A 12–20 GHz Passively-compensated Tunable Bandstop Filter with 40-dB Notch Level

A frequency-tunable quasi-absorptive tunable bandstop filter covering the 12-20 GHz range with passive bandwidth compensation is presented. The design employs a dual-coupling-slot scheme that limits the filter's 3-dB bandwidth variation to less than 48% over the entire range. This is the first demonstration above 10 GHz that improves bandwidth stability by more than 4× compared to the state-of-the-art. Furthermore, the measured filter rejection level is over 40 dB from 12-20 GHz and over 20 dB from 9-20 GHz. The design is implemented with MEMS-tunable silicon micromachined evanescent-mode cavity resonators. The filter is measured with K-band connectors through a practical PCB-silicon integration scheme that adds less than 1.5 dB back-to-back insertion loss.