Compact customisable bandstop‐bandpass‐bandstop cascaded filter based on substrate integrated waveguide coax cavities

Abstract

This study presents a highly customisable bandpass filter based on standard printed circuit board (PCB) material and process. Such a filter utilises cascaded bandstop-bandpass-bandstop (BS-BP-BS) topology. There is one substrate integrated waveguide (SIW) coax resonator in each bandstop section, whereas there are three SIW coax resonators in the bandpass section. The coax resonators are built by SIW vias, and the resonant frequency of each resonator is determined by the lumped capacitors mounted on the top side of the filter. While the bandpass section of the filter provides a necessary passband response, the bandstop sections that cascade on both sides of the filter introduce an optional notch to the spectrum. Furthermore, with additional sets of plated-through vias purposefully placed between resonators, reconfiguring the bandwidth of the passband is achievable through changing the lumped capacitors mounted on the bottom side of the vias of the filter. Measured results show centre frequency, notch frequency, and bandwidth are individually configurable, and such configurations are very intuitive and predictable. To the best of our knowledge, the proposed design is the first single layer PCB SIW coax filter deploying BS-BP-BS topology that has a configurable centre frequency, flexible 3-dB bandwidth as well as predefine transmission zero.