Dual-polarization electromagnetic window simultaneously with extreme in-band angle-stability and out-of-band RCS reduction empowered by flip-coding metasurface.

Achieving high electromagnetic (EM) wave transmission with excellent angular stability is crucial for communication, detection, and guidance but remains challenging, especially when integrating other functions like out-of-band radar cross-section (RCS) reduction, which often degrades transmission. In this work, we propose to solve this problem by utilizing the longitudinal design freedom of metasurface. To this end, a typical longitudinally-coupled structure is proposed as the meta-atom for designing metasurfaces, which is composed of one layer of metallic meshes and one layer of metallic patch. By leveraging the synergistic effect of the plasma oscillation of the metallic mesh and the Lorentz resonance effect of the metal patch within meta-atom, we obtain a dual-polarization angle stable EM window (0°-80°) within the operating band. On this basis, without altering the structural parameters of the meta-atom, we utilize the longitudinal dimension to encode the reflection phases of out-of-band EM waves by flipping the meta-atom structure longitudinally, which can integrate out-of-band radar cross-section (RCS) reduction function without affecting the in-band transmission performance. To demonstrate this idea, prototypes were designed, fabricated and measured. Fabricated prototypes show good agreement between measurements and simulations, validating the method. This opens new paths for multifunctional EM windows in next-gen communication and radar systems.