Geometry Based Analysis of an Alternative RFID Interrogator Placement for Electronic Vehicle Identification

This paper proposes a solution for reliable in-traffic electronic vehicle detection based on UHF passive RFID (ISO/IEC 18000-63 - UHF Type C). The classic overhead placement of an interrogator reading a windscreen or plate tag is shown to suffer from cost and signal path problems. A geometry based analysis of an alternative RFID interrogator placement is presented. An on road placement of the interrogator reading a license plate tag is theoretically characterised to determine the ideal radiation pattern of the interrogator antenna. This characterisation is based on the geometrical boundary conditions for RFID identification of vehicles in an open road use case. The result of the work indicates, counter intuitively, that a vertically polarised omnidirectional antenna with a "dropped toroid" radiation pattern may have several advantages above the conventional directional antennas commonly used in RFID applications.