Analysis of Surface Micro Machined RF MEMS Phase Shifters

Development of low loss radio frequency micro-electro-mechanical (MEMS) phase shifters for radar and telecommunication applications is presented. Numerical simulation results using electromagnetic simulator tools (CST - Germany) along with fabricated wafer level measurement results of two distributed MEMS phase shifters are presented herein for upstate capacitive bridge position. The distributed MEMS phase shifter consists of coplanar waveguide (CPW) transmission line and several MEMS bridges loading capacitively on transmission lines to create a slow wave structure. Two configurations of phase shifters are presented. 1) Conventional distributed MEMS transmission line (DMTL) 2) coplanar waveguide - microstrip - coplanar waveguide (CPW-MS-CPW), with microstrip as the transmission line and CPW as input and output line. The electromagnetic simulation results of gap height variation to change the phase velocity and, in turn, phase shift is presented. Work is underway to vary the gap height between transmission line and the bridge, applying the actuation voltage to bridge capacitors, which, in turn, will vary the bridge capacitance, changing the phase velocity on fabricated phase shifters. The match between simulated results and wafer level measurements are encouraging and will be presented in the full paper. Work is also underway to validate wafer level measurements along with numerical simulation using circuit models using circuit simulator. The custom model libraries for phase shifters are being developed. The results are encouraging.