The FDTD method provides a wideband simulation of your physical structure. In order to produce sufficient spectral information, an appropriate wideband temporal waveform is needed to excite the physical structure. The choice of the waveform, its bandwidth and time delay all affect the convergence behavior of the FDTD time marching loop. By default, EM.Tempo uses a modulated Gaussian waveform with optimal [[parameters]]. Another issue of concern is the numerical stability of the time marching scheme. You might expect to get better and more accurate results if you keep increasing the FDTD mesh resolution. However, in order to satisfy the Courant-Friedrichs-Levy (CFL) stability condition, the time step must be inversely proportional to the maximum grid cell size . A high resolution mesh requires a smaller time step. To let the fields in the computational domain fully evolve over time, a smaller time step will require a larger number of time steps to converge. [[EM.Cube]] automatically chooses a time step that satisfies the CFL condition.
[[Image:Info_icon.png|40px]] For more detailed informationabout the stability of the FDTD algorithm, see '''[[Waveforms_and_Discrete_Fourier_Transforms#Waveform.2C_Bandwidth.2C_Stability | Waveform, Bandwidth, Stability]]'''.
=== A Note on Pros and Cons of FDTD Simulation ===