Design of Wide-Stopband and Dual-Band Filtering Crossovers Based on Mixed Substrate Integrated Waveguide Cavities

This article proposes a new design approach for filtering crossovers featuring wide-stopband and dual-band char-acteristics based on mixed substrate integrated waveguide (SIW) cavities. The degenerate orthogonal modes in multimode full-mode SIW (FMSIW) square cavities are fully exploited as the cross-unit of dual channels for cross-transmission and good iso-lation. By developing proper coupling topology between multiple quarter-mode SIW (QMSIW) cavities and the FMSIW cavity, a compact wide-stopband filtering crossover is presented with more than -20 dB stopband rejection up to 2.11 f(0). In order to construct a dual-band filtering crossover topology which has not been reported before, half-mode SIW (HMSIW) cavities are explored to cooperate with the FMSIW cavity, thus leading to a satisfactory dual-passband crossover response for the first time. To validate the design concept, a wide-stopband and a dual-band filtering crossovers are designed, fabricated, and measured. Results exhibit excellent filtering performance and good channel-to-channel isolations over an ultrawide frequency band.