Design of high-Q absorptive bandstop filters with static and reconfigurable attenuation

This paper focuses on the design of highly selective and high quality factor (Q) absorptive bandstop filters (ABSFs) that are based on a mixed implementation scheme using acoustic wave (AW) resonators and lumped-element components. The proposed approach enables mobile form-factor notch filters with theoretically infinite attenuation even for stopbands showing 3-dB fractional bandwidths (FBWs) as narrow as 0.013–0.02% (Q=10,000–15,000). Proof-of-concept filter prototypes using commercially-available surface acoustic wave (SAW) resonators and surface-mount components are designed, built, and characterized for an example frequency of 418 MHz. Various stopbands with measured FBWs between 0.017 and 0.078% (i.e., 0.07 and 0.327 MHz in absolute terms) and attenuation levels as high as 83 dB are demonstrated. Absorptive notches with reconfigurable levels of isolation in the range of 10–83 dB are also shown through a fabricated ABSF with controllable attenuation.