Design of RF-MEMS Varactor for Phased Array Applications in the Defence Industry

Abstract

The dissertation presents the design of an electrothermally actuated in plane bidirectionally translatable and symmetric RF-MEMS varactor with a maximum achievable tuneability of 1100%. The varactor is mounted on a coplanar waveguide (CPW) transmission line. Compliant mechanical amplifiers (CMA) have been utilized to amplify the output of chevron actuators and provide greater displacements and contact forces. The main emphasis of this work is to propose the design a novel varactor having a wide and linear tuning range, with the capacitive part of the device independent of the actuation part, with the device exhibiting a high capacitance ratio and quality factor. The device is designed according to the constraints of the standardized and cost effective SOI-MUMPs fabrication process, offered by MEMSCAP Inc, USA. The proposed device has an actuation voltage of 1.3 V and a nominal capacitance of 0.70 pF. An insertion loss better than -10 dB and return loss better than -1 dB is observed at 2 GHz. The change of capacitance on the CPW transmission line, allows us to change the phase velocity of the device, hence opening the door for a phase shifter application. The device measures 4×4 mm. The finite element analysis (FEM) of the device is conducted in COMSOL.