Integral Equation Modeling of Doubly Periodic Structures With an Efficient PMCHWT Formulation

A surface integral equation modeling is described for complex doubly periodic structures. To avoid long computations of the slowly convergent pseudoperiodic Green´s function, fictitious surfaces between translated unit cells are set in order to bound regions of the structure within the symmetry cell and use the free-space Green´s function. The integral operators on top and bottom surfaces are computed with an algorithm originally used for planar frequency-selective surfaces. This approach uses a unique periodic PMCHWT formulation in all the regions, with two different kinds of Green´s function. The method and its advantages are illustrated by two cases in the near-IR domain and in the radar domain. A frequency selective structure is studied, that shows a large flat-top bandwidth under oblique incidence and TM polarization.