Novel Multi-Stub Loaded Resonators and Their Applications to Various Bandpass Filters

This paper presents a new class of multi-stub loaded resonators with flexibly controlled resonance modes, which are suitable for both tunable and nontunable filter applications. The proposed resonators, modified from a basic tri-mode resonator, include two quad-mode ones and a six-mode one. One of the quad-mode resonators is utilized to design a reconfigurable dual-band filter with tunable lower passband and fixed upper passband. The other quad-mode resonator is applied to design a bandpass filter (BPF) with very high skirt selectivity. The six-mode resonator is suitable for tri-band BPFs with individually controllable passband frequencies and bandwidths. All three circuits are theoretically analyzed and experimentally demonstrated. Comparisons of the measured and simulated results are presented to verify various applications of the resonators.