The dsPIC30F4012-based Doppler Radar System enables you to track speeding motorists in your neighborhood. The well-designed system generates a microwave energy burst with a 10-GHz transceiver. The microwave signal bounces off of a moving vehicle and the frequency (Doppler) shift is measured to determine its speed.
I must say this is the first DIY Radar system I’ve seen well documented. It’s definitely worth a try if you’re into this kind of projects.