A Concept for Self-Monitoring of Radar Devices Using a Coherently Coded Reflector

Testing and monitoring the proper function of sensor and measurement systems is an essential task with regard to their functional safety. In this paper, a concept for self-monitoring of radar distance and level measurement devices is presented and discussed. The fundamental approach is to use a passive coded reflector as a reference radar target, which causes a characteristic and known echo `signature'. With this, a good differentiation from other disturbing targets and clutter is possible. The reflector proposed here is designed for modulating the phase of the echo signal based on a binary code sequence. The echo signal is coherently processed with a correlation receiver in order to reliably detect the presence of the reflector and to accurately measure its distance from the radar. The proposed concept has been evaluated using a Barker code with a length of five code sequence elements, and a corresponding reflector has been practically realized for experimental evaluation. Measurements have been performed with a 68 to 92 GHz frequency-modulated continuous-wave (FMCW) radar. Results of the experiments show that the proposed coherent concept, utilizing the phase modulation, gives a much larger immunity against clutter signals resulting from disturbing radar targets as compared to incoherently processing the echo signal.