Miniaturized Dual-/Tri-/Quad-Band Bandpass Filters Using Perturbed Multimode SIW Cavity

This article presents a design strategy of dual-/tri-/quad-band substrate-integrated waveguide (SIW) bandpass filters (BPFs) based on a single perturbed multimode SIW cavity. By loading metallized vias or slotlines perturbed structures at the center of the proposed SIW cavity, the first four independent adjustable resonant modes of TE101, TE201, TE102, and TE202 modes are achieved. The resonant characteristics of the first four resonant modes are first investigated theoretically and numerically to show the flexibility in multiband BPF design. To demonstrate the design concept, a dual-band filter with flexible controllable center frequencies (CFs), bandwidths, and transmission zeros (TZs) is realized in a single SIW cavity. Then, a triband BPF is implemented by utilizing the proposed single perturbed multimode SIW cavity with a pair of complementary split-ring resonators (CSRRs) excited by TE101 and TE201 modes separately. Finally, by coupling TE101 and TE102 modes in bandstop dual-mode cavities with the resonant modes in perturbed multimode SIW cavity, a quad-band filter can be designed. It is worth mentioning that these three kinds of BPFs are realized using only one single perturbed multimode SIW cavity, which miniaturizes the filter size. These filters are designed, fabricated, and measured, and the measured results agree well with the simulated ones, which verifies the proposed design approach.