Defense

Active protection system with millimeter wave radar

DUSIM – four-channel radar front end with an output power of 100 mW at 94 GHz.
© Fraunhofer FHR

DUSIM – four-channel radar front end with an output power of 100 mW at 94 GHz.

Trajectory of a small caliber projectile (MG3 7.62 x 51 mm).
© Fraunhofer FHR

Trajectory of a small caliber projectile (MG3 7.62 x 51 mm).

Section of the trajectory of an RPG. The bow and stern of the rocket can be distinguished.
© Fraunhofer FHR

Section of the trajectory of an RPG. The bow and stern of the rocket can be distinguished.

Numerous deployment scenarios involve serious threats from hand-held anti-tank weapons which are now available in large quantities on the world market. One promising approach to counter this threat is the development and realization of active protection systems.

Due to the high impact force of armor-piercing projectiles and the present – almost hemispheric – threat situation, it is practically impossible to provide appropriate protection, especially for light, air-transportable vehicles, using conventional ballistic protection technologies. Hence, there is an urgent demand for active protection systems that are capable of detecting and combating an approaching projectile before it reaches its target. The efficiency of such a system depends on a number of factors: the reliability of detection (low false alarm rate), the quality of classification and three-dimensional localization, the processing speed of the measurement data as well as the initiation of appropriate countermeasures. The sensor, which detects the approaching threat, can also provide information on the type of the threat and supplies data which enables high-precision determination of the flight parameters (distance, flight direction, speed), plays a key role. This information must then be made available to fire control in real time. Due to its all-weather capability and its ability to penetrate dust and sand clouds, radar technology offers a number of advantages compared to other sensors (e.g. electro-optical or infrared).

Within the framework of the research project DUSIM (Dual Use Sensors in Medium Distance Range), a four-channel radar system was developed for active protection within a monitored range of between 8 m and 250 m. It operates at a frequency of 94 GHz with a low output emission of 100 mW. This makes the sensor almost undetectable for non-cooperative troops and harmless for persons in the immediate vicinity. The frequency-modulated continuous wave signal (FMCW) with a bandwidth of 1 GHz provides a high range resolution of 15 cm. The core of the DUSIM radar front end is the highly stable signal generation (Chirp Generation Board) which creates a linear frequency ramp at approx. 15.7 GHz. This is subsequently sextupled and amplified. Thanks to the four-channel receive system, the sensor can provide the precise location of the approaching projectile; here, use is made of the monopulse technique. The speed and flight direction of the projectile can also be determined using the Doppler effect. The immediate creation of a flight track after successful detection is the most important basis for targeted and precisely timed countermeasures. Clear classification lowers the false alarm rates as a distinction can be made between relevant and non-relevant targets. The front end shown in Fig. 1 measures 200 x 180 x 230 mm3 and weighs approx. 3 kg.

The system was successfully tested under realistic conditions in several measurement campaigns. Tests were carried out with small caliber ammunition as well as with armor-piercing projectiles (e.g. RPG 7). Examples of the results are presented in Figures 2 and 3. In 2016 and 2017, additional tests were carried out in the centrifuge facility of WTD 91 in Meppen.

Trajectory of a missile in the centrifuge facility of WTD 91 in Meppen. Two scattering centers can be seen on the target object and further scattering centers with a lower velocity can also be seen on the centrifuge itself.
© Fraunhofer FHR

Trajectory of a missile in the centrifuge facility of WTD 91 in Meppen. Two scattering centers can be seen on the target object and further scattering centers with a lower velocity can also be seen on the centrifuge itself.

Here, various threats were moved in a reproducible manner on a circular track, a section of which was tangentially illuminated by the radar. Due to the high repetition rate, it was possible to record approx. 700 individual measurements of the used missiles (11 different threats). In this way, the various radar signatures of the different projectiles used can be examined in a cost-efficient manner in very little time without elaborate shooting tests. Moreover, thanks to the large volume of measurement data, it was also possible to make statistical statements relating to the observed objects. Figure 4 shows a section of a typical centrifuge measurement.

The successful measurements and good results show that the further development of the DUSIM radar sensor for utilization in other active protection systems is indeed worthwhile. Improvement potential does exist, particularly in the area of signal processing, e.g. localization and classification of objects. An increase of the output power (to a realistic value of 1 W) could also extend the coverage area of the radar system.