== EM.Picasso's Excitation Sources ==
Your planar structure must be excited by some sort of signal source that induces electric surface currents on metal parts, magnetic surface currents on slot traces, and conduction or polarization volume currents on vertical vias and embedded objects. The excitation source you choose depends on the observables you seek in your project. EM.Picasso provides the following source types for exciting planar structures (click on each type to learn more about it):
* {| class="wikitable"|-! scope="col"| Source Type! scope="col"| Applications! scope="col"| Restrictions|-| '''[[Common_Excitation_Source_Types_in_EMGlossary of EM.Cube's Excitation Sources#Lumped_.26_Gap_Sources Strip Gap Circuit Source | Strip Gap SourcesCircuit Source]]'''* | style="width:300px;" | General-purpose point voltage source (or filament current source on slot traces)| style="width:250px;" | Associated with a PEC rectangle strip|-| '''[[Common_Excitation_Source_Types_in_EMGlossary of EM.Cube's Excitation Sources#Probe_Sources Probe Gap Circuit Source |Probe SourcesGap Circuit Source]]'''* | style="width:300px;" | General-purpose voltage source for modeling coaxial feeds| style="width:250px;" | Associated with an embedded PEC via set|-| '''[[Common_Excitation_Source_Types_in_EMGlossary of EM.Cube's Excitation Sources#De-Embedded_Sources Scattering Wave Port | De-embedded SourcesScattering Wave Port Source]]'''* | style="width:300px;" | Used for S-parameter computations| style="width:250px;" | Associated with an open-ended PEC rectangle strip, extends long from the open end|-| '''[[Common_Excitation_Source_Types_in_EMGlossary of EM.Cube's Excitation Sources#Hertzian_Dipole_Sources Hertzian Short Dipole Source |Hertzian Short Dipole SourcesSource]]'''* | style="width:300px;" | Almost omni-directional physical radiator| style="width:250px;" | None, stand-alone source|-| '''[[Common_Excitation_Source_Types_in_EMGlossary of EM.Cube's Excitation Sources#Plane_Wave_Sources Plane Wave | Plane Wave SourcesSource]]'''* | style="width:300px;" | Used for modeling scattering & computation of reflection/transmission characteristics of periodic surfaces| style="width:250px;" | None, stand-alone source|-| '''[[Hybrid_Modeling_using_Multiple_Simulation_EnginesGlossary of EM.Cube's Excitation Sources#Working_with_Huygens_Sources Huygens Source | Huygens SourcesSource]]'''| style="width:300px;" | Used for modeling equivalent sourced imported from other [[EM.Cube]] modules | style="width:250px;" | Imported from a Huygens surface data file|} Click on each category to learn more details about it in the [[Glossary of EM.Cube's Excitation Sources]].
For antennas and planar circuits, where you typically define one or more ports, you usually use lumped sources. EM.Picasso provides three types of lumped sources: gap source, probe source and de-embedded source. A lumped source is indeed a gap discontinuity that is placed on the path of an electric or magnetic current flow, where a voltage or current source is connected to inject a signal. Gap sources are placed across metal or slot traces. A rectangle strip object on a PEC or conductive sheet trace acts like a strip transmission line that carries electric currents along its length (local X direction). The characteristic impedance of the line is a function of its width (local Y direction). A gap source placed on a narrow metal strip creates a uniform electric field across the gap and pumps electric current into the line. A rectangle strip object on a slot trace acts like a slot transmission line on an infinite PEC ground plane that carries a magnetic current along its length (local X direction). The characteristic impedance of the slot line is a function of its width (local Y direction). A gap source placed on a narrow slot represents an ideal current source. A slot gap acts like an ideal current filament, which creates electric fields across the slot, equivalent to a magnetic current flowing into the slot line. Probe sources are placed across vertical PEC vias. A de-embedded source is a special type of gap source that is placed near the open end of an elongated metal or slot trace to create a standing wave pattern, from which the scattering [[parameters]] can be calculated accurately.