{{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".}}
[[ImageFile:FDTD141.png|800px500px|thumb|Magnitude and Phase of reflection coefficient from a periodic surface plotted vs. frequency.]]
[[ImageFile:FDTD142.png|800px500px|thumb]]Â Figure 1: Magnitude and phase Phase of the complex reflection and transmission coefficients of coefficient from a periodic surface plotted vs. frequency.]
===Periodic FDTD Simulation Types===