Signal Model for Coherent Processing of Uncoupled and Low Frequency Coupled MIMO Radar Networks

MIMO radar networks consisting of multiple independent radar sensors offer the possibility to create large virtual apertures and therefore provide high angular resolution for automotive radar systems. In order to increase the angular resolution, the network must be able to process all data phase coherently. Establishing phase coherency, without distributing the transmitted RF signal to all sensors, poses a significant challenge in the automotive frequency range of $\text{76 GHz} \,\text{to}\, \text{81 GHz}$ . This paper presents a signal model for uncoupled and low frequency coupled radar networks. The requirements for phase coherent processing for uncoupled radar sensors are systematically derived from the signal model. The proposed signal processing methods, which establish coherency, are sub-aperture based. Both the signal model and the proposed signal processing methods are verified by measurements with radar sensor networks composed of 2 and 3 radar sensors, providing 768 and 1728 virtual channels respectively. Measurements verify that phase noise is insignificant in the process of establishing coherency in uncoupled and low frequency coupled radar networks.