Adding an S-Parameter Configuration

Define an S-parameter configuration and add it to the model.

  1. Add an S-parameter configuration using one of the following workflows:
    • On the Request tab, in the Configurations group, click the  Multiport S-parameter icon.
    • In the configuration list, click the . From the right-click context menu, select Multiport S-parameter.

    Figure 1. The Request S-parameters dialog.
  2. In the Port column, from the drop-down list, select the port.
  3. In the Properties column, specify the following:
    • For waveguide ports, specify the type (TE1 / TM2/ TEM3), indices and rotation of the mode.
    • For ports other than waveguide and FEM modal ports, specify the reference impedance. If no impedance is specified, a default reference impedance of 50 Ohm is used.
  4. In the Active column, select the check box to use the port as a “source” (else the port is only a “receiving” port).
    Note: For example, if a Port1 and Port2 is defined, but only Port1 is active, only S11 and S21 are calculated.
  5. [Optional] Select the Export S-parameters to Touchstone file check box to export the S-parameters to a .snp file.
    For each S-parameter configuration, a separate Touchstone file is created. The file name is in the form <FEKO_base_filename>_<requestname>(k).snp where:
    file name of the model
    request name
    number of ports
    a counter (integer) to distinguish between the results of multiple requests with the same name and the same number of ports.

    Feko does not normalise the S-parameter values to a global reference impedance when exporting S-parameters to Touchstone file. The values are referenced to the impedance specified on each port.

    Some industry tools that use the Touchstone format, often assume that all values are referenced to a common impedance. When exporting S-parameters for use in an industry tool that supports only a single reference impedance, specify the reference impedance for each port to ensure the correct interpretation.

During the calculation of S-parameters, the specified reference impedances are added as loads to the ports. These loads remain in place after the S-parameter calculation. If the loads are removed once the S-parameter calculation is complete, the full matrix computation and LU decomposition step are repeated for the MoM solution method. This is typically the most time-consuming step in the analysis.

  1. [Optional] Select the Restore loads after calculation check box to remove the loads once the S-parameter calculation is complete.
  2. In the Label field, add a unique label for the request.
  3. Click Create to request the S-parameter results and to close the dialog.
The port numbers in an S-parameter solution are indexed based on the order of appearance in the port list on the Request S-parameters dialog, and not on the label of the selected port.
1 transverse electric (TE)
2 transverse magnetic (TM)
3 transverse electric and magnetic (TEM)