Microwave resonator and filter tuning by an ultrasonic piezo motor in a phased locked loop

This paper presents a technique for tuning resonators and filters using an ultrasonic piezo linear motor, a feedback oscillator, and a PLL-circuit. The concept allows an exact reconfiguration of filters even when installed and operating inside the communication system. The potential applications for tunable RF-filters and oscillators are discussed. An exemplary system is developed and tested for a resonator center frequency of 1.1 GHz with a tuning range of approximately 100 MHz. The used resonator is a loaded cavity, which is variable in its resonance frequency by a movable dielectric plate.