Passive proximity sensor method and apparatus

A passive proximity detection system and method are provided. A transmitted signal, such as a communication signal, is sampled and placed in memory. A version of the transmitted signal, reflected by a target in the vicinity of the transmitting antenna, is sampled and compared to the stored reference sample. Correlation between the reference and reflected samples indicates the presence of a target in the vicinity of the transmitting antenna. Processing of the signals can include frequency shifts to account for Doppler shifts in the reflected energy as a result of a non-zero relative radial velocity of the target. Multiple antennas for receiving reflected energy can be provided to enhance the coverage area of the system, and/or to provide information regarding the relative location of a target. In addition, signals from multiple transmitting antennas can be used as sources of energy for probing the vicinity of those antennas for targets.