Changes

=== De-Embedded Sources ===

EM.Cube's [[Planar Module]] provides de-embedded sources for the exclusive purpose of accurate S parameter calculation based on Prony's method. A de-embedded source is indeed a gap source that is placed close to an open end of a feed line. The other end of the line is typically connected to a planar structure of interest. Like gap sources, de-embedded sources can be placed only on rectangle strip objects. '''During mesh generation, EM.Cube automatically extends the length of a port line that hosts a de-embedded source to about two effective wavelengths.''' This is done to provide enough length for formation of a clean standing wave current pattern. The effective wavelength of a transmission line for length extension purposes is calculated in a similar manner as for the planar mesh resolution. It is defined as <math>\lambda_{eff} = \tfrac{\lambda_0}{\sqrt{\varepsilon_{eff}}}</math>, where &epsilon;_eff is the effective permittivity. For metal and conductive sheet traces, the effective permittivity is defined as the larger of the permittivities of the two substrate layers just above and below the metallic trace. For slot traces, the effective permittivity is defined as the mean (average) of the permittivities of the two substrate layers just above and below the metallic trace. The host port line must always be open from one end to allow for its length extension. You have to make sure that there are no objects standing on the way of the extended port line to avoid any unwanted overlaps.

Figure 1: The mesh of a patch antenna excited with a de-embedded source. Note the feed line extension in the mesh view.

* In the '''Source Properties''' section, you can specify the '''Source Amplitude''' in Volts (or in Amperes in the case of slot traces) and '''Phase''' in degrees.

* In the '''Prony Mode Extraction''' section, you can specify the '''Number of Prony Modes''', which refers to the number of positive-negative exponential pairs that are extracted from the standing wave current data. The default value is 1 and represents the dominant quasi-TEM incident/reflected signal pair.

In a planar project with de-embedded sources, if you do not define any ports, the feed lines will simply be extended, and the exciting gap sources will be placed at the open ends of these extended lines. Note that if you define a de-embedded source along with a port definition in your project, then all the other port-assigned sources of your project must be of the same de-embedded type. You can define de-embedded sources for coplanar waveguides (CPW) on slot traces. To do so, you need to place two collocated, de-embedded sources with identical offsets (same phase reference plane), same source amplitudes but 180° phase difference. Note that for CPW structures, setting the number of Prony modes to 2 can get you more accurate results. In this case, the two extracted Prony modes will include the incident and reflected, odd and even, propagating modes of the CPW.