Reconfigurable intelligent surfaces (RISs) comprised of tunable unit cells have recently drawn significant attention due to their superior capability in manipulating electromagnetic waves. In particular, RIS-assisted wireless communications have the great potential to achieve significant performance improvement and coverage enhancement in a cost-effective and energy-efficient manner, by properly programming the reflection coefficients of the unit cells of RISs. In this article, free-space path loss models for RIS-assisted wireless communications are developed for different scenarios by studying the physics and electromagnetic nature of RISs. The proposed models, which are first validated through extensive simulation results, reveal the relationships between the free-space path loss of RIS-assisted wireless communications and the distances from the transmitter/receiver to the RIS, the size of the RIS, the near-field/far-field effects of the RIS, and the radiation patterns of antennas and unit cells. In addition, three fabricated RISs (metasurfaces) are utilized to further corroborate the theoretical findings through experimental measurements conducted in a microwave anechoic chamber. The measurement results match well with the modeling results, thus validating the proposed free-space path loss models for RISs, which may pave the way for further theoretical studies and practical applications in this field.

中文翻译：

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具有可重构智能表面的无线通信：路径损耗建模和实验测量

由可调单元单元组成的可重构智能表面 (RIS) 由于其在操纵电磁波方面的卓越能力，最近引起了极大的关注。特别是，RIS 辅助的无线通信具有巨大的潜力，可以通过适当地编程 RIS 的单位单元的反射系数，以具有成本效益和能源效率的方式实现显着的性能改进和覆盖范围增强。在本文中，通过研究 RIS 的物理和电磁性质，针对不同场景开发了用于 RIS 辅助无线通信的自由空间路径损耗模型。所提出的模型首先通过广泛的模拟结果进行验证，揭示 RIS 辅助无线通信的自由空间路径损耗与从发射器/接收器到 RIS 的距离、RIS 的大小、RIS 的近场/远场效应和辐射之间的关系天线和单元格的模式。此外，通过在微波消声室中进行的实验测量，利用三个制造的 RIS（超表面）进一步证实了理论发现。测量结果与建模结果匹配良好，从而验证了所提出的 RIS 自由空间路径损耗模型，这可能为该领域的进一步理论研究和实际应用铺平道路。通过在微波消声室中进行的实验测量，利用三个制造的 RIS（超表面）进一步证实了理论发现。测量结果与建模结果匹配良好，从而验证了所提出的 RIS 自由空间路径损耗模型，这可能为该领域的进一步理论研究和实际应用铺平道路。通过在微波消声室中进行的实验测量，利用三个制造的 RIS（超表面）进一步证实了理论发现。测量结果与建模结果匹配良好，从而验证了所提出的 RIS 自由空间路径损耗模型，这可能为该领域的进一步理论研究和实际应用铺平道路。