Realization of Linearly and Circularly Polarized Vortex Electromagnetic Waves by Three Dimensional Structure

In this paper, a three-dimensional structure has been proposed for the realization of linearity and circularly polarized vortex electromagnetic waves. A plasma-based helical circular array (PBHCA) is utilized to generate linearly polarized vortex beams without the need for an external phase-shifting network. The variation in the heights of the PBHCA elements along the z-axis enables the generation of distinct vortex beam modes. Additionally, beam scanning capabilities are explored through the modulation of the plasma frequency. The PBHCL is designed for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l=1$</tex> vortex beam at direction, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Theta=20,30,40,50$</tex> and 60 degrees. Octafilar-curl antenna (OCA) is proposed to generate circularly polarized vortex beams. it consists of eight separate curl antennas: each one rotated 45 degrees with respect to each other. Full-wave EM simulations, CST and the method of moments, MoM are used to confirm the proposed design.