Microwave transmission modes in compound metallic gratings

Abstract

Microwave transmission through one-dimensional metallic compound grating is studied up to $18\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$. 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 $ab$- and $abc$-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 $ab$- and $abc$-type gratings with superlattice periodicities are plotted according to Brillouin zone folding effect, which show good agreement with the measured results.