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3D ENVIRONMENT MONITORING WITH MIMO RADAR CAMERA

Three-dimensional imaging radar camera modules are currently being developed at Fraunhofer FHR within the framework of the EU project SmokeBot. Silicon-germanium technology paves the way for highly integrated modules in very confined spaces with low power consumption.

The equipped robot in action (photomontage).
© Fraunhofer FHR

The equipped robot in action (photomontage).

Prototype of the 2 x 8  MIMO radar module.
© Fraunhofer FHR

Prototype of the 2 x 8 MIMO radar module.

Measured reflection of two punctiform targets.
© Fraunhofer FHR

Measured reflection of two punctiform targets.

Multi-channel radar systems for electronically controllable beaming and digital imaging are a long-established field at Fraunhofer FHR. Due to their size and high power consumption, previous systems were not suitable for utilization on small, mobile platforms. The increased integration of complete radar front ends on silicon-germanium chips allows the implementation of high performance radar modules with a large number of transmit and receive channels in a very confined space.

Corresponding radar modules operating at 120 GHz are presently being developed within the framework of the EU project SmokeBot. The high frequency greatly accommodates the increase in spatial integration: As the image resolution of the module is scaled according to the wavelength and the size of the module the aperture size can be greatly reduced in the presence of extremely short-wave radar signals while at the same time maintaining a very high resolution.

SmokeBot – integrated radar modules for robotics

The projects aims to construct a radar module with 32 transmit and 32 receive channels. The completed module will not only include the analogue front ends, but also the back end. All of the measurement data will be transferred via a standard Ethernet interface. The downstream processing allows a reconstruction of the recorded image information in 3D. Thanks to the utilization of the prepared Robot Operating System (ROS), the image information is available to the entire system. This software integration greatly simplifies the further processing of the data. The information that is to be processed by the system designer cannot be distinguished from information that is provided from other imaging systems, e.g. optical 3D cameras. The radar module can, however, also operate perfectly under poor visibility conditions, i.e. in the presence of fog or smoke, and can also penetrate thin visual obstructions such as tarpaulin or pre-walls. During the project, the data from the radar module will be superimposed with optical data. A complete image of the surrounding area can therefore also be generated in the presence of dense smoke or glare effects.

Integrated silicon-germanium chips for highly effective multi-channel systems

The implementation of the radar camera is based on highly integrated millimeter wave chips which are designed and tested at Fraunhofer FHR. The wafer technology used here is widely and reliably implemented in the automotive area.

Radar detection is based on linear frequency modulation (FMCW), with the result that signal generation in the transmit and receive chip is very similar. This is based on a highly stable and extremely linearly modulated reference signal at 30 GHz. The operating frequency of 120 GHz is realized by a frequency multiplier that is integrated on the chip. At the same time, up to 25 GHz bandwidth is available. The transmit chips have switchable signal outlets, which means that the individual transmitters can be activated alternately. Thanks to the large number of receive channels, all transmit and receive constellations can be used. Each transmit channel provides over 10 mW output power. Together with the highly sensitive receivers, each individual measurement has a dynamic range of over 80 dB. Depending on the antennas used, measurements at distances in excess of 100 m are possible. The integration of several channels on one chip allows the realization of a plurality of measurement channels in the smallest of spaces.

First highly integrated prototype

The first prototype with a partially equipped MIMO array has now been completed. This module, which is only a few centimeters in size, consists of two transmit and eight receive elements at 120 GHz. This prototype as it stands is capable of combining analogue radar signal processing and digital preprocessing. The external interfaces merely comprise a standard industrial Ethernet interface for the configuration and reading of the radar data as well as an interface for the module's power supply. The digital back end board is equipped with an FPGA for the first data processing steps.

The first successful measurements have already been carried out with the prototype. The data allowed the detection of a punctiform reference target with 10° resolution. Further developments, culminating in the final expansion stage, should be completed by the end of the project in mid-2018. With resolutions of less than one degree, this module will combine high-performance imaging with a compact design.