Near-Field Aperture Shaping for High-Gain Terahertz Antipodal Vivaldi Antenna Using Graphene and In-Plane double sided Grooved Superstrate.

A high-gain broadband terahertz (THz) antipodal Vivaldi antenna (AVA) enhanced by graphene loading and novel in-plane double side grooved superstrate is presented. The antenna is designed on a low-loss TOPAS substrate and optimized for operation over the 2–3 THz frequency band. Graphene is integrated along the antenna serrated flares and modeled using a surface conductivity formulation derived from the Kubo formalism, enabling tunable impedance matching and stabilization of surface current distributions through chemical potential control. While graphene loading significantly improves the reflection coefficient, its contribution to gain enhancement remains limited due to intrinsic plasmonic losses. To address this limitation, a novel double-sided in-plane periodic grooved superstrate is introduced as a lateral extension of the substrate and positioned within the antenna near-field region. The proposed superstrate reshapes the aperture field by gradually controlling the amplitude and phase of the radiating field without exciting guided or slow-wave modes. Full-wave simulation results demonstrate a realized gain improvement from approximately 11 dBi for the baseline antenna to 14–22.8 dBi, depending on the superstrate length, while maintaining broadband impedance matching. Field phase analysis and half-power beamwidth reduction confirm that the gain enhancement is primarily attributed to improved aperture field coherence and effective aperture extension. Owing to its planar profile, reduced electromagnetic complexity, and fabrication-friendly implementation, the proposed antenna is well suited for practical THz imaging, sensing, and on-chip communication applications.