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.