Here is a link to the (in)famous Philips Instrument Design Co. radar jammer plans that were once advertised in Car & Driver as "the world's most remarkable radar jammer". When it was first published it caused quite a stir.

The plans contain a decent narrative which explains doppler radar principles and jammer theory, as well as complete plans for building an X/K band jammer from discrete CMOS components. One could build it as-is or use the plans as a jumping-off point for a CarPC implementation.