The transmission spectra and far-field radiation patterns of periodic metallic aperture arrays are studied in mid-infrared region. We find that the samples have two transmission bands in mid-infrared region. The central positions of transmission bands red-shifts with the increase of the hole-diameter or the lattice constant. The periodic metallic aperture arrays can behave as electrical dipole arrays at the central positions of the transmission bands. The radiation intensity in far-field is strong at the two frequencies. The intensity increase with the decrease of the hole diameter or the increase of the lattice constant.