Anritsu S251B - Manual (Page 54)

NOTES: For best calibration results–compensation for all measurement system
uncertainties–ensure that the Open/Short/Load is at the end of the test port or
optional extension cable; that is, at the same point as the antenna or device to
be tested will be connected.
For best results, use a phase stable Test Port Extension cable. In a typical lab-
oratory cable, bending subsequent to the calibration will cause uncompensated
phase reflections inside the cable. Cables that are not phase stable may cause
measurement errors that become more pronounced as the test frequency in-
creases.
4-8
Chapter 4 Measurements
Figure 4-8. Insertion Gain Mode Calibration Results (RF Out Connected to RF In)