shown, and by virtue of the offset, raised, and overlapping position and relationship of the bridge block 1105 relative to the base blocks 1101 and 1103, the bridge block 1105 and the resonator 1118 and pole defined by the bridge block 1105 are positioned in a horizontal plane offset and parallel to the horizontal plane in which the base blocks 1101 and 1103 and the resonators 1114, 1116, 1118, and 1120 and the poles thereof.
The elements for providing direct capacitive coupling and indirect capacitive cross-coupling between the resonators 1114, 1116, 1118, 1120, and 1122 of the waveguide filter 1100 will now be described.
Initially, waveguide filter 1100 comprises a first means for providing a direct capacitive RF signal coupling or transmission between the resonator 1116 of the base block 1101 and the resonator 1118 of the bridge block 1105 and a second means for providing a direct capacitive RF signal coupling or transmission between the resonator 1118 of the bridge block 1105 and the resonator 1120 of the base block 1103 comprising respective interior windows 1560a and 1560b in the interior of the waveguide filter 1100 and, more specifically respective regions 1560a and 1560b in the interior layer of conductive material 1560 located between the base block 1500 (the joined monoblocks 1101 and 1103) and the bridge block 1105 which are devoid of conductive material, i.e., regions of dielectric material in which the dielectric material of the base block 1500 (the dielectric material of the joined monoblocks 1101 and 1103) is in contact with the dielectric material of the bridge block 1105. The windows 1560a and 1560b are located on opposite sides of the interior layer of conductive material 1520.
In the embodiment shown, the internal or interior windows 1560a and 1560b are located in the interior of the waveguide filter 1100 at opposite diagonal corners of the bridge block 1105 to maximize the length of the path of the RF signal through the resonator 1118 defined by the bridge block 1105. In the embodiment shown, the interior windows 1560a and 1560b are both generally rectangular in shape and of the same size and area; extend in the same direction relative to each other, and extend in the same direction as, parallel to, and spaced from, the longitudinal axis L.
Moreover, it is understood that the respective interior windows 1560a and 1560b are defined by respective regions in the exterior layer of conductive material that covers the respective exterior surfaces 1104a, 1104b, and 1102c of the respective blocks 1101, 1103 and 1105 that are devoid of conductive material and which are respectively aligned with each when the blocks 1101, 1103, and 1105 are coupled together to define the respective interior windows 1560a and 1560b. 
The waveguide filter 1100 additionally comprises a means for providing an indirect alternate capacitive cross-coupling or transmission of the RF signal between the resonator 1116 of the base block 1101 and the resonator 1120 of the base block 1103 in the form of an external RF signal transmission strip line 1700 that includes one end 1700a seated against the portion of the exterior surface 1102 of the base block 1500 located on one side of the interior layer of conductive material 1520 (i.e., against the exterior surface 1102a of the monoblock 1101) and an opposite end 1700b seated against the portion of the exterior surface 1102 of the base block 1500 located on the other side of the interior layer of conductive material 1520 (i.e., against the exterior surface 1102b of the monoblock 1103). Although not show, it is understood that each end of the transmission line 1700 includes a capacitive pad located below each respective end of the transmission line 1700 and a metallized via.
In accordance with the invention, an RF signal is transmitted through the waveguide filter 1100 as now described in more detail. Initially, and where the connector 1400a is the RF signal input connector, the RF signal is transmitted initially into the step 1136a and directly through the resonator 1114 of the base block 1500 (the step 1136a and resonator 1114 of the base block 1101); then directly into the resonator 1116 in the base block 1500 (the resonator 1116 in the monoblock 1101) via the direct coupling path d1 through the direct coupling RF signal bridge of dielectric material 1128 defined in the base block 1500 (base block 1101) between the resonators 1114 and 1116; then from the resonator 1116 into the resonator 1120 in the base block 1500 (from the resonator 1116 in the base block 1101 into the resonator 1120 in the base block 1103) via both the capacitive cross-coupling path, generally designated by the arrow c in FIG. 2, and defined by the external transmission line 1700, and the direct capacitive coupling path, generally designated by the arrows d2 and d3 in FIG. 2, and defined by the windows 1560a and 1560b and the bridge block 1105; then from the resonator 1120 into the resonator 1122 and the step 1136b in the base block 1500 (the resonator 1122 and the step 1136b in the base block 1101) via the direct coupling path d4 path provided by the bridge of dielectric material defined between the two resonators 1120 and 1122; and then out through the output connector 1400b. 
Thus, in the embodiment shown, the RF signal transmission and coupling paths d2 and d3 are oriented and extend in a direction generally normal to the coupling paths d1, c, and d4.
The performance of the waveguide filter 1100 is shown in FIG. 9 which shows the notch that is created below the passband as a result of the interaction between the direct coupling and Indirect capacitive cross-coupling elements of the waveguide filter 1100. In the embodiment shown, the RF signal being transmitted directly through the resonators 1114, 1116, 1118, 1120, and 1122 of the waveguide filter 1100 (i.e., through the resonators 1114 and 1116 of the base block 1101, the resonator 1118 of the bridge block 1105, and the resonators 1120 and 1122 of the base block 1103) and the alternate RF signal transmitted between the resonators 1116 and 1120 of the waveguide filter 1100 (i.e., the resonators 1120 and 1122 of the base block 1103) cancel each other at a predetermined frequency located below the passband to create the notch that improves filter rejection.
FIGS. 3 and 4 depict another embodiment of a waveguide filter 2100 in accordance with the present invention in which the majority of the elements thereof are identical in structure and function to the elements in the waveguide filter 1100 except as otherwise described below. As a result, the elements of the waveguide filters 1100 and 2100 which are identical in structure and function have been identified with the same numerals in FIGS. 1, 2, 3 and 4 and thus the earlier description of the structure and function of such elements with respect to the waveguide filter 1100 shown in FIGS. 1 and 2 is incorporated herein by reference with respect to the waveguide filter 2100 shown in FIGS. 3 and 4 except as otherwise discussed below in more detail.
Specifically, the waveguide filter 2100 differs from the waveguide filter 1100 in that the slits 1124a and 1124b defined in the base block 1500 (i.e., the slit 1124a defined in the base block 1101 and the slit 1124b defined in the base block 1103) are located on the opposite sides 1106 and 1108 of the base block 1500 (i.e., on opposite sides 1106a and 1108a of the respective base blocks 1101 and 1103) rather than on the same side 1106 as with the slits 1124a and 1124b of the waveguide 1100.
Additionally, in the waveguide filter 2100, there is not external transmission line 1700. Instead, an interior inductive alternate cross-coupling RF signal transmission line or path, generally designated by the arrow c in FIG. 4, is defined by an internal window or region 1520a in the interior layer of conductive material 1520 of the base block 1500 (the layer of conductive material 1520 between the base blocks 1101 and 1103 that separates the respective resonators 1116 and 1120 thereof) that is devoid of conductive material, i.e., a window or region of dielectric material where the dielectric material of the monoblock 1101 is in contact with the dielectric material of the monoblock 1103.
Stated another way, it is understood that the interior window 1520a is defined by respective regions in the exterior layer of conductive material that covers the respective exterior surfaces 1110a and 1110b of the respective blocks 1101 and 1103 that are devoid of conductive material and which are respectively aligned with each when the blocks 1101 and 1103 are coupled together end to end as described above.
Thus, the path of transmission of the RF signal through the waveguide filter 2100 is identical to the path of transmission of the RF signal through the waveguide filter 1100 and thus the earlier description thereof is incorporated herein by reference except that the transmission of the RF signal between the resonator 1116 of the base block 1101 and the resonator 1120 of the base block 1103 occurs not only via the direct capacitive coupling means described earlier with respect to the waveguide filter 1100 (i.e., the internal windows 1560a and 1560b) but also via indirect inductive cross-coupling (via the internal window 2520a defined in the Interior layer of conductive material 1520 that separates the base blocks 1101 and 1103) rather than the indirect capacitive cross-coupling as in the waveguide filter 1100 through the external transmission line 1700.
The performance of the waveguide filter 2100 is shown in FIG. 10 which shows the notch and RF signal transmission shunt zero that is created above the passband as a result of the interaction between the direct coupling and indirect inductive cross-coupling features of the waveguide filter 2100. In the embodiment shown, the RF signal being transmitted directly through the resonators 1114, 1116, 1118, 1120, and 1122 of the waveguide filter 2100 (i.e., through the resonators 1114 and 1116 of the base block 1101, the resonator of the bridge block 1105, and the resonators 1120 and 1122 of the base block 1103) and the alternate RF signal transmitted between the resonators 1116 and 1120 of the waveguide filter 2100 (i.e., between the resonator 1116 of the base block 1101 and the resonator 1120 of the base block 1103) cancel each other at a predetermined frequency located above the passband to create the notch that improves filter rejection.
FIGS. 5 and 6 show yet a further embodiment of a five pole waveguide filter 3100 in accordance with the present invention.
In the embodiment shown, the waveguide filter 3100 is made from two separate monoblocks or blocks 3101 and 3105 (i.e., a base block 3101 and a bridge block 3105) which have been coupled and stacked together to form the waveguide filter 3100 as described below in more detail.
The monoblock or base block 3101 which, in the embodiment shown is generally parallelepiped-shaped, is comprised of a suitable solid block of dielectric material, such as for example ceramic, and includes opposed longitudinal horizontal exterior surfaces 3102 and 3104 extending in the direction of the longitudinal axis L, opposed longitudinal side vertical exterior surfaces 3106 and 3108 extending in the direction of the longitudinal axis L, and opposed transverse side vertical exterior end surfaces or faces 3112a and 3112b extending in a direction normal to the longitudinal axis L.
The monoblock 3101 includes a plurality of resonant sections (also referred to as cavities or cells or resonators or poles) 3114, 3116, 3120, and 3122 that are spaced longitudinally along the length and longitudinal axis L of the monoblock 3101. The resonators 3114 and 3116 are separated from each other by a vertical slit or slot 3124a that is cut into the vertical exterior surface 3106 and, more specifically, is cut into the surfaces 3102, 3104, and 3106 of the monoblock 3101. The resonators 3116 and 3120 are separated from each other by a vertical slit or slot 3124b that is cut into the vertical exterior surface 3106 and, more specifically, is cut into the surfaces 3102, 3104, and 3106. The resonators 3120 and 3122 are separated from each other by a vertical slit or slot 3124c that is cut into the vertical exterior surface 3106 and, more specifically, is cut into the surfaces 3102, 3104, and 3106 of the monoblock 3101.
The slit 3124a defines a through-way or pass or bridge 3128 of dielectric material on the monoblock 3101 for the direct coupling and transmission of an RF signal between the resonator 3114 and the resonator 3116. Similarly, the slit 3124b defines a through-way or pass or bridge 3134 of dielectric material on the monoblock 3101 for the direct coupling and transmission of an RF signal between the resonator 3116 and the resonator 3120 and the slit 3124c defines a through-way or pass or bridge 3135 of dielectric material on the monoblock 3101 for the direct coupling and transmission of an RF signal between the resonator 3120 and 3122.
The slits 3124a, 3124b, and 3124c and the respective bridges 3128, 3134, and 3135 extend in a direction normal to the longitudinal axis L of the base block 3101. The slit 3124a is located adjacent and spaced from the end step 3136a and end face 3112a, the slit 3124c is located adjacent and spaced from the opposed end step 3136b and end face 3112b, and the slit 3124b is centrally located between and spaced from the slits 3124a and 3124c. 
The monoblock 3101 additionally comprises and defines first and second opposed end steps 3136a comprising, in the embodiment shown, respective generally L-shaped recessed or grooved or shouldered or notched end regions or sections of the longitudinal surface 3102, opposed side surfaces 3106 and 3108, and respective side end surfaces 3112a and 3112b of the monoblock 3101
Stated another way, in the embodiment shown, the respective end steps 3136a and 3136b are defined in and by respective opposed end sections or regions of the monoblock 3101 having a height less than the height of the remainder of the monoblock 3101.
Stated yet another way, in the embodiment shown, the respective steps 3136a and 3136b each comprise a generally L-shaped recessed or notched portion of the respective end resonators 1114 and 1122 which include respective first generally horizontal surfaces 3140a and 3140b located or directed inwardly of, spaced from, and parallel to the horizontal exterior surface 3104 of the monoblock 3101 and respective second generally vertical surfaces or walls 3142a and 3142b located or directed inwardly of, spaced from, and parallel to, the respective side vertical exterior end surfaces 3112a and 3112b of the monoblock 3101.
Further, and although not shown or described herein in any detail, it is understood that the end steps 3136a and 3136b could also be defined by respective outwardly extending end sections or regions of the monoblock 3101 having a height greater than the height of the remainder of the monoblock 3101.
The monoblock 3101 additionally comprises a pair of electrical RF signal input/output electrodes in the form of respective through-holes 3146a and 3146b which extend through the body of the monoblocks 3101 and, more specifically, extend through the respective steps 3136a and 3136b thereof and, still more specifically, through the body of the respective end resonators 3114 and 3122 defined in the monoblock 3101 between, and in relationship generally normal to, the respective surfaces 3140a and 3140b of the respective steps 3136a and 3136b and the surface 3102 of the monoblock 3101 and further in a direction generally normal to the longitudinal axis L of the base block 3101.
Still more specifically, respective input/output through-holes 3146a and 3146b are spaced from and generally parallel to the respective transverse side end surfaces 3112a and 3112b of the monoblock 3101 and define respective generally circular openings located and terminating in the respective step surfaces 3140a and 3140b and the monoblock surface 3102.
Thus, in the embodiment shown, the through-hole 3146a is positioned between the end face 3112a and the step surface 3142a and the through hole 3146b is positioned between the end face 3112b and the step surface 3142b. Still further, in the embodiment shown, the steps 3136a and 3136b terminate at a point spaced from and short of the respective slits 3124a and 3124b. 
The respective RF signal input/output through-holes 3146a and 3146b are also located and positioned in and extend through the interior of the monoblock 3101 in a relationship generally spaced from and parallel to the respective step wall or surfaces 3142a and 3142b. 
All of the external surfaces 3102, 3104, 3106, 3108, 3112a, and 3112b of the monoblock 3101, the internal surfaces of the monoblock 3101 defining the respective slits or slots 3124a, 3124b, and 3124c, and the internal surface of the monoblock 3101 defining the respective RF signal input/output through-hole 3146a and 3146b are covered with a suitable conductive material, such as for example silver, with the exception of the regions described in more detail below.
The monoblock 3101 still further comprises respective RF signal input/output connectors 3400a and 3400b protruding outwardly from the respective openings 3147a and 3147b defined in the surface 3102 by the respective through-holes 3146a and 3146b. 
The bridge block 3105 which, in the embodiment shown is generally rectangular in shape, is of the same width and height as the base block 3101 but less one fourth the length of the base block 3101, and is comprised of a suitable solid block of dielectric material, such as for example ceramic, includes opposed longitudinal horizontal exterior surfaces 3102c and 3104c extending in the direction of the longitudinal axis L, opposed longitudinal side vertical exterior surfaces 3106c and 3108c extending in the direction of the longitudinal axis L, and opposed transverse side vertical exterior end surfaces 3110c and 3112c extending in a direction normal to the longitudinal axis L.
The bridge block 3105 defines a resonant section 3118 (also referred to as a cavity or cell or resonator or pole).
The bridge block 3105 is coupled to and stacked on top of the base block in a relationship centrally located on the base block 3101 and overlying the central slit 3124b and, more specifically, in a relationship wherein a first half portion of the bridge block 3015 and the resonator 3118 defined thereby is positioned in a relationship overlapping and seated on a portion of the resonator of the base block 3101 and a second half portion of the bridge block 3105 and the resonator 3118 defined thereby is positioned in a relationship overlapping and seated on a portion of the resonator 3116 of the base block 3101. Thus, in the embodiment shown, the exterior surface 3102c of the bridge block 3105 is coupled to and seated against the top surface 3104 of the base block 3101.
Further, in the embodiment shown, the bridge block 3105 is coupled to the base block 3101 in a relationship wherein the vertical exterior side surface 3106c of the base block 3105 is vertically co-planar with the vertical exterior side surface 3106 of the base block 3101 and the opposed vertical exterior side surface 3108c of the bridge block 3105 is vertically co-planar with the vertical exterior side surface 3108 of the base block 3101.
Still further, in the embodiment shown, the bridge block 3105 is centrally located and seated against the top surface 3104 of the base block 3101 in a relationship and position wherein the bridge block 3105 is located between and spaced from the slits 3124a and 3124c and is seated over the central slit 3124b and central RF signal transmission bridge 3134.
In the embodiment shown, the waveguide filter 3100 includes an interior layer of conductive material 3560 located between the base block 3101 and the bridge block 3105 and, more specifically, an interior layer of conductive material 3560 that separates the dielectric material comprising the base block 3101 from the dielectric material comprising the bridge block 3105 and, still more specifically, an interior layer of conductive material 3560 that separates the resonator 1118 of the bridge block 3105 from the resonators 3116 and 3120 of the base block 3101.
The elements for providing direct capacitive coupling, inductive direct coupling, and inductive cross-coupling between the resonators 3114, 3116, 3118, 3120, and 3122 of the waveguide filter 3100 will now be described in more detail.
Initially, waveguide filter 3100 comprises a first means for providing a direct capacitive RF signal coupling or transmission between the resonator 3116 of the base block 3101 and the resonator 3118 of the bridge block 3105 and a second means for providing a direct inductive RF signal coupling or transmission between the resonator 3118 of the bridge block 3105 and the resonator 3120 of the base block 3101 comprising respective interior windows 3560a and 3560b and an interior window 3560c in the interior of the waveguide filter 3100 and, more specifically respective regions 3560a, 3560b, and 3560c in the layer of conductive material 3560 which are devoid of conductive material, i.e., regions of dielectric material in which the dielectric material of the base block 3101 is in contact with the dielectric material of the bridge block 3105.
Moreover, it is understood that the respective interior windows 3560a, 3560b, and 3560c are defined by respective regions in the exterior layer of conductive material covering the respective exterior surfaces 3104 and 3102c of the respective blocks 3101 and 3105 that are devoid of conductive material and which are respectively aligned with each other when the bridge block 3105 is coupled to the base block 3101 during the assembly of the waveguide filter 3100.
In the embodiment shown, the internal windows 3560a and 3560b that provide and define a capacitive direct coupling RF signal transmission path are: generally rectangular in shape; defined and located in the region of the interior layer of conductive material 3560 overlying the resonator 3116 of the base block 3101; are both positioned on the same side as and in a relationship spaced and generally normal to the central slit 3124b of the base block 3101; and positioned on opposites sides of and spaced from and generally parallel to the longitudinal axis L of the base block 3101. Thus, in the embodiment shown, the internal window 3560a is located between, and in relationship spaced from and generally parallel to, the external longitudinal surface 3106 and the longitudinal axis L of the base block 3101; and the internal window 3560b is located between, and in a relationship spaced from and generally parallel to, the opposed longitudinal surface 3108 and the longitudinal axis L of the base block 3101.
In the embodiment show, the internal window 3560c that provides and defines an inductive direct coupling RF signal transmission path is: generally rectangular in shape; defined and located in the region of the interior layer of conductive material 3560 overlying the resonator 3120 of the base block 3101; positioned on the opposite side of and in a relationship spaced and generally parallel to the central slit 3124b of the base block 3101; positioned in a relationship normal to and intersecting the longitudinal axis L of the base block 3101; and is positioned and direction generally normal to the direction of the internal windows 3560a and 3560b. 
In accordance with the invention, an RF signal is transmitted through the waveguide filter 3100 as now described in more detail.
Initially, and where the connector 3400a is the RF signal input connector, the RF signal is transmitted initially into the step 3136a and directly through the resonator 3114 of the base block 3101; then directly into the resonator 1116 in the base block 3101 via the direct coupling path d1 and through the direct coupling RF signal bridge of dielectric material 3128 defined in the base block between the resonators 3114 and 3116; then from the resonator 3116 of the base block 3101 into the resonator 3118 in the bridge block 3105 via and through the pair of direct capacitive coupling paths d2 defined by the respective interior RF signal transmission window 3560a and 3560b and also from the resonator 3316 of the base block into the resonator 3120 of the base block 3101 via the Inductive cross-coupling path c defined by the RF signal bridge of dielectric material 3134 defined in the base block 3101 between the resonators 3116 and 3120; then also from the resonator 3118 of the bridge block 3105 and into the resonator 3116 of the base block 3101 via and through the Inductive direct coupling path d3 defined by the Interior RF signal transmission window 3560c; then into the resonator 3114 via the direct coupling path d4 and through the direct coupling RF signal bridge of dielectric material 3135 defined in the base block 3101 between the resonators 3120 and 3122; and then into the step 1136b in the base block 3101; and then out through the output connector 1400b. 
Thus, in the embodiment shown, and by virtue of the offset, raised, bridging relationship of the bridge block 3105 relative to the base block 3101, the bridge block 3105 and the resonator 3118 thereof are positioned in a relationship and horizontal plane that is offset and parallel to the horizontal plane in which the base block 3101 and the resonators 3114, 3116, 3120, and 3122 thereof and further the RF signal transmission and coupling paths d2 and d3 are oriented and extend in a direction generally normal to the coupling paths d1, c, and d4.
The performance of the waveguide filter 3100 is shown in FIG. 9 which shows the notch and RF signal transmission shunt zero that is created below the passband as a result of the transmission of the RF signal through the base block 3101, the bridge block 3105, and internal RF signal transmission windows 3560a, 3560b, and 3560c as described above.
FIGS. 7 and 8 depict another embodiment of a waveguide filter 4100 in accordance with the present invention in which the majority of the elements thereof are identical in structure and function to the elements of the waveguide filter 4100 except as otherwise described below. As a result, the elements of the waveguide filters 3100 and 4100 which are identical in structure and function have been identified with the same numerals in FIGS. 5, 6, 7, and 8 and thus the earlier description of the structure and function of such elements with respect to the waveguide filter 3100 shown in FIGS. 5 and 6 is incorporated herein by reference with respect to the waveguide filter 4100 shown in FIGS. 7 and 8 except as otherwise discussed below in more detail.
Specifically, the waveguide filter 4100 differs in structure from the waveguide filter 3100 only in that the direct coupling between the resonators 3116 and 3120 of the base block 3101 and the resonator 3118 of the bridge block 3105 is provided via direct inductive coupling paths d2 and d3 defined by a pair of internal generally parallel windows 4560a and 4560b, rather than three internal windows 3560a, 3560b, and 3560c as in the waveguide filter 3100, that have been arranged and positioned in the interior of the waveguide filter 4100 as described in more detail below.
Still more specifically, waveguide filter 4100 comprises a first means for providing a direct RF signal coupling or transmission between the resonator 3116 of the base block 3101 and the resonator 3118 of the bridge block 3105 and a second means for providing a direct RF signal coupling or transmission between the resonator 3118 of the bridge block 3105 and the resonator 3120 of the base block 3101 in the form of respective interior windows 4560a and 4560b in the interior of the waveguide filter 4100 and, more specifically respective regions 4560a and 4560b in the interior layer of conductive material located between the base block 3101 and the bridge block 3105 which are devoid of conductive material, i.e., regions of dielectric material in which the dielectric material of the base block 3101 is in contact with the dielectric material of the bridge block 3105.
Moreover, it is understood that the respective interior windows 4560a and 4560b are defined by respective regions in the exterior layer of conductive material covering the respective exterior surfaces 3104 and 3102c of the respective blocks 3101 and 3105 that are devoid of conductive material and which are respectively aligned with each other when the bridge block 3105 is coupled to the base block 3101 during the assembly of the waveguide filter 4100.
In the embodiment shown, the internal window 4560a is: generally rectangular in shape; defined and located in the region of the interior layer of conductive material 3560 overlying the resonator 3116 of the base block 3101; positioned on one side of and in a relationship spaced and generally parallel to the central slit 3124b of the base block 3101; and positioned in a relationship generally normal to and intersecting the longitudinal axis L of the base block 3101.
In the embodiment shown, the internal window 4560b is: generally rectangular in shape; defined and located in the region of the interior layer of conductive material 3560 overlying the resonator 3120 of the base block 3101; positioned on the other side of and in a relationship spaced and generally parallel to the central slit 3124b of the base block 3101; positioned in a relationship generally normal to and Intersecting the longitudinal axis L of the base block 3101; and positioned in a relationship spaced and parallel to the internal window 4560a. 
In accordance with the invention, an RF signal is transmitted through the waveguide filter 4100 as now described in more detail.
Initially, and where the connector 3400a is the RF signal input connector, the RF signal is transmitted initially into the step 3136a and directly through the resonator 3114 of the base block 3101; then directly into the resonator 1116 in the base block 3101 via the direct coupling path d1 and through the direct coupling RF signal bridge of dielectric material 3128 defined in the base block 3101 between the resonators 3114 and 3116; then from the resonator 3116 of the base block 3101 into the resonator 3118 in the bridge block 3105 via and through the direct inductive coupling path d2 defined by the interior RF signal transmission window 4560 and also into the resonator 3120 via the inductive cross-coupling path c defined by the RF signal bridge of dielectric material 3134 defined in the base block 3101 between the resonators 3116 and 3120; then also from the resonator 1118 of the bridge block 3105 and into the resonator 3116 of the base block 3101 via and through the direct inductive coupling path d3 defined by the interior RF signal transmission window 4560b; then into the resonator 3114 via the direct coupling path d4 and through the direct coupling RF signal bridge of dielectric material 3135 defined in the base block 3101 between the resonators 3120 and 3122; and then into the step 1136b in the base block 3101; and then out through the output connector 1400b. 
The performance of the waveguide filter 4100 is shown in FIG. 10 which shows the notch and RF signal transmission shunt zero that is created above the passband as a result of the transmission of the RF signal through the base block 3101, the bridge block 3105, and internal RF signal transmission windows 4560a and 4560b as described above.
While the invention has been taught with specific reference to the embodiment shown, it is understood that a person of ordinary skill in the art will recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. The described embodiments are to be considered in all respects only as illustrative and not restrictive.
For example, it is understood that the invention encompasses other waveguide filter embodiments in which for example: the base blocks include no steps; the base blocks include additional slits; the bridge block includes slits; the base blocks and/or bridge blocks are of different configuration, shape, size, length, width, or height; the waveguide filter includes additional base and/or bridge blocks; and in which the size, configuration, location, orientation, and number of internal RF signal transmission windows is varied depending upon the particular application or desired performance.

## Claims

1. A waveguide filter adapted for transmission of RF signal and comprising:
a base block of dielectric material covered with a first layer of conductive material and defining first and second resonators;
a bridge block of dielectric material covered with a second layer of conductive material and defining a third resonator, the base block and the bridge block being coupled to each other in a relationship wherein the bridge block bridges the first and second resonators;
a first RF signal transmission window defined between the base block and the bridge block and defining a first path for the transmission of the RF signal between the first and third resonators; and
a second RF signal transmission window defined between the base block and the bridge block and defining a second path for the transmission of the RF signal between the third resonator and the second resonator,
wherein the base block defines a longitudinal axis and the first and second RF signal transmission windows are positioned on opposite sides of the longitudinal axis in a relationship spaced and parallel to each other and the longitudinal axis.

2. A waveguide filter adapted for transmission of an RF signal and comprising:
a base block of dielectric material covered with a first layer of conductive material and defining first and second resonators;
a bridge block of dielectric material covered with a second layer of conductive material and defining a third resonator, the bridge block being stacked on top of the base block in a relationship wherein the bridge block bridges the first and second resonators of the base block;
a first interior direct coupling RF signal transmission window defined between the base block and the bridge block and defining a first capacitive direct coupling path for the transmission of the RF signal between the first and third resonators;
a second interior direct RF signal transmission window defined between the base block and the bridge block and defining a second capacitive direct coupling path for the transmission of the RF signal between the second and third resonators;
the base block being comprised of first and second base blocks joined together in an end to end and co-linear relationship, the first and second resonators being defined on the first and second base blocks respectively a capacitive cross-coupling external transmission line extending between the first and second resonators.

3. waveguide filter adapted for transmission of an RF signal and comprising:
a base block of dielectric material covered with a first layer of conductive material and defining first and second resonators;
a bridge block of dielectric material covered with a second layer of conductive material and defining a third resonator, the bridge block being stacked on too of the base block in a relationship wherein the bridge block bridges the first and second resonators of the base block;
first interior direct coupling RE signal transmission window defined between the base block and the bridge block and defining a first direct path for the transmission of the RF signal between the first and third resonators;
a second interior direct RF signal transmission window defined between the base block and the bridge block and defining a second direct path for the transmission of the RF signal between the second and thing resonators;
the base block being comprised of first and second base blocks joined together in an end to end and co-linear relationship, the first and second resonators being defined on the first and second base blocks respectively, the first cross-coupling RF signal transmission means comprising a third RF signal transmission window defined between the first and second base blocks and defining a first in cross-coupling RF signal transmission path between the first and second resonators, the first and second interior direct coupling transmission windows defining first and second capacitive direct coupling RF signal transmission paths.

4. A waveguide transmission of an RF siqnal and comprising:
a base block of dielectric material covered with a first layer conductive material and defining first and second resonators:
a bridge block of dielectric material covered with a second layer of conductive material and defining a third resonator, the base block and the bridge block being coupled to each other in a relationship wherein the bridge block bridges the first and second resonators:
a first RF signal transmission window defined between the base block and the bridge block and defining a first path for the transmission of the RF signal between the first and third resonators; and
a second RF signal transmission window defined between the base block and the bridge block and defining a second path for the transmission of the RF signal between the third resonator and the second resonator,
the base block defining a longitudinal axis and further comprising a third RF signal transmission window defined between the base block and the bridge block and defining a third path for the transmission of the RF signal between the first resonator and the third resonator, the first and third RF signal transmission windows being positioned on opposite sides of the longitudinal axis in a relationship parallel to each other and the longitudinal axis and in a relationship normal to the second RF signal transmission window.

5. A waveguide filter adapted for transmission of an RF signal and comprising:
a base block of dielectric material covered with a first layer of conductive material and defining first and second resonators;
a bridge block of dielectric material covered with a second layer of conductive material and defining a third resonator, the bridge block being stacked on to of the base block in a relationship wherein the bridge block bridges the first and second resonators of the base block;
a first interior direct coupling RF signal transmission window defined between the base block and the bridge block and defining a first direct path for the transmission of the RF signal between the first and third resonators;
a second interior direct RF signal transmission window defined between the base block and the bridge block and defining a second direct path for the transmission of the RF signal between the second and third resonators;
a first cross-coupling path for the transmission of the RF signal between the first and second resonators; and
a third interior direct coupling transmission window defined between the base block and the bridge block and defining a third direct path for the transmission of the RF signal between the first resonator and the third resonator, the first and third interior direct coupling transmission windows defining first and third capacitive direct coupling RF signal transmission paths between the first and second resonators.

6. A waveguide filter adapted for transmission of an RF signal and comprising:
a first block of dielectric material covered with a first layer of conductive material and defining a first resonator;
a second block of dielectric material covered with a second layer conductive material and defining a second resonator;
a third block of dielectric material covered with a third layer of conductive material and defining a third resonator, the third block of dielectric material being coupled to and bridging the first and second blocks of dielectric material;
a first RF signal transmission window defined between the first block and the third block and defining a first path for the transmission of the RF signal between the first resonator and the third resonator;
a second RF signal transmission window defined between the second block and the third block and defining a second path for the transmission of the RF signal between the third resonator and the second resonator,
an RF signal input/output electrode at one end of each of the first and second blocks;
a step defined at the one end of each of the first an second blocks, the RF signal input/output electrode at each of the one ends extending through the respective step; and
a slit defined in each of the first and second blocks, the slit in the first block defining first resonator and a fourth resonator in the first block, and the slit in the second block defining the second resonator and a fifth resonator in the second block, each of the RF signal input/output electrodes and each of the steps being defined in the fourth and fifth resonators of first and second blocks respectively and the third block is located between and space from each of the respective slits defined in the first and second blocks.