A programmable hybrid metal-graphene metasurface antenna for wide-angle multi-beam steering at terahertz frequencies

Abstract

Abstract This paper presents a programmable hybrid copper–graphene metasurface antenna for simultaneous steerable beam generation in the terahertz band, targeting wide‑angle, low‑voltage multi‑beam operation for emerging 6G wireless systems. The metasurface consists of a 20 × 20 array of E‑shaped unit cells designed to operate at 2.35 THz, with overall dimensions of 800 × 800 × 10 μm³. Each unit cell integrates an E‑shaped copper resonator with tunable graphene arms on a quartz substrate backed by a polysilicon ground plane and a thin HfO 2 gate dielectric, enabling low‑voltage electronic control. The design process begins with parametric optimization of the hybrid unit-cell geometry to maximize phase tunability at 2.35 THz, followed by selection of an 8 nm HfO 2 gate dielectric to achieve practical low-voltage operation, and concludes with array-level phase distribution synthesis for beam steering and multi-beam generation. Comprehensive parametric study is conducted on the effect of graphene chemical potential ( $$\:{{\upmu\:}}_{\text{c}}$$ ), relaxation time ( $$\:{\uptau\:}$$ ), and temperature ( $$\:\text{T}$$ ) on material response characteristics for phase tuning perforFmance. At $$\:{\uptau\:}=3\:\text{p}\text{s}\:$$ and $$\:\text{T}=300\:\text{K}$$ , variation of $$\:{{\upmu\:}}_{\text{c}}$$ from 0.22 eV to 1.0 eV yields reflection magnitude ranging from − 10 dB to − 0.1 dB with 355° phase coverage. The metasurface supports beam steering over elevation angles up to $$\:\pm\:6{8}^{\text{o}}$$ with full $$\:360^\circ\:$$ azimuthal coverage, achieving a maximum gain of 17.4 dB and maintaining acceptable sidelobe levels and beamwidth across the steering range. In addition, simultaneous dual, triple, and quadruple beams radiation patterns are realized using a superposition‑based phase synthesis, enabling independently steerable directive beams without aperture partitioning. Compared with previously reported terahertz graphene metasurfaces operating at lower frequencies with narrower steering ranges (typically ±45–60°) and single/dual-beam capabilities, the proposed design offers clear advantages in steering range, multi-beam generation (up to four beams), and biasing practicality (0.2–4.3 V operation), making it well suited as a reconfigurable intelligent surface for 6G terahertz wireless communication and sensing.