Compact Ka-band filter applications based on the multiple mode rectangular cavity
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Filters based on multiple mode cavity resonator technique have the advantage of realizing a given filter function in a reduced volume and weight with the drawback of increased complexity. In order to decrease the dependence on electromagnetic analysis software and to gain a better insight on the physics of the structure, the multiple mode single rectangular cavityfilter structure is investigated with an analytical approach. Expressions are obtained for the modal frequency shifts and for the intermodal coupling due to various types of corner cuts. An algorithm is proposed predicting the physical dimensions of thefinal structure given the corresponding coupling matrix. Example designs are realized. The algorithm is able to determine the physical dimensions of the second and third-orderfilters within a few percent. The classical triple mode rectangular cavityfilter structure is altered to form a triplet. The new triplet structure can be arranged to result in either a lower or higher sideband transmission zero. An example Ka-Band design is fabricated with both machining and a novel 3D printing technology. The results are in agreement with the expectations. Thefilter structure is further tailored to allow integration to Ka-Band waveguide output microwave modules without significant increase in the module's volume requirement.