The field of millimeter-wave (MMW) imaging has progressed significantly over the last two decades. The most obvious
evidence of this is the widespread use of MMW full-body scanners, now commonly found in airports. The path to this
point has been the result of the work of a wide range of experts from many scientific and engineering disciplines. This
article represents one perspective of this progress.
The development of MMW imagers, and all their associated component technologies, image processing techniques,
clever engineering, etc. has been driven by a relatively small number of interesting applications. It has been known for
about 70 years that RF energy can be used to "see" through things like clouds and detect, for example, hostile aircraft.
As the RF frequency goes up to 35, 100, or 340 GHz, it becomes possible to image through obscurants with much
improved resolution. However, as frequency increases, attenuation increases as well, so selecting the right frequency for
the application is an important point. The challenge of seeing through obscurants such as fog, smoke and dust drives one
towards a MMW imaging solution. Typical applications include guiding aircraft through low visibility conditions,
detecting nearby watercraft in the fog, and searching for concealed weapons. So, while these capabilities have been
demonstrated numerous times over the years, the practical and affordable implementation of the systems to accomplish
these goals is where the real story lies.