Reconfigurable bandpass filter with very high skirt selectivity using lumped element dual-behavior resonators

A reconfigurable bandpass filter (BPF) with two filter states is presented. Each state exhibits very high skirt selectivity by using lumped element dual-behavior resonators to realize multiple transmission zeros (TZs). The dual-behavior resonators in the series branches define the TZs at the upper passband edges and the dual-behavior resonators in the shunt branches define the TZs at the lower passband edges. The single state filter is first realized on a PCB board using SMD components. The measured results show a very sharp cut-off response with a bandwidth of 19.2% at the center frequency of 676.5 MHz. Then the reconfigurable BPF is demonstrated. Two filter states with bandwidths of around 18% are realized with adjacent passbands and very high skirt selectivity.