Hybrid Domain-Decomposition/Physical-Optics Analysis of Finite Reconfigurable Reflectarrays Using Characteristic-Mode Macro Basis Functions

Journal article, 2026

This letter presents an efficient hybrid domain-decomposition/physical-optics framework for analyzing finite, large-scale reflectarrays and reconfigurable intelligent surfaces. The structure is decomposed into exterior and interior domains coupled through a generalized aperture-admittance formulation. The exterior response is approximated using physical optics, while element behavior is captured through admittance operators. Scalability to large arrays and many tuning states is achieved via a macro basis function expansion of the aperture current, which enables multi-state analysis by reusing pre-characterized element operators and updating only the elements that change state. Results for 8 x 8 and 20 x 20 arrays under different illuminations closely match full-wave references while substantially reducing memory usage and simulation time, demonstrating suitability for fast analysis and optimization of reconfigurable arrays.