  We report the enhanced transmission of electromagnetic waves through a single
subwavelength aperture by making use of the resonance behavior of a split ring
resonator (SRR) at microwave frequencies. By placing a single SRR at the
near-field of the aperture, strongly localized electromagnetic fields are
effectively coupled to the aperture with a radius that is twenty times smaller
than the resonance wavelength. We obtained 740-fold transmission enhancement by
exciting the electric resonance of SRR. A different coupling mechanism, through
the magnetic resonance of SRR, is also verified to yield enhanced transmission.
Good agreement is obtained between the microwave measurements and numerical
simulations.
