Design of a Narrow-Beamwidth Reflectarray Antenna for K/Ka-Band Using a Variable Rotation Technique and a Dual-Circularly Polarized Corrugated Horn Feed

This paper presents a new design for a reflectarray antenna (RAA) that utilizes a variable rotation technique (VRT) and features a compact, single-layer substrate without the use of vias or air gaps. The proposed design achieves performance comparable to that of complex, multi-layer structures in terms of high gain, broad bandwidth, circular polarization, aperture efficiency, and low sidelobe and cross-polarization levels. Additionally, it offers the narrowest beamwidth among similar designs, making it a promising solution for point-to-point communication systems that require precise directionality. The resonance characteristics of the proposed RAA unit cell have been analyzed using characteristic mode analysis (CMA). Each element in the RAA is rotated to a specific angle, creating the required reflection phase distribution across the array and steering the main beam toward the desired direction. Furthermore, to enhance overall performance, the RAA is center-fed by a wideband, dual-circularly polarized corrugated horn antenna. The main beam direction is set at (θ₀ = –20°, ϕ₀ = 90°), with a focal ratio of f / D = 1.1, which was selected to maximize aperture efficiency. A reflecting aperture measuring 143.43 mm × 143.43 mm, consisting of 37 × 37 elements, was fabricated and tested. The proposed RAA exhibits a measured 1.5-dB axial ratio bandwidth of 32% and a 3-dB gain bandwidth of 27.5%, with a measured peak gain of 28.6 dBic. The measured total aperture efficiency (TAE) reaches 40.5% at 25 GHz. The measured sidelobe and cross-polarization levels are less than –19.2 dB and –26.3 dB, respectively.