Broadband Two-dimensional Planar Luneburg Lens Composed of Gradient Index Metamaterials

A broadband two-dimensional Luneburg lens is presented based on gradient index metamaterials. The focusing condition of the lens, requiring a gradient refractive index, is achieved by using the electromagnetic resonators. A novel modified split ring resonator is chosen as the unit cell since its permeability and permittivity can keep constants when the operating band is far away from the resonant frequency. A standard retrieval procedure is used to determine the relationship between the geometry of the unit cells and the refraction index. Therefore, a new kind of Luneburg lens composed of the modified SRR arrays is constructed. Simulation results have shown that the proposed Luneburg lens, which operating in X-band, has an excellent focusing ability.