Microwave stepped-index luneberg lenses

Since materials with a continuous variation of index of refraction were unavailable for the construction of spherical Luneberg lenses, an investigation was made of stepped-index lenses in which the desired continuous variation of index with radius was approximated by a number of constant-index spherical shells. Experimental data on two-dimensional, TE_{10} mode, stepped-index Luneberg lenses indicated that 10 shells were sufficient for 18-inch diameter lenses for use at X band. Expanded polystyrene materials, developed with dielectric constants ranging from 1.1 to 2.0 in increments of 0.1, were used to construct 10-step, 18-inch diameter, spherical Luneberg lenses. Performance data for these lenses are given at wavelengths of 3.2, 1.8, and 0.8 centimeters.