Vehicular radar wayside transponder system

Abstract

Doppler control circuit for a CW or pulse Doppler radar system for monitoring not only the phase shift between echo signals from several targets but also the amplitude difference between the several targets and to further provide a phase lock loop which tunes the radar to a particular target among one or more targets from which echo signals return. The control circuit can be used in state of the art CW or pulse Doppler type radar systems. In a further system, a continuously generated radar signal is repeatedly transmitted at three different frequencies in time division fashion to define a succession of transmit and receive frames. The receive frames are divided into a plurality of time interval windows with selected windows being used to detect received signals at the different frequencies. The remaining windows can be used for subsystems of the radar system. The rate of phase shift of received signals at a center frequency is used to determine closing rate, while the phase shift difference between received signals at the other two frequencies is used to determine range. A subsystem of the vehicular radar system is provided, in which communications between the vehicle radar system and a wayside transponder take place within one of the remaining windows of the receive frames. The wayside transponders transmit multi-bit words to the vehicle to provide the vehicle with update information and to warn of possible hazards in particular locations.