Terahertz Beam Steering: from Fundamentals to Applications

Free-space transmission of terahertz (THz) waves opens great opportunities for wireless applications including sensing and communication in the 6G era and beyond. Owing to their wider bandwidths and shorter wavelengths, the use of THz waves enhances information capacity and spatial resolution while downsizing aperture sizes compared to microwaves. On the other hand, the shorter wavelengths of THz waves can involve severe path loss. To compensate for the path loss, directional transmission based on beam steering is indispensable. In this article, we review the development of THz beam steering, which has been a longstanding challenge as well as the generation of high-power THz waves. While the use of active or passive phased arrays is the predominantly utilized approach to implement beam steering, other approaches based on variable diffractive structures and frequency dispersive structures offer low-cost alternatives. We also emphasize that application-driven system design approaches, in which THz beam steering is tightly coupled to signal processing, have been emerging to overcome hardware limitations.