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Types of Excitations and Loads

Discrete Sources, Incident Field, and Loads

A structure can be excited by discrete sources or an incident field. Refer to Excitation by an Incident Field > for the second case. Discrete sources can be located on any wire segment and there can be more than one source, as many as there are segments.

A source is used to model the feed point of a transmitting antenna or generator in an electrical circuit. There are two types of sources:

  • Voltage sources
  • Current sources

Current sources can be used to model impressed currents.

For each source, its amplitude and phase must be set. Internal impedances can also be added to model imperfect sources, which can be series RL, series RC, or R+jX impedances.

Lumped loads can also be added to any wire segment, representing resistors, inductors, capacitors, or fixed impedances. There are three types of loads:

  • Series RL impedance (inductive)
  • Series RC impedance (capacitive)
  • Fixed R+jX impedance (the reactance X does not scale with frequency)

To model a pure resistor, add an inductive impedance with L = 0. The unit of inductance can be pH, nH, uH, mH or H, while that of capacitance can be pF, nF, uF, mF or F. These units can be set going to main menu > Tools > Preferences >.


  • Sources are displayed as a yellow circle in the workspace, while loads are displayed as a green highlighted segment. To change the default colors, go to main menu > Tools > Preferences > Workspace tab.
  • Voltage sources have their internal impedance in series, so set a null impedance to model a perfect source.
  • Current sources have their internal impedance in parallel, so set a very large impedance (1E6 Ohm) to model a nearly perfect source.

Excitation by Sources

To excite the wire structure with discrete sources, go to the Setup tab > Excitation panel and select the Discrete Sources option, Fig. 1.

If the Set Input Power option is checked, you can set the total input power to the structure. In this case, the amplitudes of the voltage and current sources will be adjusted to achieve the specified input power.

Fig. 1: Discrete Sources option in the Excitation panel of the Setup tabsheet.
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