Resonant transmission of a class of sub-wavelength apertures in thin conducting screen

In this paper, we have examined the resonant transmission of a class of sub- wavelength apertures such as a ridged circular aperture and a narrow rectangular slot in thin infinite conducting screen. The transmitted power for varying the ridge gap and the slot length for these apertures, respectively, has been compared with the transmission cross section of the apertures to check out the relationship between them, and the admittance of the apertures have been computed to validate the resonant behavior of them. It turns out that the transmitted power of an electrically small aperture at a resonance converges to the transmission cross section of 3/4pi square wavelengths independent of its shape and size as long as the aperture size is sufficiently small compared to the wavelength.