Page 217 - Antennas for Base Stations in Wireless Communications

190 Chapter Five

5.3.2.2 Triple-Band Antenna As just mentioned, a 90° HPBW increases
the capacity for a three-sector CDMA system, as shown in Figure 5.5b.
However, in the 800-MHz and 1.5-GHz bands, the PDC systems, as shown
in Figure 5.2a, have no interference issues. A 120° HPBW is, therefore,
good for PDC systems in the 800-MHz and 1.5-GHz bands. The optimal
HPBWs for the CDMA systems operating at 2 GHz and PCD systems
operating at 800 MHz and 1.5 GHz are 90° and 120°, respectively.
When we installed the antenna elements, mentioned in Section
5.3.2.1, in the antenna radome to form an antenna array, the HPBW of
the antenna arrays in each frequency band was 120° for a three-sector
zone scheme. Due to the recent increase in the number of 3G system
subscribers, however, the HPBW of triple-band antennas must be nar-
rowed to 90° in the 2-GHz band for 3G systems to increase system
capacity. To achieve an HPBW of 90° in 2-GHz bands, we propose using
metal conductors near the antenna elements. 15
Figure 5.15 shows an illustration and a photo of a triple frequency-
band antenna (Figure 5.8) with metal conductors. Figure 5.16 shows

z 110 mm
y Antenna Radome
x

Conductor

70 mm

4 mm

65 mm
(a) Illustration

Main beam

Antenna radome
Conductor

(b)
Figure 5.15 Triple frequency-band antenna with parasitic
conductors