Abstract
In transmission metallic gratings, quasi-total transmission of light is achieved by two different mechanisms, which are the excitation of horizontal and vertical surface-plasmon resonances. Both resonances are represented on complex photonic band structures for a wide range of grating thicknesses. The evolution of the electromagnetic field intensity provides a physical understanding of the behaviour of dispersion curves and of lifetime discontinuities in Wood-Rayleigh anomalies in particular. Both radiative and non-radiative processes are distinguished in the resonances' width, giving limits for the use of metallic gratings in photonic devices.