An Ultrawideband and High-Gain Antenna Based on 3-D Impedance-Matching Metamaterial Lens

In this article, we present an ultrawideband and high-gain antenna based on a 3-D impedance-matching metamaterial (IMM) lens. First, we design a 3-D IMM lens which can convert spherical-like waves to plane ones and is nearly perfect impedance-matching with the free space. To realize the 3-D lens, we propose and design two kinds of ultrawideband 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 ultrawideband feed source. Measured results verify that the presented lens antenna can work in an ultrawide bandwidth from 5.2 to 15.13 GHz, and the relative bandwidth is 97.7%. Moreover, it achieves a high aperture efficiency of more than 66% from 5.2 to 14.3 GHz, with a relative bandwidth of 93.3%. A maximum aperture efficiency of 85.6% is obtained at 11.5 GHz. The proposed lens antenna has an average of 2 dB gain enhancement versus optimal horn with the same aperture area. And the length of the lens antenna reduces to 22% compared to a bare horn antenna with the same gain and aperture efficiency.