Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRNATO Measurement Campaign in Switzerland
What a radar sensor can image and what it misses partly depends on the frequency of the radiation it emits. Several radar sensors of different wavelengths could, therefore, provide added value, or so the hope is. A NATO campaign on a military test site in Switzerland is set to provide insights.
From August 18 to 23, 2024, in Äuli-Village in Walenstadt, Switzerland: During a measurement campaign as part of NATO group SET-317, various drones will circle over the military test site, carrying radar sensors from Fraunhofer FHR, the French Onera, and the University of Zurich. These detect vehicles, trees, houses – even detonations were carried out to capture the state before and after destruction using radar. The uniqueness lies not only in the fact that the radar devices are operated from multicopters but also in the different frequencies with which they observe the same scenarios. “In the NATO measurement campaign, we want to investigate how much additional information can be gained in this way,” explains Dr. Michael Caris, group leader at Fraunhofer FHR.
Radar Sensor with 94 Gigahertz
The highest frequency, 94 Gigahertz, is achieved by the SAR sensor Phoenix-94 from Fraunhofer FHR. Although it could not detect a vehicle parked under a camouflage garage, as expected – until it left the camouflage garage – the high frequency offers advantages regarding the resolution of small structures. A good example is asphalt: At lower frequencies, it appears as a black area on the radar image, while at higher frequencies, it appears as a rough, gray area. Now, asphalt itself is not particularly interesting. Why is this still important? “In imaging radar, the radar shadows cast by vehicles often provide valuable clues as they depict the outline of the vehicle. However, this shadow cannot be seen on a black surface. In contrast, on the gray surface that asphalt appears at 94 Gigahertz, the shadow stands out well from the road environment,” explains Caris. For instance, a tank may be hard to distinguish in the radar image, but it can be clearly identified by a long, narrow object that can only be a cannon barrel.
Small, Lightweight, and Energy-Efficient
Before the radar system could be integrated into a multicopter, researchers had to optimize it regarding size, weight, and power consumption. For the drone to carry it, it must not only be compact and lightweight but also operate extremely energy-efficiently. After all, the drone's battery capacity is limited – the heavier the radar system is and the more energy it consumes, the shorter the drone can stay in the air. The result of the research: The multicopter can fly for about 25 minutes when loaded with the radar system. The team achieved this, among other things, by remotely controlling the radar, allowing essential functions to be activated only when needed.