Folded Evanescent-Mode Ridge Waveguide Bandpass Filters

Modeling and design of folded evanescent-mode ridge waveguide bandpass filters are presented. The filter structure is decomposed into the cascade connection of empty-to-ridge waveguide discontinuities. The generalized scattering matrix of the empty-to-ridge waveguide discontinuity is obtained using mode matching method, from which the filter response can be obtained using cascading procedure. The folded coupling junction is ridged to achieve the required coupling value. A filter example is presented to verify the design approach.