Allice Messtechnik R&S ZND, Руководство пользователя, Страница: 121 / 1252

Concepts and features
R&S
®
ZND
121 User Manual 1173.9557.02 ─ 61
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.
With a unidirectional R&S ZND (see Chapter 4.1.4.3, "R&S ZND: unidirectional vs.
bidirectional operation" , on page 80), balanced measurements are not possible.
4.3.6.1 Balanced port configurations
Defining a balanced logical port requires two physical ports.
The physical ports (on the VNA and connected External switch matrices ) are equiva-
lent and can be freely combined to balanced (logical) ports. Moreover, it is possible to
assign arbitrary, independent reference impedance values to each unbalanced port
and to the differential and common mode of each logical port.
Measurement results
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