VNA Concepts and Features
R&S
®
ZNL/ZNLE
225
User Manual 1178.5966.02 ─ 07
●
"b
1
/a
1
Src Port 1" is the ratio of the outgoing wave at DUT port 1 and the incident
wave at DUT port 1 (i.e. DUT port 1 ist stimulated). This corresponds to the forward
reflection coefficient S
11
.
8.3.5
Unbalance-Balance Conversion
Unbalance-balance conversion is the simulation of one or more unbalance-balance
transformers (baluns) integrated in the measurement circuit. It converts the DUT ports
from an unbalanced state into a balanced state and virtually separates the differential
and common mode signals. The analyzer measures the unbalanced state but converts
the results and calculates mixed mode parameters, e.g. mixed mode S-parameters. No
physical transformer is needed.
To perform balanced measurements, a pair of physical analyzer ports is combined to
form a logical port. The balanced port of the DUT is directly connected to the analyzer
ports. For a two-port analyzer, a single balanced port can be defined.
VNA
1
2
Physical VNA ports
Common
mode
Differential
mode
Physical
transformer
(balun)
DUT
VNA
1
2
DUT
Balanced port
Internal balance-
unbalance
conversion
Logical
VNA ports
Unbalance-balance conversion avoids the disadvantages of real transformers:
●
There is no need to fabricate test fixtures with integrated baluns for each type of
DUT.
●
The measurement is not impaired by the non-ideal characteristics of the balun (e.g.
error tolerances, limited frequency range).
●
Calibration can be performed at the DUT's ports. If necessary (e.g. to compensate
for the effect of a test fixture), it is possible to shift the calibration plane using length
offset parameters.
●
Differential and common mode parameters can be evaluated with a single test
setup.
8.3.5.1
Balanced Port Configurations
Defining a balanced logical port requires two physical ports.
Measurement Results
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