It can be seen that the discrete Fourier transform multiplies the samples of time-domain field quantities by the time step Δt. This means that the resulting Fourier transforms of electric and magnetic field components now have units of V/m/Hz or A/m/Hz, respectively. Moreover, the Fourier transforms of the three waveform types have different spectral values at the observation frequency f<sub>0</sub>. This makes it difficult to compare the FDTD simulation results with the results from [[EM.Cube]]'s other computational modules. For example, in the Planar, MoM3D and Physical Optics Modules, a plane wave source typically has a complex-valued functional form of exp(-jk<sub>0</sub>'''k.r'''), which has a unit magnitude. In [[FDTD Module]], the time domain plane wave source has a functional dependence of the following form:
:<math> \mathbf{E^{inc}}(r,t) = (E_{\theta}^{inc} \hat{\theta} + E_{\phi}^{inc} \hat{\phi}) f \left[ (t-t_0) - \frac{\mathbf{\hat{k} \cdot r} - l_0}{c} \right] </math>
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where f(t) is the temporal waveform, t<sub>0</sub> is the time delay, l<sub>0</sub> is a spatial shift, and c is the speed of light in the free space. The Fourier transform of the above temporal function evaluated at f = f<sub>0</sub> has an amplitude different than 1. For this purpose, EM.Cube's [[FDTD Module]] normalizes the temporal waveform by the magnitude of its Fourier transform at the observation frequency f<sub>0</sub>. As a result, a temporal plane source with any of the three waveform types will always create spectral incident source with |'''E<sup>inc</sup>'''('''r''', f<sub>0</sub>)| = 1. The temporal waveform normalization factors for the three waveform types are given below:
:<math> \begin{align} &(N.F.)_{Sinusoidal} = \frac{2}{T} = \frac{2}{N \Delta t} \\&(N.F.)_{Gaussian} = \frac{ e^{(\pi f_0 \tau)^2} }{ \sqrt{\pi} \tau } = \frac{1}{\sqrt{\pi} \tau \delta^{1/4}} \\ &(N.F.)_{Modulated} = \frac{2}{\sqrt{\pi} \tau} \end{align} </math>
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