It isn't a shield
Radar detects an incoming RPG and some form of detonation device, perhaps working like a shotgun, fires to prematurely detonate the RPG's shaped charge warhead. As cool as it is, I wonder how hard it would be to saturate the defenses. RPGs are cheap and plentiful. If you fired several of them at one time, I'd wager that at least one would get through. Still, it's definitely better than nothing.