High-Q Bandpass-to-Bandstop Reconfigurable Filter Based on SAW Resonators

In this paper, a bandpass-to-bandstop filter using surface-acoustic-wave (SAW) resonator is reported. It is based on hybrid-technology design approach in which SAW resonators loaded short-ended stubs are effectively combined with two transmission lines. The bandpass-to-bandstop transformation is realized by adjusting the PIN diodes to select the transmission path. By using this hybrid architecture, the proposed filter features high effective quality factors (Qeff) on the order of 1000. In addition, enhanced fractional bandwidth (FBW) which is larger than the electromechanical coupling coefficient (kt²) of SAW resonators can be achieved. For proof-of-concept validation purposes, a prototype operating at 917 MHz was designed, built and measured. It performs wide bandwidths of 1.42 MHz in the bandpass filter (BPF) mode and of 1.27 MHz in the bandstop filter (BSF) mode.