Realisation of new single-layer triple-mode substrateintegrated 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 triplemode 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.