In this paper we show that under the excitation of a line current of electron beam, a dielectric medium loading in the lower half-space of a sub-wavelength hole array brings essential 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. The results of numerical calculations based on analytical theory agree well with that obtained by computer simulations. The mechanism may have good potential applications in modern physics.

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University of Electronic Science and Technology of China