== Multiport Networks ==
[[File:twoport1.png|thumb|400px| Cascading two two-port network devices.]]
[[File:twoport2.png|thumb|400px| The property dialog of a multiport network device.]]
[[File:twoport3.png|thumb|400px| The property dialog of the Complex Impedance device.]]
A multiport network is a frequency-domain âblack-boxâ block that is modeled by its S-[[parameters]] as a function of frequency. [[RF.Spice]] currently offers the following models:
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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[[File:twoport1.png|thumb|400px| Cascading two two-port network devices.]]
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{{Note | Multipart Network devices do not work with âLive Simulationâ or Transient Test as their models normally contain S-[[parameters]] at high frequencies only.}}
Phase is always specified in degrees. For most passive devices, you normally use a Re/Im format. However, the manufacturer data sheets of active devices like BJTs, MOSFETs and MESFETs typically specify the S-[[parameters]] in dB/Ph format with the frequency expressed in GHz.
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[[File:twoport2.png|thumb|400px| The property dialog of a multiport network device.]]
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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.
Note that the default reference impedance of the Complex Impedance is zero and must always stay zero to function properly. In order to have a fixed impedance element, define the same Real(z11) and Imag(z11) values for the minimum and maximum frequencies of your circuit. Due to the interpolation between these two values, you will always get the same impedance value at all the frequencies in between those two limits.
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[[File:twoport3.png|thumb|400px| The property dialog of the Complex Impedance device.]]
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== Generic Transmission Lines ==