Enhanced transmission through a sub-wavelength double-slits structure accompanied with a specific pattern of grooves and pillars is studied by FDTD (Finite Difference Time Domain) simulation and compared with experiment. A plane microwave is observed not only be able to pass through the double-slits of line-width about half to incident wavelength but also lead to enhanced focus behind. To our surprise, the FWHM (Full Width at Half Maximum) of focusing point can even be smaller than the half wavelength which implies the breaking of diffraction limit.
In simulation, with aluminum material considered, I first find out the optimal structure resulted in minimum FWHM of focusing point. Then, slight adjustments on this structure are made to investigate the influence of perturbation. So far, consistent results are obtained between simulations and
experiments.

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