Learning Forum

[Guilin Sun]

Here is the grating analysis: Grating projections in FDTD overview

Please note: grating analysis is used for periodic structure with plane wave illumination, with periodic-tpye boundary conditions, Whereas the farfieldexact or farfield3D is only for non-periodic structures with PML BCs. It requires that the fields at the monitor edge is zero, and does not count the periodicity. That said, for periodic simulation you should not use farfield3D. In visualizer, it has approximate farfields from periodic simulation with assuming periodic: Understanding the Assume Periodic option in far field projections  this is an approximate method to identify the higher order diffraction.