Orbital Angular Momentum Generating Thin-Film  Сonformal Metasurface for Backscattering Control

This paper presents the design, simulation, and experimental verification of a flexible thin-film conformal metasurface for backscattering control via orbital angular momentum (OAM) wave generation in the X-band (9.5–10.5 GHz). The metasurface comprises asymmetric square loop meta-atoms fabricated on an air-equivalent dielectric substrate (εᵣ ≈ 1) with subwavelength thickness (< λ/15 at 10 GHz). Analytical modeling defines the phase difference requirement for spin-to-orbital angular momentum conversion, enabling OAM mode l = +1 generation upon circularly polarized wave reflection. Full-wave EM simulations and antenna array theory predictions confirmed a characteristic radiation pattern null along the OAM propagation axis. Experimental prototypes were fabricated using adhesive-backed foil on foam-core substrates, demonstrating: 4 dB reflected power reduction for the OAM-generating metasurface compared to a uniform-phase reference; 7 dB reflected waves reduction versus solid metal including for various radii (∞ – 2.5λ) of rounding surfaces. The measured suppression bandwidth reached 1 GHz, though alignment sensitivity due to the narrow null zone was identified as a limitation. Additional radial phase gradients for beam defocusing reduced performance by 1–2 dB due to main lobe distortion. Discrepancies between analytical models and measurements underscored the importance of mutual coupling effects in complex phase distributions. This work confirms thin-film conformal metasurfaces as a viable solution for controllable backscattering.