Resonance and extraordinary transmission in annular aperture arrays

Here the behavior of periodic annular aperture arrays in a perfectly conducting film is considered as the geometry of the apertures is varied. Using a previously developed rigorous electromagnetic modal method it is shown that the far-field transmission spectrum approaches that for an array of circular apertures as the stop size approaches zero. In the case where the diameter of the apertures is significantly less than that of the period of the array, the behavior of the array changes gradually from one where the predominant features in the spectra are due to the excitation of a waveguide resonance to one exhibiting 'extraordinary transmission'.