Sizing Antenna Arrays for Near-field Communication and Sensing

TL;DR

This paper derives analytical expressions for key performance metrics of near-field communication and sensing systems, showing how they scale with antenna array size to guide practical design.

Contribution

It provides new analytical formulas for near-field beam focusing, region span, resolvable beamspots, and channel singular values as functions of array aperture.

Findings

Near-field beam depth saturates quickly with increasing aperture.

Region span scales quadratically with array size.

Number of resolvable beamspots scales linearly with aperture.

Abstract

This paper presents key performance metrics for near-field communication and sensing systems and their scaling behavior as a function of the antenna array aperture. Analytical expressions are derived for several standard array geometries to ease the design of the large antenna arrays under given system requirements. First, the near-field beam focusing is analyzed and the minimum beamdepth is observed to rapidly saturate to a low asymptotic limit as the array aperture increases. In contrast, the near-field region span is shown to scale quadratically with the array aperture. Based on these two metrics, the maximum number of resolvable beamspots at 3 dB separation is derived analytically, exhibiting a linear dependence on the array aperture. Moreover, when considering a region where the beamfocusing resolution does not exceed a specified threshold, the extent of the region is also shown to scale linearly with the array size. Finally, the number of significant singular values of a channel observed at the array's broadside is estimated, showing a power-law dependence on the aperture. The resulting expressions provide practical design guidelines for evaluating aperture requirements in near-field communication and sensing applications.