The electromagnetic (EM) features of reconfigurable intelligent surfaces (RISs) fundamentally determine their operating principles and performance. Motivated by these considerations, we study a single-input single-output (SISO) system in the presence of an RIS, which is characterized by a circuit-based EM-compliant model. Specifically, we model the RIS as a collection of thin wire dipoles controlled by tunable load impedances, and we propose a gradient-based algorithm for calculating the optimal impedances of the scattering elements of the RIS in the presence of mutual coupling. Furthermore, we prove the convergence of the proposed algorithm and derive its computational complexity in terms of number of complex multiplications. Numerical results show that the proposed algorithm provides better performance than a benchmark algorithm and that it converges in a shorter amount of time.

翻译：可重构智能表面（RIS）的电磁特性从根本上决定了其工作原理和性能。基于上述考虑，我们研究了存在RIS的单输入单输出（SISO）系统，该系统采用基于电路的电磁兼容模型进行表征。具体而言，我们将RIS建模为由可调负载阻抗控制的薄线偶极子阵列，并提出一种基于梯度的算法，用于在存在互耦的情况下计算RIS散射元件的最优阻抗。此外，我们证明了所提算法的收敛性，并以复数乘法次数推导了其计算复杂度。数值结果表明，所提算法在性能上优于基准算法，且收敛时间更短。