Wideband Vortex Beam Reflectarray Design Using Quarter-Wavelength Element

Abstract

A wideband vortex beam reflectarray is designed and fabricated to generate the orbital angular momentum (OAM) waves for an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{l} = 2$</tex-math></inline-formula> mode. A quarter-wavelength element is proposed to achieve a reflection phase of 360° at the designed frequency of 6 GHz. The element consists of a loop patch, a cross-dipole patch, and four square patches. The symmetric structure of the element makes it suitable for dual polarization. It is revealed that the OAM mode purity and operational bandwidth of the reflectarray are increased by using the quarter-wavelength element. The array size is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{50} \times {\text{50 cm}}^2$</tex-math></inline-formula> , which achieves measured gain of 18.98 dBi at 6 GHz and operational OAM bandwidth of 42%.