Keep in mind that FDTD is a time domain algorithm. At the end of an FDTD simulation, a Discrete Fourier Transform (DFT) is performed on the time domain data to calculate frequency domain characteristics such as near fields, far field radiation patterns, RCS, S/Y/Z [[parameters]], etc.:
:<math>\tilde{F}(f) = \int_{-\infty}^{\infty} f(t) e^{-j2\pi f t} \, dt \quad \approx \quad \Delta t \sum_{n=0}^N f(n\Delta t) e^{-j2 \pi n f \Delta t} </math>
<!--[[Image:FDTD68.png]]-->