Reconfigurable intelligent surface (RIS) is an emerging technology that is under investigation for different applications in wireless communications. RISs are often analyzed and optimized by considering simplified electromagnetic reradiation models. In this chapter, we aim to study the impact of realistic reradiation models for RISs as a function of the sub-wavelength inter-distance between nearby elements of the RIS, the quantization levels of the reflection coefficients, the interplay between the amplitude and phase of the reflection coefficients, and the presence of electromagnetic interference. We consider both case studies in which the users may be located in the far-field and near-field regions of an RIS. Our study shows that, due to design constraints, such as the need of using quantized reflection coefficients or the inherent interplay between the phase and the amplitude of the reflection coefficients, an RIS may reradiate power towards unwanted directions that depend on the intended and interfering electromagnetic waves. Therefore, it is in general important to optimize an RIS by considering the entire reradiation pattern by design to maximize the reradiated power towards the desired directions of reradiation while keeping the power reradiated towards other unwanted directions at a low level. Our study shows that a 2-bit digitally controllable RIS with an almost constant reflection amplitude as a function of the applied phase shift, and whose scattering elements have a size and an inter-distance between (1/8)th and (1/4)th of the signal wavelength may be a good tradeoff between performance, implementation complexity and cost. However, the presented results are preliminary and pave the way for further research into the performance of RISs based on accurate and realistic electromagnetic reradiation models.

翻译：重新配置的智能表面(RIS)是一个新兴技术,正在对无线通信的不同应用进行研究。RIS经常通过考虑简化电磁再辐照模型进行分析和优化。在本章中,我们的目标是研究现实的RIS再辐照模型的影响,作为RIS附近元素的亚波长间距离、反射系数的四分化水平、反射系数的振幅和阶段之间的相互作用以及电磁干扰的存在。我们考虑两种案例研究,即用户可能位于远地和近地区域的初步RIS。我们的研究显示,由于设计限制,例如需要使用四分反射系数,或者阶段与反射系数的振动之间的内在相互作用,RIS可能会使动力转向不想要和干扰电磁波波波的不想要的方向。因此,总体而言,有必要通过进一步考虑重新定位模式,使用户在远地和远地区域定位,即初步RIS。我们的研究结果表明,由于设计的限制,例如需要使用四分层反射线反射系数,或阶段与反射系数之间的内在相互作用,因此,RIS可能重新定位动力向偏差方向调整。