== Defining an Excitation Source ==
An electromagnetic boundary value problem requires an excitation source that typically appears as the right-hand-side (RHS) term of a differential or integral equation. In each moduleof [[EM.Cube]]'s computational modules, you should need to choose the right source type depending on the purpose of your simulation and based on the observables you define for your project. For example, for computing the radar cross section (RCS) of a target, you need a plane wave source. If you are interested in computing the S/Z/Y parameters of your structure, then you have to choose a source type like a gap or lumped source that supports a "Port Definition" observable.
== Exciting Multiport Structures Using Linear Superposition ==