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S-Parameters
The
(Meas)
key provides access to 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
here. For additional details refer to Hewlett-Packard Application Notes A/N
95-l
and
A/N
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
Sparameter
&
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 6-8 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.
INCIDENT
521
TRANSMITTED
INCIDENT
S12
(REVERSE)
pg639d
Figure
6-S.
S-Parameters of a Two-Port Device
Application and Operation Concepts 6-26