Fundamental Improvement to the Efficiency of On-chip mmWave Phased Arrays using MEMS Suspension

A major shortcoming of current silicon-based millimeter-wave (mmWave) on-chip antennas is the low radiation efficiency ( 80% at 60 GHz. The proposed array addresses the issues of on-chip air-suspension using micro-electro-mechanical systems (MEMS) processes, thus elevating the hovering radiating elements on a substrate at the height of 35 m ( $0.007_0$ ). The micofabricated SU8 posts serve as the vertical support, ensuring mechanical stability and monolithic integration. The simulated -10 dB fractional bandwidth of this array is 5.5% or 3.4 GHz at 60 GHz. Further, the designed array is capable of scanning of 55 in the E plane and 58 in the H plane. The non-contact backscattering method is proposed and employed to derive the radiation efficiency from measured Radar Cross-Section (RCS) data. RCS measurements are performed using a precision 6-axis robotic arm with the spatial repeatability of 20 m (0/250). The measured radiation efficiency is 82% at 60 GHz. The measured peak gain of 99 array is 23.3 dBi vs. simulated value of 23.9 dBi. Fundamental enhancement in a suspended array efficiency is achieved by eliminating unwanted radiation in the silicon substrate.