Concepts and features
R&S
®
ZNA
206
User Manual 1178.6462.02 ─ 20
Open/Short vs. Open and Short compensation
A non-ideal "Open" or "Short" termination of the test fixture connections during fixture
compensation impairs subsequent measurements, causing an artificial ripple in the
measured reflection factor of the DUT. If you observe this effect, an "Open and Short"
compensation may improve the accuracy.
"Open and Short" compensation is more time-consuming because it requires two con-
secutive fixture compensation sweeps for each port, the first with an open, the second
with a short circuit. The analyzer automatically calculates suitable averages from both
fixture compensation sweeps to compensate for the inaccuracies of the individual
"Open and Short" compensations.
4.6.1.6
Application and effect of offset parameters
Offset and loss parameters can be particularly useful if the reference plane of the cali-
bration cannot be placed directly at the DUT ports, e.g. because the DUT has non-
coaxial ports and can only be measured in a test fixture. Offset parameters can also
help to avoid a new complete system error correction if a cable with known properties
has to be included in the test setup.
●
A positive length offset moves the reference plane of the port towards the DUT,
which is equivalent to deembedding the DUT by numerically removing a (perfectly
matched) transmission line at that port.
●
A negative offset moves the reference plane away from the DUT, which is equiva-
lent to embedding the DUT by numerically adding a (perfectly matched) transmis-
sion line at that port.
The offset parameters are also suited for length and delay measurements; see
on page 202. In contrast to the embedding/deembedding
functions (see
Chapter 4.6.2, "Embedding and deembedding"
parameters cannot compensate for a possible mismatch in the test setup.
Each offset parameter is assigned to a particular port. The delay parameters affect the
phase of all measured quantities related to this port; the loss parameters affect their
magnitude. An offset at port 1 affects the S-parameters S
11
, S
21
, S
12
, S
31
... Some quan-
tities (like the Z-parameters) depend on the whole of all S-parameters, so they are all
more or less affected when one S-parameter changes due to the addition of an offset
length.
To account for the propagation in both directions, the phase shift of a reflection param-
eter due to a given length offset is twice the phase shift of a transmission parameter. If,
at a frequency of 300 MHz, the electrical length is increased by 250 mm (λ/4), then the
phase of S
21
increases by 90 deg, whereas the phase of S
11
increases by 180 deg.
Equivalent relations hold for the loss.
If the trace is displayed in "Delay" format, changing the offset parameters simply shifts
the whole trace in vertical direction.
Offset parameters and de-/embedding
