Agilent Technologies 8719D, User Manual

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Deviation Linear Phase
By adding electrical length to “flatten out” the phase response, you have removed the linear
phase shift through your device. The deviation from linear phase shift through your device is
all that remains.
1.
2.
3.
4.
Follow the procedure in “Measuring Electrical Length.
increase the scale resolution, press:
and turn the front panel knob or enter a value from the front panel
.
To use the marker statistics to measure the maximum peak-to-peak deviation from linear
phase, press:
Activate and the electrical delay to obtain a minimum peak-to-peak value.
Note
It is possible to use to measure peak-to-peak deviation in only one
portion of the trace, see Calculate the Statistics of the Measurement Data”
located earlier in this chapter.
Figure 2-36. Deviation from Linear Phase Example Measurement
Group Delay
The phase linearity of many devices is specified in terms of group or envelope delay. The
analyzers can translate this information into a related parameter, group delay. Group
delay is the transmission time through your device under test as a function of frequency.
Mathematically, it is the derivative of the phase response which can be approximated by the
following ratio.
where is the difference in phase at two frequencies separated by The quantity AF is
commonly the “aperture” of the measurement. The analyzer calculates group delay from
its phase response measurements
The default aperture is the total frequency span divided by the number of points across the
display (i.e. 201 points or 0.5% of the total span in this example).
1. Continue with the same instrument settings and measurements as in the previous procedure,
“Deviation from Linear Phase.”
240 Making Measurements