A Compact Wideband Sub-THz Horn Feed Enabling Metasurface-based ISAC Systems in 6G Networks

Abstract

A novel wideband sub-terahertz (sub-THz) horn antenna featuring a parasitic dipole integrated with a compact conical horn is presented as the feeding source for a phase-change-material (PCM)-based tunable metasurface. The horn achieves a 43.48 % impedance bandwidth covering from 90–140 GHz, 11–14 dBi gain, axially symmetric E-/H-plane patterns, –40 dB cross-polarization, and –30 dB front-to-back ratio while remaining simple to fabricate via CNC milling. When used to illuminate an optically activated tunable reflective metasurface, the symmetric wideband illumination enables 1-bit phase coding for arbitrary beam steering up to ±45°, frequency-dispersive near-field sensing with 1 mm position precision over a 40 mm scanning range, and a stable 16-QAM communication link at 100 GHz. Measured results confirm that the proposed horn’s broadband symmetry and low cross-polarization are critical to enable multifunctional ISAC performance in the sub-THz regime. The design offers a practical, scalable solution for 6G perceptive networks.