Focusing Ability Enhancement in Broadside Direction of Array: From UCA to UCCA

To meet the ever-increasing demand for the data rates of wireless communications, extremely largescale antenna array (ELAA) has emerged as one of the candidate technologies for future 6G communications. The significantly increased number of antennas in ELAA gives rise to near-field communications, necessitating tailored beamforming techniques within the near-field regions to accommodate the spherical-wave propagation characteristics. Among various array geometries of ELAA, uniform circular array (UCA) has gained much attention for its distinct capability of maintaining uniform beam pattern across different azimuth angles. However, existing analysis of near-field UCA beamforming indicates that the near-field region severely declines in the broadside of UCA, where the system fails to benefit from near-field communications. To tackle this problem, the near-field beamforming technique of uniform concentric circular arrays (UCCAs) is investigated in this paper, which has the potential to enlarge the near-field region in the broadside direction. First, the analysis of beamforming gain in the 3D space with UCA and UCCA is provided. Then, the distinct beamforming characteristics that set UCCA apart from UCA are delineated, revealing the superiority of UCCA in extending the near-field region in broadside at the cost of slightly reduced near-field region in the coplane. Simulation results are provided to verify the effectiveness of the theoretical analysis of beamforming gain with UCCA and the enhanced focusing ability of UCCA in the broadside direction.