The diffraction radiation of sub-wavelength holes array with dielectric medium loading

In the paper we show that under the excitation of a line current, a dielectric medium loading in the lower half-space of the sub-wavelength holes array brings surprising changes to the diffraction radiation. In the lower half-space, the surface wave becomes a radiation wave. The fundamental space harmonic is transformed into Cherenkov radiation with unique characteristics and the first negative space harmonic is converted into a radiation wave with the angle of Smith-Purcell radiation. Consequently, in the lower half-space interference happens due to these two kinds of diffraction radiation.