HP HP 8753E, User Manual, Page: 90 / 699

The phase response shown in 2-32 is undersampled; that is, there is more than
phase delay between frequency points If the incorrect phase and delay information
may result. 2-32 shows an example of phase samples being with less than and
greater than
Figure 2-32. Phase Samples
Undersampling may arise when measuring devices with long electrical length. correct this
problem, the frequency span should be reduced, or the number of points increased until is
less than per point. Electrical delay may also be used to compensate for this effect (as
shown in the next example procedure).
Measurements 2-39