Agile Omnidirectional Terahertz Fan-Beam Steering in the WR3.4 Band Based on Gimbal-Controlled Annular Aperture Excitation

Terahertz (THz) waves offer significant potential for advanced sensing and communication applications. However, severe path loss due to short wavelengths as dictated by the Friis transmission formula requires high-gain antennas to enhance signal levels in free space. The implementation of passive phased arrays for high-gain beam steering faces challenges in the THz range due to the lack of broadband and low-loss phase shifters. In addition, the steerable range of a phased array is usually limited. To circumvent these limitations, we propose a novel antenna design capable of omnidirectional steering of a THz fan beam in the WR3.4 band (220-330 GHz). This design hybridizes spatial and waveguide optics approaches and is based on a cylindrically symmetric structure that radiates a horizontally narrow and vertically wide fan beam in an arbitrary direction. The structure incorporates a tiny gimbal reflector that converts a TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode from a circular waveguide into a guided wave in any azimuthal direction toward a narrowing taper, from which the wave is emitted into free space as a fan beam. Key design parameters, including waveguide dimensions and gimbal tilt, are optimized to balance beam collimation, fast steering, and device minimization. Experimental results validate the predicted radiation patterns and polarization, and demonstrate two types of beam scanning. Continuous beam steering is achieved in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$5^{\circ }$</tex-math></inline-formula> step with a scan rate of 387 rpm. In addition, agile beam steering between two opposite azimuthal directions (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$180^{\circ }$</tex-math></inline-formula> apart) is completed within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$13.0 \pm 2.0$</tex-math></inline-formula> ms. This result lays the foundation for agile beam steering in THz communication systems, supporting real-time tracking of users and devices.