Compact Tri-Band SIW Bandpass Filters With High Selectivity and Controllable Center Frequencies Using Perturbation Structure

In this brief, two compact tri-band substrate integrated waveguide (SIW) bandpass filters (BPFs) with high selectivity and controllable center frequencies are presented based on the proposed tri-mode SIW resonant cavity perturbed by metallized vias. The resonant characteristics of the tri-mode SIW cavity are first analyzed, and the impacts of some key parameters on the resonant frequency are comparatively analyzed to further elucidate the flexible controlling of the vias perturbated SIW cavity structure. For demonstrating the superiority of the proposed tri-mode SIW cavity, a prototype of tri-band SIW BPF, centered at 11.18, 12.61 and 13.33GHz, is designed using one-layer substrate. In order to further reduce the occupied size, a tri-band SIW BPF with controllable center frequencies of 11.93, 13.21 and 14.12GHz, is constructed based on electric and magnetic coupling structure using two layers substrates. Both of the proposed tri-band BPFs exhibit six transmission zeros (TZs), resulting in good out-of-band rejections. The measured results agree well with the simulated ones.