L-band high-Q tunable quasi-absorptive bandstop-to-all-pass filter

This paper presents a high-Q tunable quasi-absorptive bandstop-to-all-pass filter in the 1.1 to 2 GHz frequency range. The filter can continuously tune from an all-pass response to an absorptive bandstop response with high isolation (70 dB) across its entire frequency range. The insertion loss in its all-pass state varies from 2.27 to 3.14 dB. The filter topology requires only one tuning element per resonator. The filter topology is implemented with evanescent-mode cavity resonators and tuned with low-power piezoelectric actuators. The extracted unloaded resonator Q-factor is 400.