Wide-Stopband Substrate-Integrated Waveguide Filtering Crossovers With Flexibly Allocated Channel Frequencies and Bandwidths

Substrate-integrated waveguide (SIW) filtering crossovers featuring wide-stopband characteristics and flexibly allocated center frequencies (CFs) and bandwidths (BWs) for two intersecting channels are presented and studied. The development is devised upon a scheme of an over-mode dual-mode substrate-integrated rectangular cavity (SIRC) coupled with multiple single-mode cavities. First, by exploiting the orthogonal TE
₁₀₂
and TE
₂₀₁
modes in the dual-mode SIRC, cross transmission and acceptable isolation can be obtained and implemented for the dual channels. Furthermore, by controlling the resonant frequencies and mutual couplings of the coupled cavities accordingly, especially the over-mode dual-mode SIRC, both the CFs and BWs of the two channels can be allocated flexibly. In addition, by incorporating three kinds of intrinsic spurious-mode suppression techniques, namely, the harmonic staggered technique, centered coupling windows, and offset centered feeding ports, wide-stopband characteristics can be achieved intrinsically and uniquely. Four practical design examples, including fifth-order direct-coupled and fifth-order cross-coupled SIW filtering crossovers with identical channel CFs and BWs, a third-order crossover with the same channel CFs but different channel BWs and another third-order case with different channel CFs but the same channel BWs are synthesized, designed, fabricated, and tested to demonstrate and validate the proposed collaborative design concepts.