Highly-Compact Dual-Band Bandpass Waveguide Filter Based on Cross-Shaped Frequency-Dependent Coupling

This work reports the design of an original class of highly-compact dual-band bandpass filter based on dual-mode waveguide resonators inter-coupled through a novel type of frequency-dependent coupling (FDC). The devised FDC consists of a cross-shaped metallic structure placed in the broad wall of a rectangular waveguide. This FDC produces two additional poles and three extra transmission zeros (TZs). Specifically, each pole is surrounded by a pair of TZs, thus generating a dual-band bandpass filtering response. An equivalent lumped-element circuit model of the proposed FDC is provided to facilitate the filter synthesis process. For validation purposes, electromagnetic-(EM)-simulation results for a third-order dual-band bandpass filter design made up of two dual-mode rectangular waveguide resonators inter-coupled with a cross-shaped FDC are presented.