3-6 GHz Tunable Bandpass Filter using Heavily Loaded EvanescentmodeCavity Resonators and Piezoelectric Actuators

摘要

In the present work, a widely tunable, high quality factor (Q), narrow bandpass filter is demonstrated usingrnevanescent-mode cavity resonators as building blocks. The frequency and Q variation of the evanescent-mode cavityrnare predicted using analytical expressions, which give design variables for the building blocks. A widely tunablernevanescent-mode cavity resonator is fabricated to verify the theoretical analysis. A tunable filter can be tuned continuouslyrnfrom 3 to 6 GHz with a very narrow bandwidth (～0.58% is demonstrated). The filter is fabricated in lowrntemperature co-fired ceramics with a low loss Rogers Duroid? flexible substrate forming the top of the filter andrnhosts the feed lines for the filter. The flexible substrate acts as a deformable membrane that allows variable frequencyrnloading of each of the resonators. A commercially available piezoelectric actuator is mounted on the Duroid?rnsubstrate for precise electrical tuning of the filter center frequency. The narrow band filter demonstrates the potentialrnof the tuning mechanism to compensate for fabrication tolerances, which are especially important for such arnnarrow bandwidth filter. The high-Q and the sensitive tuning combine to allow for high quality pre-select filteringrnfor a front-end receiver.