MICROWAVE AUTOMATIC VEHICLE IDENTIFICATION SYSTEM.

A microwave system using the second-harmonic reflection principle is used as a basis for an automobile labeling system. This system is capable of accommodating over 100 million different codes and can identify a vehicle passing at full speed from distances up to ten feet. Tolerances required for the interrogator-responder distance and orientation are quite loose. Optical systems and low-frequency induction systems (loop embedded in roadway) were also considered. Optical systems do not appear to have the capability of identifying one in over 100 million vehicles moving at highway speeds (the only such system known to have this capability is one designed to read railroad cars and employs a label 7 multiplied by 18 inches (18 multiplied by 46 cm), which is probably too large for use on private cars). Low-frequency induction systems require fairly large transponders on the vehicle, are somewhat critical in their mounting, and are not easily adaptable to other applications. The experimental microwave system described uses a label 6 multiplied by 3 multiplied by 7/8 inches (15. 2 multiplied by 7. 6 multiplied by 2. 2 cm), and it is expected this size could be reduced further. Systems operation and circuit design are described, and other possible applications for such a system are discussed.