A new full-wave method for the design and realization of dual-mode circular waveguide filters is presented. The rigorous CAD is a combination of the mode-matching and the finite-element techniques, which permits obtaining the Generalized Scattering Matrix for all the blocks that compose the structure (rectangular slots, cross-irises, and screws). The finite thickness of the irises, the higher order mode interaction, as well as the coupling and tuning screws are rigorously taken into account. A systematic design process for the different elements is described. A full prediction of resonant out-of-band spurious modes is accomplished prior to the filter construction. Special attention is devoted to the circuital model in order to save a great deal of computational effort in the final adjustment. A four-pole elliptic circular waveguide cavity filter has been designed and constructed. The experimental filter results show excellent agreement with theory.
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