Substrate Integrated Waveguide Filter With Flexible Mixed Coupling

This article investigates flexibly using mixed coupling in substrate integrated waveguide (SIW) filters to efficiently improve selectivity. To this end, a mixed coupling structure is proposed, which can be used as a universal coupling module to efficiently produce transmission zeros (TZs) in an inline/conventional SIW filter without degrading the superiority of SIW. On this basis, a trisection with mixed cross-coupling is further proposed, which encloses all the structures inside two general SIW cavities and can be used as a universal cavity module to efficiently produce a quasi-elliptic response in an inline/conventional SIW filter without degrading the superiority of SIW. Three prototypes are designed, fabricated, and measured, and the results agree with the expectations well. The proposed techniques should facilitate the development of high-performance SIW filters in microwave/wireless circuits and systems.