Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR
Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR

Imaging Radar: Real-time SAR Imaging From a Drone

Initial high-resolution images were delivered by a drone-carried synthetic aperture radar (SAR) with real-time imaging—developed for reconnaissance and surveillance. In disasters, rescue teams must quickly gain an overview. Similar requirements exist for border protection or the military. Drones are well suited for this. However, optical cameras depend on weather. Fog, rain, smoke, or darkness severely limit use. Radar, in contrast, penetrates these obstacles. Powerful systems with high resolution have so far been too large and heavy for drones and required larger platforms such as micro-light aircraft.

© FRAUNHOFER FHR
Multicopter with integrated SAR sensor Phoenix-94. Weighing under 5 kg and with a carrier frequency of 94 GHz, the experimental sensor Phoenix-94 serves to evaluate drone-based SAR data and real-time imaging algorithms.
Hochaufgelöstes SAR Bild bei 94 GHz aufgenommen mit dem Drohnen-SAR Phoenix-94 bei einer Flughöhe von ca. 50 m AGL. Das Bild hat eine Auflösung von ca. 5 cm und zeigt mehrere Testobjekte wie parkende Fahrzeuge und Personen auf einer freien Wiese neben einem Feldweg.

94 GHz radar, under five kilograms

Researchers at Fraunhofer FHR have now miniaturized such high-frequency SAR radars: The revised Phoenix-94 radar weighs less than five kilograms, including the antenna, light enough for a multirotor drone. The researchers had to adapt not only the hardware but also the underlying algorithms designed for real-time processing. This is particularly important given the flight dynamics of a drone, which typically differ significantly from those of an aircraft: the drone makes tight, rapid turns and circles and is much more influenced by wind — it wobbles and vibrates more.

For the miniaturized radar to produce usable images, the flight path must be known to the millimeter. Corresponding highly accurate position sensing is heavy and extremely expensive, costing over €100,000. Therefore, the researchers tested more affordable MEMS sensors (Micro-Electro-Mechanical-Systems), which are available for under €20,000. How does imaging change? Which components still provide sufficient output power despite the high and broadband transmit frequency? The transmit power question was resolved in particular with components from Fraunhofer IAF in Freiburg.

Vehicle tracks visible in the grass – in real time

Even at altitudes of 30 to 70 meters, the system can detect not only parked vehicles, buildings, and people with a resolution of up to 2.5 cm, but also visualize tire tracks in the grass. In addition, a high-performance compact computer processes the measured SAR data in real time on board the drone. Via a data link, the SAR images are transmitted to a ground station and can be evaluated there immediately.

This is a game changer for image analysts who previously often had to wait hours or days for processed data. This capability has attracted attention, among others, during a NATO measurement campaign in Walenstadt, Switzerland (2024), and at a technology demonstration in Thun (2025).