Control System for Piezoelectric-Actuator-Based Tunable Evanescent-Mode Cavity Microwave Filters

A control system for automatic tuning of substrate-integrated, evanescent-mode cavity, microwave filters, with piezoelectric actuators, is developed. The system is based on an elegant sensing method using monitoring capacitors mounted on top of the actuators, where the digital value of them is directly measured. The system first requires us to characterize the resonators in the filter and then can automatically tune the filter without any extra instrument. Characterization is used to circumvent the hysteresis and creeping effects of the piezoelectric actuators. This procedure extracts a unique frequency-capacitance relationship, which is modeled using a quadratic polynomial and saved into the system for tuning. Polynomial coefficients, extracted from the characterization data, are utilized to implement a closed-loop feedback control algorithm for the standalone tuning operation. The capability of the control system in automatically tuning a variety of microwave filters using this methodology is experimentally demonstrated.