By exploiting the in-house finite-difference time-domain (FDTD) program, the optical properties of a designated 2-D array of U- to H-shaped holes perforated on a metallic film are analyzed. Some specific near-field features are found to be associated with the three mechanisms underlying the transmission spectral profiles, namely, excitation of surface electromagnetic (EM) modes, Wood's anomalies (WAs), and shape resonances (SRs), thus providing a way to reveal the physical nature of the enhanced transmission phenomenon.