Reconfigurable intelligent surfaces (RISs) provide an interface between the electromagnetic world of wireless propagation environments and the digital world of information science. Simple yet sufficiently accurate path loss models for RISs are an important basis for theoretical analysis and optimization of RIS-assisted wireless communication systems. In this paper, we refine our previously proposed free-space path loss model for RISs to make it simpler, more applicable, and easier to use. The impact of the antenna’s directivity of the transmitter, receiver, and the unit cells of the RIS on the path loss is explicitly formulated as an angle-dependent loss factor. The refined model gives more accurate estimates of the path loss of RISs comprised of unit cells with a deep sub-wavelength size. Based on the proposed model, the properties of a single unit cell are evaluated in terms of scattering performance, power consumption, and area, which allows us to unveil fundamental considerations for deploying RISs in high frequency bands. Two fabricated RISs operating in the millimeter-wave (mmWave) band are utilized to carry out a measurement campaign. The measurement results are shown to be in good agreement with the proposed path loss model. In addition, the experimental results suggest an effective form to characterize the power radiation pattern of the unit cell for path loss modeling.

中文翻译：

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毫米波频段可重构智能表面的路径损耗建模和测量

可重构智能表面 (RIS) 在无线传播环境的电磁世界和信息科学的数字世界之间提供了一个接口。RIS的简单但足够准确的路径损耗模型是RIS辅助无线通信系统的理论分析和优化的重要基础。在本文中，我们改进了我们之前提出的 RIS 自由空间路径损耗模型，使其更简单、更适用和更易于使用。发射器、接收器和 RIS 的单位单元的天线方向性对路径损耗的影响被明确表述为与角度相关的损耗因子。改进后的模型可以更准确地估计由具有深亚波长尺寸的晶胞组成的 RIS 的路径损耗。基于所提出的模型，根据散射性能、功耗和面积评估单个晶胞的特性，这使我们能够揭示在高频段部署 RIS 的基本考虑因素。两个在毫米波 (mmWave) 波段工作的制造 RIS 被用来进行测量活动。测量结果表明与所提出的路径损耗模型非常吻合。此外，实验结果提出了一种有效的形式来表征单元电池的功率辐射模式，用于路径损耗建模。两个在毫米波 (mmWave) 波段工作的制造 RIS 被用来进行测量活动。测量结果表明与所提出的路径损耗模型非常吻合。此外，实验结果提出了一种有效的形式来表征单元电池的功率辐射模式，用于路径损耗建模。两个在毫米波 (mmWave) 波段工作的制造 RIS 被用来进行测量活动。测量结果表明与所提出的路径损耗模型非常吻合。此外，实验结果提出了一种有效的形式来表征单元电池的功率辐射模式，用于路径损耗建模。