Wideband OAM Vortex Beam Generation Through a Thin Transmitarray in the Ka-Band
Muhammad Ishfaq, Xiuping Li, Zihang Qi, Wenyu Zhao, Abdul Aziz, Liangjie Qiu
Abstract
This letter proposes a thin transmitarray for generating wideband orbital angular momentum (OAM) vortex beams in the Ka-band. Our proposed element achieves a 360 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> transmission phase within a 3 dB transmission magnitude, with a total thickness of 1.8 mm (0.18 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{0}$</tex-math></inline-formula> at 30.0 GHz). The symmetrical configuration of the unit cell enables its applicability in dual-polarized applications. We investigate the transmitarray performance across four OAM modes ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$l = +1, +2, +3, +4$</tex-math></inline-formula> ), specifically focusing on the +1 mode during fabrication and measurement. Our experimental findings validate the successful generation of a wideband vortex beam with OAM mode <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$l = +1$</tex-math></inline-formula> . The performance of the beam is observed over a broad frequency range from 27.0 to 39.0 GHz (about 40% OAM bandwidth). Moreover, the proposed structure exhibits a peak gain of 21.9 dBi with a corresponding aperture efficiency of 12.3%, while the overall mode purity exceeds 71%.