AF Card

This card defines a uniform electric current filament impressed between two arbitrary points inside of the FEM region (it does not have to coincide with the edges of tetrahedra). This can be used to excite for instance a patch antenna.

On the Source/Load tab, in the Sources on geometry group, click the  Current source (AF) icon.

Figure 1. The AF - Impressed electric current (FEM) dialog.


New source
A new excitation is defined which replaces all previously defined excitations.
Add to sources
A new excitation is defined which is added to the previously defined excitations.
Define port (old format)
Source position
When this item is selected, the feed segment is determined by specifying the Cartesian coordinates in the Segment centre group. These values are in m and are scaled by the SF card if the SF card has Modify all dimension related values checked.
Reference defined port
The label of the referenced port defined using the PT card.
Amplitude of source (A)
Amplitude in A of the impressed line current.
Phase of source (degrees)
Phase of the current in degrees.
X, Y, Z coordinate
Coordinates of the start and end points in m. (Note that all the coordinate values are optionally scaled by the SF card.)
Reference impedance (Ohm)
The reference impedance of the excitation is used for S-parameter calculations and is the reference impedance used for realised gain calculations. It is also the default reference impedance used to calculate and display the reflection coefficient in POSTFEKO. If this field is empty or 0 in an S-parameter calculation, the value specified at the SP card is used. For realised gain and reflection coefficient calculations, 50 Ohm will be assumed when the field is empty or 0.
The following restrictions apply when using the impressed current elements of the AF type inside a FEM region:
  • The electric current source would usually be connected to metallic surfaces at its terminals, but this is neither enforced nor checked in Feko. If a physical connection to a metallic structure is required, then the user should ensure that the feed terminals are also attached in the discretised model.
  • Input impedance is computed for this source from the line integral over the electric field solution between the terminals of the source. The length of the impressed current should therefore be small compared to the shortest wavelength in the band of interest to render a reasonable accuracy.
  • An intrinsic limitation of this model is that no radius is taken into account, therefore the field is singular in the vicinity of the filament. This affects the accuracy of the computed input impedance of the source.