325 GHz to 500 GHz Single-Layer Planar Goubau-Line Antenna With Endfire Radiation Based on Substrate Mode

This article presents a 325–500 GHz single-layer planar Goubau-line antenna with endfire radiation based on substrate mode. The electromagnetic (EM) fields along the Goubau line will penetrate into the substrate due to the substrate modes, which cannot operate well compared with the conventional transmission line. The undesired
$E_{\text{z}}^{11}$
substrate mode is engineered here to achieve vertically polarized endfire radiation. Since the higher substrate mode is excited and there is a deviation between the propagation constants of the Goubau line and the
$E_{\text{z}}^{11} $
substrate mode, the phase difference between the center and edges of the truncated aperture will deteriorate the antenna radiation at higher frequencies. Inspired by the conventional Goubau-line divider, the branches can compensate the wavefront and increase the antenna gain by 2 dB at higher frequencies. This terahertz (THz) antenna on a 300
$\mu \text{m}$
thick quartz substrate (
$0.4~\lambda _{0}$
at 400 GHz) possesses robust mechanical properties and consists of single-layer metal, reducing the fabrication complexity. The proposed THz antenna was fabricated and measured, which can operate in a 325–500 GHz band with endfire radiation and achieve 8.5–11.3 dBi gain.