Ankit Agrawal, Bob Fougere, Mridula Oravakandy and Greg Siemens wrote up their B.S. report Design, Construction and Testing of a Microwave Radar System for Through-Wall Surveillance (PDF) format. I have only skimmed the report, but it appears they were able to detect people standing behind a test wall by using SAR (synthetic aperature radar) techniques. I’ve often wondered if you could do this with cheap 10ghz Gunnplexer horns. I’ll have to read this over in greater detail later.