[[Image:MORE.png|40px]] Click here to learn more about the various '''[[FDTD Source Types]]'''.
[[Image:FDTD48.png|thumb|300px|The Port Definition dialog]]
[[Image:FDTD49.png|thumb|300px|Reassigning sources to ports and defining coupled ports.]]
===Defining a New Source===
=== Excitation Waveform & Frequency Domain Computations ===
[[Image:FDTD48A.png|thumb|600px|EM.Tempo's Excitation Waveform dialog.]]
When an FDTD simulation starts, your project's source starts pumping energy into the computational domain at t > 0. [[Maxwell's Equations|Maxwell's equations]] are solved in all cells at every time step until the solution converges, or the maximum number of time steps is reached. A physical source has a zero value at t = 0, but it rises from zero at t > 0 according to a specified waveform. [[EM.Tempo]] currently offers four types of temporal waveform:
===Defining Ports===
[[Image:FDTD48.png|thumb|300px|EM.Tempo's Port Definition dialog.]]
[[Image:FDTD49.png|thumb|300px|Reassigning sources to ports and defining coupled ports in EM.Tempo.]]
Ports are used to order and index sources for circuit parameter calculations like S/Y/Z [[parameters]]. That is why they are defined in the '''Observables''' section of Navigation Tree. In [[EM.Cube]]'s [[FDTD Module]], you can define ports at the location of '''Lumped Sources''', '''Waveguide Sources''' and '''Distributed Sources'''. In other words, ideal sources or other types of sources cannot be used to define ports or calculate port characteristics.