Single-Layer Substrate-Integrated Waveguide Inline Filters With Flexible Transmission Zeros

This letter presents a novel class of single-layer substrate-integrated waveguide (SIW) inline filters with flexible transmission zeros (TZs). The basic structure is an oversized half-mode SIW (HMSIW) rectangular cavity (RC) perturbed by a pair of metallic via-holes or an open-ended slotline. Each perturbed HMSIW RC can provide one pole and two TZs. By changing the distance between the perturbation via-holes or the length of the perturbation slotline, one TZ can be moved either above or below the passband, while the other is always located above the passband. Based on these perturbed HMSIW RCs, two SIW three-pole inline filters are fabricated and measured to validate the design concept.