Integrated MEMS-Based Phase Shifters

Abstract

Multilayer microwave circuit processing technology is essential in developing more compact radio frequency (RF) electronically scanned arrays (ESAs) for next generation radar systems. ESAs are typically realized using the hybrid connection of four discrete components: RF manifold, phase shifters or Butler matrices, antennas and T/R modules. The hybrid connection of these components increases the system size, packaging cost and introduces parasitic effects that lead to higher losses. In order to eliminate these drawbacks, there is a need to integrate these components on the same substrate, forming a monolithic phased array. RF MEMS technology enables the monolithic integration of the ESA components into one highly integrated multifunctional module, thereby enhancing ESA designs by significantly reducing size, fabrication cost and interconnection losses.

A novel capacitive dual-warped beam shunt MEMS switch is presented that utilizes warped beams to enhance its RF performance. This switch exhibits an off-to-on capacitive ratio of almost 170, isolation better than 40dB, switching speeds as low as 6μs without the need for thin dielectrics or high dielectric constant materials. These MEMS switches are implemented into single pole three throw (SP3T) and single pole four throw (SP4T) configurations.

A novel 3-bit finite ground coplanar waveguide switched delay line MEMS phase shifter is developed with four cascaded SP3T dual-warped beam capacitive switches to achieve low-loss performance and simplify ESA design. The fabricated prototype unit exhibits an insertion loss of 2.5∓0.2dB with a phase error of ∓6°. Moreover, a compact 4 x 4 Butler matrix switchable with the use of a MEMS SP4T switch is investigated as an alternative passive beamforming method. The overall beam-switching network is monolithically integrated within a real-estate area of 0.49cm2. This technique provides a unique approach to fabricate the entire beamforming network monolithically.

An 8-mask fabrication process is developed that monolithically integrates the MEMS phase shifter and RF combining network on one substrate. The wafer-scale integrated ESA prototype unit has an area of 2.2cm2. It serves as the basic building block to construct larger scanning array modules and introduces a new level of functionality previously achieved only by the use of larger, heavier and expensive systems