Wide-Band Polarization Control of Leaky Waves on Anisotropic Holograms

Abstract

Isotropic leaky-wave holograms have great potential in the synthesis of single-beam and multibeam radiations in the desired directions. However, conventional methods are based only on the phase synthesis of the object wave front and do not have the ability to control the polarization of waves. A solution to this problem is the use of anisotropic holograms that provide more degrees of freedom. In this paper, the aperture field estimation theory is proposed for the synthesis of anisotropic holograms. Its advantage is the accurate prediction of far-field wave front characteristics, including phase, amplitude, and polarization. This method is used in the design of two different types of holograms in order to generate the pencil beam and vortex beam radiations. The pencil beam hologram is designed to have a high polarization purity across the visible region. In addition, a surface-wave reflector is implemented for eliminating the unwanted backward modes and adding a scannability property from 16 to 19 GHz to the hologram with an appropriate level of cross-polarization across the bandwidth. In the second section, the theoretical equations for the synthesis of vortex beam hologram with circular polarization is developed. As an example, an anisotropic hologram with topological charge of $l=2$ is synthesized. Both theoretical and numerical results show that the anisotropic leaky-wave holograms are capable of generating orbital angular momentum (OAM) mode with the desired topological charge and polarization, which are simpler and more compact than other methods of generating OAM mode. For the proof of concept, a pencil beam hologram with a surface-wave reflector is fabricated and measured.