Uniform Circular Arrays in Near-Field: Omnidirectional Coverage With Limited Capacity

Abstract

Recent studies suggest that uniform circular arrays (UCAs) can extend the angular coverage of the radiative near-field region. This work investigates whether such enhanced angular coverage translates into improved spatial multiplexing performance when compared to uniform linear arrays (ULAs). To more accurately delineate the effective near-field region, we introduce the effective beamfocusing Rayleigh distance (EBRD)—an angle-dependent metric that bounds the spatial region where beamfocusing remains effective. Closed-form expressions for both beamdepth and EBRD are derived for UCAs. Our analysis shows that, under a fixed antenna element count, ULAs achieve narrower beamdepth and a longer EBRD than UCAs. Conversely, under a fixed aperture length, UCAs provide slightly narrower beamdepth and a marginally longer EBRD. Simulation results further confirm that ULAs achieve a higher sum-rate under the fixed element constraint, while UCAs offer marginal performance gain under the fixed aperture constraint.