Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRImaging methods such as radar are extremely important for the German armed forces, especially aerial reconnaissance provides essential information. With a radar system developed and continuously optimized by Fraunhofer FHR in a German-Swiss cooperation with the University of Zürich and Armasuisse, moving targets as well as altitude differences can be detected. During the test flight, the captured data are processed in real time and sent directly to Fraunhofer FHR’s own ground station.
Miranda-35: High-resolution Synthetic Aperture Radar (SAR) detects, identifies, and analyzes objects
The five receiving antennas of the MIRANDA-35 are arranged in a “cross” configuration – data are recorded simultaneously on four of the five channels. In this way, along-track information can be obtained to detect ground targets in motion, while cross-track data can be recorded for interferometric processing to detect, for example, height differences. In addition to radar data, the system also captures optical camera images, which are also sent to the ground station to support the interpretation of the radar images. One of the receiving channels is also designed for polarimetric operation: The emitted radar waves are linearly polarized in a plane. When they strike edges, corners, and similar human-made objects, their polarization direction can rotate – from this rotation, additional inferences can be drawn. Another Fraunhofer FHR radar, the SAR system Phoenix-35, currently has only one receiving channel and lower transmit power, but is considerably more compact. It is particularly suitable for use on medium-sized drone platforms at mid altitudes.
Test flights with ultralight aircraft
The German-Swiss cooperation has existed for more than ten years: Fraunhofer FHR developed the two radar systems MIRANDA-35 and Phoenix-35 and conducts annual measurement campaigns; the University of Zürich handles processing and evaluation of the measurement data. The developments and measurement campaigns are financed by Armasuisse. The systems are usually flown for testing with the Fraunhofer FHR’s own ultralight aircraft “Delphin” and integrated into specially designed wingpods. Last year’s measurement campaign with both radar systems took place from September 8 to 19, 2025 at Mönchsheide airfield – the FHR grounds, Lake Laacher See, the Weisweiler power plant, and the Etzweiler open pit were among the areas overflown. A focus of the campaign was topography and change detection as well as the comparison of the two radar systems. The results are impressive: all components are fully functional and deliver the desired high-resolution SAR images in both cases.
Special features: Online SAR and own ground station
The data are processed in real time on board the “Delphin” and sent as image files to Fraunhofer FHR’s mobile ground station. From there, the radar can be controlled, the flight track managed and monitored, and data received within a 40 to 50 kilometer radius from the aircraft. In a development step, Fraunhofer FHR is working to enable measurements with full bandwidth and thus high range resolution at high altitudes. The background: The radar system illuminates the ground at a certain angle. If the aircraft climbs higher, the illuminated area increases – and the amount of data increases. With an expansion board, the system will in the future be able to produce high-resolution SAR images at greater heights.