Click here to go to our page on radiometric receivers
Click here to learn about biological hazards of microwave radiation
New for March 2020! We've add a video on research into terahertz imaging conducted at NASA's JPL.
Microwave imaging is a very broad topic, we've only scratched the surface here. Maybe someone out there has more to contribute?
Imaging for security
Microwave imaging is a growing field, it is used in airports throughout the world in concert with other security measures such as metal detection and baggage X-ray.
There are principally two type of imagers, passive and active. Passive uses "natural" radiation from people to take a peek, while active illuminates the subject with RF energy and examines the backscatter.
Imagers in airports can be handheld, or full-body.
There is controversy surrounding the ability of imagers to see beneath clothing. However, the quality of the image makes it a poor substitute for pornography, and your image is not really identifiable, so quit your whining and do what the nice officer says. It takes a few seconds to gather and process the RF energy, be sure to hold still!
Back on June 25, 2003, TSA security lab director Susan Hallowell allowed her body to be scanned by an early version of the backscatter system. This one image set the industry back five years! Now full body scanners are deployed at many airports, it has become part of routine screening.
Scan of Susan Hallowell with hidden weapons
Photo of Director Hallowell showing the hidden weapon.
Imaging at Terahertz Frequencies
Terahertz frequencies can provide high resolution with modest apertures, but still have the ability penetrate clothing. They're not affected by environmental factors like dust or rain, and are increasinglly used in defense and space-related industries.
There is a great video on the topic from Dr. Goutam Chattapadhyay from NASA's Jet Propulsion Laboratory (part of IEEE MTT's webinar series). In this video, Dr. Chattapadhyay describes an ultra-wideband radar-based terahertz imaging system (active imaging, as opposed to passive):
The system uses a 675 GHz solid-state transmit/receive system in a frequency modulated continuous wave (FMCW) radar mode working at room temperature. The imager has sub-centimeter range resolution by utilizing a 30 GHz bandwidth. It has comparable cross-range resolution at a 25m stand-off distance with a 1m aperture mirror. A fast rotating small secondary mirror rapidly steers the projected beam over a 50 x 50 cm target at range to produce images at frame rates exceeding 1 Hz.