Now you see 'em, now you don't.
gr4techie,
The same principle is used in GCA (and other ?) airfield ground radars to produce the Moving Target Indicator (MTI) effect. Most of the "ground effects" are suppressed (but sometimes the leaves on trees, moving to an fro in a strong wind, will show up - and of course birds !)
The problem of aircraft going round you in a circle (parts of a circuit) remain. But as a GCA (you hope) has the aircraft coming directly towards you, and it cannot stop (except a helicopter !), all you have to worry about is a chap on finals (whom you cannot see) possibly coming round at your man.
Local and Runway Controllers are employed at vast expense to make sure that never happens.
In the Bloodhound case, would going round it in ever-decreasing circles be any good ? (just asking).
D.