Photonically synchronized radar for advanced driver assistance systems

Within advanced driver assistance systems, long-range radar devices with a frequency around 77 GHz are widely used. They have several advantages for automotive use, e.g. the wide bandwidth available improves accuracy and object resolution, combined with small antennas and limited interference with other systems due to atmospheric absorption. Nowadays, these sensors must provide better separation of objects and elevation estimation, translating to a higher angular and velocity resolution, which will be enabled by utilizing cascaded, off-the-shelf, radar front-end devices. In order to guarantee precise beam forming, all modules need to be synchronized. For the distribution of these signals, which are in the range of 20 GHz, optical technologies are of great advantage. They are lightweight, show low loss, are insensitive to electromagnetic interference and have the capability to be integrated. Within the proposed system, the electrical synchronization signal from a central master chip is transferred to the optical domain by a Mach-Zehnder modulator, amplified by an EDFA and distributed with an optical splitter to 4 separate modules. O/E conversion is carried out by a photodiode. Long time stable operation over a wide temperature range is ensured by an external bias voltage regulation of the modulator. First results of the complete system show improved accuracy and object resolution of the targets. The already space-saving design could be made even more compact with special integrated photonic devices. In addition, the realization of a complete optical radar, where the radar signals and echoes are transmitted with optical fibers, would be possible.