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calculation.
2) Apply the smoothing function of the analyzer.
Perform sweep once, enable the smoothing function and change the value percentage in smoothing settings. This is similar to change
of the frequency interval between sweep points. This method allows a wider group delay aperture, and the phase shift is allowed to
exceed 180° within the smoothing aperture.
Group delay measurement can be done in the following scanning types:
a) Linear frequency;
b) Logarithmic frequency;
c) Segment sweep.
The group delay aperture depends on the frequency interval and the sweep point density, therefore, it changes in the logarithmic
frequency and segment sweep mode.
8.5.4.
Improvement of Measurement Accuracy of Group Delay
It is important to keep the phase difference of adjacent measurement points less than180° during group delay measurement;
otherwise, the phase and group delay information will be incorrect, as shown in Fig. 8.15. Insufficient sampling may occur in
measurement of the device of long electrical delay. Adjust the following settings until the measurement trace does not change so as to
ensure that the phase difference of two adjacent points is less than 180°.
1) Increase the number of points.
2) Reduce the frequency span.
Fig. 8.15 Influence of Insufficient Sampling on Group Delay Measurement
The frequency response is a main error of group delay measurement. This error can be significantly reduced by means of through
type response calibration. Perform the full 2-port calibration to realize higher accuracy. For the amplifier, the response may vary with
the temperature. Therefore, the test should be done at the working temperature of the amplifier.
8.5.5.
Steps of Group Delay Measurement
1) Reset the analyzer. Adjust the source power of the analyzer to test the amplifier.
a) Set the source power of the analyzer within the linear zone of the analyzer response (generally at least 10dB less than the
1dB input compression point).
b) If required, connect one attenuator to the output port of the amplifier to fully attenuate the output power of the amplifier and
prevent the receiver at the reception end of the analyzer from compression or burning.
2) Connect the tested device, as shown in Fig. 8.16.
