A Low‐Sidelobe W‐Band Gaussian Corrugated Horn With Stable Phase Center for Terahertz Quasi‐Optical Systems

High‐quality Gaussian beams with low sidelobes and stable phase centers are essential for efficient beam focusing and low‐loss energy coupling in terahertz quasi‐optical systems. However, conventional corrugated horns usually require costly electroforming processes. The complex corrugated structures impose stringent fabrication requirements and increase manufacturing costs. In addition, phase‐center drift over frequency degrades the focusing efficiency and beam‐coupling performance of broadband quasi‐optical systems. In this study, a fabrication‐oriented W‐band Gaussian corrugated horn antenna is proposed. The horn antenna employs a multistep rectangular‐to‐circular waveguide converter, which achieves broadband TE 10 ‐to‐TE 11 mode conversion while reducing fabrication difficulty and tolerance requirements through a machining‐friendly stepped geometry. By optimizing the corrugated tapered and parallel sections of the horn, stable HE 11 ‐mode radiation, low‐sidelobe Gaussian beam generation, and a stable phase center are achieved over the 75–110 GHz frequency band. A prototype antenna was fabricated using mechanical machining and laminated assembly techniques. The measured results show that the proposed antenna achieves a reflection coefficient below −20 dB, a gain of 24–26 dBi, a normalized sidelobe level below −31 dB, and a cross‐polarization level better than 35 dB across the operating band, while the phase‐center variation remains within ±20 mm. The proposed design significantly reduces the fabrication complexity and manufacturing cost of terahertz corrugated horns while maintaining excellent radiation performance.