A Broadband High-Gain Low-Profile Folded Transmitarray Antenna for OAM Generation

In this letter, a broadband, high-gain, low-profile folded transmitarray antenna (FTA) is proposed to generate orbital angular momentum (OAM) beam. The FTA consists of a top metasurface, a bottom metasurface, and an open waveguide feed. The top metasurface exhibits sensitivity to linear polarization, reflecting expected linearly polarized incident waves while transmitting the orthogonal ones. The bottom metasurface acts as a polarization conversion metasurface, and it is polarization insensitive. A proof-of-concept prototype for OAM beam generation is meticulously designed and measured. Simulation results are consistent with measured results. The measured gain variation less than 3 dB is 23<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> [(26.9 to 33.9) GHz]. The measured peak gain attains 20.5 dBi at 28 GHz, accompanied by a peak aperture efficiency of 20.4<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula>, and reduces the profile by 2/3 compared to traditional transmitarray. The significant performance improvements underscore its significant utility in miniaturization OAM communications systems.