Reconfigurable Waveguide Bandpass Filter with Piezoelectric Motors in the W-Band

This paper presents a fully reconfigurable bandpass filter in the W-band. The third-order filter utilizes contactless tuning plungers, which are under the control of piezoelectric motors, to tune its transmission characteristic. This arrangement allows exceptionally precise adjustments, enabling highly accurate tuning options. The tuning element incorporates coupling resonators to change coupling strength between resonators. Notably, both the main resonators and the coupling resonators use identical contactless plungers, simplifying the overall design. The filters' center frequency can be adjusted between 78 GHz and 82 GHz while the bandwidth can be changed independently between 300 MHz and 600 MHz. For most tuning states, an unloaded Q-factor $Q^{0}$ above 1000 can be measured and the filter is able to realize a return loss of better than 20 dB.