Design of a Metasurface Based High Gain Dual Mode Orbital Angular Momentum Transmit-Reflect Array (TRA) Antenna

This work presents a high-gain dual-mode orbital angular momentum (OAM)-based transmit-reflectarray (TRA) antenna using a low-profile metasurface (MS) array. A wideband transmit-array (TA) and reflect-array (RA) metaatom (MA) have been integrated into a single unit cell, with a wideband Vivaldi antenna as the source feed. To simplify the feeding mechanism, uniform circular array (UCA) and MSbased TA and RA elements have been excited with equal amplitude and phase, independent of polarization. The proposed TRA antenna generates OAM mode <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1=+1$</tex> for the TA antenna and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{l}=-\mathbf{1}$</tex> for the RA antenna. The proposed TRA antenna achieves peak gains of 22.6 dBi and 21.5 dBi in RA and TA modes respectively together with the respective aperture efficiencies of 41.2 % and 36.5 %. Further, the proposed TRA offers a 1 dB gain bandwidth of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 45 \%$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 38 \%$</tex> in RA and TA modes; thereby outperforming similar designs. Additionally, it ensures high mode purity and sidelobe levels lower than 10 dB in both configurations. With its simple feed, bidirectional functionality, compact profile, and high gain, the design is wellsuited for wireless communication, radio astronomy, and allied applications.