R&S
®
ZVA/ZVB/ZVT Measured Quantities
1145.1084.12 3.27 E-1
• S
22
is the output reflection coefficient, defined as the ratio of the wave quantities b
2
(reverse
measurement with matched input, b
2,rev
in the figure above and a
1
= 0) to a
2
, measured at
PORT 2.
Meaning of squared amplitudes
The squared amplitudes of the incident and outgoing waves and of the matrix elements have a simple
meaning:
|a1|
2
Available incident power at the input of a two-port (= the power provided by a
generator with a source impedance equal to the reference impedance Z
0
)
|a2|
2
Available incident power at the output
|b1|
2
Reflected power at the input of a two-port
|b2|
2
Reflected power at the output
10*log|S
11
|
2
(= 20*log|S
11
|) Reflection loss at the input
10*log|S
22
|
2
Reflection loss at the output
10*log|S
21
|
2
Insertion loss at the input
10*log|S
12
|
2
Insertion loss at the output
Multiport Parameters
The multiport S-parameters extend the standard 2-port S-parameters to a larger number of incoming
and outgoing waves. For a 4-port DUT,
∗
=
a
a
a
a
SSSS
SSSS
SSSS
SSSS
b
b
b
b
4
3
2
1
44434241
34333231
24232221
14131211
4
3
2
1
,
where again a
i
(i = 1 to 4) denote the incident, b
i
(i = 1 to 4) denote the outgoing waves, and the S-
parameters are expressed as S
<out>< in>
.
The indices of the S-parameters described so far number the output and input ports of a DUT; the
parameters are referred to as single-ended S-parameters. The S-parameter description can also be
used to differentiate between different propagation modes of the waves at the output and input ports.
This results in the so-called mixed mode S-parameters. The analyzer measures either single-ended or
mixed mode S-parameters.
Impedance Parameters
An impedance is the complex ratio between a voltage and a current. The analyzer provides two
independent sets of impedance parameters, essentially based on different n-port circuit models:
• Matched-circuit impedances, converted from reflection S-parameters
• Open-circuit Z-parameters
Converted Impedances
The converted, matched-circuit impedances describe the impedances of a DUT that is terminated at its
outputs with the reference impedance Z
0i
displayed in the Port Configuration dialog. i numbers the
analyzer/DUT port.
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