RADAR -- which stands for radio detection and ranging -- is a technique that's used all around us in everyday life. It can determine the presence and the velocity of an object such as an airplane or even a person. Radar works via a transmitter that shoots a pulse of electromagnetic energy. The pulse travels to a target, bounces off, and then the radar listens for the echo off that target. Engineers at the MIT Lincoln Laboratory in Lexington, Massachusetts, build the most advanced radar systems in the world. With the help of a special testing chamber, these scientists can test their radar antennas indoors -- before taking them out into the real world.