I just read an interesting article on page 54 of the 24 October 2005 issue of Aviation Week, "Through the Walls: High-power microwave devices examined to play roles of sensors as well as weapons", David A. Fulghum.
The title pretty well tells the story. Near the end of the article, they talk of a "Ping" system that fires a high-power microwave pulse at the target area, then listens for the microwave-frequency ringing in any metal in the target area.
Despite the resemblance, this is not a radar: the time interval between pulse and return energy isn't measured to estimate range. Instead, it does the standard PI dance of waiting for the drive pulse to decay and then listening to see if anything is still ringing. The only difference is that PI works at baseband (DC pulses), while Ping works at microwave (bursts of microwave).
Different kinds of objects ring at different RF frequencies, allowing some degree of discrimination. Many of the sought-for objects are made of steel; few weapons are made of pure gold.
The title pretty well tells the story. Near the end of the article, they talk of a "Ping" system that fires a high-power microwave pulse at the target area, then listens for the microwave-frequency ringing in any metal in the target area.
Despite the resemblance, this is not a radar: the time interval between pulse and return energy isn't measured to estimate range. Instead, it does the standard PI dance of waiting for the drive pulse to decay and then listening to see if anything is still ringing. The only difference is that PI works at baseband (DC pulses), while Ping works at microwave (bursts of microwave).
Different kinds of objects ring at different RF frequencies, allowing some degree of discrimination. Many of the sought-for objects are made of steel; few weapons are made of pure gold.