A New Polar-Domain Dictionary Design for the Near-field Region of Extremely Large Aperture Arrays

Abstract: A grid of orthogonal beams with zero column coherence can be easily constructed to cover all prospective user equipments (UEs) in the far-field region of a multiple-antenna base station (BS). However, when the BS is equipped with an extremely large aperture array, the Fraunhofer distance is huge, causing the UEs to be located in the radiative near-field region. This calls for designing a grid of beams based on a near-field dictionary. In the previous work, a polar-domain grid design was proposed to maintain control over the column coherence. A limitation of this approach is identified in this paper, and we propose an enhanced methodology for the design of a polar-domain dictionary specifically tailored for the near-field of an extremely large aperture uniform planar array. Through simulation results, it is demonstrated that the proposed dictionary, employing a non-uniform distance sampling approach, achieves lower column coherence than the benchmark and significantly improves the localization of UEs compared to uniform distance sampling.