面向6G的超大规模阵列下近场波束方向图

摘要：由于超大规模阵列中天线数目急剧增加，用户与基站之间的通信将处于阵列的瑞利距离内，导致传统的基于平面波前的远场波束方向图不再适用。为解决此问题，基于近场球面波前，利用泰勒展开得到近似近场场强表达，绘制出近场波束方向图。在此基础上，根据得到的近场波束方向图，揭示出波束角度偏转现象，并引入回归距离来刻画角度偏转程度。回归距离拟合函数体现了回归距离与目标波束角度、阵列尺寸、以及载波波长之间的关系。仿真结果表明，所提回归距离拟合函数较好地表征了近场波束方向图特性。

关键词：超大规模阵列；近场通信；球面波前；波束方向图

Abstract: Due to the sharp increase in the number of antennas in extremely large-scale arrays (XL-array), the communication between users and base station (BS) will be within the Rayleigh distance of the XL-array, resulting in the traditional far-field beam pattern based on the plane wavefront no longer applicable. In order to solve this problem, an approximate near-field field strength expression is firstly obtained by considering the near-field spherical wavefront and using Taylor expansion. According to the obtained near-field beam pattern, a novel phenomenon i.e., the beam angle deflection, is revealed, and a new metric, i.e., the regression distance, is introduced to characterize the degree of the beam angular deflection. Next, the regression distance fitting function is proposed, which describes the relationship between the regression distance and the target beam angle, the array aperture, and the carrier frequency. The simulation results demonstrate that the proposed regression distance fitting function can well characterize the near-field beam pattern characteristics.

Keywords: XL-array; near-field communication; spherical wavefront; beam pattern