Concepts and Features
R&S
®
ZNB/ZNBT
180
User Manual 1173.9163.02 ─ 38
Auto Length and Loss vs. Direct Compensation
"Auto Length and Loss" compensation is a descriptive correction type: The effects of
the test fixture connection are traced back to quantities that are commonly used to
characterize transmission lines.
Use this correction type if your test fixture connections have suitable properties in the
considered frequency range:
●
The electrical length is approximately constant.
●
The loss varies essentially due to the skin effect.
"Direct Compensation" provides a frequency-dependent transmission factor. The
phase of the transmission factor is calculated from the square root of the measured
reflection factor, assuming a reciprocal test fixture. The sign ambiguity of this calcula-
ted transmission factor is resolved by a comparison with the phase obtained in an Auto
Length calculation. This compensation type is recommended for test fixture connec-
tions that do not have the properties described above.
A "Direct Compensation" resets the offset parameters to zero.
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 in order to compensate for the inaccuracies of the indi-
vidual "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 176. 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.
Offset Parameters and Embedding
