Design of a Wideband Vortex Beam Reflectarray Using Subwavelength Element

A new subwavelength reflective unit cell is designed and used in reflectarray to generate orbital angular momentum (OAM) waves. The metallic single layer subwavelength element consists of a cross dipole patch, four symmetric square patches and a loop patch, which is printed on one side of a substrate layer. An air layer is also inserted between metallic ground and the substrate. Size of the square unit cell is quarter wavelength at designed frequency and it achieves 360° reflection phase range. A reflectrarray is designed to generate OAM waves of mode 1 for linearly polarized feed at 6 GHz. Using the proposed subwavelength element, its far-field radiation patterns and E-field phase distribution are analyzed through CST Microwave Studio. The simulated results show that the required OAM waves are generated successfully with a maximum gain of 23.3 dBi at 6 GHz.