R&S ZVB - Page 59

R&S
®
ZVA / R&S
®
ZVB / R&S
®
ZVT System Overview
Measured Quantities
Operating Manual 1145.1084.12 – 30 44
linear equation:
The four 2-port S-parameters can be interpreted as follows:
 S
11
is the reflection coefficient of port 1, i.e. the ratio between outgoing wave b
1
and incident wave
a
1
in a forward measurement with matched port 2:
S
11
= b
1
/ a
1
, if |a
1
| > 0 and a
2
= 0
 S
21
is the forward transmission coefficient, defined as the ratio between outgoing wave b
2
and
incident wave a
1
in a forward measurement with matched port 2:
S
21
= b
2
/ a
1
, if |a
1
| > 0 and a
2
= 0
 S
12
is the reverse transmission coefficient, defined as the ratio between outgoing wave b
1
and
incident wave a
2
in a reverse measurement with matched port 1:
S
12
= b
1
/ a
2
, if |a
2
| > 0 and a
1
= 0
 S
22
is the reflection coefficient of port 2, i.e. the ratio between outgoing wave b
1
and incident wave
a
1
in a forward measurement with matched port 1:
S
22
= b
2
/ a
2
, if |a
2
| > 0 and a
1
= 0
Meaning of squared amplitudes
The squared amplitudes of the incident and outgoing waves and of the matrix elements have a simple
meaning:
|a
i
|
2
Available incident power (= the power provided by a generator with a source impedance equal to the
reference impedance Z
0
) at DUT port i=1,2
|b
i
|
2
Reflected power at DUT port i=1,2
10 log|S
ii
|
2
= 20
log|S
ii
|
Reflection loss at DUT port i=1,2
10 log|S
21
|
2
= 20
log|S
21
|
Insertion loss of forward transmission
10 log|S
12
|
2
= 20
log|S
12
|
Insertion loss of reverse transmission
Multiport Parameters
The multiport S-parameters extend the standard 2-port S-parameters to a larger number of incident and
outgoing waves. For a 4-port DUT,
,
where a
i
denotes the incident and b
i
the outgoing wave at DUT port i = 1 to 4, and the S-parameters are
expressed as S
ij
(i,j = 1 to 4).
The S-parameters considered so far are referred to as single-ended. However, the S-parameter
description can also be used to describe different propagation modes for balanced DUT ports. This results
in the so-called mixed mode S-parameters. The analyzer measures either single-ended or mixed mode S-
parameters.