Mobile communication higher-order-mode microstrip antennas for VICS

The Vehicle Information and Communication System (VICS) is one of the intelligent transport systems (ITS) in Japan. The system commenced in the Tokyo area and Tohmei and Meishin highways in 1996. VICS consists of a radio beacon system, a light beacon system and an FM broadcasting system. The radio beacon system antennas installed on cars are desired to have the ability to receive sufficient level signals in the area ranging from just below the beacon antenna to a great distance along the road. Our purpose is to develop car installation microstrip antennas conforming as much as possible to such a particular receiving ability. To evaluate the receiving characteristics, we define and use effective directivity, which can evaluate real relative receiving power depending upon the distance between the beacon antenna and car antenna and the relative inclination of both antennas. As a result of investigation, we point out that conventional microstrip antennas using the dominant mode do not have suitable properties for this system, and that those using higher order modes are preferable.