A Wideband High Gain Circularly Polarized Antenna Based on Nut-Shape Metasurface

Abstract

This paper proposes a wideband high gain circularly polarized (CP) antenna based on a novel metasurface (MS) at 5.8 GHz. The struture of the antenna consists of two parts are stacked on top of each other. The bottom part is a square patch antenna with a diagonal slot at the center and four parasitic elements added to the sides of the driven patch to improve reflection coefficient and axial ratio of the proposed antenna. The top part is a novel MS, formed by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4\times 4$</tex> nut-shape unit cells for improvement gain, matching impandance and CP bandwidth expansion. The antenna has a high gain of 9.35 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{\text{dBi}}$</tex> and compact size of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{31\times 31\times 6.7\text{mm}^{3}}$</tex> . Wide bandwidth is another advantage of the proposed antenna: impedance bandwidth (S11 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{ &lt; -10\text{dB}}$</tex> BW) of 1.8 GHz (29.66%) and axial ratio bandwidth (AR BW) of 1.34 GHz (21.42%). The anenna has left hand circularly polarized (LHCP) is suitable for electronic toll collection (ETC) application.