You can define ports for lumped sources, waveguide sources and distributed sources. In that case, the FDTD simulation engine calculates the scattering (S) parameters of your multiport network over the entire bandwidth specified in your project. From the scattering matrix, EM.Cube determines the impedance and admittance matrices of your network over the operational bandwidth. You can plot the S/Y/Z parameters in EM.Grid. If your project has more than one port, the FDTD time loop will be run as many times as the number of ports, N. In each time loop run j (j = 1, 2, ..., N), the source(s) associated with the jth port is (are) excited with a unit amplitude and all the other sources are turned off. In this run, all the S<sub>ij</sub> parameters (i = 1, 2, ..., N) are calculated. At the end of the Nth run, the entire S matrix is completed.
===The FDTD Simulation Engine Settings=== [[Image:FDTD58.png|thumb|300px|[[FDTD Module]]'s Engine Settings dialog]]
An FDTD simulation involves a number of numerical parameters that can be accessed and modified from the FDTD Engine Settings Dialog. To open this dialog, select '''Menu > Simulate > Simulation Engine Settings... '''or open the '''Run Dialog''', and click the '''Settings''' button next to the engine dropdown list.
{{Note|Keep in mind that for highly resonant structures, you may have to increase the maximum number of time steps to very large values above 20,000.}}
[[Image:FDTD58.png]]
Figure 1: [[FDTD Module]]'s Engine Settings dialog.
The "'''Acceleration'''" section of the FDTD Simulation Engine Settings dialog give three options for the FDTD kernel: