Compact Bandpass Filter with a Sharp Roll-off Response Using Multi-Path Coupling Scheme of H-Shaped Resonator

This paper develops a compact bandpass filter consisting of a new three-mode H-shaped resonator. Even-and odd-mode resonance conditions of the resonator are first derived analytically, and the behavior of the resonant modes is investigated for a circuit modeling of the filter. Using such a multi-resonance characteristic enables one to express the filter circuit with a multi-path network formed by resonance paths and a direct source/load coupling path, thereby producing multiple transmission zeros. The developed filter shows a three-pole passband response with low insertion loss less than 1 dB and a sharp passband skirt because of four transmission zeros, as well as a relatively wide stopband property in both simulation and measurement results.