Near-Field Plates: Subdiffraction Focusing with Patterned Surfaces

Abstract

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