Revolutionising radar for unmanned systems and homeland surveillance

Counterterrorism efforts in the past decade have been responsible for surveillance in the skies to extreme security measures on the ground. Now, one research institute is bringing a whole new surveillance technique to the table.
As the presence of unmanned aerial vehicles (UAVs) shows no signs of easing up, the demand on these assets to provide clear-cut surveillance is rocketing, particularly as bad weather and dust clouds can often reduce air-to-ground visibility.
A modern synthetic aperture radar (SAR) system is the only apparent sensor that can yet penetrate dust, smoke, clouds and other environmental conditions and generally provides very high resolution images but, problematically, these systems also need to be light and small in order to fit onto small aircraft.
Help however seems to be at hand in the form of the Millimetre Wave Radar using Analogue and New Digital Approach (MIRANDA) from the Fraunhofer Society.
The Society is Europe’s largest application-oriented research organisation and is comprised of sixty institutes across Germany. Of these, the Institute for High Frequency Physics and Radar Techniques (FHR) has pioneered a new SAR system using a high flexible frequency generation module that has successfully been tested on a microlight.
With components developed particularly in the 94 GHz frequency range and newly developed light-weight antennas, very large areas of surveillance can now be covered and the necessary evaluation algorithms can be implemented in a comparatively easy manner.
An analogue video link, which is already available for a wide range of unmanned aircraft, is used to transmit the radar signal. As a result, a video-like SAR image, which changes continuously in line with the flight speed, can be read on the ground.
While Fraunhofer FHR has solved the issue of miniaturisation through the use of millimetre wave technology and switching to Frequency-Modulated Continuous Wave (FMCW) systems (simultaneously ensuring that weight and power consumption is adapted to the possibilities of UAVs), the other issue is the shock-like movement of the unmanned platform, which is measured inside the radar system and then corrected in real-time in the SAR processing unit.
Progress continues on the research, but the outlook is promising, particularly as the analogue signal can of course be digitized, recorded and stored for later analysis.
Homeland security applications
“We have been developing the radar techniques for security applications for several years,” said Dr Stephan Stanko, the leader of the Millimetre Wave Radar Team.
“One main feature is the selection of the transmitted frequency, as millimetre wave and lower Terahertz radiation may penetrate clothing. In addition, systems at higher frequencies need smaller antennas for the same image resolution.
“The third aspect comprises the fact that the range resolution of a radar sensor is directly connected to its bandwidth.”
This means that with the MIRANDA 300 system having a bandwidth of 40 GHz, it can provide a range resolution of 3.75 mm, independent of the range of the observed object. Using this, detailed images of people and objects are feasible at large distances of more than a hundred metres.
The lower terahertz regime shows many advantages. On the one hand, electromagnetic waves of 1 mm wavelength can easily penetrate clothes, shirts, and other materials. On the other hand, explosives do not show total transparency, so they can be distinguished underneath garment.
Furthermore, because of the high range resolution, objects carried by a person cannot only be detected but also be identified, thereby offering a wide range of possibilities for the security sector, most obviously for weapon detection in public areas.
Meanwhile, as electromagnetic waves in the lower terahertz regime exhibit only low absorption by smoke, fog and dust, 300 GHz radars are also applicable for safety applications, such as forest fire or disaster control.
“The millimetre wave SAR systems are in a demonstrator state and can be reproduced for operational applications, Stanko said.
“As customers usually have different demands on a system, several modifications are applied to the systems for delivery. These include the selection of the frequency, the adaptations to the platform and the characteristics of the planned mission.”
Where Dr Stanko will look to understand the varying demands and market potential of Fraunhofer’s innovations for both security observation and UAV integration will be at the Military Radar 2013 event in London this November.
He will be updating attendees on the programme and seeking feedback on the requirements from both military personnel and defence industry professionals.

Source Richard De Silva

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