Three-dimensional broadband and broad-angle transformation-optics lens.

Luneburg lenses have superior performance compared with conventional lenses made of uniform materials with specially designed surfaces, but they are restricted by the difficulty of manufacturing the required gradient-index materials and their spherical focal surfaces. Recently, a new two-dimensional (2D) imaging lens was proposed and realized using transformation optics. Such a 2D lens overcomes the aberration problem, has a flattened focal surface and is valid for extremely large viewing angles. Here, we show the design, realization and measurement of a three-dimensional (3D) approximate transformation-optics lens in the microwave frequency band. The 3D lens is made of non-resonant metamaterials, which are fabricated with multilayered dielectric plates by drilling inhomogeneous holes. Simulation and experimental results demonstrate excellent performance of the 3D lens for different polarizations over a broad frequency band from 12.4 to 18 GHz. It can also be used as a high-gain antenna to radiate or receive narrow beams in large scanning angles.