Enhanced transmission through subwavelength metallic coaxial apertures by excitation of the TEM mode

We present here the first theoretical demonstration of enhanced transmission (up to 90%) through annular aperture arrays engraved into opaque metallic plates thanks to the excitation of the TEM guided mode inside each coaxial cavity. The generation of this peculiar mode is obtained, first, by illuminating the structure under oblique incidence and, second, by considering a TM polarization. Analytical demonstration is performed to confirm the involvement of these two conditions for the emergence of this guided mode. The originality of this configuration comes, first, from the fact that the TEM mode has no cut-off wavelength and, second, from the fact that the transmission peak position is independent of the angle of incidence.