Planar Dual-Mode Bandpass Filters Using Perturbed Substrate-Integrated Waveguide Rectangular Cavities

Abstract

This article presents a novel class of dual-mode substrate-integrated waveguide (SIW) bandpass filters exploiting perturbed SIW rectangular cavities. By introducing metallized via-holes along the central line of an SIW rectangular cavity, the resonant frequency of TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> mode can be shifted close to that of TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</sub> mode, thus creating a dual-mode resonator. This structure implements a doublet, which provides two poles and one or two transmission zeros (TZs). The pass bandwidth, spurious-free bandwidth, and positions of the TZs can be fully controlled by modifying the length of the perturbation, the side ratio of the rectangular cavity, and the offset of the input/output ports, respectively. Eight two-pole SIW filters are designed and investigated to demonstrate the high design flexibility. Moreover, a four-pole SIW filter with the asymmetric response and a five-pole SIW filter with quasi-elliptic response are designed, fabricated, and measured to describe the extension of the proposed approach to higher order filters.