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/* Multiport Networks */
== Multiport Networks ==
A multiport network is a frequency-domain “black-box” block that is modeled by its S-[[parameters]] as a function of frequency. [[RF.SpiceA/D]] currently offers the following models:
* Complex Impedance (a two-pin device)
Each pair of pins form a port of the device. In other words, an N-port device has 2N pins or terminals. In most cases, the negative pin of a port is grounded, while its positive pin is connected to the other parts of your circuit. It is very important that all the pins of a multiport device are properly connected to ensure a successful simulation.
An N-port device is characterized by a complex-valued NxN scattering (S) matrix. A one-port has only one S-parameter, i.e. s11. A two-port has four S-[[parameters]]: s11, s21, s12 and s22. A Complex Impedance is a special type of one-port that is defined by its complex-valued z11 parameter rather than by s11. [[Multiport Networks|Multiport networks]] can be connected to one another through their ports. For example, you can cascade two two-ports as shown in the opposite figure. Note how the negative pins of the two devices have been grounded.
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{{Note | Multipart Network devices do not work with “Live Simulation” or Transient Test as their models normally contain S-[[parameters]] at high frequencies only.}}
=== Defining S-Parameters ===
Among RF.Spice's multiport network device, the one-port, two-port, three-port and four-port are all defined based on their S-parameters. All multiport network devices have a "Port Reference Impedance" parameter. The default value of the reference impedance is 50 Ohms for the one-port, two-port, three-port and four-port. For most RF circuits, you do not have to touch the 50Ω default value.
Besides entering the S-parameter values manually using in the parameter table, you can directly import these values from a text file with a ".TXT" file extension. For this purpose, click the button labeled "Load from File..." in the property dialog. This opens up the standard [[Windows]] Open dialog, with the file type set to text files. Browse your folders and select the text file to load the data from. The S-parameters you import to [[RF.Spice A/D]] can come from manufacturer data sheets or they can be generated by electromagnetic simulation suites such as [[EM.Cube]]. For example, among [[EM.Cube]]'s computational modules, the FDTD, Planar MoM, Wire MoM and Surface MoM simulation engines all generate S-parameter text files for structures with port definitions. These files can directly be loaded into [[RF.Spice A/D]].
===The Complex Impedance Device ===
