Scattering and focusing effect of stepped index Luneberg lens

Focusing effect of the Luneberg lens for wide bandwidth is studied with emp hasis on experiment. A model experiment was performed using a stepped index (six-layer) spherical lens. The total electric field amplitude along the p ropagation axis has the maximum value (focal point) on the surface of the l ens. As the size parameter ka (k: wave number, a: radius of the sphere) is larger, the electric field amplitude at the focal point becomes larger. The se results correspond with the power of convergence (focusing effect) by th e Luneberg lens. The experimental values are in a good agreement with theor etical ones that are calculated using homogeneous multilayered approximate method. They are also in a good agreement with the results using exact solu tions for the inhomogeneous dielectric sphere (the ideal Luneberg lens). Th erefore, it is found that the six-layer spherical lens has the optimum vari ation of dielectric constants for the Luneberg lens and maintains focusing effect for wide bandwidth.