Gratingless enhanced microwave transmission through a subwavelength aperture in a thick metal plate

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Abstract
Remarkably enhanced transmission of microwave radiation through a single subwavelength slit in a thick metallic substrate surrounded by just a pair of parallel deep and narrow grooves is recorded. By also patterning the output face of the metal slab with two grooves there is strong exit beam confinement. There are no gratings in this structure and, hence, the transmission mechanism is not related to the conventional grating coupling of surface plasmons on the upper and lower surfaces of the substrate. Instead, the slit and the four grooves are all resonant, which is the essence of the functioning of the arrangement. The enhancement is due to the collective excitation of the Fabry–Pérot mode in the slit and the cavity modes in the grooves. A finite-element modeling code is used to optimize the response of the structure, and to investigate the electromagnetic fields in the vicinity of the substrate.