A concentrically corrugated near-field plate

We present a concentrically corrugated near-field plate which can form a subwavelength near-field focus. The experimental plate consists of a coaxial aperture surrounded by non-periodic concentric corrugations. The measured subwavelength patterns are compared to those created by a coaxial probe with similar dimensions and are shown to be narrower. Excellent agreement between measurements and simulated results is observed. Finally, the frequency response of the plate is experimentally studied. The presented near-field plate will find applications in near-field probing.