A Fourier equivalent model is introduced to research the thermal transfer behavior of a terminating-type MEMS microwave power sensor.The fabrication of this MEMS microwave power sensor is compatible with the GaAs MMIC process.Based on the Fourier equivalent model,the relationship between the sensitivity of a MEMS microwave power sensor and the length of thermopile is studied in particular.The power sensor is measured with an input power from 1 to 100 mW at 10 GHz,and the measurement results show that the power sensor has good input match characteristics and high linearity.The sensitivity calculated from a Fourier equivalent model is about 0.12,0.20 and 0.29 mV/mW with the length at 40,70 and 100μm,respectively,while the sensitivity of the measurement results is about 0.10,0.22 and 0.30 mV/mW,respectively,and the differences are below 0.02 mV/mW. The sensitivity expression based on the Fourier equivalent model is verified by the measurement results.
In order to reduce the mismatch error, a direct current （DC） calibration method is introduced when the modulated microwave signal is measured. The microwave power is input to the left section of the power sensor, and the DC power is input to the right of the power sensor. Due to the existence of parasitic loss and electromagnetic coupling, the microwave power results in a mismatch error. However, the DC power does not have the mismatch error. So the DC power applied in the right section can calibrate the mismatch error of the microwave power in the left section. The calibration factor is measured at different modulation rates and modulation depths.The measurement results show that the carrier frequency is the major factor influencing the measurement results. After calibration, the carrier frequency and the modulation rate have little effect on the output voltage. The frequency response becomes relatively flat in the frequency range up to 20 GHz, and the sensitivity on average is enhanced by about 0.12 mV/dBm. Therefore, the DC calibration method has a certain reference value for the terminal-type microwave power sensor.
