Abstract: A zone plate focusing radiation comprises a plurality of surface portions (20a, 20b, 20c, 20d, 30) corresponding to zones of the zone plate. The surface portions are positioned in a plurality P of parallel planes such that each surface portion diffracts radiation out of phase with respect to adjacent surface portions such that radiation diffracted by the surface portion constructively interferes at a focus of the zone plate. The p.sup.th plane is dielectrically spaced from the first plane by n.lambda., where .lambda. is the wavelength of the radiation and n is an integer.

Abstract: A zone plate for focusing microwave energy is provided comprising a plurality of reflective portions corresponding to zones of the zone plate, each reflective portion reflecting energy .lambda./P out of phase with respect to adjacent reflective portions, where .lambda. is the wavelength of the energy. The reflective portions are positioned in P parallel planes mounted on low dielectric loss sheets and separated by a distance of .lambda./2P such that energy reflected from the reflective portions constructively interfere at a focus of the zone plate.