A Novel Design Approach Using Zero-Pole-Based Multiport Model for Reconfigurable Intelligent Surfaces

Reconfigurable intelligent surfaces (RISs) are of potential use in 5G/6G wireless communications due to their tunable electromagnetic (EM) parameters for flexible beam manipulations. Two important parameters for RIS design are the reflection coefficient of the RIS element and the scattering pattern of the RIS. To realize rapid design of RISs, we propose a zero-pole-based multiport model to calculate the reflection coefficients and scattering patterns of RISs in this work. Specifically, the developed model establishes an accurate mapping relation between the element reflection coefficient and the loads on multiple internal ports by using the multiport S-parameter matrix. Additionally, the vector fitting method is employed to reduce the time cost of data acquisition for multiport S-parameters, in which a hybrid sampling scheme is employed to accelerate computation speed while keeping high accuracy. Using this model, we further develop an efficient far-field pattern prediction and synthesis algorithm for large-scale RIS design based on the antenna radiation superposition principle. The feasibility of the proposed model is demonstrated by an example of 3-bit RIS design, where the simulation results agree well with the measurement.