RF MEMS True-Time-Delay Phase Shifter

A radio frequency microelectromechanical system (RF MEMS)-based true-time-delay (TTD) phase shifter is one of the key components in a modern electronically steerable phased array for satellite communication, radar systems, and high precision instrumentation. The phase shifter controls the signal phase in order to steer the direction of the beam [3]. RF microelectromechanical systems (MEMS) technology provides a superior performance in terms of low loss, low power consumption, and excellent linearity compared to other technologies. MEMS-based digital phase shifters provide a large phase shift and low sensitivity to electrical noise with a high tuning ratio compared to analog versions. This chapter describes different types of TTD phase shifters utilizing MEMS switches and MEMS varactors. A gold-based surface micromachining process is used to develop different kinds of MEMS phase shifters on alumina (ε _r  = 9.8) substrates. All phase shifters are implemented using coplanar waveguide (CPW) transmission lines and actuated by electrostatic actuations. These include the analog-type distributed MEMS transmission line (DMTL) phase shifter using push-pull actuation, a 5-bit DMTL phase shifter using MEMS bridge and a fixed capacitor, 5-bit switched line phase shifter using DC-contact MEMS switches and a 2-bit and 5-bit phase shifter using MEMS SP4T and SPDT switches. This chapter includes details on the design, development, and characterization of MEMS phase shifters. Furthermore, all experimental results are validated with a circuit analysis and full-wave EM simulation.