FDTD analysis of resonant transmission in an electrically small circular aperture with a ridge

In this paper, we have examined the convergence of the transmitted power of an electrically small aperture to the transmission cross section 3lambda²/4pi of it for a case of a circular aperture with a ridge. This property can be applied for any electrically small aperture regardless of size or shape even though only one example of the circular aperture is shown. Although not shown here, the comparison of the field distributions on the aperture with and without the ridge shows that the aperture fields for the original circular aperture is mainly reactive, while those are radiating for the ridged aperture.