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.