Common Projection Subspace-Based Reduced-Order Coarse Modeling for ROM-Based Space-Mapping Electromagnetic Optimization

Space mapping (SM) accelerates full-wave electromagnetic (EM) optimization, but its efficiency depends strongly on the quality of the coarse model. In reduced-order modeling (ROM)-based SM, a reduced basis constructed at a nominal design may lose approximation capability under geometric deviations, thereby restricting the validity region of the reduced-order coarse model (ROCM). To address this issue, this article presents a common projection subspace (CPS)-based reduced-order coarse-modeling approach for ROM-based SM. By constructing a CPS from reduced bases extracted at multiple neighboring geometries, the proposed method improves the local modeling validity of the ROCM over the sampled neighborhood within each SM iteration while preserving high computational efficiency. Combined with mesh-deformation techniques, the method enables efficient coarse-model updating without repeated remeshing. Three representative microwave design examples, together with comparisons against direct EM optimization, mesh SM (MSM), aggressive SM (ASM), and nominal-basis ROM-SM, demonstrate that the proposed coarse-modeling strategy can reduce the number of SM iterations and total CPU cost in the tested cases while maintaining comparable final design accuracy.