Holographic multiple-input multiple-output (H-MIMO) is considered as one of the most promising technologies to enable future wireless communications in supporting the expected extreme requirements, such as high energy and spectral efficiency. Empowered by the powerful capability in electromagnetic (EM) wave manipulations, H-MIMO has the potential to reach the fundamental limit of the wireless environment, and opens up the possibility of signal processing in the EM-domain, which needs to be depicted carefully from an EM perspective, especially the wireless channel. To this aim, we study the line-of-sight (LOS) H-MIMO communications with arbitrary surface placements and establish an exact expression of the wireless channel in the EM-domain. To further obtain a more explicit and computationally-efficient channel models, we solve the implicit integrals of the exact channel model with moderate and reasonable assumptions. Numerical studies are executed and the results show good agreements of our established approximated channel models to the exact channel model.

翻译：在电磁波操纵的强大能力下,H-MIMO有可能达到无线环境的根本极限,并有可能在EM-Dormain中进行信号处理,这需要从EM角度,特别是无线频道进行仔细的描述。为此,我们以任意的表面布置来研究视线(LOS)H-MIMO通信,并在EM-Domain中建立无线频道的准确表达方式。为了进一步获得更明确和计算效率更高的频道模型,我们用中度和合理的假设来解决确切频道模型的隐含组成部分。进行了数字研究,结果显示我们建立的近似频道模型与精确频道模型的一致。</s>