Stopband-Improved SIW Triplexer and Triple-Band Filters Using Alternately Cascaded Triple- and Single-Mode Cavities

Stopband-improved substrate-integrated waveguide (SIW) triplexer and triple-band filters are presented based on the novel realization method of coupling topologies composed of common triple-mode resonators coupled with multiple single-mode ones. Thanks to the common triple-mode cavities acting as T-junction proposed in our previous work, the three passbands can be flexibly controlled. The utilization of single-mode cavities not only simplifies the control of internal couplings but also supplies more degrees of freedom to stagger the higher order harmonics for stopband improvement. The implementation methodology for SIW triplexer and triple-band filters is presented and three examples including a third-order triplexer and two third- and fifth-order BPFs are synthesized, designed, fabricated, and tested with excellent performances and compact sizes. Good agreement is realized between the measured and the simulated results.