Millimeter-wave technology has always represented the "high end" of RF/microwave engineering, with frequencies extending well beyond 30 GHz. The design challenges, of course, have to do with generating, channeling, and processing such small wavelengths, which requires that the circuit features be physically small. But in spite of the challenges, the technology has found niche applications over the years, from missile guidance and activation to secure line-of-sight (LOS) communications.
The technology is also getting a huge push from the US Transportation Security Administration (TSA) for airport security. Millimeter-wave-based whole body imagers were introduced by the TSA late last year at Hartsfield-Jackson Atlanta International Airport to detect weapons, explosives, and other threats under passengers' clothing without the need for a physical search. Passengers for the scan are randomly selected, and are given an option for a different form of check, such as a physical pat-down search. Most passengers have opted for the millimeter-wave approach. The technology is currently in use at 16 airports, including at JFK in New York and LAX in Los Angeles, with additional airports planned for deployment this year.