By Rick Robinson
GEORGIA TECH PIONEERED HIGH-FREQUENCY RADARS
The term millimeter wave refers to radar that operates at extremely high frequencies and is used for short-range applications. Millimeter waves can help guide or detect missiles, aid airplanes landing in bad weather, help vehicles avoid collisions, and support security screening.
Millimeter waves are lower in frequency than the electromagnetic waves that produce light and heat, but higher than the waves used by radio broadcasts and cellular phones. Also known as mmW or MMW, they occur in the extremely high frequency (EHF) area of the electromagnetic spectrum, from 30 to 300 gigahertz (GHz).
The Georgia Tech Research Institute (GTRI) has been a leader in millimeter wave technology for decades. During and after World War II, the Engineering Experiment Station (EES) — as Georgia Tech’s applied research arm was then known — made a name for itself in radar research. By the 1970s, EES investigators were deeply involved in the basic science behind the behavior and performance of the quirky but valuable mmW spectrum.
“During those early days of millimeter wave research, Georgia Tech led in developing applications for millimeter wave technology — certainly in the areas of radar, radiometry, and sensing in general,” recalled Edward K. Reedy, retired director of GTRI. “We contributed heavily to the phenomenology of millimeter waves: We had at least 50 people working in electro-optics and materials characterization, as well as radar.”
One reason for the intense interest in millimeter waves was their size. Millimeter waves are shorter than other radar waves, so unlike the conventional radars that use those large rotating antennas seen in movies, mmW systems require only small antennas. These diminutive antennas can be etched into semiconductors that fit into a car bumper or the tip of a missile.
From the start, moreover, GTRI researchers were intrigued by how millimeter wave behavior varies throughout the EHF band. On the negative side, those short wavelengths limit how far mmW signals can travel — a kilometer or less is the rule.
However, the fact that the waves tend to weaken turned out to offer certain advantages. For instance, mmWs can be used in security applications involving body scanning because they scarcely penetrate the skin.
GTRI researchers also found that though millimeter waves moving at one frequency might travel poorly through fog or rain, at a neighboring frequency, they might propagate much more effectively under the same conditions.
“We were able to identify a number of windows, such as around 95 GHz and 225 GHz, where millimeter wave radars worked much better than at other regions,” Reedy said. “We also helped pioneer millimeter wave technology for collision avoidance in automobiles.”
GTRI’s recent mmW work has focused on applications such as automated landing for aircraft and helicopter guidance under dusty conditions.