High-Q bandpass filters using hybrid acoustic-wave-lumped-element resonators (AWLRs) for UHF applications

This paper focuses on a new family of narrow-band bandpass filters, along with its coupling-matrix-based design approach which feature quasi-elliptic frequency response, effective quality factors (Qs_eff) of the order of 1,000 and small form factors. Hybrid acoustic-wave-lumped-element resonator (AWLR) architectures are proposed as fundamental elements of these filters leading to low-loss passbands with fractional bandwidth (FBW) that is much broader (3.8-7.5 times) than in all acoustic wave (AW) filters and Qs_eff that are 10-20 times larger than in traditional lumped-element filters. Experimental prototypes based on commercially-available surface acoustic wave (SAW) resonators were built and tested at 418 MHz. Measured Qs_eff between 750-1550 and bandwidths ranging from 0.65 to 0.94 MHz (i.e., 2-3 times the electromechanical coupling coefficient of the AW resonator) are presented.