The Luneburg lens - a type of gradient-index (GRIN) lens, proposed by R. K. Luneburg in 1944 - is a spherical lens that focuses a plane wave to a point on the lens surface.
Luneburg lenses exhibit broadband behavior and have many useful applications in antenna applications as they can form multiple beams in arbitrary directions due to their symmetry. The disadvantages of the spherical Luneburg lenses include lens weight and size as well as the manufacturing complexity.
For an ideal Luneburg lens, the relative permittivity must decrease continuously from the center of the lens to 1 on the surface. In practice Luneburg lenses are constructed using a series of concentric dielectric shells whose permittivity is discretely varied. The implementation in Antenna Magus consists of 6 concentric shells and the lens is fed using a waveguide-fed pyramidal horn....
The lens can produce a high gain, symmetrical pencil beam with low side lobes and good cross-polarization.
The figures below show patterns for a 20 dBi design.Typical radiation pattern at the center frequency. Normalized radiation pattern cuts at the center frequency.