Wander,
The Airbus FCOM is less than helpful about how it works, but I'm pretty sure that the scanner tilt is irrelevant to its operation. As to whether it requires droplets, I guess it must have to have something to 'bite' on - however small. A google search on 'predictive windshear radar' came up with quite a few websites. I don't have time right now to look at many, but
this one seemed to be a Honeywell site which might be of assistance.
Cheers,
mcdhu