How Does Adding or Restoring Loads for an S-Parameter Configuration Affect the Load Setup for the Next Configuration

This FAQ summarises by means of an example how the settings of an S-parameter configuration affects the load setup for the next configuration (standard or S-parameter).

Example: A model has three ports where port 1 has a load of 10 Ohm. There are two S-parameter configurations defined in the model that use port 1, port 2 and port 3. The system/reference impedance for all three S-parameter configurations are 50 Ohm.
Figure 1. Diagram showing the model port set up.

Scenario 1

For the first S-parameter configuration, the following options are selected at the SP card in EDITFEKO:
Figure 2. The SP card in EDITFEKO.

The port S-parameter reference load of 50 Ohm is added to the existing user-defined loads of 10 Ohm at port 1, resulting in 60 Ohm. Port 2 and Port 3 will have 50 Ohm loads.

After executing the S-parameter configuration, the load at port 1 is restored to its prior state of 10 Ohm (the S-parameter reference loads that were added in this S-parameter configuration are removed).

The load at port 1 will be 10 Ohm for the standard- or S-parameter configuration that follow. Port 2 and port 3 will be restored to its prior state of no loads

Scenario 2

For the first S-parameter configuration, the following options are selected at the SP card in EDITFEKO:
Figure 3. The SP card in EDITFEKO.

The port S-parameter reference load of 50 Ohm is added to the existing user-defined loads of 10 Ohm at port 1, resulting in 60 Ohm. Port 2 and Port 3 will have 50 Ohm loads.

After executing the S-parameter configuration, the S-parameter reference loads are maintained.

The load at port 1 will be 60 Ohm for the standard- or S-parameter configuration that follow. Port 2 and port 3 will maintain the S-parameter reference loads of 50 Ohm.

Scenario 3

For the first S-parameter configuration, the following options are selected at the SP card in EDITFEKO:
Figure 4. The SP card in EDITFEKO.

The port S-parameter reference loads are not added but replaces the existing user-defined loads of 10 Ohm at port 1, resulting in 50 Ohm. Port 2 and Port 3 will have 50 Ohm loads.

After executing the S-parameter configuration, the load at port 1 is restored to its prior state of 10 Ohm (the S-parameter reference loads that were added in this S-parameter configuration are removed).

The load at port 1 will be 10 Ohm for the standard- or S-parameter configuration that follow. Port 2 and port 3 will be restored to its prior state of no loads

Scenario 4

For the first S-parameter configuration, the following options are selected at the SP card in EDITFEKO:
Figure 5. The SP card in EDITFEKO.

The port S-parameter reference loads are not added but replaces the existing user-defined loads of 10 Ohm at port 1, resulting in 50 Ohm. Port 2 and Port 3 will have 50 Ohm loads.

After executing the S-parameter configuration, the S-parameter reference loads are maintained.

The load at port 1 will be 50 Ohm for the standard- or S-parameter configuration that follow. Port 2 and port 3 will maintain the S-parameter reference loads of 50 Ohm.