VNA concepts and features
R&S
®
ZNL/ZNLE
282
User Manual 1178.5966.02 ─ 19
"Fixture Compensation" complements a previous system error correction and replaces
a possible manual length offset and loss correction. For maximum accuracy, it is rec-
ommended to place the reference plane as close as possible towards the outer test fix-
ture connectors using a full n-port calibration. The "Fixture Compensation" is then car-
ried out in a second step, it only has to compensate for the effect of the test fixture con-
nections.
The following features can further improve the accuracy of the fixture compensation:
●
"Direct Compensation" provides a frequency-dependent transmission factor
(instead of a global electrical length and loss).
●
"Open and Short" causes the analyzer to calculate the correction data from two
subsequent sweeps. The results are averaged to compensate for errors due to
non-ideal terminations.
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 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 to compensate for the inaccuracies of the individual
"Open and Short" compensations.
9.6.1.6
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
Offset parameters and de-/embedding
