Multi-Band Acoustic-Wave-Lumped-Element Resonator-Based Bandstop Filters with Continuously Tunable Stopband Bandwidths
A new class of multi-band acoustic-wave-lumped-element-resonator (AWLR)-based bandstop filters (BSFs) is reported. It is based on N multi-resonant AWLRs — shaped by K AWLRs and 2K inverters — that are connected to an all-pass network and result in K Nth order rejection bands. The proposed concept allows the realization of multiple rejection bands with the following characteristics: i) fractional bandwidths (FBWs) larger than the electromechanical coupling coefficient kt2 of its constituent acoustic-wave resonators, ii) continuously variable and independently-controlled FBWs, iii) intrinsically-switched stopbands, and iv) an all pass state. For proof-of-concept validation purposes a dual-band prototype was designed, built, and tested. It exhibits two stopbands centered at 418 and 433 MHz that can be continuously-tuned in FBW (up to 7.7:1 tuning range) and in number.