Reflectarray for 120-GHz beam steering application: Design, simulations, and measurements

Development of a 120-GHz FMCW radar with a reflectarray as focusing element is described. The reflectarray is realized on a 150-mm silicon wafer and it has 3700 phase-modulating elements on it. The phase shifters have four discrete values to cover full phase modulation with 90° steps. The reflectarray element is realized with a conductor-backed coplanar waveguide patch antenna with a phase shifter coupled to it. The required phase modulation for each reflectarray element is determined with an in-house physical optics simulation combined with genetic-algorithm-based optimization. The reflectarrays are developed in two stages. First, preliminary reflectarrays with static phase shifters have been manufactured and tested at 120-GHz antenna measurement range. The static reflectarrays are found to perform as designed in their capability to steer the beam to a desired direction and to a distance of 3 m. The reflectarrays have-3-dB beam width from 1.1° to 1.3° depending on the beam tilt. After the preliminary verification with the static phase shifters, the reflectarrays will be assembled together with actively controlled MEMS-based phase shifters. The MEMS switches are controlled with dedicated high-voltage CMOS electronics, forming a system-in-a-package (SiP). First, the MEMS phase shifters are modeled, are being fabricated, and will be measured separately to verify their phase-shifting capability.