Base-Station Applications

Base-Station Applications

For base-station installations (where an omnidirectional pattern is desired), there are two practical implementations of the vertical dipole. The first type is the sleeve antenna, as illustrated in figure 7(a). The sleeve antenna is a vertical dipole with the feed (transmission line) entering from one end of a hollow element. The second type is a monopole over a ground plane, as illustrated in figure 7(b). The monopole in this illustration uses a set of four wire elements to rovide the ground plane. Figure 8 shows a typical pattern for a base-station monopole.

Figure 7. Omnidirectional base-station antennas

Figure 8. A monopole antenna horizontalplane pattern, base-station application.

The uniform maximum gain corresponds to the outer line on the polar plot A variation of the dipole antenna is the folded dipole as shown in figure 9. Its radiation pattern is very similar to the simple dipole, but its impedance is higher and it has a wider bandwidth.

Figure 9. A folded-dipole antenna