S820E UG PN: 10580-00343 Rev. H 6-5
VNA Mode 6-3 Calculating and Displaying S-Parameters
6-3 Calculating and Displaying S-Parameters
S-parameters are a measure of the ratio of two complex voltage levels, one
measured by the port receiver, and one measured by the reference receiver.
S-parameters therefore consist of unitless complex numbers.
Depending on the application, S-parameters can be displayed in many ways
and can be used to calculate other parameters. S-parameters consist of real
and imaginary numbers. More typically, however, they are represented as
magnitude and phase. In most cases, the magnitude is displayed in dB (this
term is often called log magnitude). We can display phase as “linear phase”.
With phase, we cannot tell the difference between one cycle and the next.
After going through 360 degrees, we are back to where we began. We can
display the measurement from – 180 degrees to + 180 degrees, which keeps
the phase transition point at the top and bottom edges of the display and
away from the important 0 degrees area that is used as the phase reference.
The S820E supports the following display types. Each type is associated with
a particular S-parameter:
(where j is the square root of –1).
Log Magnitude
Applications
To measure return loss at Port 1 (or Port 2), use the Log Mag display with S
11
(or S
22
).
To measure the gain or loss in a DUT that is connected between Port 1 and
Port 2, use the Log Mag display with S
21
or S
12
.
LogMagnitude (dB) 20Log
10
S
xy
=
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