Maybe, with all the different bands the cops can run, and with laser, it is getting harder and harder to make them work well enough.
I was a Radar Technician in the Army for 8 years. Why do you think I signed up for the MOS? I wanted to learn how to jam cop radar!!!
You probably gain more by trying to mask your radar picture. Think of it this way. Dip your car in chrome. Now, from the cops vantage point, shine the worlds brightest spotlight on your car, whatever reflects back is your radar picture. Block it....
Now, as for radar jamming? Fun topic really...
You have to find out what freq they are running on. ANYTHING transmitted back to them is gonna mess up their reciever. High enough power can (if they aren't protected) fry the rx. The RX is designed to RX only a few micro volts of signal, send a signal back in a watt or 2 and you fry it. They have reciever protectors likely there to protect it, so it probably won't work anymore. Finding the freq and transmitting back before the other gun gets a signal back on you is tough. Called speed of light... 1 pulse and they can have you.
I don't know how much they vary in freq and what is favorite band now, but you would need some pretty $$ test equipment to work on designing something. That freq range isn't for just anyone, it is not easy to tune in that range and parts are $$$$.
So, if you determine the band (K, Ka, Ku, X, etc) and you can determine the range of the gun (contact the manufacturer!) and then get a Gunn Diode and a waveguide horn you can try it. Gunn diodes are cool.
And the one you really want to read: http://www.shfmicro.com/diode.htm
All you need to is tune for the freq range you need and transmit. You may need a license to transmit there, so broadcasting on that range can get you a $10K fine from the FCC. But, if it falls in the Ham bands, you can get a license there, or if you just need a General Radiotelephone license, you can do that too. Then a cop can do a darn thing legally! It would be hard for them legally to bust you anyway, as it is WAAAY our of their juridiction. They would need the FCC to do it, and they don't have any evidense that you are doing it. Just a radar gun that doesn't work when you are around.
A friend of mine and I got into some interesting thoughts on it, but never got too far, it would be interesting though to revive it!