Luneberg Lens

Luneberg lens [′lü·nə‚bərg ‚lenz]

(electromagnetism)

A type of antenna consisting of a dielectric sphere whose index of refraction varies with distance from the center of the sphere so that a beam of parallel rays falling on the lens is focused at a point on the lens surface diametrically opposite from the direction of incidence, and, conversely, energy emanating from a point on the surface is focused into a plane wave. Accurately spelled Luneburg lens.

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Luneberg Lens 

a lens antenna in which the maximum of the directivity pattern may be controlled over a wide angular sector. It was proposed by the American scientist R. K. Luneberg in 1944. It is used mainly in radar installations in the centimeter wavelength range.

A Luneberg lens is spherical or cylindrical and is characterized by the fact that the index of refraction of the lens material is not constant throughout the lens but rather is a function of the distance to its center (for a spherical lens) or its axis (for a cylindrical lens). This function is chosen so that the wavefront becomes a plane after passing through the lens. By shifting the radiator along the lens surface, the direction of maximum radiation may be varied through a solid angle of up to 2π without altering the shape of the directivity pattern.