  Hybrid beamforming (HBF) transceiver architectures based on
frequency-independent phase shifters (PS-HBF) are sensitive to the phases and
physical directions with limited capability to compensate for the detrimental
effects of the beam squint. Motivated by the fact that switches are
phase-independent and more power/cost efficient than PSs, we consider the
switch-based HBF (SW-HBF) for wideband large-scale multiple-input
multiple-output systems in this paper. We first derive a closed-form expression
of the beam squint ratio and compare the expected array gains of both SW-HBF
and PS-HBF architectures. The results show that SW-HBF is more robust to the
beam squint effect. We then focus on the SW-HBF designs to maximize the
spectral efficiency (SE) in both single-user and multiuser systems, which are
both non-convex mixed-integer problems. For the former, by combining the tabu
search (TS) method and projected gradient ascend (PGA), we propose an efficient
heuristic PGA-TS algorithm to design analog beamformers while the digital ones
admit closed-form solutions. For the latter, we develop a two-step algorithm
based on fractional programming and the PGA-TS method. Simulations show that
the proposed SW-HBF schemes are efficient and can outperform PS-based HBF
architectures in terms of both SE and energy efficiency in terahertz
communication systems.
