detection response? For example, I'd like to have maximum value, 1.8V, when
phase difference is -45 degrees, avoiding to use a phase shifter on inputs.
It is definitely a better idea to do the offsetting at the output rather than
trying to manipulate the phase at the RF input.
The section entitled "Modulating Slope and centre point" on page 18 of the
datasheet(RevA) shows you how to modify the offset and gain of both the
magnitude and phase outputs.
You may also figure 3 on page 16 of the datasheet instructive in understanding
the Magnitude and Phase output interfaces.
Looking at figure 5 of the datasheet which shows the Idealized transfer
characteristic, you can see that you can have 1.8V occurring at -45deg by
modifying the gain and offset.