China Electronics Technology Instruments AV3672 Series, User Manual

Page: 197 / 424

6 Measurement Optimization
6.5 Improvement of Phase Measurement Accuracy
193
Fig. 6.9 Automatic Port Extension
6.5.4 Frequency Point Interval
1) Sample the data of discrete frequency points, connect each sampling point and form a trace on the screen.
2) If the phase deviation of two adjacent frequency points of the device is more than 180°, the displayed phase
slope will look like the reverse phase. This is caused by mixing as a result of insufficient data sampling.
If the group delay is measured but the phase slope is opposite, the symbol will be changed as a result of the group
delay. For example, Fig. 6.10 shows the measurement results of the surface acoustic wave (SAW) bandpass filter.
a) The first figure shows the measurement results of 51 points, and the group delay is negative. But this is
impossible in the actual situation, as the response will not be below the reference line (0s).
b) The second figure shows the measurement results of 201 points, and the group delay is positive, that is, the
response is above the reference line (0s).
Fig. 6.10 Influence of Frequency Interval on Phase Measurement
Prompt
Mixing check
In order to check mixing in measurement, you can check whether the display data change by reducing the
frequency interval. You can increase the number of frequency points or reduce the frequency interval to avoid
mixing.
6.5.5 Specific Operations
1) Compensation of linear phase deviation
Menu path: [Response] > [Scale] > [Electrical Delay...] .
Enter the required value in the [Electrical Delay] box or select the value with the arrow.
Enter the value in the [Velocity Factor] box or select the value between 0 and 1.0 with the arrow.
➢
1.0 corresponds to the light velocity in vacuum.