Miniaturized Dual-band Bandstop Filter based on Parallel Connected SAW Resonators

In this paper, a dual-band bandstop filter (DBBSF) topology based on parallel-connected surface acoustic wave (SAW) resonators is proposed. Series resonators and parallel resonators generate transmission zeros (TZs) at their anti-resonant frequency and resonant frequency, respectively. By connecting two resonators with different frequencies in parallel, a miniaturized dual-bandstop unit is realized. The dual-bandstop unit is analyzed, and it is demonstrated that the bandwidth and isolation of each band can be independently controlled by adjusting the parallel resonators. Multiple dual-bandstop units are cascaded to design and implement higher-order DBBSFs. The matching of the DBBSF is achieved by adjusting the parallel input/output inductors and the dimensions of the resonators. A fifth-order DBBSF is designed and fabricated, with a compact size of 1.2 mm × 1.2 mm. The simulation results show high consistency with the measured results.