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We studied the diffraction of electromagnetic waves from subwavelength metallic circular apertures in the microwave spectrum. The metallic samples had a subwavelength hole with a diameter of 8 mm and had concentric grooves with a periodicity of 16 mm. We present the angular transmission distributions from circular annular apertures, and circular annular apertures surrounded by concentric periodic grooves. At the surface mode resonance frequency the transmitted electromagnetic waves from the subwavelength circular annular aperture surrounded by concentric periodic grooves have a strong angular confinement with an angular divergence of 3°. This represents a fourfold reduction when compared to the angular divergence of the beam transmitted from the subwavelength circular aperture. © 2006 IOP Publishing Ltd

Plasmonic structures with highly directional beaming properties