Tunable Acoustic-Wave-Lumped-Element Resonator (AWLR)-Based Bandpass Filters

摘要

Hybrid acoustic-wave-lumped-element resonator (AWLR)-based bandpass filters (BPFs) with reconfigurable bandwidth (BW) and tunable out-of-band isolation (IS) are reported in this paper. They are based on a new BPF architecture in which the AWLRs are in-parallel cascaded to an all-pass network through variable lumped-element (LE) impedance inverters. In this manner, passbands with arbitrarily-large BW - i.e., no longer limited by the electromechanical coupling coefficient (k_t~2) of its constituent acoustic-wave resonators (AWRs)-can be created and continuously controlled whilst preserving the high-quality-factor (Q: order of 10,000) characteristics of the AWR. Furthermore, tuning of the out-of-band IS is obtained by adjusting the location of the AWLRs transmission zeros (TZs: 2N for an N-pole BPF) through variable LE capacitors. The operating principles of the devised AWLR-based tunable BPF concept are experimentally validated through a three-pole/six-TZ prototype at 418 MHz made up of commercially-available surface acoustic wave (SAW) resonators and LEs. It exhibits tunable BW between 0.16-0.49 MHz (0.5-1.5k_t~2), minimum in-band insertion loss (IL) between 3.3-1.2 dB (effective Q >10,000), and out-of-band IS reconfigurability.