Research on the phase of an inline coupling RF MEMS power sensor

This paper presents the research on the phase of an inline coupling RF MEMS power sensor based on the microwave lumped network theory. The principle of the power sensor accomplished with GaAs MMIC process is to measure a certain percentage of the RF signal power coupled from a CPW line by a MEMS membrane. In the method, a phase shift of the RF signal is introduced by the MEMS membrane during the power detection, which affects the phase characteristic of the incident RF signal. In this paper, the lumped phase model of the inline power sensor is given and verified by measured results. Using this model, the effects of the height and the width of the MEMS membrane on the phase of the power sensor are studied. A good linearity of the output response at X-band and a sensitivity of about 52.6 μV·mW^-1 at 12 GHz are obtained under the normal ambient temperature. Experiments show that the inline power sensor with the MEMS membrane 100 μm and 147 μm in width respectively has resulted in the average phase changes of about 14% and 33% at X-band compared with that 50 μm in width above the same CPW line.