A Microwave Power Sensor

This chapter mainly introduces microwave power sensors based on the microelectromechanical system (MEMS) technology, in order to achieve the power detection, gain control, and circuit protection. In RF and microwave frequencies, the MEMS power sensors have the advantages of miniaturization, low power, high sensitivity, and compatible with GaAs monolithic microwave integrated circuits (MMIC), etc. In structure, several kinds of the power sensors are described according to different application requirements. They utilize the form of coplanar waveguide transmission lines, with small structural dimensions (generally <1 mm²). In theory, they adopt conversion principles of microwave power-heat-electricity or microwave power-force-electricity. In fabrication, they are accomplished with the GaAs MMIC process. In measurement, experiments demonstrate the validity of the proposed design and model. These sensors meet the characteristics of high performance and low cost. They can be used as implant devices and embedded in microwave communication and radar systems, such as the self-detection of the transceiver module and the measurement of leakage power in microwave module circuits. The MEMS microwave power sensors can directly measure the power of below 500 mW. For a higher microwave power measurement, it is usually necessary to couple or extract a portion of the microwave power by some structures. These MEMS power sensors have the ability to extend the frequency and phase measurements of microwave signals, constituting frequency and phase detectors.