Predicting the Bistatic Scattering of a Multiport Loaded Structure Under Arbitrary Excitation: The S-Parameters Approach

Various applications, including reconfigurable intelligent surfaces (RISs), radio frequency identification, and ambient backscatter devices, are based on scattering. Predicting the scattering properties of these systems accurately and universally in a computationally efficient manner is crucial. In this article, we propose a model for predicting the scattering properties of an electromagnetic structure controlled by loads terminated to multiple ports. This model is based on: 1) S-parameters describing the coupling between the ports; 2) embedded element radiation patterns associated with each port; and 3) structural scattering under multiple incident wave directions. To construct the model, one set of electromagnetic descriptions (e.g., simulations or measurements) needs to be done for a structure before computing the scattering properties of the structure for arbitrary tunable load values. Unlike many other methods, the proposed method fully takes into account structural scattering in different directions simultaneously and requires no simplifications or approximations to the scattering structure, such as the assumption of local periodicity or element identity. This method facilitates characterizing the scattering ability of the structure in terms of bistatic cross section (BCS), also known as bistatic radar cross section (bRCS), and can be beneficial, for instance, in designing RISs and backscatter systems. Simulations and experiments at different frequencies verified the proposed model.