4.1.1 System Requirements [1]

The role of antennas in mobile communication systems is to establish a radio transmission line between radio stations, at least one of which is moving. There are two types of mobile communication systems: one where a transmitter and receiver communicate directly, and the other where they communicate through a base station. It is the latter type that has advanced around the world in recent years. Examples include automobile telephone systems, portable telephone systems, and multichannel access (MCA) systems for private use. Automobile telephone and portable telephone systems adopt a cellular structure, and the relation between system requirements and the necessary antenna technology is illustrated in Figure 4.1. In order for the base station to communicate with the mobile station located in the service area, radio wave energy must be radiated uniformly inside the area. Moreover, antenna gain should be as high as possible. Since the width of the service area is already specified, antenna gain cannot be increased by narrowing the beam in the horizontal plane. Therefore, it is necessary to narrow the antenna beam in the vertical plane to increase gain; a vertically arranged linear array antenna is effective to achieve this. Normal cellular systems use antennas with a gain from 7 to 15 dBd as the base station antennas. Antenna heights of these antennas are from 3m to 5m. So, slender mechanical designs are required...