# '''[[Common_Excitation_Source_Types_in_EM.Cube#Gaussian_Beam_Sources |Gaussian Beam Source]]''': A distributed source with a complex-valued focused Gaussian beam profile defined using a virtual box object enclosing the entire physical structure.
[[Image:FDTD_FF4.png|thumb|400px|A lumped source defined on a vertical PEC line object and a waveguide source defined across a hollow PEC box.]]
A lumped source is the most commonly used way of exciting a structure in EM.Tempo. A lumped source is an ideal source that must be placed on a line object that is parallel to one of the three principal axes and shows up as a small red arrow on the host line. Lumped sources are typically used to define ports and compute the port characteristics like S/Y/Z [[parameters]]. Using simple lumped sources, you can simulate a variety of transmission line structures in EM.Tempo including filters, couplers or antenna feeds. This approach may become less accurate at very high frequencies when the details of the feed structures become important and can no longer be modeled with highly localized lumped ports. In such cases, it is recommended to use âDistributed Sourcesâ, which utilize accurate modal field distributions at the ports for calculation of the incident and reflected waves. Waveguide source is used to excite the dominant TE<sub>10</sub> mode of a hollow rectangular waveguide. Waveguide sources typically provide more accurate results for scattering [[parameters]] of waveguide structures compared to lumped sources as they represent the actual dominant propagating modes at the transmission line ports.
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<td> [[Image:FDTD_FF4FDTD_FF5.png|thumb|320px360px|A lumped source defined on plane wave box enveloping a vertical PEC line object and a waveguide source defined across a hollow PEC boxplate at normal incidence: θ = φ = 0°.]] </td><td> [[Image:FDTD_FF5FDTD_FF5A.png|thumb|350px360px|A plane wave box enveloping Gaussian beam source illuming a PEC sphereplate at oblique incidence: θ = 135°, φ = 225°.]] </td>
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