  Enhancing high-speed wireless communication in the future relies
significantly on harnessing high frequency bands effectively. These bands
predominantly operate in line-of-sight (LoS) paths, necessitating
well-configured antenna arrays and beamforming techniques for optimal spectrum
utilization. Maximizing the potential of LoS multiple-input multiple-output
(MIMO) systems, which are crucial for achieving high spectral efficiency,
heavily depends on this. As the costs and power demands of mixed-signal devices
in high frequency bands make a fully-digital architecture impractical for
large-scale MIMO setups, our focus shifts to a hybrid analog-digital hardware
configuration. Yet, analog processors' limitations restrict flexibility within
arrays, necessitating a nuanced understanding of hardware constraints for
optimal antenna configuration design. We explore array design that optimizes
the spectral efficiency of hybrid systems, considering hardware constraints. We
propose an optimal antenna configuration, leveraging the prolate matrix
structure of the LoS channel between two planar arrays. Building on the optimal
array configuration, we introduce a low-complexity explicit analog-digital beam
focusing scheme that exploits the asymptotic behavior of the LoS channel matrix
in the near-field region. Simulation results validate that the proposed antenna
configuration and beam focusing scheme achieves near-optimal performance across
a range of signal-to-noise ratios with low computational complexity, even under
arbitrary rotations relative to the communication link.
