Low-Profile Wideband Unidirectional Circularly Polarized Metasurface-Based Bowtie Slot Antenna

In this paper, the design of a wideband circularly polarized (CP) bowtie slot antenna that uses metasurfaces is presented. The antenna consists of a single-layer substrate with the metasurface made of $4\times4$ periodic corner-truncated patches printed at the top side of the substrate and a bowtie-shaped slot etched on the ground plane. The metasurface made of corner-truncated patches are utilized to convert the linearly polarized wave into a CP wave. The antenna is fed by a 50- $\Omega $ coplanar waveguide. The antenna, with an overall size of 42 mm $\times42$ mm $\times2.3$ mm ( $0.71\,\,\lambda _{\mathrm {o}} \times 0.71\,\,\lambda _{\mathrm {o}} \times 0.038\,\,\lambda _{\mathrm {o}}$ at 5.1 GHz), was fabricated and measured. The measured reflection coefficient for $\vert \text{S}_{11}\vert dB yielded an impedance bandwidth of 3.75–6.67 GHz (55.7%), an axial ratio (AR) bandwidth of 4.38–5.98 GHz (31.37%), a 3-dB gain bandwidth of 3.75–6.0 GHz (46.88%), a peak gain of 7 dBic, and a high radiation efficiency of more than 93% within the AR bandwidth.