Enhancing Broadside Focusing in 6G Near-Field Communications Using HOBFs within UCCA

The ability of antenna arrays to achieve sharp broadside focusing is pivotal for near-field communications in sixth-generation (6G) systems, where Extremely Large-Scale Antenna Arrays (ELAAs) are envisioned as a core technology. Although Uniform Concentric Circular Arrays (UCCAs) have been demonstrated to outperform conventional Uniform Circular Arrays (UCAs) in extending the near-field region-mainly by exploiting zero- and first-order Bessel functions-the role of higher-order Bessel functions has received limited attention. This paper introduces a comprehensive analytical framework that systematically incorporates HOBFs to refine the broadside focusing capability of UCCAs. Through mathematical derivations and numerical evaluations, it is shown that HOBFs contribute additional degrees of freedom for beam pattern control, leading to more accurate depth focusing, flexible beam shaping, and enhanced user separation. The analysis reveals that the integration of HOBFs significantly enlarges the Effective Rayleigh Distance (ERD) and reduces inter-user interference, thereby improving spatial resolution and system robustness. These findings highlight the potential of HOBF-assisted UCCAs as a cornerstone in designing near-field multi-user multiple-input multiple-output (MIMO) systems for 6G. The proposed methodology provides theoretical insights and practical guidelines for future beamforming strategies aimed at overcoming the challenges of dense deployments, interference mitigation, and high-capacity demands.