Near-field plates: Subdiffraction focusing with patterned surfaces

Using a patterned, grating- like plate to control the electromagnetic near field, we demonstrate focusing well beyond the diffraction limit at similar to 1 gigahertz. The near- field plate consists of only capacitive elements and focuses microwaves emanating from a cylindrical source to a spot of size approximate to lambda/20 ( half- power beamwidth), where lambda is the free- space wavelength. These plates will find application in antennas, beam- shaping devices, nonradiative wireless power- transfer systems, microscopy, and lithography.