An Ultra-wideband and High-gain Antenna Based on Three-dimensional Impedance-matching Metamaterial Lens

In this paper, we present an ultra-wideband and high-gain antenna based on three-dimensional (3D) impedance-matching metamaterial (IMM) lens. First, we design a 3D IMM lens which can convert spherical-like waves to plane ones and is nearly perfect impedance-matching with the free space. To realize the 3D lens, we propose and design two kinds of ultra-wideband sandwich-structured metamaterial unit cells that can cover the refraction index ranges from 1.25 to 1.4 and from 1.4 to 3.8, respectively. We also design a double ridged pyramid horn antenna as an ultra-wideband feed source. Measured results verify that the presented lens antenna can work in an ultra-wide bandwidth from 5.2 to 15.13 GHz, and the relative bandwidth is 97.7%. Moreover, it achieves high aperture efficiency more than 66% from 5.2 to 14.3 GHz, with the relatively bandwidth of 93.3%. A maximum aperture efficiency of 85.6% is obtained at 11.5 GHz. The proposed lens antenna has an averaged 2 dB gain enhancement versus optimal horn with the same aperture area. And the length of the lens antenna reduces to 22% comparing to a bare horn antenna with same gain and aperture efficiency.