Cellular radio car antenna

       January 1, 0000    1552

 

The function of antennas at base stations of cellular radio systems has been proven to be a successful way to increase the performance and the channel ability of personal communication systems. In compare to those technically highly developed base station antennas, the exterior and the practical principle of car antennas with omni directional pattern has been nearly the same during the last few years. In spite of the comparatively low technical effort and the small dimensions this highly effective antenna configuration opens the possibility for smart antenna application in vehicles too.
Cellular and PCS base station:
The signal from a cellular base station antenna is basically directed toward the horizon in a comparatively narrow beam in the vertical plane. As with all forms of electromagnetic energy, the power density from a cellular transmitter decreases rapidly as one move away from the antenna. As a result, normal ground-level exposure is much less than that might be encountered if one were very close to the antenna and in its main transmitted beam. Measurements made close to distinctive cellular and PCS installations have shown that ground-level power densities are well below limits.
Mounting of antenna:
Car mounted antennas used for cellular communications normally operate at a power level of 3 watts or less then that. These cellular antennas are typically mounted on the roof, on the trunk or on the rear window of a car. In order to be exposed to RF levels that approach the safety guidelines it would be necessary to remain very close to a car mounted cellular antenna. The results of this study showed that the highest exposure occurred with a female model at a distance of 9.7 cm from one of the antennas operating at a power level of 3 watts. Analysis of the data indicated that the antenna would have to be driven to 7 W of power before the limit for specific absorption rate. From the gathered it appears that properly installed, car mounted, personal wireless transceivers using up to 3 watts of power would result in maximum exposure levels in or near the vehicle that are well below the safety limits. This assumes that the transmitting antenna is at least 15 cm or more from car occupants. Time averaging of exposure will usually result in still lower values when compared with safety guidelines.

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