Multi-resonant acoustic-wave-lumped-element resonators (AWLRs) for multi-band bandpass filters with enhanced fractional bandwidth

This paper reports on the design of multi-band acoustic-wave-resonator-(AWR)-based bandpass filters (BPFs) with enhanced-fractional-bandwidth (FBW) quasi-elliptic-type passbands. They are based on multi-resonant acoustic-wave-lumped-element resonators (AWLRs) that are shaped by the inparallel cascade of multiple (equal to the desired number of transmission bands) one-port-type AWRs and one lumped-element (LE) resonator. By cascading them in-series through impedance inverters, passbands with increased selectivity and enhanced FBW (i.e., larger than the electromechanical coupling coefficient kt
²
) can be obtained. In addition, they preserve the high-quality-factor (Q) characteristics of the AWRs. For experimental-demonstration purposes, two UHF-band dual-band BPF prototypes with alternative levels of FBW were designed, manufactured, and measured. They exhibited two transmission bands centered at 418 MHz and 434 MHz, respectively, with FBWs of 1-3k
_t
²
and minimum in-band insertion loss (IL) in the range of 0.5-1.25 dB (i.e., effective Q >10,000).