Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRHow valuable is it to examine the same scenario using radar systems with different frequencies? Can this help distinguish decoys from real weapons more reliably? And what additional information can be gained by capturing the same object from different viewing angles? These questions are addressed by a NATO measurement campaign in which Fraunhofer FHR is also participating with its own radar systems.
As part of the campaign, the ultralight aircraft "Delphin" circled over a military training ground in England. The special feature: Various radar systems from Fraunhofer FHR were alternately mounted under its wings, surveying the training ground from above. This was the "Multidimensional Radar Imaging" measurement campaign by the NATO research group SET-250, with participants from Italy, Poland, the United Kingdom, South Africa, Switzerland, the Netherlands, Australia, and Germany. For the measurements described here, the radar systems from England, the Netherlands, and the German Fraunhofer FHR were especially combined.
What Do Multidimensional Radars Achieve in Practice?
The campaign participants investigated the added value of multisensor technology and flexible imaging geometries – that is, measurements with different frequencies, polarizations, viewing angles, and resolutions – and found significant advantages over conventional single systems. Typically, military radar systems operate at around ten gigahertz. However, different materials reflect differently at various frequencies: An object may be transparent to a beam of a certain frequency but visible at another. Therefore, using radar signals at different frequencies to observe a target should be beneficial. This multi-frequency approach allows for better detection of decoys – for example, empty plastic tubes attached to tanks instead of weapons. A kind of 3D effect can also be achieved by examining an object from multiple sides and then fusing the images.
Radar Systems with Frequencies from 1 to 94 Gigahertz
While the Dutch L-band radar operated at 1 to 2 gigahertz, the frequency of the British X-band radar was about 10 gigahertz. The two Fraunhofer FHR systems operated at 34 and 94 gigahertz, respectively: The Ka-band system PAMIR-Ka has a wide bandwidth; in the long term, the antenna is to be steerable in two directions – enabling precise observation even when the aircraft drifts. The special feature of the MIRANDA-94 system is its high frequency of 94 gigahertz and the use of a gimbal mount that automatically compensates for unwanted aircraft movements. In addition, the main components of the system were manufactured in Germany, mostly at Fraunhofer IAF in Freiburg. The data collected during the campaign was jointly analyzed and fused by the partner organizations, with the aim of deriving robust recommendations for the operational use of multi-frequency radar systems.