Modified luneberg lens for defocused source

A spherical Luneberg lens has the property of focusing the rays from a point source on the surface of the lens into a collimated beam on the diametrically opposite side of the lens. In microwave applications a point source on the surface of the lens is usually not obtained. Curves are given for the required index of refraction for a modified Luneberg lens which possesses the same collimating property for a point source located at a small distance outside of the lens.