[DonRotolo]

Essentially, doppler "spins" the antenna in a circle very fast - fast enough to create a measurable doppler shift at several hundred Megahertz. You could just mount a single antenna onto a turntable (think phonograph) and spin it really fast (think CIM at full speed), but mechanical issues favor the electronic switching method, since the difficulties created by switching are easier to manage than the mechanical ones of spinning an antenna really fast.

Your system is phase-differential time of arrival (ToA), which has the potential to be more accurate but at a two or three order-of-magnitude uptick in complexity. You need N receivers in most implementations, fer instance.