Beam Squint Effects in THz Communications with UPA and ULA: Comparison and Hybrid Beamforming Design

Abstract

Future 6G and beyond wireless systems aim at ultra-high data rates from very large bandwidths in millimeter-wave and terahertz bands. Large bandwidth signals in antenna arrays lead to beam squint or frequency-selective array response causing losses in the beamforming gain. Recently, several hybrid analog-digital beamforming (HBF) schemes, such as the delayphase precoding employing time delay networks or wider-beam codebook design, have been proposed to tackle the beam squint. However, the severity of beam squint has not been thoroughly investigated in the literature. In this paper, by analyzing the impacts of the beam squint on the uniform planar array (UPA) and uniform linear array (ULA) structures, we analytically and numerically show that the effect of beam squint is less severe in the former. Based on this fact, we propose a simplified HBF design in which the analog beamformer is designed for the center frequency, while digital beamformers for all subcarrier frequencies are obtained based on water-filling and minimum mean square error solutions. Simulation results show that the proposed scheme for UPAs performs very close to the optimal digital beamforming scheme.