Microwave transmission modes in compound metallic gratings

Microwave transmission through one-dimensional metallic compound grating is studied up to 18 GHz. The metallic compound grating consists of a basic unit of one slit a type , two slits ab type , and three slits abc type of different widths. Greatly enhanced transmission is observed at the frequencies near the first and second order waveguide harmonics. The splitting of transmission peak is found for the aband abc-type grating. This effect is explained by the multiphase patterns of the E-field distributions inside the slits, predicted by the numerical calculations. These resonance modes are further physically understood in terms of their photonic band structures. The theoretical bands for the a-type grating are calculated using a quasianalytic model and those for the aband abc-type gratings with superlattice periodicities are plotted according to Brillouin zone folding effect, which show good agreement with the measured results.