A Broadband Circularly Polarized Single-Layer Metasurface Antenna Using Characteristic-Mode Analysis

Abstract

In this work, we propose a low-profile single-layer coplanar waveguide (CPW)-fed metasurface (MTS) antenna with broadband circular polarization (CP) radiation. With the help of characteristic-mode analysis (CMA), a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textbf {3}\times \textbf {4}$ </tex-math></inline-formula> MTS is analyzed to reveal the useful modes supported by the structure. Consequently, two modes with orthogonal current distribution, broadside radiation, and nearly <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{90}^{\circ} $ </tex-math></inline-formula> phase difference over a wide frequency band are chosen as operation modes. Moreover, the modal near field of the aforementioned modes shows that, unlike conventional microstrip patches, the entire proposed MTS supports two kinds of extraordinary TM modes, namely, e-TM30 and e-TM04. Accordingly, a rotated CPW feeding line is used to excite the two modes without adding an extra layer as reported in the literature, making the design simpler and easier to manufacture. Based on that, a low profile antenna of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textbf {0.058}\lambda _{0}$ </tex-math></inline-formula> has been designed and fabricated. The measured results show an impedance bandwidth (IBW) of 25% (4.870–6.26 GHz), 3 dB axial ratio (AR) band of 19.42% (5.30–6.44 GHz), and a maximum gain of 8 dBi.