A Graphene-Based Intelligent Reconfigurable Reflective Surface for Circularly Polarized Beam Scanning in 6G Applications

This paper presents a novel graphene-based circularly polarized reconfigurable intelligent reflective surface (CP-GRIS) enabling wideband beam scanning at sub-THz and THz frequencies. Unlike conventional RIS designs, which have limited polarization and phase-control flexibility, the proposed CP-GRIS integrates graphene-enabled active phase tuning and circular polarization conversion within a compact 1-bit coding metasurface. The structure consists of a 45 × 45 array (15λ ×15λ) of unit cells, each formed by two inverted semilunar-shaped gold patches and an embedded graphene strip that produces a controllable 180◦ phase difference via current reversal. Two stable phase states with an approximately 180◦ phase difference are achieved over 266-332 GHz, while maintaining a reflection magnitude above 0.87. Dynamic phase reconfigurability is realized by modulating the graphene chemical potential in both ON and OFF states, enabling linear-to-circular polarization conversion for both left- and right-hand circular polarizations without sacrificing reflection efficiency. Electromagnetic analysis demonstrates single-beam operation with full two-dimensional (2D) and three-dimensional (3D) beam-scanning capability. At 300 GHz, the proposed CP-GRIS achieves a maximum broadside gain of 24.8 dBi, a beamwidth of 4.4◦, and a sidelobe level of 15.3 dB, corresponding to a gain enhancement of 12.4 dBi over the feed horn antenna. Beam scanning up to ±40◦ is achieved with a low scan loss of 1.2 dBi, highlighting the proposed CP-GRIS as an efficient and versatile platform for sub-THz and THz beam manipulation and emerging sixth-generation (6G) wireless systems.