In this paper, a 3-D Luneburg Lens has been designed, fabricated and characterized. Refractive index control of the lens is based on the mixing ratio of air voids and a polymer. The 12 cm (4λ0 at 10 GHz) diameter lens is designed to work at X-band. The effective permittivity of the unit cell is estimated by effective medium theory and calculated by the finite-element simulation software Ansoft HFSS. Fabrication is implemented by a polymer jetting rapid prototyping method. In the measurement, the lens antenna is fed by an X-band waveguide. The half-power beam width of the antenna is 14 degrees and no obvious side lobe is found in the measurement above the noise floor. © 2011 IEEE.