{{Note|It is very important to keep in mind that only in the case of normal incidence does [[EM.Cube]] compute the reflection and transmission coefficients over the entire specified bandwidth of the project. At oblique incidences when θ > 0, the computed R/T coefficients after the discrete Fourier transformation are valid only at the center frequency of the project for the given value of the incident θ<sub>0</sub> angle. In other words, the computed R/T coefficients at all the other frequencies away from the center frequency correspond to different values of the incident θ angle. As a result, [[EM.Cube]] only saves the reflection and transmission coefficients at the center frequency into the output data files "reflection_coefficient.CPX" and "transmission_coefficient.CPX".}}
[[File:FDTD141.png|500px|thumb|Magnitude and Phase of reflection coefficient from a periodic surface plotted vs. frequency.]]
{| border="0"|-| valign="top"|[[File:FDTD141.png|300px|thumb|Magnitude and Phase of reflection coefficient from a periodic surface plotted vs. frequency.]]| valign="bottom"|[[File:FDTD142.png|500px300px|thumb|Magnitude and Phase of transmission coefficient from a periodic surface plotted vs. frequency.]]|-|}
===Periodic FDTD Simulation Types===