A single-layer substrate integrated waveguide (SIW) is developed to design a dual-band band-pass filter (BPF) operating below the cut-off frequency of the SIW, known as evanescent-mode excitation. Gap-coupled excitation is used to demonstrate multiple transmission poles (TPs) and transmission zeros (TZs) below the cut-off frequency of the SIW. The structure is reported to realize two independent evanescent-mode poles on a single-layer SIW which reduces the size and complexity of the structure compared to those of the recent multi-layer evanescent-mode structures. Lumped-element equivalent circuit is employed to describe the EM behavior of the structure for TZs and TPs realization. A compact single-layer dual-band SIW filter is fabricated based on the proposed structure. A good agreement is reported between the measured and simulated performances.
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