Realisation of new single-layer triple-mode substrate-integrated waveguide and dual-mode half-mode substrate-integrated waveguide filters using a circular shape perturbation

A method of ‘mode shifting’ is presented for realisation of triple-mode and dual-mode filters, in which the resonant frequency of one mode is shifted near to the resonant frequency of another mode using a perturbation. To realise a triple-mode filter, a single-layer substrate-integrated waveguide (SIW) square cavity is perturbed by introducing vias at the middle of the structure. This perturbation causes mode shifting of the dominant mode (TE101) near to the next modes (TE102 and TE201). Operation of this triple-mode resonator is analysed and resonant frequencies of the perturbed cavity are obtained theoretically. A triple-mode filter is realised using this resonator and the filter is modelled by a coupling matrix based on the global eigenmodes. Moreover, by using the mode shifting technique, a novel dual-mode bandpass filter with half-mode SIW (HMSIW) structure is presented. Both the triple-mode SIW and dual-mode HMSIW filters are fabricated on a single-layer substrate using a printed circuit board process.