Reconfigurable All-Pass-to-Bandstop Acoustic-Wave-Lumped-Element Resonator Filters

Acoustic-wave lumped-element resonator (AWLR)-based filters with reconfigurable all-pass-to-bandstop transfer function are reported. They are based on in-series cascaded resonant stages that comprise two parallel RF signal paths, namely: 1) a thru-line and 2) an AWLR-based resonant section. Reconfigurability is achieved by altering the phase of the thru-line through varactors. In this manner, the filter response can be reconfigured from an all-pass to an enhanced fractional bandwidth (FBW) - i.e., wider than the electromechanical coupling coefficient k_{t}^{2} - bandstop one. For practical validation, two prototypes were designed and tested. They include 1) a single-stage prototype with insertion loss (IL) < 0.38 dB in the all-pass mode and a bandstop mode with a center frequency of 917.5 MHz, an FBW of 0.29% ( 2.4~k_{t}^{2} ), and a stopband isolation of 21.2 dB and 2) a two-stage prototype that exhibits an all-pass mode with IL < 0.67 dB and a bandstop mode centered at 916.9 MHz, with an FBW of 0.47% ( 3.8~k_{t}^{2} ) and a tunable isolation between 20 and 43 dB.