Design and simulation of a 2-bit distributed S-band MEMS phase shifter

Abstract

In this paper, a wideband distributed coplanar waveguide (CPW) phase shifter has been designed for S-band operation. The phase shifter is developed on a high impedance CPW transmission line periodically loaded with microelectro-mechanical system (MEMS) shunt switches. To reduce the insertion loss due to the transmission line, a 525 µm high resistivity silicon substrate (ρ=10 kΩ·cm) and 2 µm thick aluminium center conductor are used. A large metal-insulator-metal (MIM) capacitor is implemented on the CPW center conductor between the two bits to separate the DC actuation voltage during operation. There are 41 MEMS shunt switches utilised in the design. The simulated reflection coefficients are less than −10 dB from 2 to 4 GHz for all 4 states (0°, 90°, 180° and 270°). The simulated average insertion loss at 2.45 GHz is 1.69 dB. The size of the phase shifter has been optimized by employing 60° mitered CPW bends to result in overall size of 11.62 mm × 28.35 mm. The simulated pull-in voltage of the fixed-fixed beams implemented in the design is 9.68 V. The true time delay characteristic of the phase shifter makes it suitable for use in smart antenna applications, radar systems and ultra-wideband (UWB) microwave imaging.