A wideband 8-12 GHz inline type microwave power sensor, which has both working and non-working states, is presented. The power sensor measures the microwave power coupled from a CPW line by a MEMS membrane. In order to reduce microwave losses during the non-working state, a new structure of working state transfer switches is proposed to realize the two working states. The fabrication of the power sensor with two working states is compatible with the GaAs MMIC （monolithic microwave integrated circuit） process. The experimental results show that the power sensor has an insertion loss of 0.18 dB during the non-working state and 0.24 dB during the working state at a frequency of 10 GHz. This means that no microwave power has been coupled from the CPW line during the non-working state.
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.
The concepts of substrate eddy influence factor and distribution-effects-occurring frequency are presented. The effects of substrate resistivity and inductor spiral length on the substrate eddy and distribution effects are captured. The substrate eddy influence factors of an inductor （6 turn, 3 060 μm in length） fabricated on low （ 1 Ω. cm） and high resistivity（ 1 000 Ω.cm） silicon substrates are 0. 3 and 0. 04, and the distribution-effects- occurring frequencies are 1.8 GHz and 14. 5 GHz, respectively. The measurement results show that the equivalent circuit model of the inductor on low resistivity silicon must take into consideration substrate eddy effects and distribution effects. However, the circuit model of the inductor on high resistivity silicon cannot take into account the substrate eddy effects and the distribution effects at the frequencies of interest. Its simple model shows agreement with the measurements, and the contrast is within 7%.
