| Since Ebbesen reported the extraordinary transmission phenomenon through2D arrays of subwavelength holes milled in an opaque metal screen§the trans-mission properties of electromagnetic wave through subwavelength metal structureshave gradually becomes a hot issue. The explanations on the peculiar phenomenoncontain surface plasmons resonance, Fabry-P′erot-like resonance and the compositedi?racted evanescent wave, and so on. To investigate the enhanced transmissione?ect, the paper develops a new model, called as transmission line model. Assimi-lating the Fabry-PWrot-like resonance explanation, the metal aperture is regarded asa transmission line, and the transmission line performs as a Fabry-PWrot-like cavity,which channels the currents to the output plane. Combining with the compositedi?racted evanescent wave, the currents transform as a localized decayed sources,and emission energies in form of antennas in the output plane of aperture as anoutput antenna. The field enhancement at the edge of aperture is interpreted as theresult of surface plasmons excitation. Make use of the transmission line model, thepaper researches the transmission properties of a single aperture in metal films, anal-yses the transmission mechanism and the near-field distribution of three subwave-length structures, which contain a single subwavelength slit, a single subwavelengthrectangle hole and a single subwavelength hole. The agreement between results intransmission line model and results in other numerical or experimental results con- firms the validity of the transmission line model. The main achievements are asfollows:(1) The paper finishes the design of transmission line model, obtains agree-ments with other numerical and experimental results from references, and gets thered-shift appearance of transmission peak with the thickness of metal films.(2) Basing on transmission line model, the paper discusses the position oftransmission peak, introduce a phrase-shift elements§which is determined by theincident wavelength and the width of the aperture in polarization direction of inci-dent electric field, into transmission model, get the formula of wavelength in whichthe enhanced transmission appears. Meanwhile the role of Fabry-P′erot-like e?ect inenhanced transmission e?ect is discussed.(3) The paper investigates the near-field distribution of a single subwavelengthhole, and verifies the action of surface plasmons in enhanced transmission.The study of transmission properties of a single aperture in metal films o?ers theoret-ical foundation for researching complicated structures, such as metal subwavelengthgratings and arrays of metal subwavelength holes. The transmission line also canbe a theoretical supporting of developing subwavelength devices basing on enhancedtransmission.
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