A lumped model with phase analysis for inline RF MEMS power sensor applications

Abstract

This paper proposes a microwave lumped model with attenuation and phase mechanisms for GaAs monolithic microwave integrated circuits (MMIC)-compatible inline RF MEMS power sensors, in order to evaluate reflection and insertion losses and phase characteristics of the sensors. The purpose of the power sensors is measuring a certain percentage of the incident RF power coupled by a MEMS membrane, and their model is achieved based on the microwave port network theory. During the inline power detection, an undesired phase shift is generated by the MEMS membrane. Using this model, the additional phase shift is analyzed to show the phase change of the detected RF signal, with the effects of the membrane height and width on the phase. The three power sensors with the MEMS membrane 50μm, 100μm and 147μm in width are measured to validate the lumped model up to 13.5GHz, and the sources of small errors are discussed. Furthermore, experiments show that the inline RF MEMS power sensors with the membrane 100μm and 147μm in width have resulted in average phase changes of about 14% and 35% over the entire frequency compared with that 50μm above the same coplanar waveguide (CPW) lines, respectively.