Calibration Data And Indications - Anritsu MS2024B Manual

VNA Measurements 4-7 Calibration Considerations

Calibration Data and Indications

When you perform a calibration, the correction coefficients are calculated for specific
S-parameters (depending on the type of calibration chosen) and for instrument settings
(frequency range, number of points, and power level). The term "calibration correction" refers
to the measurement correction coefficients that are applied to measurements as a result of
your calibration.
When calibration correction is On, the correction is applied to all applicable S-parameters.
For example, if a Full S (1-port) calibration is performed, then only traces that measure S
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have a valid calibration. For those traces, the calibration information data in the Instrument
Settings Summary (described in your instrument user guide) shows "CAL: ON (OK)". All
other traces that do not measure S will display "CAL: --" to indicate that no valid calibration
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is available for those traces. The calibration correction can also be turned off manually under
the Calibration menu by toggling the Cal Correction soft key from On to Off. In that case, the
display will show "CAL: OFF" for all traces that have valid correction data available.
Note that "CAL: OFF" means that a calibration correction has been created, but it is not
currently being used. This is different from "CAL: --", which means that no valid calibration
correction is available for the current setting.
When you have Cal Correction on, you cannot increase the frequency range or the number of
points. You can, however, reduce the frequency range or decrease the number of points
without forcing the calibration to become invalid. When reducing the frequency range, the
VNA Master uses the appropriate points within the new frequency range that have correction
coefficients applied to them. In that case, you can observe that the number of points that are
being used for calibration correction are automatically reduced.
If you reduce only the number of points, then the frequency range is not changed. The
VNA Master finds a subset of the original points in the sweep that can be used. You can
therefore notice that the instrument may not use the exact number of points that you have
entered. It picks a specific number of points that allow the calibration correction to continue
to be valid. If you use the rotary knob, then you will more easily find the available number of
points that can be set. For example, if you calibrated with 201 points, then you can observe
that you can reduce the number of points to 101, 68, 51, 41, and so forth.
If you change the source power setting, then the calibration status will be changed to
"CAL: ON (?P)", which indicates that source power has changed since the instrument was
calibrated (from Low to High, or from High to Low). Refer to "Source Power Menu (MS20xxB
and S412E only)" on page 6-58. In this case, the calibration may still be valid, but a new
calibration is recommended.
Another status information display that you may see is "CAL: ON (?T)" which indicates that
the instrument temperature has deviated by more than a set amount since the time that the
calibration was conducted. The calibration is most likely still valid, but a new calibration is
recommended. If you see "CAL: ON (X)" on the display, this indicates that the instrument
temperature has deviated (since the time the calibration was conducted) by an amount that
has more than likely rendered the calibration invalid. When this occurs, a new calibration is
highly recommended before further measurements are conducted.
Only one calibration is available at one time. Performing a new calibration overwrites any
existing calibration. You can, however, store a measurement setup (with CAL), which also
stores the calibration. You can therefore have multiple calibrations available (as long as the
calibration settings and conditions continue to apply).
Vector Network Analyzer MG PN: 10580-00289 Rev. K 4-19