RADIO WAVE EMISSION SOURCE DETECTION SENSOR, AUTOMATIC TOLL COLLECTION SYSTEM AND ROAD-SIDE UNIT

PROBLEM TO BE SOLVED: To provide a radio wave emission source detection sensor which is capable of preventing erroneous charging on an in-vehicle unit by interrupting an erroneous communication set up between a road-side unit which is installed on a predetermined lane, and the in-vehicle unit which is present on an adjacent lane, an automatic toll collection system using the sensor, and the road-side unit.SOLUTION: A radio wave emission source detection sensor is connected to a road-side unit which is installed on a predetermined lane, receives a response signal from a transponder carried on a mobile through a first receiving beam and communicates with the transponder. The radio wave emission source detection sensor includes an antenna section, a detection section, a direction identification section and an erroneous communication determination section. The antenna section receives the response signal through a second receiving beam. The detection section detects a required signal in a predetermined detection frequency. On the basis of a result of the detection, the direction identification section measures a radio wave strength and identifies an arrival direction of the response signal. On the basis of the radio wave strength, the arrival direction and the like, the erroneous communication determination section determines whether a communication between the road-side unit and the transponder is erroneous and, if erroneous, outputs an erroneous communication notice to the road-side unit.