Real-time temperature compensation control system for tunable cavity-based high-Q filters

In this paper, a real-time temperature compensation control system for a tunable high-Q cavity-based filter is designed, implemented and experimentally validated. A high-Q (Q = 400) bandstop resonator that can be tuned by a piezoelectric actuator from 1.27 GHz to 1.79 GHz is monitored in real time by an integrated monitoring resonator that shares the same piezoelectric actuator. Consequently, the RF resonance has a one-to-one correspondence to the monitoring resonance. A VCO is coupled with the monitoring resonator resulting in an oscillatory output signal at a frequency that depends on the RF resonator frequency. The monitoring resonance is controlled by comparing it to a user-provided resonance through a closed-loop in real-time. The system resolution varies from 2 MHz to 13 MHz depending on the resonators center frequency with a 1.6 μs sensing period and averaging set at 512. The system is capable of compensating for frequency drifts by adjusting bias voltage to the piezoelectric actuator for a wide range of temperatures between -40°C and 40°C. The frequency control error at 1.5 GHz is measured at 4 MHz (0.25%), which is much smaller than the open-loop change of 195 MHz (12.97%) for the same temperature change.