simon

was it really busy on the highway at the time? were there alot of cars around you?
you can *try* and argue that there were too many cars and how can he be certain his radar hit your car. I'm not sure what the radar guns show, so you might want to confirm that first. If it shows the license plate then you are out of luck.

Basically in court you can ask the officer "What kind of training you received to ensure that your gun is pointed at the car you want to check on? When did you last receive your training?" etc etc