Changes
/* Modeling Transmission Lines Using EM.Ferma */
To add a new wire current source group to a project, right-click on "Wire Currents" on the Navigation Tree, and select "Insert New Current Source..." From the Wire Current Source Dialog, you can change the default brown color of the source group or set the values of the Current and Wire Radius. There is also a check box for "Reverse Current Direction". Note that this will reverse the direction of all the wire currents belonging to the same group. When you draw a line or polyline object under a wire current group in the Navigation Tree, you will notice that direction arrows are placed on the drawn CAD object. You can draw any curve object in the project workspace and convert it to a polyline using [[EM.Cube]]'s Polygonize Tool.
{{Note| If you draw [[Curve Objects|[[Curve Objects|[[Curve Objects|curve objects]]]]]] under a wire current group, they will be permanently converted to polyline objects before running the simulation engine.}}
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Then effective permittivity of the transmission line structure is then calculated from the equation:
<math> \epsilon_{eff} = \frac{C}{C_a} </math>
and its characteristic impedance is given by:
<math> Z_0 = \eta_0 \sqrt{ \frac{C_a}{C} } </math>
where η<sub>0</sub> = 120π Ω is the intrinsic impedance of the free space.
The guide wavelength of your transmission line at a given frequency f is then calculated from:
<math> \lambda_g = \frac{\lambda_0}{\sqrt{\epsilon_{eff}}} = \frac{c}{f\sqrt{\epsilon_{eff}}} </math>
and its propagation constant is given by:
<math> \beta = k_0\sqrt{\epsilon_{eff}} = \frac{2\pi f}{c}\sqrt{\epsilon_{eff}} </math>
where c is the speed of light in the free space.
