A microwave automatic vehicle identification system

A microwave system using the second harmonic reflection principle is being used as a basis for an automobile labeling system. This system is capable of accommodating over 100 million different codes and can read a vehicle passing at full speed from a distance of up to ten feet. Very loose tolerances for the interrogator-responder distance and orientation are required. Optical systems and loop in the roadway systems were considered but they do not appear to have the capability of identifying one in over 100 million vehicles moving at highway speeds. The only optical system that is known to have the capability is one designed to read RR cars but that system uses a label about 7" × 18", which is believed to be much too large for use on private cars. The microwave system to be described in this paper uses a label which in its initial design is 6" × 3" × 7/8". It is expected to be made even smaller in later designs. Systems operation and circuit design will be presented. This system is expected to have application to automatic billing at toll booths thus avoiding the long traffic delays that occur there at rush hours. It is also expected to aid in anti-hijacking operations and in the recovery of lost and stolen vehicles.