A Wideband Circularly Polarized Antenna Based on Anisotropic Metamaterial

Abstract

This article presents a novel circularly polarized (CP) antenna based on an anisotropic metamaterial. The antenna is capable of performing linear-to-circular polarization conversion over a wideband of frequencies in the X-band (8–12 GHz). The proposed antenna was constructed from a metamaterial-based polarizer mounted above the aperture of a rectangular waveguide. The polarizer was oriented at 45° to E-plane of the waveguide. The proposed polarizer is composed of multiple metamaterial layers. The unit cell of the proposed polarizer consists of a single dielectric slab incorporating a series of rectangular split ring resonators that are printed on both sides of the slab. Impedance matching layers (IML) are introduced to enhance the axial-ratio (AR) bandwidth. The polarizer has a low profile in terms of electrical length (thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.41 \lambda _{0}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the free-space wavelength at 10.5 GHz). A full-wave electromagnetic simulator was used to verify the anisotropic characteristics of the unit cell. This was achieved by showing that the metamaterial exhibits two different refractive indices along the orthogonal components of the incident electric field. The prototype of the proposed design is fabricated and measured to validate the performance. The measured results agree with the simulated ones and demonstrated a wide impedance bandwidth of 62.4% ranging from 7.08 to 13.5 GHz with a 3 dB AR bandwidth of 29.9% (9.25–12.5 GHz).