Concepts and features
R&S
®
ZNA
277User Manual 1178.6462.02 ─ 29
4.7.5 True differential mode
Option R&S ZNA-K61
Differential transmission lines and circuits are widely used, because their characteris-
tics give them a lower susceptibility to electromagnetic interference. Linear balanced
devices can be tested with sufficient accuracy using the virtual differential mode, where
the vector network analyzer generates unbalanced stimulus signals and uses a mathe-
matical transformation to convert unbalanced wave quantities into balanced S-parame-
ters. A different behavior is expected for nonlinear balanced devices, where the trans-
mission characteristics of the DUT may depend on how closely the stimulus signal
matches real operating conditions.
In true differential mode, a R&S ZNA with two or more internal sources generates true
differential and common mode stimuli at arbitrary reference planes in the test setup
and determines mixed-mode S-parameters, wave quantities and ratios. It can also per-
form true differential measurements on frequency-converting DUTs or to use true differ-
ential mode in combination with external frequency converters. Moreover the true dif-
ferential mode provides two additional sweep types, the Amplitude Imbalance and
Phase Imbalance Sweep.
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Like the virtual differential mode, the true differential mode requires a port configu-
ration with at least one balanced port. However, in true differential mode a bal-
anced source port requires independent sources for the constituent physical ports.
– On a 2-port R&S ZNA, the optional internal second source is required.
See Chapter 4.7.23, "Internal 2nd source and 2nd LO generator for 2-port
R&S ZNA", on page 303.
– To have two balanced ports, a 4-port R&S ZNA with 4 sources is required.
See Chapter 4.7.20, "Internal 3rd and 4th source for 4-port R&S ZNA",
on page 302.
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Because true differential mode is a special kind of Phase coherent source control,
option R&S ZNA-K6 is a prerequisite for option R&S ZNA-K61. The Prerequisites
for accurate phase control also apply to true differential mode
4.7.5.1 Virtual vs. true differential mode
The analyzer uses different stimulus signals and different mathematical methods to
obtain results in normal, virtual differential, or true differential mode. The following table
gives an overview.
Optional extensions and accessories
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