When visibility is poor, instrument landing systems (ILS) create an image of the runway for pilots so that they can safely land a plane. Under the Department of Defense's Dual-Use Technology Initiative, a TRW-led consortium of industrial companies and government agencies, including NASA, has adapted millimeter-wave technology to an airborne camera for civilian, commercial, and military users.
A demonstration unit of the Passive Millimeter Wave Camera has been completed for checkout tests and flight demonstration. The camera operates in the millimeter wave portion of the electromagnetic spectrum to "see" through fog, snow, clouds, smoke, and dust, creating visual-like video images of objects, people, runways, obstacles, and the horizon. Since millimeter-wave technology can penetrate fabrics and other materials, it is also suitable for concealed weapons detection.
"The Holy Grail for low-visibility landing has always been to give pilots an image of the runway though fog in order to land the aircraft as though it were clear," explains Merit Shoucri, department manager of electro-magnetic systems and technology at TRW Inc. There are two basic techniques for creating ILS images: lower cost synthetic vision systems and more costly enhanced vision systems.
Synthetic vision systems indirectly interpret readings from conventional instrumentation to "predict" how the runway should look and create a corresponding image. However, such an image is not as reliable as images created using the direct observation techniques of enhanced vision systems. "With enhanced vision systems, what you see is what you get," says Shoucri. "A true image of the runway is displayed."
Enhanced vision systems typically use some type of radio frequency (RF) device. One landing aid, for instance, has a sophisticated radar system that requires a complex antenna array. Another entails an onboard RF "camera" that calls for a large number of detectors receiving ground-transmitted signals to create a "picture" of the runway. "Since most of these enhanced vision systems involve extensive and expensive equipment installation on the ground and in the aircraft," Shoucri explains, "only the busiest airports are equipped."
In contrast, the Passive Millimeter Wave Camera is an enhanced vision system that requires no ground-based transmitters. Instead, it detects black body radiation. Shoucri says, "This camera is no different from the infrared (IR) cameras that pick up IR radiation, except it detects the very low frequency millimeter waves, which propagate better through fog, snow, smoke, clouds, and dust."
The enabling technology is known as the monolithic millimeter wave integrated circuit (MMIC). A two-dimensional millimeter wave focal plane array with 1,040 elements captures the scene in front of it in much the same way as a conventional camera. While millimeter wave receiver technology has been around for decades, the technology has been too bulky and expensive, according to Shoucri. "Using modern production techniques we can put a whole millimeter wave receiver on a 2 × 7-mm chip." From one 3-inch gallium arsenide wafer, he says, "120 receivers can be produced at very low cost."
For more information about millimeter wave technology from TRW Inc.: Enter 538