High-Selectivity Dual-Band Bandpass Filter Using a Quad-Mode Resonator With Source-Load Coupling

This letter presents a novel dual-band bandpass filter with controllable frequencies and bandwidths as well as a high out-of-band rejection level. The proposed filter utilizes a novel stub-loaded quad-mode resonator. Every two modes, which can be flexibly controlled, are utilized to form a passband with controllable frequency and bandwidth. Source-load coupling and hook-shape feed lines are introduced and high selectivity is achieved. An experimental filter is implemented and the experimental results are presented for validation.