R&S
®
ZVL
System Overview
Measured Quantities
Quick Start Guide 1303.6538.62-01
90
E
S
12
is the reverse transmission coefficient, defined as the ratio of the wave
quantities b
1
(reverse measurement with matched input, b
1,rev
in the figure above
and a
1
= 0) to a
2
.
E
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
3.2.2 Impedance Parameters
An impedance is the complex ratio between a voltage and a current. The analyzer
provides converted impedances: each impedance parameter is obtained from a single
S-parameter.
The converted, matched-circuit impedances describe the impedances of a DUT that is
terminated at its outputs with the reference impedance Z
0i
. i numbers the analyzer/DUT
port.
The analyzer converts a
single
measured S-parameter to determine the corresponding
converted impedance. As a result, converted Z-parameters cannot completely describe
general n-port DUTs:
E
A reflection parameter Z
ii
completely describes a one-port DUT. For n-port DUTs
(n>1) the reflection parameters Z
ii
describe the input impedances at ports i (i = 1 to
n) under the condition that each of the other ports is terminated with its reference
impedance (matched-circuit parameters).
