On the Behavior of the Near-Field Propagation Matrix between two Antenna Arrays, with Applications to RIS-Based Over-the-Air Beamforming

Abstract

In this paper, we empirically study the behavior of the near-field over-the-air (NF-OTA) propagation matrix between two antenna arrays, with applications to reflective intelligent surface (RIS) based over-the-air beamforming antenna for very high carrier frequencies (mmWaves and sub-THz) and very large signal bandwidth. The NF-OTA propagation matrix T is a deterministic complex matrix which depends on the feeder array and the RIS array sizes and their geometry. We conduct numerical investigations of the rank of T and its left singular vectors, which play an important role in determining the OTA beamforming capability of the whole architecture.