Circuit S-Parameter Technical Notes
S-parameter elements or N-ports are generic components whose characteristics are defined by user-supplied network-parameter data. They are black box elements because no information regarding their function is provided except for their network parameters. S-parameter elements can introduce measured data into the simulation for comparison or modeling, or represent a part of a circuit for which modeling is difficult or undesired.
The network parameters are frequency-dependent and must be specified at many frequency points. The network parameters may be supplied as complex scattering parameters (S parameters), complex admittances (Y parameters), complex impedances (Z parameters), complex propagation constants (gamma parameters), or complex terminal characteristic impedances (Z0 parameters). The data may be given in either polar form or in rectangular form.
Network parameter data may be entered in spreadsheet form in the N-port import window, but is more commonly read from external files. This data then may be extracted on the data files and used in the simulation. Several data file formats are supported:
- Touchstone/EESof Data — This format uses the .s*p, .y*p, or .z*p filename extension. Only one dataset may be present in each .s*p, .y*p, or .z*p data file. See Touchstone Data Format.
- HFSS V6.0+ (Z 0-Gamma) – This format uses the .szg file extension, and contains gamma or Z0 parameter data.
- Circuit (Compact FLP) – This format uses the .flp filename extension, and may contain several data groups, each of which is preceded by a header. The data group header identifies the group by means of a label, which is used as a reference name. See Compact FLP Data File.
- CITIfile – This format uses the .cit filename extension, and contains S-parameter data in a proprietary format. See CITIfile Format.
- SSS file – This format uses the .sss filename extension, and contains data in a proprietary state-space format. See State-Space Method .
The same set of methods for handling frequency-dependent data is applied throughout Circuit designs. Most data is processed using a state-space method. Convolution is also available.
Since network data may come from any source, they may contain violations of causality and passivity that prevent simulation from succeeding. Topics in the following list describe the methods for identifying violations and correcting for them.
Links to S-Parameter Topics
Troubleshooting S-Parameter Issues
S-Parameter General References
Causality Checking and Enforcement
Passivity Checking and Enforcement
Causality, Passivity, and Fitting Errors
Reference Nodes on S-Parameter Elements