Design of the microwave frequency sensor for power-unknown signal based on MEMS technology

Abstract

In this paper, an 11–13GHz frequency sensor is proposed for power-unknown signal application. The incident microwave signal is divided to three parts with equal magnitude and equal phase in different tracks. The signal in track 1 is the referenced signal. Then, the signal in track 3 travels through a phase shifter and is synthesized with the signal in track 2. Two cascaded power sensors are designed to measure the synthesized and the referenced power, respectively. As a result, the frequency of the incident signal can be deduced by the output ratio of the power sensors. The frequency sensor is designed and fabricated by GaAs MMIC process. The measured return loss is close to −28dB at the center frequency of 12GHz and −13dB over the edge of 11–13GHz. For the signal with low power, the measured voltage ratio (V2/V1) decreases from 1.25@11GHz to 0.7@13GHz with the frequency of the input signal, and the measured sensitivity is close to 0.323/GHz. For the signal with high power, the capacitance change ratio (C2/C1) decreases from 1.15@11GHz to 0.8@13GHz. The shake exists in the capacitance measurement and the reason is that two MEMS cantilever beams produces warp during the releasing process in fabrication.