Microwave absorbers for the ETC systems were developed to suppress multiple reflections from surrounding structures. Our new absorber has a dielectric layer placed on a fiber type density-gradient absorber base for absorption from high incident angles. It has been installed in over 70 tollgates in Japan, working in excellent condition. The Electronic Toll Collection system (ETC) was developed to improve the tollgate environment by easing the traffic and also be economically effective at the same time. Of the Intelligent Transport Systems (ITS), it is the first system to be put to practical use in Japan. In the ETC, which uses microwaves of 5.8GHz, the wave radiated from roadside antennas reflects on road surface, vehicle roofs or tollgate canopy underside, interfering with vehicles still far away from the gate or neighboring lanes. As a result, there may be abnormal communication with vehicle devices outside the communication area. As a countermeasure against undesirable reflections, a research group lead by Japan Highway Public Corporation (JH) standardized a method for suppressing multiple reflections on roads, underside of canopies and other surrounding structures.
Abstract