===Time Domain Simulation Of Periodic Structures===
[[Image:fdtd_perdiag_tn.png|thumb|350px250px|Diagram of a periodic structure illuminated by an obliquely incident plane wave in [[FDTD Module]]]]
A periodic structure is one that repeats itself infinitely in one, two or three directions. [[EM.Cube]]'s [[FDTD Module]] allows you to simulate doubly periodic structures with periodicities along the X and Y directions. Many interesting structures such as frequency selective surfaces (FSS), electromagnetic band-gap (EBG) structures and metamaterial structures can be modeled using periodic geometries. In the case of an infinitely extended periodic structure, it is sufficient to analyze only a unit cell. In the FDTD method, this is accomplished by applying periodic boundary conditions (PBC) at the side walls of the computational domain.