RF design of acoustic-wave-lumped-element-resonator-(AWLR)-based bandpass filters with constant in-band group delay

This papers reports on the design of a new class of acoustic-wave-resonator-(AWR)-based bandpass filters (BPFs). Unlike conventional ladder- and lattice-type AWR architectures, it allows the realization of passbands with constant group delay (Tg) and larger bandwidth (BW). The devised configuration makes use of N identical hybrid acoustic-wave lumped-element resonators (AWLRs) — each of them contributing to one pole and two transmission zeros (TZs) — and N+1 lumped-element impedance inverters. As an added benefit, it exhibits power transmission response whose maximum realizable BW and Tg flatness does not depend on the electromechanical coupling coefficient (kt²) of its constituent AWRs. For experimental-demonstration purposes, a UHF-band three-pole/six-TZ BPF prototype with in-band linear phase was designed, manufactured, and measured using commercially-available surface-acoustic-wave (SAW) resonators. Its measured characteristics are summarized as: BW of 0.3 MHz, insertion- and return-loss of 2.1 dB and 32 dB, respectively, effective quality factor Qeff of 9,000, and in-band Tg between 1.78 ± 0.02 ps.