Dual-to-quad-band evanescent-mode substrate-integrated waveguide band-pass filters

A new design methodology is presented for multi-band evanescent-mode band-pass filters (BPFs) realisation by integrating substrate-integrated waveguide structure with multiple short-circuited irises. The electro magnetic (EM)-behaviour of the distributed-element structure is modelled with the lumped-element equivalent circuit in a wide frequency range. Arbitrary transmission poles (TPs) and transmission zeros (TZs) corresponding to the different irises are characterised. Moreover, a rigorous prescribed filtering function is developed to design dual-band evanescent-mode BPFs in terms of independently tunable TPs and TZs. The proposed structure is reported to not only demonstrate miniaturised high quality-factor dual-band BPFs but also obviate the design challenges of multi-band BPFs below the cut-off frequency. Furthermore, two triple- and quadruple-band evanescent-mode BPFs are experimentally examined for the proposed concept verification.