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Multiport Network device, i.e. one-ports, two-ports, three-ports and four-ports, are all modeled based on their frequency-domain S-[[parameters]]. Most active and passive RF devices can be modeled as multipart networks. For example, RF diodes can be modeled as one-ports, while RF transistors (BJTs, JFETs, MOSFETs, and MESFETs) can be modeled as two-ports. Many semiconductor manufacturers publish S-parameter data sets for their RF devices. The manufacturer data sheets usually contain S-[[parameters]] in Mag/Phase format tabulated as a function of frequency expressed in GHz. On the other hand, you can model many passive devices such as filters, directional couplers, hybrids, etc. as multiport structures using full-wave electromagnetic simulators like [[EM.Cube]]. The port characteristics of such devices are typically written into data files as a function of frequency. A particular case of interest is transmission line components with complex geometries or material composition, for which [[RF.SpiceA/D]] does not provide any database models. as an example, consider the case of a "Finline" transmission line. In a finline-based circuit, you may need one of more of the following general transmission line components:

[[RF.SpiceA/D]] allows you to import S-parameter-based models of RF devices from text files. Before describing how to import S-parameter data files, let us first discuss the format of the data files in more detail. S-parameter data files must have a ".TXT" file extension. These files must start with a ".model", a ".symbol" statement, and a format statement starting with the character "#". The model text file can have any number of comment lines at the beginning of the file or elsewhere. Comment lines are preceded by "*" or "!". All the text after these characters on the rest of the line will be ignored.

The model statement specifies the name of your RF device model, in this case, MyNewRFBJT. The symbol statement determines the device type and schematic symbol. The symbol_name can only be one of the choice given in the table below. The frequency units can be hz, khz, mhz or ghz. "s" implies the s-[[parameters]]. If the complex_data_format is left blank, the S-[[parameters]] are interpreted to have Mag/Phase format, with the magnitude on a linear scale and phase expressed in degrees. The other options for complex_data_format are "ma" for magnitude expressed in dB, or "ri" for Real/Imag format. The last part specifies the reference impedance value, which must come after letter "r". In the above example, the reference impedance is 50 Ohms.