Aperture-backed microstrip line multiple-mode resonator for design of a novel UWB bandpass filter

A novel ultra-wideband (UWB) bandpass filter is proposed, designed and implemented using an aperture-backed microstrip line multiple-mode resonator. With a backside aperture on ground plane, a nonuniform resonator is constructed with the first three resonant modes occurring within the interested UWB band while the parallel coupling between a resonator and two feed lines gets a large enhancement. The designed and fabricated UWB filter exhibits a good UWB passband behavior with insertion loss < 1.0dB and group delay variation < 0.25ns in both theory and experiment.