s2p

S2P is a common file format used to store two-port network S-parameters as a function of frequency. It is widely used in RF and microwave engineering to describe how a device or circuit reflects and transmits signals across a range of frequencies. An S2P file typically contains data that represent S11, S21, S12, and S22 for each frequency point, providing a complete characterization of a two-port network.

In typical ASCII S2P files, each data line corresponds to a single frequency and lists the complex values of the four S-parameters in a fixed order, usually S11, S21, S12, and S22. Each parameter may be encoded as real and imaginary parts or as magnitude and phase, depending on the file’s formatting. A header line usually specifies the frequency units (GHz, MHz, or Hz) and the data encoding (for example RI for real/imaginary or MA for magnitude/angle). The file also designates a reference impedance, commonly 50 ohms.

S2P files are generated by vector network analyzers after calibration and are used directly in simulations, cascade analyses, and impedance or matching studies. They enable engineers to model how devices interact in a network, perform conversions to other parameter representations (such as Z, Y, or T parameters), and assess performance across the frequency band. Software tools that read S2P files include MATLAB, Python (with libraries like scikit-rf), Keysight ADS, NI AWR, Ansys HFSS, Microwave Office, and other RF design packages. The format supports various port counts, with S2P specifically referring to two-port data; other formats exist for higher port counts, such as S3P and S4P.