Sizing Antenna Arrays for Near-field Communication and Sensing

TL;DR

This work analyzes how near-field communication and sensing performance scales with antenna array aperture across common geometries. By deriving closed-form expressions for metrics such as the minimum beamdepth $BD_{min}$, near-field region span $R_{NF}$, the span of the guaranteed resolution region, the maximum number of 3 dB separated beamspots $N_{BD}$, and the number of significant singular values $N_{SV}$, the authors provide actionable aperture-sizing guidelines. Key findings include that the minimum achievable near-field resolution saturates to $BD_{min}\to \alpha \beta^2 \lambda$ as the aperture grows, the NF region span grows quadratically with aperture, and $N_{BD}$ scales linearly with aperture while $N_{SV}$ follows a geometry-dependent power law $N_{SV}=\left\lfloor \kappa\left(\frac{D}{\lambda}\right)^{\gamma} \right\rfloor$. These results offer practical design insights for configuring extremely large antenna arrays for NF communication and sensing, enabling designers to translate system requirements into aperture specifications across ULA, UCA, URA, and UPCA geometries.

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.

Figures (9)

• Figure 1: System diagram.
• Figure 2: Array factor per geometry for $D=60\lambda$ and beamfocusing at $d'= 120 \lambda$.
• Figure 3: Beamdepth vs distance from the center of the array for two aperture sizes of $30\ \lambda$ and $60\ \lambda$, and selected array geometries.
• Figure 4: Minimum beamdepth $\mathrm{BD_{min}}$ vs the aperture $D$ for $\beta=1.2$ and selected array geometries.
• Figure 5: Span of the guaranteed resolution region as a function of the aperture $D$, for threshold resolution set to 5 times the minimum asymptotic resolution $\mathrm{BD_{th}} = 5 \alpha \beta^2 \lambda$.