China Electronics Technology Instruments AV3672 Series, Руководство пользователя

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7 Calibration
7.4 High-accuracy Measurement Calibration
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the measurement error will be obvious, especially in reflection measurement, as the adapter is not calibrated. If the
applied calibration kit is different from the calibration kit specified for calibration, the calibration accuracy will be
reduced. The degree of accuracy reduction depends on the difference between the specified calibration kit and
actual calibration kit.
3) Accuracy of interpolation measurement
If the instrument settings are different from calibration settings, calibration data can be automatically interpolated
into the analyzer. In this case, the measurement accuracy cannot be predicted and may drop greatly or not be
affected. The measurement error must be determined depending on the actual situation. If the phase shift added by
two measurement points exceeds 180 degrees, the measurement accuracy will drop greatly as the correct phase data
cannot be interpolated. Generally, the probability of accuracy reduction may increase as a result of interpolation in
the following cases:
➢
When the frequency span between measurement points is increased;
➢
When the frequency span between measurement points is too large;
➢
When the measurement frequency is high, especially above 10GHz.
4) Influence of power level
The power level must not be changed after calibration in order to realize the highest accuracy of error correction.
However, if the power level is changed under the same conditions as the attenuator settings in calibration, the
accuracy of S-parameter measurement only declines a little. If the attenuator settings are changed, the accuracy of
error correction will decline further.
5) System impedance
The system impedance must be changed in measurement of the impedance device (not 50Ω) such as the waveguide
device. The default system impedance is 50Ω.
a) Setting of system impedance
Menu path: [System] > [Configuration] > [Impedance...] .
Enter the system impedance value in the [Impedance] box and click [OK] to close the dialog box.
6) Port extension
The measurement reference plane may be changed as a result of connection of the cbale, adapter or fixture after
calibration, which may lead to increase of the phase shift. In this case, the additional phase deviation can be
compensated by means of port extension. Port extension is the simplest method to compensate the additional phase
shift between the calibration plane and DUT plane, but cannot be used to compensate the loss and mismatch of the
path between the calibration plane and DUT plane. Therefore, the loss and mismatch should be minimized to
realize the highest measurement accuracy. For setting of port extension, refer to “
Setting of port extension
” in “
6.5
Improvement of Phase Measurement Accuracy
”.
7) Correct isolation calibration
Isolation calibration in full 2-port calibration is applied to correct the crosstalk error between ports. It is required
only in measurement of large insertion loss, such as the out-of-band suppression of the filter, isolation of the switch,
etc. When the crosstalk signal is close to the base noise of the analyzer, additional noise will be produced in the
error model as a result of isolation calibration. In order to improve the calibration accuracy, you should:
➢
Perform isolation calibration if necessary;
➢
Use the narrow intermediate frequency bandwidth;
➢
Reduce noise by sweep averaging.
The test port of the analyzer should be connected with a load in isolation calibration. In order to realize the highest
calibration accuracy, it is preferred to connect the loads to two measurement ports at the same time for isolation
calibration. If only one load is provided, connect a well-fitted device to the non-measurement port.