Array Geometry-Centric Axial Sidelobe Interference Analysis for Near-Field Multi-User MIMO

TL;DR

This paper analyzes how array geometry affects axial sidelobe interference in near-field multi-user MIMO systems, deriving formulas and comparing array types to optimize interference suppression and data rates.

Contribution

It provides the first closed-form expressions for axial sidelobes in near-field MU-MIMO and compares different array geometries to identify the optimal design for interference mitigation.

Findings

Uniform square arrays have the lowest axial sidelobes.

USA achieves a peak sidelobe level of -17.6 dB.

Numerical results show USA outperforms other arrays in sidelobe suppression and sumrate.

Abstract

With the deployment of large antenna arrays at high-frequency bands, future wireless communication systems are likely to operate in the radiative near-field (NF). Unlike far-field beam steering, NF beams can be focused on a spatial region with finite depth, enabling user multiplexing in both range and angle. In NF multiuser multiple-input multiple-output (MU-MIMO) systems, achievable rates are limited by interference arising from sidelobes in both the axial (range) and lateral (angle) dimensions. This work investigates how axial sidelobes (ASLs) vary with array geometry. Closed-form array gain expressions are derived to characterize ASLs for uniform planar arrays. Analytical results show that the uniform square array (USA) yields the lowest ASLs, followed by the uniform concentric circular array (UCCA), uniform linear array (ULA), and uniform circular array (UCA). Specifically, the USA achieves a peak sidelobe level (PSLL) of -17.6 dB versus -7.9 dB for the UCA. Numerical simulations confirm that the USA provides superior sidelobe suppression and highest sumrate performance.