Locally Optimal Periods in Periodic Optically Transparent Two-Metal-Layered Refractive Metasurfaces for Outdoor-to-Indoor Communication

This study presents a novel electromagnetic analysis and mathematical derivation for determining the locally optimal unit cell period that minimizes phase error losses in the macroscopic design of a periodic two-metal-layered refractive metasurface (TRM) for outdoor-to-indoor communication. The TRM's periodicity is investigated for three main advantages: reducing design complexity, lowering lifecycle costs, and increasing area efficiency. The existence of locally optimal unit cell periods for each pair of incidence and refraction angles, along with a method to find them, was derived. Finally, a 6G upper-mid optically transparent TRM with a locally optimal unit cell period was fabricated, and its path losses in both far-field and near-field scenarios were measured to validate the proposed technique.