Since his designs use solar power to run the electric fans that maneuver the craft, they could fly above ecologically-sensitive areas without creating noise or air pollution. Military radar works by sending a radio wave out from a radar transmitter. When the wave hits an object it reflects some of the wave back. A radar receiver located at the same place as the transmitter can then detect the wave. By knowing how long it took for the wave to return, what direction it returned, and if the frequency of the wave was shifted, the distance, location and speed of the object can be calculated and shown on the radar screen.
Some objects reflect radio wave better than others.
Flat objects will reflect a wave strongly in a particular direction. Circular or rounded objects reflect the wave more poorly because they scatter it in many directions. In normal flight they are designed to present their perfectly flat surfaces away from potential radar sites at an angle. A competing stealth design, though, would use a rounded aircraft, like a saucer, to scatter the waves. Before photos of the F-117A were released many engineers speculated that the plane would be round and flat with a short, sharp, pointed nose at the forward end.