It is well known that there is inherent radiation pattern distortion for the commercial base station antenna array, which usually needs three antenna sectors to cover the whole space. To eliminate pattern distortion and further enhance beamforming performance, we propose an electromagnetic hybrid beamforming (EHB) scheme based on a three-dimensional (3D) superdirective holographic antenna array. Specifically, EHB consists of antenna excitation current vectors (analog beamforming) and digital precoding matrices, where the implementation of analog beamforming involves the real-time adjustment of the radiation pattern to adapt it to the dynamic wireless environment. Meanwhile, the digital beamforming is optimized based on the channel characteristics of analog beamforming to further improve the achievable rate of communication systems. An electromagnetic channel model incorporating array radiation patterns and the mutual coupling effect is also developed to evaluate the benefits of our proposed scheme. Simulation results demonstrate that our proposed EHB scheme with a 3D holographic array achieves a relatively flat superdirective beamforming gain and allows for programmable focusing directions throughout the entire spatial domain. Furthermore, they also verify that the proposed scheme achieves a sum rate gain of over 150% compared to traditional beamforming algorithms.

翻译：众所周知，商用基站天线阵列存在固有的辐射方向图畸变，通常需要三个天线扇区才能覆盖整个空间。为消除方向图畸变并进一步提升波束成形性能，本文提出一种基于三维超指向性全息天线阵列的电磁混合波束成形方案。具体而言，该方案由天线激励电流矢量（模拟波束成形）与数字预编码矩阵构成，其中模拟波束成形的实现涉及对辐射方向图的实时调整，以适应动态无线环境。同时，数字波束成形基于模拟波束成形的信道特性进行优化，以进一步提升通信系统的可达速率。本文还建立了包含阵列辐射方向图与互耦效应的电磁信道模型，以评估所提方案的性能优势。仿真结果表明，采用三维全息阵列的电磁混合波束成形方案能实现相对平坦的超指向性波束成形增益，并支持在整个空间域内进行可编程的聚焦方向控制。此外，仿真结果也验证了所提方案相比传统波束成形算法可获得超过150%的和速率增益。