Tailoring near-field patterns with concentrically corrugated plates

We present a device that can form a two-dimensional subwavelength focus along a specified near-field focal plane. The device, referred to as a corrugated near-field plate, consists of a coaxially fed aperture in a concentrically corrugated metallic surface. A procedure for designing such devices is outlined. In addition, simulation results are reported for a design that operates at around 1 GHz and forms a focus with a null-to-null beamwidth of lambda/20 at a focal plane lambda/15 from its surface. The effect of losses is also studied. Such devices will find use in near-field microscopy and probing systems. (C) 2009 American Institute of Physics. [doi:10.1063/1.3224882]