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Calibration—purpose and types
Calibrating an analyzer eliminates systematic
errors and makes measurements more accurate.
This note has shown calibrations for various con-
figurations and where in the test setup to perform
these calibrations. Of the two types of calibration
discussed, full two-port calibration is the most
accurate because it removes all systematic errors
in the measurement setup, ideally up to where the
DUT connects to the analyzer. Response calibration
is less accurate and removes only the frequency-
tracking errors. Frequency-tracking errors are
associated with the differences in frequency
response between one channel and another. In a
full two-port calibration, the analyzer sweeps in
both forward and reverse directions, while in a
response calibration, the analyzer sweeps only
in the forward direction.
Calibration tips for best results
In addition to understanding what type of calibra-
tion is possible for each configuration and where
to perform the calibration, it is important to
understand how to get the most out of a calibra-
tion. The following topics discuss techniques and
considerations for achieving the best calibration
results.
Dynamic accuracy
By examining the dynamic accuracy response of
an analyzer, you can optimize the power levels for
calibration and measurement. Dynamic accuracy
refers to the uncertainty associated with calibrating
at one signal level and measuring at another.
The dynamic accuracy plot for the Agilent 8753E
shows extremely low uncertainty (0.02 to 0.06 dB)
if receiver power is between –10 and –50 dBm
independent of the calibration power level (Figure 5).
Perform calibration and measurements so that the
signal level at the receiver is in this high-accuracy
range. At lower signal levels, noise is a factor; at
higher levels, receiver compression is a factor.
Reference power level
–10 dBm
1
–20 dBm
–30 dBm
0.1
0.01
0 –10 –20 –30 –40 –50 –60 –70 –80 –90 –100
10
Test port power (dBm)
Figure 5. Agilent 8753E dynamic accuracy
17
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