We investigate the benefits of mutual coupling effects between the passive elements of intelligent reconfigurable surfaces (IRSs) on maximizing the achievable rate of downlink Internet-of-Things (IoT) networks. In this paper, we present an electromagnetic (EM) coupling model for IRSs whose elements are connected minimum scattering antennas (i.e., dipoles). Using Chu's theory, we incorporate the finite antenna size constraint on each element of the IRS to obtain the IRS mutual impedance matrix. By maximizing the IRS phase shiters using the gradient ascent procedure, our numerical results show that mutual coupling is indeed crucial to avoid the achievable rate degradation when the spacing between IRS elements is down to a fraction of the wavelength.

翻译：我们研究了智能可重构表面（IRS）无源单元间互耦效应对最大化下行物联网（IoT）网络可达速率的增益。本文提出了一种电磁（EM）耦合模型，适用于单元连接最小散射天线（即偶极子）的IRS。基于Chu理论，我们在IRS每个单元上引入有限天线尺寸约束，从而获得IRS互阻抗矩阵。通过采用梯度上升法优化IRS相位偏移器，数值结果表明：当IRS单元间距降至波长量级时，互耦效应对于避免可达速率衰减至关重要。