Keysight N9912A Service Manual page 62

Theory of Operation
Operation in Modes
Figure 5-4 Signal Paths for One Port CAT/NA Measurements
The source and receiver step through each frequency point in the sweep.
Single sweep measures both NA-A and NA-R signals. Because two ADC's are
used simultaneously, phase relationship is preserved. (Phase information is
available to the user only in NA mode.)
Details About Two Port Measurements
Refer to the block diagram below showing the signal paths highlighted in
color.
5-22 Keysight N9912A Service Guide