The influence of perturbations of a screen with below-cutoff holes on the enhanced transmission resonance response

The regularities appeared at the scattering of normally incident electromagnetic wave on the screen having two below-cutoff holes in the periodic cell are considered. It is shown that the spacing or element perturbations together with well-known transmission phenomena cause not only the new enhance transmission resonances but the total reflection resonances as well. The explanation of such frequency response behavior is given from spectral theory point of view when the screen is considered as an open resonator, and his lower complex-frequency eigen-oscillations are responsible for the frequency-response forming over the single-mode range. In the context of simple approximated model taking into account a part of eigen-frequency spectrum the main possible peculiarities of frequency response are discussed.