As the backbone of the fifth-generation (5G) cellular network, massive multiple-input multiple-output (MIMO) encounters a significant challenge in practical applications: how to deploy a large number of antenna elements within limited spaces. Recently, holographic communication has emerged as a potential solution to this issue. It employs dense antenna arrays and provides a tractable model. Nevertheless, some challenges must be addressed to actualize this innovative concept. One is the mutual coupling among antenna elements within an array. When the element spacing is small, near-field coupling becomes the dominant factor that strongly restricts the array performance. Another is the polarization of electromagnetic waves. As an intrinsic property, it was not fully considered in the previous channel modeling of holographic communication. The third is the lack of real-world experiments to show the potential and possible defects of a holographic communication system. In this paper, we propose an electromagnetic channel model based on the characteristics of electromagnetic waves. This model encompasses the impact of mutual coupling in the transceiver sides and the depolarization in the propagation environment. Furthermore, by approximating an infinite array, the performance restrictions of large-scale dense antenna arrays are also studied theoretically to exploit the potential of the proposed channel. In addition, numerical simulations and a channel measurement experiment are conducted. The findings reveal that within limited spaces, the coupling effect, particularly for element spacing smaller than half of the wavelength, is the primary factor leading to the inflection point for the performance of holographic communications.

翻译：作为第五代（5G）蜂窝网络的支柱技术，大规模多输入多输出（MIMO）在实际应用中面临一个重大挑战：如何在有限空间内部署大量天线单元。近期，全息通信作为该问题的潜在解决方案崭露头角，它采用密集天线阵列并提供可解析的模型。然而，实现这一创新概念仍需解决若干挑战。其一为阵列内天线单元间的互耦效应：当单元间距较小时，近场耦合成为主导因素，严重制约阵列性能。其二是电磁波的极化特性——这一固有属性在先前的全息通信信道建模中未得到充分考虑。其三则是缺乏实测实验来揭示全息通信系统的潜在优势与可能缺陷。本文基于电磁波特性提出一种电磁信道模型，该模型同时包含收发端互耦效应与传播环境中的退极化效应。此外，通过逼近无限大阵列情况，从理论上研究了大规模致密天线阵列的性能限制，以挖掘所提信道的潜力。最后，我们开展了数值仿真与信道测量实验。结果表明：在有限空间内，耦合效应（特别是当单元间距小于半波长时）是导致全息通信性能出现拐点的首要因素。