Development of Multiple Frequency Band Antenna for ITS

Recently, the number of wireless telecommunication equipments installed in the car increases rapidly because of the spread of ITS (Intelligent Transport Systems). Especially, GPS (Global Positioning System), VICS (Vehicle Information and Communication System), and ETC (Electronic Toll Collection System) are becoming indispensable telecommunication item. However, because space in the car is limited, it is impossible to set up the antenna for GPS, VICS, and ETC individually. Accordingly, these antennas should be integrated. Actually, two or more antennas are electromagnetic coupled with MSL (Micro Strip Line). As the point that should be noted, VICS needs linear polarized antenna though GPS and ETC use circular polarized antenna. In circular polarized antenna, two point feeding method by power divider is adopted. In two point feeding method, when the phase difference between feed points is 90 degrees, the circular polarized radiation is caused. On the other hand, the linear polarized radiation is caused when there is no phase difference between feed points. Consequently, the circular polarized and the linear polarized radiation is divided only by the phase difference adjustment between feed points. In addition, because the use frequency for GPS, VICS, and ETC is 1.5GHz, 2.5GHz and 5.8GHz respectively, the antenna size can be gradually reduced. Hence, if each antenna is arranged in the nest, the integration of different polarized antennas becomes possible. The requirement to the antenna for ITS has “Compact size”, “Coexistence of circular polarized wave and linear polarized wave”, and “Adaptability to multi band”, etc.. The most important technology for ITS antenna is method of radiating circular polarized wave. There are two methods that radiate circular polarized wave. The one point feeding method is advantage in simple feeding. On the other hand, two point feeding method is advantage in easier phase control. It is necessary to synthesize these methods so those circular polarized waves coexist with linear polarized wave. Multi loop antenna is reported as the antenna, which obtains adaptability to multi band [1]. Therefore, the antenna which combined two point feeding method with multi loop antenna is designed. Fig. 1 shows the structure of that antenna. The antenna radiates circular polarized wave for the structure of Fig. 1 in the multi band.Accordingly, The requirement to the antenna for ITS can be achieved.