Luneberg dielectric lens and method of producing same

A hemispherical dielectric lens comprising:

• a hemispherical center layer having a hemispherical outer surface;
• and
• a plurality of hemispherical dome-shaped layers each having concentric hemispherical inner and outer surfaces, the outer surfaces of said center layer and dome-shaped layers having different diameters and the inner surfaces of said dome-shaped layers having different diameters,
• said center layer and dome-shaped layers being successively concentrically fitted into one another and integrated into a hemispherical shape,
• said center layer being a foam molding of ceramic-containing thermoplastic resin expanded beads,
• each of said dome-shaped layers being a foam molding of thermoplastic resin expanded beads containing 0 to 80% by weight of a ceramic,
• wherein the ceramic content per unit volume of said center and dome-shaped layers decreases from said center layer to the outermost dome-shaped layer,
• wherein each of said center and dome-shaped layers has a standard deviation of the apparent density of 0.07 g/cm3 or lower, and
• wherein the ratio (V/N) of the number of voids (V) to the number of expanded beads (N) at a region adjacent to the outer surface of said center layer or adjacent to the outer and inner surfaces of each of said dome-shaped layers except said outermost dome-shaped layer is in the range of 0.2 to 1.0.