Page 113 - Antennas for Base Stations in Wireless Communications

86 Chapter Two

of time it should be possible to relate changes in performance to factors
related to design, procurement, and manufacture. Without some history
of results, pinning down the reasons for changes is very difficult.

2.3.13 RADHAZ
The possibility that the radio emissions from mobile radio base sta-
tions may present a long-term hazard to health has been of concern to
radio engineers and to members of the public for many years. Because
of the distance between a typical base station antenna and members
of the general public, the levels of electromagnetic field (or power flux
density) the public encounters are typically three orders of magnitude
below the levels recommended by the International Committee on Non-
ionizing Radiation Protection (ICNIRP) and most national authorities.
In some countries, however, there is considerable public anxiety about
this matter and large numbers of base stations are moved every year
because of public concern. The public perception of the electromagnetic
radiation hazard (RADHAZ) issue relating to base stations is prob-
ably that the larger the number of antennas and the greater the visual
profile of an installation, the higher the possible risk, so more compact
systems are likely to draw less criticism on this matter.
In general the levels of power flux density created by a handset in
use next to the head are much closer to the ICNIRP limits, and the total
dose of electromagnetic energy received by most individuals is heavily
dominated by their handset use.
Riggers and engineers who work on BS systems should be made
aware that in close proximity to an antenna they may be exposed to field
intensities that exceed recommended limits, and when working on radio
towers, all personnel should be required to wear calibrated field hazard
monitors. The transmitter(s) connected to any antenna on which they
intend to work should always be turned off before accessing the anten-
nas; if they must pass close to the front of any operating antenna in
order to reach their working location, the connected transmitter should
also be turned off to allow them to pass safely.
Where base station antennas are mounted on short towers or on
masts erected on roofs that can be accessed by building residents or
other members of the public, it is good practice to install barriers to
identify any area in which high power flux densities may be encoun-
tered. Small compact base stations built into street furniture usually
operate at low power, and there is no area in which fields exceed safe
limits for public exposure.
Everyone working with base station antennas, their design, testing,
planning, installation, and maintenance should be aware of issues relat-
ing to RADHAZ. They should take responsibility for their own safety and