High Angular Resolution Beam Steering Terahertz Antenna Arrays for Imaging Applications

Abstract

Terahertz antenna arrays can produce Terahertz electromagnetic waves that can be steered by electronic control. They are a promising technology for many applications, including imaging, radar, communications and other sensing applications due to bandwidth availability, penetration of dielectric materials, and short wavelength, enabling smaller structures. There is particular application in automotive radar imaging, where a narrow FMCW radar beam is swept across a scene to produce a depth image which, unlike LIDAR, is tolerant to environmental conditions such as rain and snow. However, challenges exist in the design of large dense THz arrays, limiting demonstrations to hundreds of antennas, a fraction of the size required for high-resolution imaging. This is explained by challenges including THz phase shifters which are high-loss and too large for dense integration, consume large DC power, and introduce amplitude and phase errors. In addition, challenges exist with high-loss on-chip RF power distribution, array scalability and phase control.

The approaches taken in this work address these issues, enabling a 98x98 antenna array at 265GHz which employs passive one bit phase shifters based on two MOSFET switches. These phase shifters are low-loss, low-area and consume no DC power. A reflector array (reflectarray) architecture and in-unit memory address RF distribution and digital control challenges, and a scalable design allows for arbitrary array sizes. In-unit memory additionally enables performance-enhancing algorithms to mitigate beam squint and radiation sidelobes which improve effective resolution of a wideband FMCW radar image and enable radiation performance approaching that of ideal phase shifters. The concepts are demonstrated on-chip in a 22nm FinFET CMOS process, with a 4x4mm2 chip containing a dense 7x7 antenna array.

An on-PCB tiling of 14x14 chips produces a 98x98 antenna array, which demonstrates electronic steering over a 120 degree window of a 1x1 degree THz beam with 42dBi of directivity, and is further enhanced by algorithmic approaches. The antenna array is employed in a radar imaging application where the high-directivity beam is used to produce 90x90 pixel radar images. This represents the largest beam-steering THz antenna array demonstrated to date, and a step towards practical solid-state THz imaging.