Active cancellation
Active cancellation is a theoretical military jamming system that involves the sampling of an incoming radar signal, analyzing it, then returning ths signal slightly out of phase, thus "cancelling" it out. While there are no official systems using this in service, it is rumoured to be in use on USAF Stealth Aircraft like the B-2, F-117, F-22A, and possibly the F-35. It is also speculated that the Thales SPECTRA aicraft protection suite also uses this system.