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Operating Concepts
S-Parameters
S-Parameters
The key accesses the S-parameter menu which contains softkeys that can be used to select the
parameters or inputs that define the type of measurement being performed.
Understanding S-Parameters
S-parameters (scattering parameters) are a convention used to characterize the way a device modifies
signal flow. A brief explanation of the S-parameters of a two-port device is provided, however, for additional
details, refer to Application Notes 95-1 and 154.
S-parameters are always a ratio of two complex (magnitude and phase) quantities. S-parameter notation
identifies these quantities using the numbering convention:
S out in
where the first number (out) refers to the test-device port where the signal is emerging and the second
number (in) is the test-device port where the signal is incident. For example, the S-parameter S
21
identifies
the measurement as the complex ratio of the signal emerging at the test device's port 2 to the signal
incident at the test device's port 1.
Figure 7-3 is a representation of the S-parameters of a two-port device, together with an equivalent
flowgraph. In the illustration, "a" represents the signal entering the device and "b" represents the signal
emerging. Note that a and b are not related to the A and B input ports on the analyzer.
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