Time and frequency synchronization for spread radar systems

A method of operating an automotive spread multiple-input multiple-output configured radar system comprising a plurality of transceiver antenna units that are configured to transmit mutually orthogonal radar signals, and for each transceiver antenna unit of the plurality of transceiver antenna units a plurality of range gates for indicating a range detected by the transceiver antenna unit, the method comprising steps of:

• transmitting modulated, mutually orthogonal radar waves by the plurality of transceiver antenna units in a continuous-wave manner,
• by at least one specific transceiver antenna unit (TRx1) of the plurality of transceiver antenna units, directly transmitting a reference signal that is synchronized with the radar wave transmitted by the at least one specific transceiver antenna unit (TRx1), to at least one transceiver antenna unit (TRx2) that is separated by an a priori known distance from the specific transceiver antenna unit (TRx1),
• reading out the plurality of range gates for the at least one transceiver antenna unit (TRx2) that received the reference signal, and
• based on the read-out range gate of the plurality of range gates that indicates the received reference signal and the a priori known distance, synchronizing the specific transceiver antenna unit (TRx1) and the transceiver antenna unit (TRx2) that received the reference signal.