Page 114 - Antennas for Base Stations in Wireless Communications

Base Station Antennas for Mobile Radio Systems 87

that of their colleagues and the general public. Although most research
findings indicate that there is probably little ground for concern at field
intensities below the recommended limits, the engineering community
should remain fully informed about the results of current research,
both in order to reassure members of the public and to respond in an
effective and timely manner if future findings require any changes in
current practice.

2.3.14 Visual Appearance
and Planning Issues
For the engineering reasons discussed in this chapter, base station
antennas are large devices and have a substantial visible profile. The
provision of an extended high-capacity mobile radio network requires
very large numbers of base stations, and in many countries each region
is served by several competing network operators. Whether in historic
cities, residential areas, or rural and wilderness landscapes, the erec-
tion of base stations is frequently a matter of controversy, the antennas
and their associated supporting structures attracting most criticism.
Network operators must usually obtain planning consent for proposed
base stations from local authorities, and both to increase their probabil-
ity of successful planning applications and to be seen as organizations
responsive to the feelings of local communities, they have developed a
number of solutions to soften the impact of their installations on the
visual environment.
Figure 2.20a shows a typical three-sector cell site with pairs of space
diversity antennas. The large-diameter monopole is needed to provide
sufficient stability for the high-gain microwave back-haul antennas,
which in this example operate on 18, 23, or 38 GHz. The presence of the
microwave antennas and LNAs adds to the cluttered appearance of the
installation; the headframe and safety rails add to the visual impact;
and the wind forces on all these components must be taken into account
when dimensioning the monopole. Large-diameter cables cannot be bent
easily—in this example no attempt has been made to hide them and
some smaller cables have been left hanging untidily.
The example in Figure 2.20b is clearly an improvement. The use of
dual-polar antennas has removed the need for a large headframe and the
cable installation has been well managed. The monopole is still heavy for
a 10-m structure, and various components appear to be standard fitments
that were not really needed for this installation. The access ladder and
the rail for the fall-arrest system are seen to the left of the monopole.
Dual-polar antennas as so small—at least for the high bands—that a
variety of low-profile solutions has been created. Figure 2.21 shows typi-
cal Streetworks installations, both free-standing and wrapped around