Changes

===Lumped Source===

A lumped source is the most commonly used way of exciting a structure in [[EM.Tempo]]. A lumped source is indeed 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]]. Lumped sources can also be place on line arrays. The property dialog of a lumped source has a drop-down list that contains the name of all the legitimate line objects (i.e. lines that are parallel to one of the principal axes) and line arrays. The '''Offset''' parameter of a lumped source is its distance from the start point of the host line. A lumped source by default is placed at the center of its host line. In other words, the default offset value is equal to half the length of the host line object.

A real waveguide structure is usually excited using some type of strategically located probe mechanism. EM.Tempo also provides the '''Waveguide Source''', a special type of source that excites a prescribed TE₁₀ modal field distribution in a hollow rectangular waveguide structure. The scattering [[parameters]] are calculated from knowledge of incident and reflected fields at designated waveguide ports. Waveguide sources typically provide more accurate results for scattering [[parameters]] compared to lumped ports as they represent the actual dominant propagating modes at the transmission line ports.

{{Note|In order to define a waveguide source, you must have at least one hollow box object with no caps or only one end cap or a hollow box array in your project.}}

=== Distributed Source===

Waveguide sources are a special case of distributed sources in [[EM.Tempo]]. A Distributed Source is defined in a rectangular plane of finite extents, parallel to one of the three principal coordinate planes. An impressed electric field component is assumed across the specified rectangular area, which pumps energy into the computational domain. The current version of [[EM.Tempo]] provides three spatial field profiles for a distributed source:

===Plane Wave Source===

In [[EM.Cube]]'s [[FDTD Module]], you can excite a structure with an arbitrary incident plane wave and compute its scattering pattern or bi-static radar cross section. A plane wave excitation is defined by its propagation vector indicating the direction of incidence and its polarization. [[EM.Cube]]'s [[FDTD Module]] provides the following polarization options:

===Gaussian Beam Source===

[[EM.Cube]] gives you an option to illuminate objects with a focused beam instead of a uniform plane wave. The focused beam is a Gaussian beam, which is a solution of the paraxial approximation to the Helmholtz equation. The fundamental Gaussian beam is rotationally-symmetric about its propagation axis, and its transverse field distribution follows a Gaussian function profile. The critical parameter is the beam radius w₀; it is the point where the field drops by 1/e from its value at the center. The beam opens up into a cone along the propagation direction, with a cone angle of tan θ = λ₀/(π.ω₀) (λ₀ is the free-space wavelength).

A Gaussian beam box placed around a horizontal PEC plate. The trident at the corner of the box shows the propagation vector as well as the E-field and H-field polarization vectors. The titled transparent green circle shows the footprint of Gaussian beam at its focal (waist) point.