they do make radar jammers (or "shifters"), and are highly illegal in most (not all) states. these are devices which the FCC has sanctioned, but have been made illegal by the state legislature (note the device itself is illegal), such as all radar detectors are illegal in Virginia, even tho they are entirely passive.

Make sure that you speak to several people in state DOT, as well as state law enforcement BEFORE purchasing these jammers--as they can get you a ticket up to $1000---because keep in mind its hard for the radar/lidar gun to pin down your speed, but these jammers put out highly detectable emmisions(in otherwords, your driving around with a giant billboard that says "I'm a speeder, pull my ass over, for no reason at all")