A low-profile ultra-wideband circularly polarized antenna array with metasurface

In this article, a low-profile ultra-wideband (UWB) circularly polarized (CP) antenna array with metasurface is presented. The antenna array consists of a 2 x 2 polarization conversion metasurfaces (PCMs) and a sequential feeding network. The PCM is composed of 4 x 4 polarization conversion unit-cells. The unit-cell is obtained by putting an ellipse patch into a rectangular ring, connecting the ellipse and the ring with two stubs, and then rotating it by 45 degrees. A linear polarization (LP) slot antenna with a PCM can achieve a CP antenna, which has an impedance bandwidth of about 33.8% (5.4-7.6 GHz) of |S-11| < -10 dB and a 3-dB axial ratio (AR) bandwidth of about 24.8% (5.8-7.3 GHz), respectively. The UWB CP characteristics can be achieved when a UWB sequential feeding network is added to the 2 x 2 PCMs. Simulated and measured results show that the proposed antenna array has an impedance bandwidth of about 117% (1.75-6.75 GHz) of |S-11| < -10 dB and a 3-dB axial ratio (AR) bandwidth of about 105.7% (2.24-7.35 GHz), respectively. The usable bandwidth can reach 100.3% (2.24-6.75 GHz). Besides, the proposed antenna array achieves a higher gain compared to the traditional slot array and the peak gain of 12.5 dBic at 6 GHz. The overall size of the antenna is 0.6 lambda x 0.6 lambda x 0.03 lambda (lambda refers to the wavelength of the lowest operating frequency in free space). The proposed antenna array can be widely applied to various wireless communication systems.