Millimeter wave SAR for UAV-based remote sensing

The airborne monitoring of civilian and military scenes (using unmanned aircraft) is becoming increasingly important. Several types of airborne sensors - in the optical, infrared or millimeter wave spectrum - are available for the different platforms. Beside the all-weather suitability of the sensors, the recent deployment scenarios, often in deserts or arid environments, also demand for the ability to look through dust clouds and sandstorms. The only sensor, which is capable to cope with such environmental restrictions and is able to deliver high-resolution images, is the synthetic aperture radar (SAR). In this paper we focus on miniaturized SAR systems which were developed and optimized for utilization in a UAV (unmanned aerial vehicle) with a low loading capacity. This not only requires a compact and light radar sensor but the processing also has to cope with the unstable flight conditions of a small aircraft. Therefore, a high-precision inertial measurement unit (IMU) and motion compensating SAR-algorithms are needed. Thanks to the utilization of a high transmit frequency of either 35 GHz or 94 GHz, the sensors are suitable for the detection of small-scale objects and a very high resolution of 15 cm x 15 cm can be achieved when used in combination with modern FMCW (frequency modulated continuous wave) generation with a high bandwidth (up to 1 GHz) and small antennas.