Miniaturized Dual-Mode Substrate Integrated Waveguide Bandpass Filters With Wide Stopbands Using Mixed-Mode Cavities

This article presents, for the first time, a novel class of miniaturized dual-mode substrate integrated waveguide (SIW) bandpass filters (BPFs) with wide stopbands using mixed-mode cavities (MMCs). The proposed MMCs uniquely support TEM, TE, and folded TE (FTE) modes simultaneously. By exploiting the TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> and FTE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> modes as resonant modes and the TEM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100</sub> mode as a nonresonanting mode, a dual-mode resonator (doublet) exhibiting two poles and two transmission zeros (TZs) is realized. A detailed characterization of the MMCs is provided. Subsequently, a class of miniaturized four-pole SIW BPFs with two flexible TZs is proposed, employing one dual-mode and two single-mode MMCs. By strategically staggering the spurious resonances of the dual- and single-mode MMCs, enhanced stopband performance is achieved. To validate the proposed concept, a four-pole BPF with quasi-elliptic response and two four-pole BPFs with asymmetric responses are designed, fabricated, and measured. The measured results agree well with the simulated ones.