Concepts and Features
R&S
®
ZNC
96
User Manual 1173.9557.02 ─ 13
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 charac-
terize 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 calculated transmis-
sion factor is resolved by a comparison with the phase obtained in an Auto Length cal-
culation. This compensation type is recommended for test fixture connections 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 com-
pensation 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 individual
"Open and Short" compensations.
3.6.1.6
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 inclu-
ded 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 equivalent
to embedding the DUT by numerically adding a (perfectly matched) transmission line
at that port.
The offset parameters are also suited for length and delay measurements; see
, on page 93. The parameters cannot compensate for a possible
mismatch in the test setup.
Offset Parameters and Embedding
