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Radar networks and multistatic synthetic aperture radars (SARs) allow overcoming the limitations of single radar sensors. However, a good synchronization of the radar sensors is crucial to avoid performance loss due to phase noise and frequency offsets. While this is usually done via cables or dedicated synchronization signals, digital radars allow for new techniques. This work proposes a new concept for the synchronization of phase-modulated continuous wave (PMCW) radars. The synchronization is performed solely by digital signal processing on the receiver side, adapting techniques known from digital communications. It mitigates effects caused by incoherency, which are phase noise, carrier frequency offsets and phase deviations of the local oscillator (LO), and sampling frequency offsets. At first, the impact of these effects is mathematically derived and analyzed in detail. Then, the proposed synchronization concept is presented, and its performance is thoroughly evaluated. Very good results are obtained not only in simulations but also in measurements with a 77-GHz radar demonstrator.