Extraordinary transmission spectrum of a copper film pierced with a periodic array of subwavelength rectangular holes is
measured by the terahertz time-domain spectroscopy. The transmission coefficient is strongly depended on the angle
between the polarization of terahertz electric field and the latitudinal direction of the periodic apertures. When the angle
increases from 0° to 90°, a transmission peak becomes stronger and another peak reduces. The transmission is proposed
to be the contributions of the localized surface plasmons inside the apertures. The finite-difference-time-domain (FDTD)
simulation results are in good agreements with the experimental observations.