Compact Substrate-Integrated Waveguide Filtering Crossover by Embedding CPW Quarter-Wavelength Resonators

A compact substrate-integrated waveguide (SIW) filtering crossover is presented by embedding CPW quarter-wavelength resonators. By fully exploiting the orthogonality of the degenerate TE201 and TE102 modes in an SIW square cavity, cross transmission and excellent isolation can successfully be realized for the two channels. Additionally, with four CPW quarter-wavelength resonators coupled at the central symmetrical plane of the SIW cavity, third-order filtering responses can be implemented for both transmission channels while maintaining an acceptable isolation level. Benefitting from the embedded scheme of CPW resonators, a significant footprint reduction has been achieved for the crossover. A prototype centered at 10 GHz with the ripple-fractional bandwidth of 4.05% is synthesized, designed, fabricated, and tested for demonstration, showing an isolation better than 22.5 dB over the interested band.