  We present an intuitive analytical model for extraordinary optical
transmission (EOT) through corrugated metallic films. In the framework of this
model, EOT emerges from standing wave resonances of the different diffraction
orders, and is an inherent property of periodic structures, which does not
require specific polarization dependent properties such as surface plasmons.
The model correctly predicts the conditions for the EOT resonances in various
geometrical configurations, in both TE and TM polarizations,and in the
subwavelength and non-subwavelength spectral regimes, using the same underlying
mechanism.
