An S-parameter data file is generated outside of AWRDE, and is later imported into a project in AWRDE. However, when plotted, the S-parameters do not look the same as they did in the tool where they originated.
This is a normalization issue.
- If the S-parameter measurement in Microwave Office specifies the data file as the Data Source Name (i.e. if you are plotting the S-parameters directly from the file, not from a schematic where the file is used), then the measurement will assume 50 Ohm terminations at all ports. To see the data when the ports are terminated in an impedance other than 50 Ohms, the imported S-parameter data file must be placed in a schematic as a SUBCKT block, and terminated with ports that have the desired Z value.
- When the data file is generated, the S-parameter data must be normalized to a constant real system reference impedance, ideally 50 Ohms. Some EM simulators write unnormalized data in a format that meets the Touchstone 1.1 format specification, but according to that format, will be interpreted as being normalized to 50 Ohms. In these files, the frequency dependent complex reference impedance for each port is written as a comment line that is completely ignored. Such data files will import without error, but will not behave like they did in the tool that generated them.