# SP Card

This card defines an S-parameter (S-matrix) request for active sources.

On the Request tab, in the Configurations group, click the  S-parameter (SP) icon.

## Parameters:

Request name
The name of the request.
When S-parameters are computed, each port is automatically loaded by Feko with the S-parameter reference impedance of the port. If this option is checked, and the user has manually defined a load at a port, then the S-parameter load will be added to the existing load at the port. If this option is not checked, then Feko will automatically add the S-parameter reference loads at the various ports, but possible user defined loads of the same load type (see discussion below) will be overwritten (not added) at these ports.
As discussed above, Feko automatically adds loads to ports when computing S-parameters. With this option the behaviour can be controlled after the SP card processing is finished. When this option is enabled, the loads that were automatically added will be removed, and the load situation (for instance for a subsequent far field request) is the same as if the SP card was not used. Otherwise, all the loads as set during the SP card processing will remain in place afterwards.
Calculate all result requests
All result requests (for example, near field, far field and SAR) are calculated for each port excitation / loading scenario included in the S-parameter configuration.
System impedance
The reference impedance in Ohm. This is used for all sources for which no impedance value is specified when defining the source. If this field is empty, it defaults to 50. Note that for waveguide sources (AW card) S-parameters are always related to the corresponding waveguide impedance.

All the ports must be defined before using the SP card. They are identified simply by defining excitation cards. Currently only A1, A2, A3, AE, AF, AN, AB and AW sources are supported. A1, A2 and A3 sources must be selected by label (not with position), and unique labels must be used (no other segments or triangles may have a label which is used for a port).

If the amplitude of any port is set to zero, it will be used as a receive port (or sink) but not as a source. For example, if only S21 and S11 are required for a two port network, one may set the amplitude of the source defining port 2 exactly to zero. Then S12 and S22 are not calculated. In some cases this could save considerable computation time.

The S-parameter load impedance for each of the port sources can be specified at the source itself. If no such impedance was specified, the system impedance ( $\Omega$ ) value specified with the SP card will be used (if this value is not specified it defaults to 50 $\Omega$ ). This S-parameter load impedance will be added automatically to each port. The only exception is the waveguide port (AW card) and the modal port (AB card) where S-parameters are related directly to the corresponding waveguide impedance.