Compact Hybrid Bandpass Filters Using Substrate-Integrated Waveguide and Stripline Resonators

This article presents a novel class of compact hybrid bandpass filters (BPFs) using substrate-integrated waveguide (SIW) and stripline resonators. As the stripline resonators are inserted between two SIW cavities, they are able to increase the filtering order without occupying any additional area. This is beneficial for circuit miniaturization. To verify the concept, several third-order hybrid filters with various responses are designed by combining a half-wavelength stripline resonator (HWSLR) or a full-wavelength stripline resonator (FWSLR) and two SIW resonators. Their sizes are reduced by more than 33% compared with standard third-order SIW filters. In addition, a class of fourth-order box-like hybrid filters with two flexible transmission zeros (TZs) is also proposed by using the HWSLR and FWSLR simultaneously. Compared with previously reported box-like SIW filters, a size reduction of more than 65% is obtained. Three filter prototypes are fabricated and measured for validation.