Acoustic-wave-lumped-element resonator (AWLR) architectures for high-Q reflective bandstop filters

Abstract

The RF design of a new family of reflective-type bandstop filters (BSFs) with small form factor, narrow bandwidth (BW) and large stopband attenuation is presented in this paper. The proposed filter geometries are based on mixed acoustic-wave-lumped-element resonator (AWLR) architectures that are effectively combined with lumped-element impedance inverters. Contrary to conventional all-AW filter topologies, the achieved stopband BW is no longer limited by the electromechanical coupling coefficient (kt2) of the acoustic wave (AW) resonator. Furthermore, their resulting stopbands exhibit effective quality factors (Qseff) that are at least 50 times higher than in traditional lumped-element filters. First- and second-order BSF prototypes that consist of commercially-available surface acoustic wave (SAW) resonators and surface mounted devices (SMDs) have been designed, built and measured at 418 MHz. Measured stopbands with 3dB-BWs between 0.25 MHz and 0.72 MHz, maximum stopband attenuation ranging from 20 to 30 dB, and passband loss between 0.4 and 1 dB are presented as proof-of-concept demonstrators.