Scattering parameters or S parameters are used to analyze the behavior of RF devices and their networks at any frequency.
S parameters are complex numbers that characterize a device. Since the response of electronic devices varies with frequency, the S parameters of the device will be frequency dependent too.
These parameters are usually used to characterize one port and two port devices.
There are two types of 1 port devices - loads and sources.
A 1 port load is characterized by just one S parameter - S1. S1 corresponds to the voltage reflection coefficient of the device.
A 1 port source is characterized by one S parameter, S1, its reflection coefficient and also by its supply voltage.
A two port device is characterized by a 2 x 2 matrix of S parameters.
S = | |
For a RF amplifier, S11 is the input impedance, S22 is the output impedance, S21 is the gain of the amplifier and S12 is close to 0.
S parameters can be measured by vector network analyzer or Time Domain Reflectometry.
Various formulae exist to convert from S parameters to Impedances, and convert S parameters to Y parameters.
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