Analytical modeling of non-symmetric and non-uniform compound gratings

Analytical models based on suitable equivalent circuits are proposed to analyze transmission compound gratings made of non-symmetric and/or non-uniform slits. These structures exhibit transmission dips related with the so-called phase resonances, which are known to appear, in the case of highly symmetrical structures and under normal incidence, when the number of air-tilled slits per period is three o more. however, if non-uniform identical slits are properly grouped, simpler structures may exhibit such resonances. This work reports on the analytical modeling of this kind of structures, which have been studied before making use of experimental or numerical approaches. The circuit model provides a relatively simple explanation to the observed transmission spectra and drastically reduces the computation time.