United Stalw OMca of Radafon Program* EPA 520/1-85-014
Environmental Protection Office of Air and Rotation July 1986
Agency Washington, D.C. 20460
Radatfon
&EPA The Radiofrequency
Radiation Environment:
Environmental Exposure
Levels and RF Radiation
*
Emitting Sources
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EPA 520/1-85-014
The Radiofrequency Radiation Environment: Environmental Exposure
Levels and RF Radiation Emitting Sources
Herbert N. Hankin
July 1986
Office of Radiation Programs
Office of Air and Radiation
U.S. Environmental Protection Agency
Washington, D.C. 20460
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, IZtn
Chicago, !L 60604-3590
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FOREWORD
The Office of Radiation Programs conducts a national program to evalu-
ate the exposure of the population to ionizing and nonionizing radiation, to
recommend radiation protection guidance for the use of Federal agencies, to
publish environmental radiation standards and criteria, and to advise the
States on radiation protection matters, so as to protect public health and
to assure environmental quality.
The applications of radiofrequency radiation in communications,
transportation, defense, industry, consumer products, security, science,
traffic control, and medicine have produced a radiofrequency radiation
environment to which the entire population is continuously exposed.
Everyone in the United States is exposed to low levels of radiofrequency
radiation, and some people who live or work near powerful sources are
exposed to higher levels. As the number of radiofrequency radiation sources
increases, the probability of public exposure to higher radiation levels
also increases.
This document summarizes the radiofrequency radiation environment,
discusses the sources and levels of radiofrequency radiation to which the
public is exposed, and provides information pertinent to the development of
radiofrequency radiation exposure guidelines.
Sheldon Meyers, Director
Office of Radiation Programs
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ABSTRACT
This document summarizes the radiofrequency radiation environment to
which the public is exposed. The contents consist of information on
environmental levels of radiofrequency radiation produced by systems in
common use such as AM and FM radio, VHF and UHF television, microwave
communications, radar, and mobile radio. The exposure environment is
discussed in terms of the system characteristics important to its creation.
The information presented in this document resulted from a nationwide
exposure measurement program conducted by the Environmental Protection
Agency (EPA) to determine typical and atypical public exposure levels and
from modeling efforts to estimate environmental exposure levels. Most of
this work has been documented in previously published technical reports and
papers as referenced herein.
The exposure environment is examined from two aspects: the typical,
relatively low-level environment to which most persons are exposed,
occurring far from the sources of the radiation; and the higher-level
environment to which relatively few persons are exposed, which occurs
close to the radiation producing systems. The information acquired by EPA
leads to the conclusion that the principal sources of the radiofrequency
radiation environment to which the public is exposed in urban areas are
radio and television broadcast systems. They produce most of the low-level
radiofrequency radiation exposure to which the public is continuously
subjected, and are the systems responsible for the majority of the
higher-level exposure situations experienced by a smaller proportion of the
public.
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CONTENTS
Foreword
Abstract ii
Figures iv
Tables vi
1. Introduction
2. Radiofrequency Radiation — Concepts and Characteristics
3. General Environmental Exposures 13
4. Exposures from Selected RF Radiation Sources 25
5. Summary 74
References 76
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FIGURES
Figure Number Page
1. The electromagnetic spectrum 5
2. Spherical coordinate system used to describe antenna radiation
characteristics 10
3. Representation of spatial distribution of radiated fields
from isotropic and high-gain directional antennas 10
4. Cumulative population exposure for 15 cities 17
5. Differential fraction of population exposed within given
power density intervals (15 cities) 17
6. Cumulative distribution of power densities at 193 measurement
sites 20
7. Vertical plane radiation pattern of an FM antenna
a. rectangular coordinates
b. polar coordinates
c. visual representation 31
8. Vertical plane radiation pattern of a typical UHF-TV
transmitting antenna 32
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Figure number Page
9. Ground-level power density vs. distance for an FM antenna 33
10. Power density vs. distance for a 1 megawatt (ERP) UHF-TV
station 34
11. Groundwave field strengths for 50 kW single monopole AM
radio broadcast stations 40
12. Cassegrain paraboloidal antenna 45
13. Radiation field regions for a circular cross-section
reflector antenna 48
14. Relative power density contours for a circular aperture
antenna 50
15. Measured 100 yU/cm3 contours for 50- and 100-watt mobile
transmitters at 164.45 MHz 73
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TABLES
Table number Page
1. Applications and sources of radiofrequency radiation.
2. Stannary of information relevant to environmental RF radiation
measurements and population exposure estimates for 15 cities..... 18
3. Estimated population exposure in 15 U.S. cities (54-806 MHz) 19
4. Maximum exposure power density measured for each frequency band
in determination of general environmental RF radiation exposures. 21
5, Cumulative population exposure in the AM broadcast band
(0.535-1.605 MHz) 23
6. Typical urban radar environments in San Francisco, California.... 24
7. General characteristics of FM and TV broadcasting 29
8. Power density in the grating lobe for 5 FM radio antennas at
3 feet above ground level 36
9. Power density measurements at high-rise buildings located near
FM and TV broadcast antennas 37
10. Electric field strength at various distances from a 50 kw
AM radio broadcast station 42
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TABLES (Continued)
Table Mumber Page
11. Radiation characteristics of some existing satellite
communications systems 51
12. Acquisition and tracking radar measurements (on-axis) 58
13. Tracking radar characteristics 59
14. Predicted and measured characteristics of ATC radars 61
15. Predicted exposures from ARSE radars 63
16. Height-finder radar system characteristics 64
17. Weather radar characteristics 66
18. PAVE PAWS system characteristics 67
19. PAVE PAWS environmental exposure characteristics 68
20. Calculated radiation characteristics of some commonly used
microwave radio systems 71
VII
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SECTION 1
INTRODUCTION
This document provides a summary of our knowledge of environmental
levels of radiofrequency (RF) radiation. The systems producing this
radiation, i.e., broadcast radio and television, microwave communications,
and radar, are discussed in this report. This knowledge has been developed
from a comprehensive measurement and analysis program designed to define
public exposure to radiofrequency radiation.
In 1982, EPA announced its intent to develop Federal Guidance to limit
exposure of the public to RF radiation (ANPR 82). To support the develop-
ment of this guidance, EPA published reports on the biological effects of RF
fields (E184), and the potential impact, economic and otherwise, that the
proposed guidance might have on affected RF sources and users of the electro-
magnetic spectrum (Ha85). In this document we will discuss the RF radiation
environment in terms of environmental exposure levels and the RF sources
producing these levels.
Before the production of radio waves by Heinrich Hertz in 1888, the
earth's RF radiation environment resulted from natural phenomena such as
lightning and solar radiation. With the introduction of radio communica-
tions in 1895, however, the RF radiation environment has been increasingly
artificially produced. Although environmental levels of nonionizing
radiation were negligible before the 1930s, the applications of RF radiation
in modern society, i.e., communications', transportation, defense, industry,
consumer products, security, traffic control, and medicine, have produced an
RF radiation environment to which the entire population is continuously
exposed (Te80a). The dramatic rise in the numbers and types of radiating
sources has increased the magnitude of environmental levels, extended the
frequency range to which members of the public are exposed, and increased
the number of persons exposed. Table 1 lists some of the applications and
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common sources that produce the radiofrequency radiation exposure
environment.
The Environmental Protection Agency's studies of radiofrequency sources
and levels have characterized the radiofrequency radiation environment to
which most of the population is exposed. These studies have also resulted
in an understanding of the environmental significance of the major high-
power source categories, which include satellite communications earth
terminals, radars (military and civilian), and broadcast transmitters
(UHF-TV, VHF-TV, and AM and FM radio). Information obtained through
measurements and analyses, when combined with other factors such as number
of sources in each category, general system characteristics and operating
procedures, and relative numbers of persons possibly exposed and their
exposure locations, indicates that broadcast transmitters are the most
environmentally significant source category.
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Table 1
APPLICATIONS AND SOURCES OF RAOIOFREQUENCY RADIATION
Applications
Broadcast Connuni cat ions
Microwave Carman i cat ions
Military
Transportation
Science
Medicine
Crime Prevention
Consumer Products
Sources
AH and FM Radio
VHP and UHF Television
Radar
Satellite Comuni cat ions
Microwave Radio
Land-Mobile Radio
Amateur Radio
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SECTION 2
RADIOFREQUENCY RADIATION — CONCEPTS AND CHARACTERISTICS
Radiofrequency (RF) radiation is a part of the electromagnetic radiation
spectrum. The term RF radiation applies to electromagnetic radiation
frequencies between 3 kilohertz (kHz) and 300 gigahertz (GHz). Figure 1
depicts the electromagnetic spectrum and shows the conventional partitioning
of the radiofrequency spectrum into specific bands. For example, the
microwave frequency band covers the range 300 megahertz (MHz) to 300 GHz,
and the FM radio broadcasting service in the United States uses frequencies
within the VHF or very-high-frequency band.
Energies associated with microwave radiation at its. extreme of 300 GHz
are about 10,000 times less than is needed to cause cellular damage by
ionization. The ionization potentials of the principal components of living
tissue (water, atomic oxygen, hydrogen, nitrogen, and carbon) are between
11 and 15 electron volts (eV). The lower limit for ionization in biological
systems is approximately 12 eV, but some weak hydrogen bonds in macro-
molecules may have lower ionization potentials, possibly even as low as
about 3 eV. For reference, an ultraviolet wavelength of 180 nanometers
corresponds to an energy of about 7 eV. Thus, RF radiation having energies
less than 10 eV is nonionizing radiation, as is infrared radiation,
visible light, and lower frequency ultraviolet radiation.
However, RF and microwave radiation is absorbed and interacts with
biological systems. Absorbed energy is converted to electronic excitation
and to molecular vibration and rotation. The RF energy is primarily absorbed
by increasing the kinetic energy of absorbing molecules. The amount of
energy absorbed depends on the radiation intensity and wavelength, and the
shape, size, and the electrical characteristics of the absorber. A complex
structure such as the human body absorbs energy differently in specific
parts, so that non-uniform absorption may result.
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The characteristics of RF radiation, necessary to an understanding of
the information presented in this document, are briefly summarized here.
Textbooks and references are available for a more comprehensive description;
•ee, for example, Chapter 6 in Si65.
Electromagnetic radiation is characterized by coupled electric and
magnetic fields that oscillate periodically in time as the fields propagate
away from the source of the radiation at the velocity of light, equal to
xo
3 x 10 cm/sec in vacuum or air. This radiation has a wavelength equal
to the distance traveled by the wave during one complete cycle. The
wavelength, X, is expressed as:
X * c/f = 3 x 1010 cm/sec x T, (1)
where f is the oscillation frequency of the electromagnetic wave, expressed
in units of cycles per second or hertz (Hz), and T is the period of one
oscillation, i.e., the time duration of one cycle, and is related to the
frequency by the expression T = 1/f.
Radiofrequency electromagnetic fields are generated by the oscillation
of electrons within a system's antenna. The frequency of the field is equal
to the electron oscillation frequency. The field generated by any radiating
system has two components: the induction field and the radiation field.
The induction field occurs in the immediate vicinity of the radiating
system; the energy in the induction field oscillates back and forth between
the antenna and nearby space. At sufficiently large distances the induction
field becomes negligible relative to the radiation field. The radiation
field represents a continual flow of energy outward from the antenna. At a
distance r »X/2*. the radiation field becomes dominant, and the induction
field can be neglected (Si65). This distance is generally taken to be equal
to a few wavelengths.
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All KF systems consist of a power source (transmitter) and an antenna.
The transmitter produces the RF power by which information is transmitted
through the application of selected amplitude/frequency/time modulation; the
antenna radiates that energy, some of which impinges on another antenna or
object at come distance.
The total emitted power is directly related to the transmitter power.
The distribution of that power in space is determined by the antenna.
Environmental levels at any location are determined not only by the
transmitter power and the antenna, but also by the location and orientation
of the antenna and other objects (such as structures that reflect
emissions), and the operating characteristics of the system (including the
time-dependent motion of rotating or nodding antennas and the on-off
operation of the transmitter).
The primary function of the antenna is to emit power with a specific
spatial distribution pattern. The radiation intensity at any location in
free space is determined by the power radiated and the inherent ability of
the antenna to radiate that power in a given direction relative to the
antenna axis or center of radiation. This directive property of an antenna
is its gain function. Antenna gain represents the increase in the power
radiated in a given direction over that from an isotropic radiator emitting
the same total power. At large distances from the source, the antenna can
be considered to be a point source radiating power as a function of
direction. The radiation propagates in space through a surface having an
area equal to 4»r2, where r is the distance from the radiation
source. The energy density varies inversely with the square of the
distance. This can be understood by realizing that the power radiated by
the antenna into space is propagating into an increasingly larger volume,
with the surface area of the wavefront increasing as the distance from the
source increases.
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The propagation of the electromagnetic wave away from the antenna can
be represented as the motion of a wavefront in space. As the wavefront
(represented by simultaneously emitted, in-phase electric and magnetic
components of the field) becomes more distant from the radiation source, its
surface becomes progressively more planar. At a sufficiently great
distance, the wavefront appears to be a perfect plane. Theoretically, this
occurs when the distance from the source is infinite; practically, it occurs
in what is known as the far-field (Fraunhofer) region, which begins at a
finite distance from the antenna. For the purposes of describing the RF
radiation environment, the electric and magnetic fields and the direction of
wave propagation can be considered to be mutually orthogonal at a distance
of a few wavelengths from the antenna (Si65), i.e., for distances much
greater than X/2*. From that distance through the far-field region, the
electric and magnetic field vectors are perpendicular to each other and form
a plane perpendicular to the direction of radiation propagation. The
radiation field at any point is expressed in terms of the magnitude and
direction of both the electric and magnetic fields at that point.
In free space or in air, at a distance from the antenna where E and H
are essentially orthogonal, the absolute values of the electric field E and
the magnetic field H are related as follows:
E(V/m)/H(A/m) = 377(ohms), (2)
where E has units of volts per meter (V/m), H has units of amperes per meter
(A/m), and 377 ohms is the impedance of free space.
Another quantity commonly used to describe the intensity of RF
radiation exposure is the power density, i.e., the RF power (in the
direction of radiation propagation) incident on a unit area to which it is
perpendicular. The magnitude of the power density, S, is expressed as the
product
S * EH. (3)
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The power density has the magnitude given by the following expression for S
in units of watts per square meter (W/m2):
S(W/ma) « lE(V/m)]2/337(ohms) « lH(A/m)l2 x 377(ohms). (4)
The power density value of interest is the energy flow over a cycle rather
than the instantaneous flow. This time-averaged value is derived from the
root-mean-square (rms) values of E and H.
The units in which power density is commonly expressed are watts per
square meter (W/m2), milliwatts per square centimeter (mW/cm2),
microwatts per square centimeter (yU/cm ), and nanowatts per square
centimeter (nW/cm ). These are related as shown below:
1 W/m2 * 0.1 mW/cm2
* 100 yW/cm2
a !05nW/cm2.
The general expression for radiation intensity, in terms of the power
density, at a point in space at a distance, r, from the antenna at angles
6 and *, in a spherical coordinate system centered at the antenna
(Figure 2) is given by the expression
S = PG(e,*)/4*r2, (5)
where power density, S, is the radiated power from the antenna incident on a
unit area at a distance, r, from the antenna, and the gain, G(6,*), is
the ratio of the power radiated in a given direction per unit solid angle,
P(6,*), to the average power radiated per unit solid angle, P/4«, where P is
the total power radiated.
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ANTENNA SURFACE
ANTENNA
AXIS
UNIT AREA
Figure 2. Spherical Coordinate System Used to Describe Antenna
Radiation Characteristics
The total energy radiated by the antenna is never greater than the
energy provided to it; however, the energy can be directed so that the
resulting radiation distribution pattern can show intensity enhancement in
preferred directions and intensity reductions in other directions. By
comparison, an isotropic radiator produces a uniform spatial distribution
pattern of equal radiation intensities in all directions at a specific
distance. The radiation distribution pattern at a given distance from the
antenna has the same angular dependence as the antenna gain. Figure 3
illustrates the general case for the spatial distributions of radiation from
two antennas, one being an isotropic radiator and the other having a
high-gain characteristic. Relative radiation intensity or antenna gain is
shown as a function of angle in a polar coordinate system. An isotropic
radiator has a gain equal to 1 in all directions.
G (0 - 0)
G -1
MAIN BEAM
SIDE LOBES
Figure 3. Representation of Spatial Distribution of Radiated Fields
from Isotropic and High-Gain Directional Antennas. (For
the Isotropic Antenna, G « 1 for any Direction and
S = P/4*r2.)
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The gain, G(6,t), of an anisotropic antenna varies with angle and
can be touch greater than 1 for high-gain antennas at 6 « 0 degrees. In
fact, G(8-0) can exceed 10* for very large area reflector antennas that
radiate energy with wavelengths that are very snail compared to the antenna
dimensions. The radiation intensity, in terms of power density, is
generally a maximum at 0 - 0 degrees, i.e., in the direction of the
antenna axis.
The electric field intensity, E, in free space far from an antenna, can
be expressed in terms of transmitter power and antenna gain, using Equations
(4) and (5) as follows:
E(V/m) » [30PG(e,*)]1/a/r. (6)
Radiation intensity enhancement in a preferred direction for anisotropic
antennas is directly characterized by the gain. High-gain antennas concentrate
more radiated energy into a main beam, which is generally symmetric about the
antenna radiation axis, and distribute relatively little energy in other
directions. Greater antenna gain results in greater radiation intensity in the
main beam (which has a decreasing angular divergence as the gain increases) and
less in the side-lobe radiation pattern.
High-gain antennas are typically used to produce usable signal intensities
with available transmitter power at great distances from the transmitting
antenna. They reduce the possibility of interference from other radiating
systems, a result of having a main beam with small angular divergence and
reduced intensity side lobes. Systems using high-gain antennas include
satellite communications, microwave relay, and radar. Low-gain antennas are
used in systems that must radiate energy in all directions to produce a more
even intensity distribution, so that radiation can be received at every location
in a given region. Such applications include AM and FH radio, VHF and UHF
television, land-mobile radio, paging systems, and low-powered hand-held radio.
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In general, for systems of equal power output, those employing high-gain
antennas produce higher signal intensities in the main beam of radiation at a
point at a given distance from the antenna than those using low-gain antennas.
Because the radiation from high-gain RF radiating systems is intended for
receivers that need not be near people, environmental exposures from these
high-gain systems are usually relatively low. Systems using low-gain antennas
generally distribute radiation into the environment where people wish to receive
it, i.e., where radio and television receivers and their listeners and viewers
are located. As a result, radio and television broadcast systems make the
largest contribution to the RF radiation environment to which everyone is
exposed.
The radiation intensity pattern of any antenna system can be represented in
a manner similar to the mathematical expression for the signal intensity far
from a broadcast antenna (Equation 5). While this expression can become very
complex, depending upon the antenna and system operation, it is possible to
estimate radiation intensities produced by the operation of any of the radiating
systems previously identified. These analytically derived exposures can be used
to estimate the environmental radiation levels produced by any system and to
assist in implementing and assuring compliance with exposure guides and
standards.
At distances close to an antenna, where the antenna does not appear to be a
point source, the expressions for power density and the electric and magnetic
field intensities are different from those shown in the equations previously
used. They will be discussed later for specific antenna systems.
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SECTION 3
GENERAL ENVIRONMENTAL EXPOSURES
BACKGROUND
The most common exposure to RF fields consists of a superposition of
the fields from many different RF sources operating at different frequencies
and occurs at distances far from individual radiation sources. To determine
these general environmental exposures, EPA began measuring levels of RF
radiation in urban areas in October 1975. Measurements have shown that the
principal sources of environmental RF radiation are AM and FM radio and VHP
and UHF television transmitters (Te74a, Ja77a, Ja77b, Ja79a, Te78a), with
other bands making only minor contributions to general environmental
exposure levels (Te74a, Ja77a, Ja77b, Te77a, Ha76a). Instrumentation was
developed to measure general environmental exposure levels (Te76a) in the
broadcast bands. The frequency bands initially measured included VLF
communications and the standard AM broadcast band (0-2 MHz), the VHP
television bands (54-88 and 174-216 MHz), the FM radio band (88-108 MHz),
two land-mobile bands (150-162 and 450-470 MHz), and the UHF television band
(470-806 MHz).
This multisource, multifrequency general RF radiation environment was
measured at 486 sites in 15 large cities (TeSOa, Te78a. Ja79b, At78, Ja80).
The data represent approximately 14,000 measurements and have been used to
estimate the RF radiation exposure within some 47,000 census enumeration
districts for the 44 million people residing in these 15 cities. The
estimate used 1970 census data and represents only outdoor residential (not
occupational) exposures. The estimated residential exposure for more than
99 percent of the total population of those 15 cities is less than
1 microwatt per square centimeter (lyU/cm2) at AM, FM, and TV frequencies
(TeSOa, Ja79b, At78, Ja80). The estimated median residential exposure is
0.005 tiU/cm2 at FM radio and TV frequencies and 0.019 vW/cma at AM radio-
frequencies (TeSOa, Ja80). (The median exposure level is the time-averaged
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power density that separates the exposed population into two groups, such
that 50 percent of the population is exposed above that level and 50 percent
is not.) Further analysis indicates that for frequencies above 806 MHz,
negligible levels are found in the general environment.
The analytic approach used to estimate population exposure does not
take into account the following: the normal daily movements of the
population residing within an area, exposures at heights greater than 6
meters above ground (where exposures can be greater due to non-uniform
antenna radiation patterns), attenuation effects of typical buildings, and
periods of time when sources are not transmitting. The results are simply
estimates for the population residing in areas where an unobstructed
measurement 6 meters above ground would result in the indicated exposure
values.
These estimates of population exposure represent general environmental
exposures for the public residing far from RF radiation sources. Exposures
occurring close to sources can be much greater; however, estimating
population exposed at these greater levels is much more difficult.
METHOD OF DETERMINING POPULATION EXPOSURE
The RF radiation exposure levels measured at selected locations in the
15 cities were used to estimate the radiofrequency radiation exposure within
47,000 census enumeration districts (CEDs) out of the 257,000 CEDs in the
1970 census. Each CED is a small geographic area within which approximately
900 to 1,000 people reside. The data base provided a description of each
CED, i.e., the geographical coordinates of the population centroid and the
number of residents. In densely populated cities, a CED is a relatively
small geographic area, while it is generally much larger in less densely
populated suburban and rural areas.
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The method used to determine population exposure included:
1. Selecting tha sites at Which to perform HF exposure measurements;
2. Measuring RF exposure power densities at these locations;
3. Estimating, the exposures at each population centre id within the
general urban area studied; and
4. Counting the number of persons residing in all of the CKDs (in that
particular metropolitan area) who are exposed to specific power
density intervals within the entire existing range of exposures.
The procedures used to predict residential exposures from exposures measured
at a limited number of locations in a city are described by Tell and
Hantiply (TeBOa).
In the first seven cities, measurement sites were selected on the basis
of population distribution within a city as inferred from city maps. For
the remaining eight cities, a random selection process was adopted to
specify the CKDs in which measurements were to be made. Each CEO was
assigned a weighting factor according to its population, so that all
individuals in a city had an equally likely chance of having the centroid of
their CED chosen as a measurement site. In addition to these locations, a
few additional measurement sites very close to broadcast station antennas
were selected to allow the full range of environmental exposure levels to be
defined.
Typically, measurements of RF exposure power densities and their
frequency dependence were made at one particular site within each of the
CEOs chosen. The field intensities obtained for each broadcast station at
each measurement site were used to develop a model describing electric field
intensity variation as a function of distance from each specific station.
This model was used to calculate the field intensity resulting from each
broadcast source at each CED centroid. The exposure 'power density as a
function of frequency at each CED centroid was summed to obtain the total
power density within each frequency band and the total power density from
all frequency bands. The predicted exposure levels at each CEO centroid
were assumed to apply to everyone residing within that CED. The population
exposure for the entire metropolitan area under study was obtained by adding
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the number of persons exposed to the same intensities within each frequency
band for all CEOs. Since most of the RF radiation sources in a metropolitan
area are generally far from any CED centroid and the population assumed to
reside there, these population exposure estimates represent general
environmental exposures (far from sources) for the public. They therefore
exclude population exposures for individuals living or working close to RF
radiation sources.
POPULATION EXPOSURES
The method previously described to estimate population exposures was
applied to the data obtained at each of the measurement sites in the 15
cities selected for the study of general population exposure to
environmental RF radiation. The combined results of the analysis, presented
as the cumulative fractions of population exposed within power density
ranges defined by the values 0.001, 0.002, 0.005, 0.010, 0.020, 0.050,
O.lOOyW/cro , etc., are shown in Figure 4 for all 15 cities. Results
of this type were obtained for the population of each city and for the total
population of the 15 cities. A more complete description of the study and
results is contained in references (TeSOa, Te78a).
The cumulative population exposures shown in Figure 4 are derived from
the percent of population exposed within various power density intervals, as
presented in Figure 5.
The number of measurement sites and FM and TV transmitters, as well as
the number of CEOs and the population for each city involved in the study,
are summarized in Table 2.
The median population exposure and the percent of population exposed at
2 »
and below 1 yW/cm are presented in Table 3 for each of the 15 cities. The
median exposure values vary from 0.002 yW/cm in Chicago and San Francisco
to 0.02 yW/cm in Boston and Portland. The median exposure for all cities
together is 0.005 yw/cma.
-16-
-------
.99
.95
.9-
.8-
.7-
6*
:§•
.4-
.3-
.2-
.1-
.05-
.01-
*
BOSTON
ATLANTA
. MIAMI
PHILADELPHIA
• NEW YORK
CHICAGO
. WASHINGTON
LAS VEGAS
' SAN DIEGO
> PORTLAND
, HOUSTON
. LOS ANGELES
DENVER
• SEATTLE
SAN FRANCISCO
•
*
»
• •
• •
• • *
• * * A
S A "
1
t *
• A
• . m.
1 * "
. * •
•
* • "
«
«
•
• TOTAL
A FM RADIO
• LOW VHF TV
• HIGH VHF TV
• UHFTV
r I i i i
-5 -4-3-2-1 0 1
LOGARITHM OF POWER DENSITY IN JUW/CM2
Figure 4. Cumulative Population Exposure for 15 Cities
t.
•OSTON
ATLANTA
MIAMI
PHILADELPHIA
NIW VOMK
CHICAGO
WASHINGTON
LAS VEGAS
SAN OH GO
PONTLANO
HOUSTON
LOS ANGELES
OENVfH
SEATTLE
SAM FRANCISCO
. nW/cm
POWtN DENSITY
Figure 5.
Differential Fraction of Population Exposed Within
Given Power Density Intervals (15 Cities)
-17-
-------
Table 2
SUMMARY OF INFORMATION RELEVANT TO ENVIRONMENTAL RF RADIATION
MEASUREMENTS AND POPULATION EXPOSURE ESTIMATES FOR IS CITIES
City
Boston
Atlanta
Miami
Philadelphia
New York
Chicago
Washington
Las Vegas
San Diego
Portland
Houston
Los Angeles
Denver
Seattle
San Francisco
No. CEDs
2,003
1,249
1,897
3,606
11,470
4,646
2,291
356
1,113
1,194
1,127
7,596
1,629
1,315
5,297
Population
1,953,665
1,221,431
1,661,012
3,407,059
12,269,374
4,743,905
2,516,917
264,501
1,071,887
818,040
1,265,933
6,951,121
1,148,016
872,422
3,959,893
Number of Stations
FM Low High UHF
VHP VHP
14
11
13
17
23
20
17
• 6
17
12
14
29
10
16
26
3
2
3
2
3
2
2
2
1
3
1
3
3
2
3
1
2
2
2
4
3
2
3
2
3
3
4
2
2
2
3
2
2
3
3
3
3
0
2
0
2
7
0
0
3
No. Sites
9
16
16
31
36
39
37
42
38
38
33
38
43
35
35
TOTAL
46,789
44,125,176
245
34
37
34
486
-18-
-------
Table 3
ESTIMATED POPULATION EXPOSURE IN IS U.S. CITIES (54-806 MHz)
City
Boston
Atlanta
Miami
Philadelphia
New York
Chicago
Washington
Las Vegas
San Diego
Portland
Houston
Los Angeles
Denver
Seattle
San Francisco
Median Exposure
(liM/cm*)
0.018
0.016
0.0070
0.0070
0.0022
0.0020
0.009
0.012
0.010
0.020
0.011
0.0048
0.0074
0.0071
0.002
Percent Exposed
<1 yU/Cffl2
96.50
99.20
98.20
99.87
99.60
99.60
97.20
99.10
99.85
99.70
99.99
99.90
99.85
99.81
97.66
All Cities 0.0048 99.44
-19-
-------
The general environmental exposure measurements (Te80a, Te74, Ja77a,
Ja77b, Te78a, At78) demonstrated that the RF radiation exposure environment
is dominated by the FM radio and VHF television frequencies. The
contribution from UHF television transmitters is not as significant
(Figure 4). In the frequency range 27 to 806 MHz, land-mobile radio
contributes the least exposure. This is shown by the distribution of power
densities, presented as the fraction of sites at which the total power
density exceeds any given value (Figure 6). This distribution was derived
from the data representing the total power density in each frequency band
measured at each of the 193 measurement sites in the seven metropolitan
areas first studied (At78). The value of total power density measured at
2 3
each of the 193 measurement sites ranged from O.OOOlyW/cm to lOyW/cm , and the
maximum exposure power densities are shown in Table 4 for each of the
frequency bands measured.
*5
lO-
ii*
^ 70-
PERCENT OF
w *> v» o>
o o o o
1 1 I 1
20—
10—
5
1 •* y
"" LAND * .» '• • ~
MOBILE • I .*" •"
\ ••' ,''/•''
\. • elf
: I .»/
- • i4 * • —
WIP-TV / * *"
X //\
- :•' J \U \
/ . ••'../ """ -
A • •
f •
» • *••
1 •
* f*
1
-6 -5 -4 -3 -2 -1
LOG S; S" POWER DENSITY in
Figure 6. Cumulative Distribution of Power Densities at 193
Measurement Sites
-20-
-------
Table 4
MAXIMUM EXPOSURE POWER DENSITY MEASURED FOR EACH FREQUENCY BAND
IN DETERMINATION OF GENERAL ENVIRONMENTAL RF RADIATION EXPOSURES
Frequency Band
0-2 MHz
LOW VHF-TV
High VHF-TV
FM Radio
UHF-TV
Low Land-Mobile Radio
High Land-Mobile Radio
Total (for all bands)
Location
Atlanta
Miami
Washington, D.C.
Washington, D.C.
Chicago
Washington, D.C.
Washington, D.C.
Philadelphia
Chicago
Power Density
(vW/on2)
0.94
0.94
1.49
0.77
10.9
0.40
0.029
0.039
10.9
-21-
-------
The FM radio band makes the largest contribution to the overall
population exposure because of lower antenna height and greater relative
intensity of the vertically directed radiation from FM antennas.
The population exposure estimates for the AM radio band are treated
separately from those for the 54- to 806-MHz bands because of the large
difference in absorption at these frequencies. The absorption rates differ
by a factor of almost 4000; i.e., an exposure of 1 yW/cm at AM
radiofrequencies is required to produce the same rate of energy absorption
as 0.00025 yW/cm at FM frequencies (Ja80). Population exposure
estimates for the AM radio band, using the measured electric field
intensities, are shown in Table 5. The median exposure level is about
0.28 V/m. These results are based on measurements at 203 sites in seven
cities.
Other RF radiation sources contribute very little to the general RF
exposure environment. This is demonstrated by the contribution of radar
systems in the San Francisco area. Measurements by the Institute for
Telecommunications Sciences (Te77a) were used to estimate the exposures at
three locations far from the radar sites. These estimates are presented in
Table 6.
To develop a basis for comparison between the general environmental
exposures measured in large metropolitan areas and an RF radiation
environment with no nearby broadcast transmitters, measurements were
made in a known RF radiation "quiet zone," Greenbank, West Virginia, where
the power density in the broadcast frequency bands is on the order of
10~11yW/cm2.
-22-
-------
Table 5
CUMULATIVE POPULATION EXPOSURE IN THE AH
BROADCAST BAND (0.535-1.605 MHz)
Electric Field Strength emulative Percent
(V/m) of Population**)
0.07
0.12
0.16
0.20
0.25
0.28
0.35
0.45
0.50
0.63
0.79
1.00
2.51
2.0
5.9
19.2
33.5
44.8
51.2
66.0
75.9
81.3
87.7
92.6
97.0
99.9
For example, 21 are exposed to less than 0.07 V/m, 33.5% are exposed
to less than 0.2 V/m, etc.
-23-
-------
Table 6
TYPICAL URBAN RADAR ENVIRONMENTS IN SAN FRANCISCO, CALIFORNIA
Exposure
Location
Hi. Diablo
Palo Alto
Bernal Heights
Number of
Radars Detected
8
10
10
Average Power Density
(yW/cma)
0.000026
0.00027
0.0011
-24-
-------
SECTION 4
EXPOSURES FROM SELECTED RF RADIATION SOURCES
BACKGROUND
Exposures at locations in the immediate vicinity of a particular source
can be considerably higher than those in the general RF environment and are
dominated by the source or sources at those locations. The exposure
situations to be discussed here occur at distances from antennas that range
from the near field (Fresnel zone) to the beginning of the far field
(Fraunhofer region). The information describing this "specific source"
environment consists of exposure measurements and of estimates obtained
through analyses for the most common categories of both high- and low-power
systems; i.e., broadcast transmitters, satellite communications earth
stations, radars, microwave radio, land-mobile radio, and low-power
hand-held radio. Exposure measurements and estimates are given for
locations close to sources within these categories.
Measurements have been performed for a number of different types of RF
sources including FM radio and VHP and UHF television antennas (Te79, Te78b,
Te?6b, Te77b), satellite communications systems (Ha74a), military
acquisition and tracking radars (Ha76a, Ha74b, Te74b), civilian air traffic
control radars (Te74c), aircraft weather radars (Te76c, Te74d), microwave
relay systems used in communications and data transmission (Te80b), police
radar units (Ha76b), microwave ovens (Te78c), and land-mobile and hand-held
radio (La78, Te76e, Ru79). Many of these studies provided data useful in
developing analytical techniques to calculate the power densities and peak
electric field intensities produced by most sources. Analytical models
predicting power densities produced by sources having parabolic reflector
antennas have been described by Hankin (Ha76a, Ha76c, Ha77) and Lewis (Le85)
-25-
-------
Analytical methods used to predict exposure power density at distances
close to antennas are presented here for the systems of greatest interest,
i.e., broadcast FM and TV, microwave communications, and radar. The on- and
off-axis power density characteristics of systems will be presented for
locations in the Fresnel region as well as for locations farther from the
antennas. Analysis of broadcast radiation sources has been given by Tell
and others (Te72, Te78d, Te74e, Te76d, Ga85). Satellite communications
earth terminals have been analyzed by Hankin (Ha74a), air traffic control
radars by Hankin (Ha76a, Ha76d), and airborne radars by Tell and Nelson
(Te74d), Tell, Hankin, and Janes (Te76c), and Hankin, Tell, and Janes
(Ha74b). The overall impact of high-power sources based upon measurements
and theoretical analyses has been discussed by Hankin and others (Ha76a,
Ha74b).
Broadcast sources are usually located near densely populated areas so
that the radio and television signals can be received by a large audience.
The radiation patterns for broadcast antennas are not highly collimated, and
exposure of persons to main-beam radiation intensities near the radiating
antennas is not uncommon. Relatively high exposures compared to those in
the general environment can occur at ground level close to broadcast station
antennas and at higher elevations, e.g., in hilly terrain and on the upper
floors of high-rise buildings, where exposure locations are in or close to
the axis of the main beam.
Measurements and observations have shown that exposures to these higher
fields are not unusual, although the total number of persons exposed is
likely to be relatively small. The extent to which such exposures occur and
the size of the exposed population remain to be determined.
Radiofrequency radiation emitting systems with highly directional (high-
gain) aperture antennas used for satellite communications, radar, and
microwave radio, ordinarily are used in ways that preclude possibilities of
-26-
-------
main-beam exposure at locations close to the antenna systems. Exposures
that occur close to high-power sources are usually due to the antenna
side-lobe radiation patterns rather than main-beam radiation (refer to
Figure 3). Public exposure at locations close to the antenna (in the
Fresnel region) usually occurs far from the antenna axis, i.e., at an
-off-axis" distance of at least several antenna diameters as measured along
a line perpendicular to the axis, where "off-axis" exposure intensities are
very likely to be at least three orders of magnitude (xlO ) less than
Fresnel region on-axis exposure. At exposure locations beyond the Fresnel
region in the far field (Fraunhofer region), main-beam divergence results in
a decrease of power density proportional to 1/r as the distance, r,
from the antenna increases. Main-beam divergence in the far field increases
the probability of population exposure to main-beam radiation for some
systems, but usually at distances very far from the antenna, where
intensities are low.
Although high-power microwave sources such as radar and satellite
communications earth terminals are capable of producing intense main-beam
radiation levels at considerable distances from the source antenna, actual
exposure levels (due to side-lobe radiation) have been found to be
considerably lower. Many of these RF radiation sources are remotely located
and are surrounded by an exclusion area that further limits the probability
of exposure. Some sources are mechanically or electrically equipped to
limit the pointing directions of antennas or to reduce or shut off power
when occupied areas are scanned. The rotational motion of many radar
antennas further reduces the average exposure.
While fewer persons are exposed to main-beam radiation produced by
systems having very directive antennas and high-powered transmitters
(relative to broadcast systems), some radars and satellite communications
earth terminals can produce main-beam power densities of 10 mW/cm and
greater (Ha76a, Ha74a, Ha74b). Individuals near airports and military bases
-27-
-------
may bo exposed to aide-lobe radiation from systems having stationary or
slowly moving antennas or to main-beam radiation from many types of radars
with rapidly moving antennas, where exposure to the main beam is short but
repetitive. The results of analysis indicate that continuous or
time-averaged power densities in the range 10 to 100 vW/cm* may occur
at distances up to 0.5 mile from some of these systems (Ha74a, Ha77a).
Associated instantaneous peak electric field intensities can be on the order
of 2,000 V/m.
Other short-term, intermittent exposures to relatively strong electric
fields occur when persons are close to transmitting land-mobile radio or
citizens-band radio antennas (La78, Te76e, Ru79).
FM RADIO AND TELEVISION
FM radio and VHP and UHF television are treated together in this
discussion because of similar antenna radiation patterns and roughly
equivalent effective radiated powers (ERP), with ERF being the product of
the transmitter power and the antenna gain. ERP is used as a combined
characteristic for broadcast stations in place of transmitter power and
antenna gain. The frequency and maximum power characteristics for FM radio
and television broadcasting are presented in Table 7.
The exposure levels produced by the radiation from FM radio and VHF and
UHF television antennas depend on the location of the exposure site relative
to that of the transmitting antenna. Antenna height strongly influences
exposure power density. An FM or TV antenna generally consists of a
vertical arrangement of radiating elements, the exact configuration being
determined by the desired radiation pattern. A more complete discussion of
FM and TV antenna structure and the related radiation pattern is contained
in reference (Ga85). To provide good reception over a large area, antennas
are often placed atop mountains, tall buildings, or tall antenna towers.
Frequently, a single tower may support several FM and TV antennas.
-28-
-------
Table 7
GENERAL CHARACTERISTICS OF FM AND TV BROADCASTING
Service
Frequency (MHz)
Maximum ERP (kW)
FM Radio
Low VHF-TV
High VHF-TV
UHF-TV
88-106
54-72 (Channels 2-4)
76-88 (Channels 5-6)
174-216 (Channels 7-13)
470-806 (Channels 14-67)
100 (may use 100 kW
in both horizontal
and vertical planes)
100 visual
22 aural
316 visual
69.5 aural
5000 visual
1100 aural
-29-
-------
The FM or TV antenna has a radiation pattern that is uniform around the
axis of the vertically oriented array of elements. While the primary beam
of radiation is in the horizontal direction, a significant amount of power
nay be concentrated into a beam with a relatively small angular divergence
in the vertical plane. The major difference between FM and TV transmission,
with regard to RF radiation exposures, lies in the antenna radiation pattern
at locations close to the antenna at large angles from the direction of
maximum gain, i.e., near the base of the antenna support structure.
An example of a vertical plane radiation pattern for a typical FM
antenna with six dipole elements, having a 1.0 wavelength separation between
elements, is shown in both rectangular and polar coordinates in Figures 7a
and 7b. A visual representation of the pattern is shown in Figure 7c. The
vertical radiation lobe, called the grating lobe, occurs at about 90°
relative to the horizontal. The maximum antenna gain for the primary beam
and the maximum antenna gain in the grating lobe may in some cases be
approximately equal, i.e., G(6=0°) = 0(6=90"), although the primary beam
is generally narrower than the grating lobe.
The vertical plane radiation pattern for a typical UHF-TV transmitting
antenna is shown in Figure 8 (Te76d). This graph does not show the
intensity for large vertical plane angles out to 90". The maximum
intensity, where G(6) is a maximum, occurs just below the horizontal plane
(0.5°) to optimize the coverage. For UHF-TV and VHF-TV antennas, the E
field at large depression angles is approximately 10 percent and 20 percent,
respectively, of the maximum intensity (main beam) E fields (Ga85).
The previously introduced Equations 4, 5, and 6 for electric field
intensity and power density at a few wavelengths from the antenna, change
slightly for FM and TV when effective radiated power, P-ooO), is
-30-
-------
RELATIVE FIELD PATTERN WITH N » 6
nUM-OOUMES •MCMO-1X
RELATIVE FIELD PATTERN WITH N - 6
PHAM'ODiORUS SMCIMa>1X
M JO 10 0 -10 •» •*• ** •« -40 -70
AMOLE ABOVE AND BELOW AXIS OP CENTER OP
RADIATION (DEGREES)
WATHM
MMMANV ANTENNA
tOMK
OMN10IMCTKMAL
IN THE AilMUTM
ORATING LOK MFWf tf NTS
UNOCSIRED MAOIATION
M VERTICAI. tMMCTKWS
(0
Figure 7. Vertical Plane Radiation Pattern of an FM Antenna in
(a) Rectangular Coordinates and (b) Polar Coordinates.
(c) Visual Representation of Radiation Pattern.
-31-
-------
i.e
MAJOR LOBE
POWER GAIN-24.0
HOI. CAIN-JO 3
0.2
e.i
~i • U- " , ! ! IT/ \/ : \:
o.o
Degrees Front Horizontal Plane
Figure 8. Vertical Plane Radiation Pattern of a Typical
UHF-TV Transmitting Antenna
used to characterize the system instead of antenna gain and radiated power.
The equation for power density at an angle 6,
S. - PG(e)/4irr2,
(5)
becomes
se - pERp(e)/4irr •
(7)
and the electric field strength at an angle 6,
Ee
-------
becomes
Ee(V/m) - [30PgRp(e)]1/a/r.
(8)
can be expressed as RepERP<°"> for FM and
However,
TV antennas, where Ra is the relative field strength and is a function
U
of 6, and P_.B(0*) is the maximum value of P_BD(0>. Then,
EKP EKF
e
V30pRRp(0')]1/2/r
(9)
and
e
(10)
An example of exposure power density variation with distance from the
antenna support tower, calculated at ground level, is shown in Figure 9 for
the FM antenna pattern depicted in Figure 7. It is assumed that the E field
is reflected from the ground and adds to the incident field, so that the
exposure E field is approximately twice that of the incident E field.
teeee
tees
tee
•- II II
Figure 9. Ground-Level Power Density vs. Distance for an FM Antenna
Distance from tower
(Meters)
-33-
-------
Figure 9 illustrates why high-intensity exposures can be found near the
base of a tower supporting an FM antenna and at elevated locations (in the
•main beam) such as the upper. stories of high-rise buildings or at high
elevations in hilly terrain.
The power density variations for a UHF-TV station for various heights
below the center of the antenna are presented in Figure 10. Again, the
pattern of exposure is similar to that for FM antennas. Intensities are
generally greatest near the base of the support tower and decrease with
horizontal distance from the antenna for constant height below the antenna.
Because the grating lobe gain for TV antennas is generally not equivalent to
the main-beam gain, however, relatively higher intensity exposures are more
likely to occur at locations farther away from the antenna tower than is the
case for FM antennas, where high-intensity exposures can occur near the base
of the antenna support tower. These locations are generally at upper floors
of nearby high-rise buildings.
POUER DENSITY VS. DISTANCE AT
VRRIOUS HEIGHTS BELOW ANTENNA FOR
1 MEGAWATT E. R. P. UHF TV STATION
MAIN IEAN EXPOSURE
10
10
10
-5
I I I I III! . 1 1 I I I Mil
DISTANCE CHI)
i i i i mi
10
Figure 10. Power Density vs. Distance for a 1 Megawatt (ERP) UHF-TV Station
-34-
-------
Several aeries of measurements verify the analytical predictions
illustrated in Figure 9. At Mt. Wilson, California, where 12 FM radio and
15 TV antennas are located in a relatively small area, measured exposure
levels ranged from 1.0 to 7.2 mU/cm beneath the FM antennas (Te77b).
Maximum power densities in a nearby post office building were about
120 yW/cma. Power densities of 55.9 tiW/cm2, with 29.5 vW/cm* from FM
radio, 14.2 vW/cm* from VHF-TV, and 12.2 uW/cm* from UHF-TV were
measured in a nearby parking lot. At other sites close to FM radio
antennas, ground-level exposures ranging up to more than 700 pW/cm
were found in publicly accessible locations near residential areas (Te85a,
Te85b). An analytical assessment of exposures near a residential area
predicted exposures of nearly 3 tnW/cm (Te84).
To investigate the relative number of FM antennas exhibiting strong
grating lobes, electric field intensities were measured near the bases of 58
FM radio antennas (Te79). The results for five of these antennas are
presented in Table 8 (Ja80) for power density measured at locations 3 feet
above ground level, directly below the antennas out to horizontal distances
of 61 m (200 feet). The values range from almost 20,000 pW/cm to
less than 1 yW/cm to within 200 feet of the support tower. The
station characteristics are included in Table 8.
The expectation that exposures at higher elevations would increase as
the vertical distance between the main-beam axis and the exposure locations
decreased, as predicted by the FM and TV radiation patterns shown in the
preceding figures, was supported by the results of a series of measurements
made in high-rise buildings in several cities (Te78b, Te85a). The results
of these measurements are summarized in Table 9.
The exposures at the Empire State Building and the roof of the Sears
Building were due to the antennas mounted on those buildings. The exposures
at the Pan Am Building and the World Trade Center in Hew York City were
caused by the transmitting antennas on the Empire State Building located
-35-
-------
Table 8
POWER DENSITIES IN THE GRATING LOBE FOR 5 FH
RADIO ANTENNAS AT 3 FEET ABOVE GROUND LEVEL
Distance
(m) (ft)
0.3 1
1.5 5
3 10
4.6 15
6.1 20
7.6 25
9.1 30
12.2 40
15.2 50
30.5 100
61 200
Station
KXLU
KFAC
KRTH
KPRI
KWVE
KXLU KFAC
27 —
— 52
223 60
193
166 —
86 60
32 —
0.3 165
- 60
— —
Frequency
Wz)
88.9
92.3
101.1
106.5
107.9
Power Density
KRTH KPRI KWVE
106 19,337
5,199 -
106 2.652 -
— 2,394 —
239 1,413 —
106 862 1,300
_ —
424 - 106
_ — 166
— — 38
_ — 27
Effective Antenna
Radiated Power Height
(KW) (ft)
2.9 32
39 157
58 • 144
50 60
50 98
-36-
-------
Table 9
POWER DENSITY MEASUREMENTS AT HIGH-RISE BUILDINGS
LOCATED NEAR FM AND TV BROADCAST ANTENNAS
Location Power Density (vM/ana)
FH TV Total
EMPIRE STATE BUILDING (New York City)
86th Floor Observatory 15.2 — 15.2
102nd Floor Observatory
NearUindOM 30.7 1.79 32.5
Near Elevator 1.35 — 1.35
WORLD TRADE CENTER (New York City)
107th Floor Observatory 0.10 1.10 1.20
Roof Observatory 0.15 7.18 7.33
PAN AM BUILDING (New York City)
54th Floor 3.76 6.52 10.3
ONE BISCAYNE TOWER (Miami)
26th Floor 6.69 — 6.69
30th Floor 5.24 — 5.24
34th Floor 62.1 — 62.1
38th Floor 96.8 — 96.8
Roof (shielded location) 134 — 134
Roof 148 — 148
SEARS BUILDING (Chicago)
50th Floor 31.7 34.2 65.9
Roof 201 29.0 230
FEDERAL BUILDING (Chicago)
39th Floor 5.74 .73 6.47
HOME TOWER (San Diego)
10th Floor 18 — 18
17th Floor 0.22 — 0.22
Roof 119 - 119
Roof 180 — 180
MILAM BUILDING (Houston)
47th Floor 35.8 31.6 67.4
ALA MOANA AMERICANA HOTEL (Honolulu)
Observation Deck 57 254 311
COTY TOWER (Honolulu)
Rooftop — — 375
-37-
-------
some distance from both structures. The measured exposures at the other
buildings, with the exception of the roof of the Sears Building in Chicago,
were produced by antennas on other high-rise buildings located within 100 to
1,000 meters. Total power densities measured inside the buildings ranged
from less than 1 pW/cm* (in a shielded location) to 97 tiW/cm2.
A building in Miami, One Biscayne Tower, illustrates the effect of
approaching the main-beam radiation axis, where antenna gain increases to
its maximum value. The power density measurement at the 17th floor of the
Home Tower, San Diego, was less than expected because of attenuation of the
FM field by a transparent metallized film used to cover the windows above
the tenth floor. The film is used to reduce solar heat input by reflecting
the sun's rays. Since these measurements were first reported in 1978, many
TV and FM antennas in New York City have been relocated, undoubtedly
significantly affecting the building exposures reported. This may also be
true for other cities.
More recently, measurements of RF exposure levels were conducted in
Honolulu, Hawaii, where most broadcast antennas are located on or very near
tall buildings that in some cases have rooftop recreational areas (Te85a).
Exposures on rooftop recreational and observation areas on buildings in
Honolulu ranged up to 300 to 400 yW/cm .
AM RADIO
AM radio transmission is very different from FM radio and VHF and UHF
television transmission. The AM broadcast band covers the frequency range
of 535 to 1605 kHz. The associated wavelengths, 560 m to 190 m, are 100 to
1,000 times longer than those of the FM radio and television broadcast
bands. The antennas used are vertical monopoles with lengths that vary from
0.1 to 1.0 wavelength. The entire tower structure acts as the antenna and,
in general, the antenna tower height varies with the transmission
frequency. Most AM antenna towers are 0.1 - 0.25 wavelength tall.
-38-
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The primary «ode of AM radio transmission is.not line-of-sight, as in
FM radio and television, but through propagation of a vertically polarized
"groundwave" that follows the contour of the ground in an omnidirectional
pattern. At night, radiation that propagates upward, called skywaves, is
reflected back to earth by the electrically charged particles of the
ionosphere, resulting in radiation being detected at greater distances at
night than during the day. Daytime reception is largely dependent upon
groundwaves, a more reliable AM radio transmission process. The skywave
effect produces possibilities for interference with reception from other AM
stations. To prevent nighttime interference, stations operating at night
with transmitted powers of 50 kW (the power range for AM broadcast is 100 W
to 50 kW) typically use a multiple-tower configuration to minimize radiation
in some particular direction instead of enhancing the signal in a given
direction.
Because the earth acts as a ground plane for the vertical antennas used
in AM radio transmission, ground conductivity plays an important role in
determining the strength of the emitted signals. The greater the soil
conductivity, the greater the signal strength at a given point for a fixed
power. Other factors that affect the intensity of an AM radio signal are
the tower height (some heights are more effective than others in maximizing
field strengths), the radiation frequency, the terrain characteristics
immediately around the antenna site, and the power being transmitted.
The calculated ground-level field strengths near two AM radio towers
are shown in Figure 11. These two curves represent the extremes in field
strength for variations in ground conductivity, antenna tower height, and
frequency, and were determined through application of the FCC rules and
regulations as used in reference (Te76d). Each curve is computed for a
transmitter output power of 50 kW and assumes that the power is delivered to
the antenna without loss. A maximum field strength of 22 V/m is obtained at
100 meters for the 550 kHz case and decreases approximately with the inverse
of the distance. Two qualifications need to be placed on these results:
(1) the indicated field strength values are not valid at distances closer
than 100 meters due to near-field effects, and (2) it is possible that some
-39-
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particular station with an optimum tower height for its operating frequency
and an excellent ground system might produce slightly higher field
strengths. The two cases selected here are intended to be representative of
typical but not necessarily absolute extremes. A field strength of 22 V/m
is equivalent to a plane-wave power density of 0.13 mU/cm in free space
(refer to Equation 4).
2 14.
0.1
tAJtTM nCUCTWC CONSTANT • W
t.1
OOTAMCt FftOM ANTf NNA
Figure 11. Groundwave Field Strengths for 50 kW Single
Monopole AH Radio Broadcast Stations
-40-
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A description of the methods used to calculate fields for AM radio
stations is contained in reference (Ca85). Table 10 presents the calculated
electric field intensity over a wide range of distances for a 50-kH station
using one of the methods described (Jo68).
In this example (Table 10) the field strength varies from 56 V/m near
the tower (4.6 meters) to 11 V/m at 93.8 meters (308 feet) to 1 V/m at
1,757 meters (1.1 mile). Measurements made by the Federal Communications
Commission (Wa76) at two different 50-kW stations are consistent with the
values in Table 10. Both stations consisted of three Antenna towers
arranged in an in-line configuration with only one tower radiating during
the day and all three operating at night. The electric field intensity at a
distance of 300 feet from the antennas of the 1,500 kHz station was
17.3 V/m; at 295 feet from the antenna of the station operating at 1,090
kHz, it was 40.8 V/m. An electric field intensity of 1.7 V/m was measured
at a distance of 1 mile from a 50 kW, 720 kHz station (Ha77b).
Ground-level exposures from AM transmitters have been found to be as
great as 300 V/m (electric field) and 9.0 A/m (magnetic field), corre-
sponding to equivalent plane-wave power densities of 24,000 vW/cm ,
and 3xlO*yW/cma, respectively, in publicly accessible locations.
Measurements of the exposures at recreational areas on the roofs of
high-rise buildings (Te85a) revealed AM electric field intensities of 100 to
200 V/m (equivalent plane-wave power density of 2,650 to 10,600 yw/cm ).
HIGH-FREQUENCY (HF) RADIO
Exposures from transmitting systems operating in the HF band, 3 to 30
MHz, have been investigated. Radio transmission in the HF band is used for
international communications. Transmitter powers can vary considerably,
with effective radiated power (ERP) being restricted to a minimum of 50 kW
for FCC-licensed international broadcast stations. Other communication
systems using the HF band operate at much lower ERP values.
-41-
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Table 10
ELECTRIC FIELD STRENGTH AT VARIOUS DISTANCES
FROM A 50 kW AH RADIO BROADCAST STATION
Distance Electric Field Strength
(m) (V/m)
4.6 56.2
8.8 .32.7
20.9 27.2
46.4 12.7
93.8 11.2
121 12.7
147 9.3
202 6.8
479 3.0
1,000 1.9
1,757 1.0
2,021 .7
5,275 .4
10,000 .2
20,000 .1
-42-
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Measurements of environmental magnetic field intensities (Te78e) for an
international broadcast station operating at 5.980 MHz with an KRP of 250 kw
and at 9.615 MHz with an EBP of 50 kW found maximum H field intensities of
0.251 A/m and 0.112 A/in, respectively, at generally accessible locations
near the antennas. Corresponding plane-wave equivalent power densities
would be 2.38 aw/cm* at 5.980 MHz and 0.47 mu/cm* at 9.615 MHz.
Another international broadcast system proposed to operate at 9 MHz
with an BRP of 100 kw was analyzed; for this system an equivalent plane-wave
power density of 0.11 mw/cm* was predicted at a distance of 750 feet and
at a height of 30 feet above ground (Te82).
The environmental exposure levels produced near a facility with a
number of HF transmitters were determined by an analysis of the radiating
systems (Ha78a). Systems operating simultaneously with frequencies varying
over a range of 3 to 17.4 MHz, having ERPs of 10 kW (for seven of the
systems) and 12 kW (for two of the systems), were predicted to produce a
total plane-wave equivalent exposure power density of 81 iiW/cm at a
distance of 100 meters and 0.3 yU/cm at 1 mile.
The results of the three studies are consistent and indicate that
exposure power densities in accessible areas close to high-power (ERP on the
order of 100 kW) HF systems can be equal to or greater than 1 mW/cm .
SATELLITE COMMUNICATIONS EARTH TERMINALS (SATCOMS)
Satellite communications earth terminals communicate with earth-
orbiting satellites that are used for communications, scientific research,
weather forecasting, national defense, and geological exploration of earth
resources. These SATCOM systems can produce significant power densities at
greater distances from the antenna than is possible for other types of
radiating systems. Exposure of people to radiation from SATCOM earth
-43-
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terminal antennas, When it occurs, is not to main-beam radiation, but to the
lower intensity side lobes (refer to Figure 3). These side lobes may
irradiate a particular region of the environment for long periods of time
While the earth terminal antenna is in contact with satellites in various
earth orbits out to geostationary (synchronous) orbits at a height of 22,300
miles above earth.
Satellite communications (SATCOM) systems use high-gain antennas that
radiate power into well collimated main beams with very little angular
divergence. The need to transmit power over great distances and the number
of communications channels involved determine the transmitter power to be
used with an antenna having a diameter usually determined on the basis of
reception requirements. Generally, as systems are required to provide
higher data transmission rates over great distances, the earth terminal
transmitter power and antenna diameter increase. The combination of high
transmitter power and antenna diameter is responsible for producing a region
of high power density (in the main beam) that extends over very large
distances. Two of the highest power systems included in this discussion,
located at Goldstone, California, are used to communicate with space probes
performing research many millions of miles from earth.
The antennas of satellite communications system earth terminals have
paraboloidal surfaces and circular cross sections. Many have Cassegrain
geometries (Figure 12) where power is introduced to the antenna from the
primary radiating source (power feed) located at the center of the
paraboloidal reflector. The radiation is incident on a small hyperboloidal
subreflector located between the power feed and the focal point of the
antenna. . Radiation from the power feed is reflected from the subreflector,
illuminates the main reflector as if it had originated at the focal point,
and is then collimated by the reflector. While the reflector surface can be
illuminated by means other than Cassegrain geometry, the example shown
illustrates the general radiation characteristics of circular cross-section
paraboloidal reflectors.
-44-
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ruo
MYttftBOLOlD
SMNEFLtCTOM
'ANA10LOIO
•EFUCTOK
Figure 12. Cassegrain Paraboloidal Antenna
The radiation frequencies used by SATCOM systems usually range from
about 2 to 14 GHz (14x10 Hz), with some special systems employing
frequencies in the range of 20 to 94 GHz. The high frequencies used and the
relatively large antenna diameters result in the antenna being highly
directional (high gain); the ratio of wavelength (X.) to diameter (D) is
the determining factor. The generally directional nature of the radiation
distribution pattern of the antennas of most high-power systems
significantly reduces the probability of exposure to high levels; i.e., the
power densities at locations accessible to the public are usually
substantially less than on-axis or main-beam power densities. The exposures
depend upon antenna height above ground, main-beam orientation, location of
the system in relation to public access areas, and operational procedures
used, in adddition to transmitter power, antenna diameter, and wavelength.
-45-
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Selected SATCOMS were studied analytically and by measurement of
on-axis power densities to determine methods of estimating potential
environmental exposure levels and to determine the relative environmental
significance of this category of radiation sources.
An empirical model, based upon aperture-antenna theory (Si65, Ha76a,
Ha74a, Ha76c, Ha77) and many measurements (Ha74a, Ha74b, Te74b, Te76c,
Te74d, Ha76b), has been developed and used to calculate the characteristics
of satellite communications earth terminals and to evaluate potential
environmental exposures. The model applies directly to antennas
(reflectors) that are circular cross-section paraboloids. It expresses the
on-axis power density, the maximum existing at any given distance from the
antenna, as a function of distance from the antenna in terms of basic
characteristics; e.g., the reflector diameter, radiation wavelength,
aperture efficiency, and the power that can be introduced to the antenna
system. An earlier version of the model was used in a study of SATCOM
systems (Ha74a); the results have been updated and included in this section.
An in-depth treatment of paraboloidal antennas is given by Silver
(Si65). General characteristics are presented here to enable the reader to
better understand the information provided. In general, the reflector is
illuminated so that beyond a specific distance from the antenna, in the
Fraunhofer (far-field) region, power is distributed in a series of maxima
and minima as the off-axis angle (defined by the antenna axis, the center of
the antenna, and the specific fieldpoint) increases. For constant phase
over the aperture, there is one maximum that is much greater than the
others, i.e., the main beam. The power distribution is characterized by the
gain function, C(6) . For the special case of uniform illumination, the
main-beam gain is the maximum possible, G (9=0 ) = 4*A/\a, where A is the
antenna area, and X is the radiation wavelength. In general, for any
o
other field distribution over the aperture, the gain is less than GQ(e=O ).
If the illumination decreases in magnitude from the aperture center toward
-46-
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the edge, then the gain decreases, the bean width (of the main beam)
increases, and the intensities (gains) of the side-lobe maxima decrease
relative to the peak intensity (gain) in the main beam. An important
characteristic of an illuminated aperture is the efficiency of the aperture
in concentrating the available energy into the peak intensity of the main
beam. The maximum gain occurs with uniform illumination, and the efficiency
is equal to 1. In practical use, side-lobe gain is reduced so that
interference may be reduced, illumination is not uniform, and the efficiency
is less than 1. The overall gain of the antenna and the efficiency also
include the fraction of the total power to the antenna that illuminates the
aperture. The overall antenna efficiency is called the aperture efficiency,
and for Cassegrain antennas is usually equal to about 0.55.
The on-axis radiation field characteristics for circular cross-section
paraboloidal antennas can be described using Figure 13 (Ha76c). The
magnitude of the on-axis power density oscillates as a function of distance
in the near field (Fresnel region) of an antenna due to the integrated
contribution from adjacent Fresnel- zones to the field at a point on the
antenna axis; the maximum value of the near-field on-axis power density,
S f, is given by Equation 11. The beam of radiation is collimated so that
most of the power in the near field is contained in a region having
approximately the diameter of the reflector. The power density in the far
field, S (Equation 15), decreases inversely as the square of the
distance from the antenna. The intermediate-field region is a transition
region between the near and far fields in which the intermediate-field power
density, S, (Equation 14), decreases inversely with distance. The extent
of the Fresnel region is defined by the point on the axis for which the
entire aperture is a single Fresnel zone; the extent of the Fresnel region,
R ,, is equal to Da/4X.
nf
-47-
-------
R.. -
Rff - B.BD'/X
Figure 13. Radiation Field Regions for a Circular
Cross-Section Reflector Antenna
S , = 16nP/irD
nf
(11)
R . * D /4\
nt
(12)
Rff = 0.6D
Sif = Snf(R/Rn£)
-i
S,, * 2.47S ,(R/R ,)"2 » PG/4*Ra
tr nt nt
for R - < R < R,.r
nf — ff
for R
_ ,
(13)
(14)
(15)
where:
nf
n
P
0
R
R
nf
R
ff
5if
!ff
naximuin near-field power density (on-axis)
aperture efficiency, typically 0.5 < n < 0.75
power fed to antenna
antenna diameter
distance from antenna (on-axis)
extent of near field
distance to the onset of the far-field region
power density (on-axis) in transition (crossover) region
power density (on-axis) in the far field.
-48-
-------
To calculate on-axis power density as a function of distance from an
antenna, the extent of the near field, R ., oust be determined, i.e., the
distance over which the power density can be a maximum before it begins to
decrease with distance. This parameter and the maximum power density in
the near field determine the on-axis power density at any distance from the
antenna. Although these equations are applicable to circular paraboloidal
antennas, they show that in general the important system parameters are
antenna diameter, power delivered to the antenna, radiation wavelength, and
aperture efficiency.
The on-axis radiation field characteristics presented for circular
paraboloidal antennas yield the maximum power density the system can
produce at any distance from the antenna. This provides the basis for an
assessment of the potential environmental exposure levels that can be
produced. Exposure at distances closer to the antenna than the onset of
the far field are generally at off-axis locations where relative
intensities are much less than on-axis power densities at the same
horizontal distance from the antenna. The radiation pattern and relative
intensities close to the antenna, out to a distance of D /\ along the
antenna axis and out to an off-axis distance of four antenna diameters, are
presented in Figure 14 for an aperture antenna having a diameter/wavelength
ratio > 30 (Le85). These radiation patterns have been determined for
off-axis distance up to four antenna diameters for a range of D/X ratios
appropriate for practical microwave communications antennas.
The anticipated exposure power densities have been calculated for many
communications systems operating at normal transmitter powers. A
comparison of measured and predicted values is presented in references
(Ha74a, Ha74b, Te76c), showing good agreement with the model. The results
for systems having typical SATCOM characteristics are presented in
Table 11. Shown are basic system characteristics that include the
-49-
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Z-«1» dlttmct dlvldtd by D*A
Figure 14. Relative Power Density Contours for a Circular Aperture
Antenna. Contours are Shown in the y-z Plane for the Case
D > 30X, where -4D * y * 4D and 0 * z 4 Da/X. The
Aperture Illumination is ll-(p/a)2]2, where p is the
Radial Distance Variable, 0 * p 4 a, and a * D/2. Each
Contour Corresponds to an Increment of -2.5dB.
-50-
-------
Table 11
RADIATION CHARACTERISTICS OF SOME EXISTING SATELLITE COMMUNICATIONS SYSTEMS
Dian
(ft)
60
60
97
85
I 210
H 105
1 105
42.6
42.6
40
39.4
36.1
32.8
17.9
15
10
eter
(m)
18.3
18.3
29.6
25.9
64.0
32.0
32.0
13.0
13.0
12.2
12
11.0
10
5.45
4.57
3.05
Frequency
(GHz)
8.15
8.15
6.25
2.38
2.38
14.25
6.18
6.0
7.98
8.15
6.42
6.40
5.%
8.15
8.15
14.0
X
(cm)
3.68
3.68
4.8
12.6
12.6
2.1
4.86
5.0
3.76
3.68
4.69
4.69
5.03
3.68
3.68
2.14
Gain
(dBj)
60.8
60.8
62.7
53.8
61.9
69.0
64.0
56.4
58.0
57.3
55.4
55.0
53.6
52.1
48.8
50.0
P
(W)
4x10*
10x10*
2.5x10*
225x10*
225x10*
5x10*
5x10*
2.6xl02
80
5x10"
5x10"
2x10"
2x102
4x10"
1.26x10"
1.4x10"
*nf
(m)
2.27x10"
2.27x10"
4.55x10"
1.33x10*
8.13x10"
1.22x10*
5.27x10"
8.45x102
1.12x10"
1.01x10"
7.71xl02
6.45xl02
4.97xl02
2.02x102
1.42xl02
l.OSxIO2
"ff
(m)
5.45x10*
5.45x10*
1.09x10*
3.20x10*
1.95x10*
2.92x10*
1.26x10*
2.03x10*
2.70x10*
2.42x10*
1.85x10*
1.55x10*
1.19x10*
4.84x10*
3.41x102
2.6x102
n
0.5
0.5
0.5
0.57
0.61
0.35
0.57
0.65
0.53
0.5
0.54
0.58
0.59
0.75
0.5
0.5
3.0x10*
7.5x10*
7.2x10*
9.81x10*
17.0x10»
8.66x10*
1.46x10*
5.19x10*
1.29x10*
8.5x10*
9.5x10*
4.9x10*
6.0x10*
5. 15x10*
1.53x10*
3.84x10*
(yW/cm*)
3.0
7.5
0.72
98.1
17.0
0.87
1.46
0.52
0.13
8.5
9.5
4.9
0.60
51.5
15.3
38.4
-------
calculated on-axis, near-field power density; on-axia power density at 100
meters (usually in the near field); and maximum off-axis power density at
100 meters from the antenna (along the antenna axis) with the relative
intensity (the ratio of off-axis power density to on-axis power density)
taken to be 10~*.
Although the maximum on-axis power densities that can be produced
range from 1.29 x 10 to 9.81 x 10* yU/cm2, the maximum exposure
power density at a distance of 100 meters is less than 100 yW/cm , because
the relative intensity in the off-axis radiation region where exposure could
occur is less than 10 '.
RADAR SYSTEMS
Radar systems use microwave frequencies, with the radiation emitted and
received in pulses that are generally short in duration compared to the time
interval between the emission of succeeding pulses. The reflected pulse
must be detected before the next pulse is emitted, thus determining the
maximum time interval between pulses and affecting the distance range for
which the system is used.
The power radiated per pulse for radars is generally much greater than
the average power transmitted by continuously radiating systems, and thus
the values of peak radiated fields are greater than those of equivalent gain
systems that radiate power continuously. The analysis of potential
environmental impact due to radar systems may involve use of peak
transmitter power to determine near-field, on-axis peak power density; the
variation of peak on-axis power density as a function of distance from the
source; or the distance from the source at which specific values of peak
on-axis power density levels may exist. This type of an evaluation is
appropriate when considering the potential for interference effects on the
operation of certain electronic systems in a pulsed microwave radiation
field. It would also be the correct approach in evaluating the potential
-52-
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for the occurrence of certain kinds of affects, such as "microwave hearing,"
that are caused by pulsed fialds. In such eases, tha appropriate physical
radiation field parameter to be determined is peak field intensity rather
than time-averaged power density.
Exposure evaluation analysis involving time-averaged values of
transmitter power to determine the corresponding time-averaged field
characteristics is appropriate when considering exposure in relation to
effects that depend upon time-averaged power density (or more directly,
time-averaged specific absorption rate).
Selected radar systems have been studied, and the results have been
used to specify the range of exposure levels produced. The systems studied,
analytically and by measurement, are military acquisition and tracking
radar, civilian and military air traffic control (ATC) radar, and weather
radar. The variation of system characteristics is greatest for acquisition
and tracking radars, resulting in a wide range of on-axis, near-field power
densities and effective near-field distances.
Time-averaged power density is the characteristic of primary interest
in radar system radiation exposure measurements, although peak-power density
is certainly important. The radiation emissions are pulsed, and, for most
systems, the pulse width and repetition rate are such that the time-averaged
transmitter power and power density at any point are two to four orders of
magnitude less than the peak value. In addition, many radar system antennas
rotate, further reducing the time-averaged power density. The results of
measurements and analysis of radar system exposure characteristics are
presented in Tables 12 to 19. Power density measurements at the indicated
distances are time-averaged values for stationary mode operation and are
based on time-averaged transmitter power. The scan reduction factor is
shown for those antennas that normally rotate.
-53-
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Most of the radars studied have antennas with paraboloidal surfaces.
Those with circular cross sections can be analytically treated by the model
used for analysis of SATCOM system antenna radiation characteristics. The
acquisition and tracking radar category includes radars having circular,
rectangular, and ellipsoidal cross sections. Honcircular cross-section
antennas collimate radiation so that the radiation beam is better collimated
in the plane containing the larger of the antenna axes. The beam has
greater divergence in the plane containing the smaller antenna axis, the
axes being mutually orthogonal.
The system characteristics used in evaluating radar systems depend upon
the peak power delivered to the antenna, pulse duty cycle, antenna
dimensions and area, aperture efficiency, and radiation wavelength. For
rotating or rapidly moving antennas, these characteristics also include the
angle through which the scan occurs and the half-power beam width in the
plane of scan.
The model, used to determine on-axis, time-averaged power densities at
a distance beyond the near field of the antenna, has been modified for
paraboloidal antennas that have other than circular cross sections. The
effective near-field distance (assuming an aperture .efficiency equal to 0.5)
is expressed as:
Rnf eff * 5-07 * 10~a GX- <16)
The differences between peak values of transmitter power and on-axis
near-field power density and the corresponding time-averaged characteristics
are determined by the pulse duty cycle, (i.e., the ratio of the pulse width
to the time interval between pulaes), and is equal to the pulse width, At,
(in units of time) mutiplied by the pulse repetition frequency, PHF.
Duty cycle » At x PRF. (17)
-54-
-------
The average transmitter power is then P » P . x duty cycle =
P , (At/T), where T, the tine interval between pulses, * 1/PRF.
peak
Simplified exposure evaluation models used to estimate exposures for
radar systems are basically the same as those used for circular
cross-section paraboloidal antennas, previously described for SATCOM system
antennas. This assumes that the noncircular cross-section antenna can be
represented by a circular aperture of the same physical area and gain. The
on-axis power density equations applicable to noncircular cross-section
paraboloidal antennas are described below with n * 0.5.
S . » 12.6 P /GX2 For R < 5.07 X 10"2 GX (18)
nf av -
(when R , ,, = 5.07 x 10~a GX)
nf err
S>JC = S C(R/R . .r>~X For 5.07 X 10~a GX < R < 1.22 X 10"1 GX (19)
it nr nt err
Sec - 2.47 S ,(R/R , .,)~2 R > 1.22 X 10~X GX (20)
ti nt nr err ~
Sff ' Pav G/**R C21)
Antenna rotation further reduces the time-averaged power density
produced by a stationary (nonrotating) radar antenna, because exposure to
main-beam or side-lobe radiation (in the far field) is not continuous.
Therefore, time-averaged exposures include a reduction factor compensating
for variation in radiation intensity with time due to antenna motion. The
power density produced at any point by a system with a rotating antenna is:
S - Ss f, (22)
where S is the time-averaged power density produced by the antenna if it
were stationary, and f is the rotational reduction factor applying at the
exposure point of interest.
-55-
-------
In practice, the rotational reduction factor depends on the antenna
radiation pattern (main-beam and side-lobe structure), antenna motion, and
location of an exposure point relative to the antenna. For main-beam
exposure, the factor, f, is defined as the fraction of time the radiation
beam is incident at some point relative to the time interval required for
the beam to return to the same point during the next rotation. For rotating
antennas it is equivalent to the ratio of the length of the arc that
contains the beam at a distance, R, compared to the total arc length at
distance, R, for the angle through which the antenna rotates.
In the near field, the beam is considered to have a dimension in the
plane of rotation equal to the length of the antenna axis, L, in that
plane. The near-field rotational reduction factor, f ,, at R is given by
f , = L/R6 , (23)
nf s'
where L equals the antenna dimension in the plane of rotation, R is the
distance from a point in the near field to the antenna, and 0 is the
scan angle in radians. The power density calculated in the near- and
intermediate-field region for a scanning antenna, using the reduction factor
determined by the method described, is an overestimate, but it is consistent
with the conservative approach employed in exposure evaluations.
The reduction factor used in determining the time-averaged power
density produced in the far field of a scanning antenna is given by
f « e . /e , (24)
i/a s'
where 6 is the half-power beam width of the antenna and has the
i/a
same units as 9 .
-56-
-------
Acquisition and Tracking Radars
The results of measurements of on-axis power density for acquisition
and tracking radars are shown in Table 12. For the first three ays teas, a
point was found at which an on-axis power density of 10 mW/cm occurred,
and the distance from that point to the antenna was measured. The remainder
of the systems were evaluated at distances of closest approach to the
systems, i.e., at the boundaries of the facility. The power densities
listed in Table 12, measured while the antennas were stationary, can be
reduced further for the normally rotating systems by using the scan
reduction factors to obtain the time-averaged power density at the specified
distances from the antenna. The scan reduction factors presented are
applicable in the near field and result in overestimating the average power
densities that would exist in the far field. For these systems, all of
which are military radars, those operating in a scanning mode produce
time-averaged power densities of less than 1 mW/cm at distances beyond
the near field of the antenna.
The tracking radars (nonscanning) are capable of producing
time-averaged, main-beam power densities much greater than 1 mW/cm ,
depending upon the transmitter power, duty cycle, and antenna dimensions.
Since these system characteristics are defined by the function for which a
specific system has been designed, there is a great variation in the
resulting near- and far-field, time-averaged power densities.
Because of the variety of system specifications, acquisition and
tracking radars cannot be described by categorical radiation field
characteristics. This conclusion is supported by measurement results
(Table 12) and an analytical study of a number of tracking systems having
circular cross-section paraboloidal antennas (Table 13).
-57-
-------
Table 12
ACQUISITION AND TRACKING RADAR MEASUREMENTS (ON-AXIS)
System
TPN-18(a)
FPN-40(a)
TPS-lD{a>
M-33 Acq.W
LOPAR
H33-C Band(b)
M33-X Band
TTR
Antenna
Dimensions
(ft)
4x6.5 azim
2x8 elev.
3x9 azim
2.5x10 elev.
4x15
3.92x14.33
-
8 (diam.)
6 (diam.)
6 (diam.) .
-
Freq.
(GHZ)
9.0
9.0
.1.3
3.1-3.5
-
5.45-5.82
8.50-9.60
2.70^2.90
-
P(av.)
(kW)
0.192
0.180
0.492
1.39
-
3.8x10-'
4.8xlO~a
2.9X10"1
-
S
(mw/on2)
10
10
10
10
10
6
4
0.2
0.65
0.65
7.5
R
Calc. Meas.
(m) (m)
22.2 24.4
11.8 10.7
28.1 28
24.2 24
10 7.6
65 61
94
95
95
81
85
Scan
Reduction
Factor
?
3.8xlO~2
3xlO~2
l.lxlO"2
IxlO"2
lxlO~2
-
-
-
-
Measurements performed with antennas stationary
(a) Fort Monmouth, Mew Jersey.
(b) Grumman ECU Site, Calverton, New York.
-58-
-------
Table 13
TRACKING RADAR CHARACTERISTICS
Source
Diameter
(ft)
4.0
5.0
5.0
6.65
28.8
31.0
34.7
36.5
37.5
47.2
52.0
68.6
85.94
112.8
Gain
(dB)
39.0
51.9
51.8
54.0
45.5
46.0
53.2
53.2
53.2
60.0
50.5
52.8
48.0
66.0
Frequency
(GHz)
9.8
35.0
34.5
33.4
2.90
2.85
5.84
5.55
5.40
9.38
2.85
2.82
1.30
7.84
Wave-
length
(on)
3.06
0.857
0.869
0.898
10.3
10.5
5.14
5.40
5.56
3.20
10.5
10.6
23.2
3.83
Transmitter Power
Peak
-------
In general, the tracking systems presented in Table 13 are either
unique systems, some of which can produce on-axis, time-averaged power
densities of 1 mw/cm or greater at great distances from the antenna, or
relatively low-power radars with a limited region of influence, the
rotational mode acquisition radars studied are expected to be typical of
this source category in that the time-averaged power densities produced in
the far field should be a factor of approximately 100 less than the
stationary mode power density produced at the same point. Thus, tracking
radars with high average transmitter powers would constitute the group
capable of producing the greatest time-averaged power densities.
Air Traffic Control Radars
Some air traffic control (ATC) radars, used to track aircraft flights
and control landings at airports, have been studied. Measurements were made
at the Federal Aviation Administration (FAA) Aeronautical Center, Oklahoma
City, Oklahoma, on three types of systems installed at and around airports
in the United States (Te74c). These systems are scanning radars with
antennas that rotate through a 360° sector. Measurement results, system
characteristics, and corresponding predictions made through use of the model
previously discussed are presented in Table 14.
The results of the measurements (Table 14) are off-axis power densities
at specified distances from the antenna, time-averaged to include
transmitter modulation but not reduced to compensate for rotation of the
antennas. The table includes the horizontal and vertical dimensions (L.
n
and L ), the operating frequency, and both peak and time-averaged
transmitter power. The extent of the near field; the maximum near-field,
on-axis, time-averaged power density; and the distance where on-axis,
time-averaged power densities of 10 and 1 mW/cm occur have been
calculated for stationary antennas. In addition, the on-axis, time-averaged
power density has been calculated at the point of measurement for each
system along with the corresponding power density, which includes the
-60-
-------
Table 14
PREOIC1EI) AND MEASURED CHARACTER IS1ICS OF ATC RADARS
Dimensions (ft.)
Frequency (GHz)
Transmitter Power
Peak (kU)
Av (W)
Near-Field Extent (m)
Near-Field Power Density,
(nW/cm2)
Distance (m) For
10 nW/cm2
1 nW/cm2
Power Density (mV/cm2) at
Stationary
Measured (off -ax is)
Calculated (on-axis)
Rotating
Calculated (on-axis)
Rotational Reduction Factor
(far field)
ASR-7
lv=9.0, lh=17.5
2.620
425
336
22.6
4.15
65.0
880'
0.016
0.059
2.3xHT*
3.89x10-'
ASR-4B
lv=9.0, ln=17.5
2.720
425
402
18.6
5.82
63.4
750' 1480* 1800*
1.37xMr* 8.80xUT» 3.2xKT*
7.7lxlO-2 1.98xHT2 1.34xlO~2
3.0xlO~4 7.69x10-* 5.21x10-*
3.89x10-'
ARSR-10
Lv=18.0, ln*42.0
1.335
500
360
31.2
1.94
60.5
1000'
5.42x10-'
4.05xKT2
1.52x10-*
4000
2880
31.2
15.5
48.3
174
1000' 1240'
0.165 1.2x10-'
0.324 0.211
1.22x10-' 7.9x10"*
3.75x10-'
-------
far-field rotational reduction factor. Whan rotational reduction factors
are considered, the tine-averaged power densities produced are much less
than 0.1 row/cm at distances of 100 meters or greater from the antenna,
for all of the systems included in Table 14. Even the air route
surveillance radar (ARSE) systems, having peak transmitter powers of
10,000 lew, would also produce time-averaged power densities of less than
0.1 mW/cm'
rotation.
0.1 mW/cm at distances of 100 meters or greater under conditions of
The ARSR-1 system and the more powerful ARSR-3 were analyzed to predict
environmental exposures that could exist in two actual situations (Ha76d).
The system characteristics and exposure conditions are summarized in
Table 15. Actual distances at which exposures could occur were used. The
relatively large main-beam divergence in the vertical plane is responsible
for producing ground-level exposures, for typical antenna elevation angles,
that are about a factor of 10 less than on-axis exposures.
Height-Finder Radars
Height-finder radars can produce environmental exposure power densities
that range from greater than 1 mW/cm in the far field to about 17
mW/cm in the near field. The primary antenna motion associated with
the height-determining operation is a periodic nodding motion in the
vertical plane. The angular excursion is limited, and the far-field
reduction factors used to derive time-averaged, exposures for vertical beam
motion are on the order of 10 . However, because the nodding motion
can direct the beam axis toward the ground at distances relatively close to
the antenna, high-intensity exposure to on-axis radiation can readily occur.
The exposure characteristics of two military height finders are
presented in Table 16 (Ha78b). It should be noted that time-averaged
exposures, including reduction for beam motion, at the beginning of the
far field (roughly 100 meters from the antenna) can be as high as 500 to
1,200 yW/cm . Prolonged public exposures would depend on accessibility.
-62-
-------
Table 15
PREDICTED EXPOSURES FROM ARSR RADARS
System Characteristics
Antenna dimension (m)
X (cm)
Rnf (m)
Rff (m)
G (dBi)
n
Pav (kw)
Snf av (vw/cm*)
Sff (>iW/cma)
Relative off -ax is intensity
Beam motion reduction factor
Saw, off -axis, (yW/cma)
ARSR-3
12.8 horizontal
6.86 vertical
22.2
35.2
84.5
34.2
0.42
4.38
29.9 xlO3
5.83 x 102 at 396m
0.1
3.06 x 10"a
1.78 x 10'1
ARSR
12.8 horizontal
5.49 vertical
22.2
29.8
71.5
34.2
0.49
3.6
34.3 x 10a
16.8 x 10a at 61m
0.1
3.6 x 10~a
6.05
-63-
-------
Table 16
HEIGHT-FINDER RADAR SYSTEM CHARACTERISTICS
System Characteristic
FPS-26A
FPS-90
Antenna Gain (dB^)
Frequency (GHz)
wavelength (on)
Aperture Efficiency (assumed)
Near-Field Extent (m)
(ft)
Distance to Onset (m)
of Far Field (ft)
Half-Power Beam width (deg)
- Vertical
Half-Power Beam Width (deg)
- Horizontal
Beam Notion Reduction (vert)
Factor
Pulse Width (vsec)
Pulse Repetition Frequency (sec'1)
Duty Cycle
Peak Power to
Reflector (kW)
Average Power
to Reflector (kW)
On-Axis Near-Field Power
Density, Average (nU/cm2)
On-Axis Power Density at Start
of Far-Field, Average (nM/cma)
Power Density at Start of
Far-Field, Corrected for
Beam notion, (mW/cm2)
43
5.9
5.06
0.5
51.4
169
123
405
0.56
2.30
1.65 x 10~2
4.4
333.3
1.47 x 10~»
2383 4766
3.495 6.990
85.13 170.3
36.4 72.8
0.601 1.20
38.5
2.9
10.34
0.5
37.1
121
89.1
292
1.02
3.30
3.00 x 10~a
2.0
400
8.00 x 10~*
2780
2.224
37.0
15.9
.477
(a) Normal mode.
(b) Power add mode.
-64-
-------
Weather Radars
Table 17 (Ha79, Ha82) presents radars used in meteorological
activities, their characteristics, and tine-averaged, on-axis power
densities (including rotation), at two specific distances. The large
diameter radars are unique systems located at the national Severe Storms
Laboratory at Hot-man, Oklahoma. The small diameter radar is typical of
those used by local television stations for their weather reports. On-axis,
time-averaged power densities at distances of several hundred feet are on
the order of 1 to 10 yW/ctn2. Off-axis exposures are expected to be on
the order of 1 to 10 nW/cma (1 nW/cma * 10~* yW/cma) or
less.
Special High-Power Radar Systems
A radar system that has received considerable attention from the public
and EPA is the PAVE PAWS, a phased-array radar system. The PAVE PAWS
system, four of which are to be operating in the continental United States,
was evaluated analytically to determine its potential for creating
environmental exposures (Ha77a). The basic system is characterized in
Table 18.
The antenna was treated as a circular cross-section aperture in the
analysis, the results of which are contained in Table 19. In the near
field, any exposure is likely to be less than 0.87 mW/cm . At the
beginning of the far field, the maximum exposure possible is 37
vW/cm*. The closest community is approximately 1 mile away, with the
predicted maximum possible exposure being 2.9 iiW/cm . A detailed
description of the system, analytical procedures, and environmental impact
evaluation for the system located in Massachusetts is contained in reference
(Ha77).
-65-
-------
Table 17
WEATHER RADAR CHARACTERISTICS
0
(ft) (m)
30 9.14
12 3.66
16 4.88
1.83 0.56
X
(on)
10.4
10.4
5.45
5.56
"of
(m)
200
32
109
1.40
Rff
(m)
4.8tx10a
7.69x10
2.62x10a
3.37
G
(dBj)
46.8
38
46.4
28
n
0.63
0.52
0.55
0.63
P
-------
Table 18
PAVE PAWS SYSTEM CHARACTERISTICS
System Characteristics
Peak Power (ku)
Duty cycle (max)
Scan mode
Track mode
Time-averaged transmitter
power (kU)
Gain (dB.)
Antenna diameter (ft)
Frequency (MHz)
Beam width (-3dB), (degrees)
Main beam null (degrees)
First side lobe - max. (degrees)
First side lobe relative
power (max.), (dB)
First side lobe null (degrees)
Secondary side lobe relative
power (max.), (dB)
Angle of antenna relative
to vertical (deg)
Minimum elevation angle (deg)
Basic System
582.4
0.25
0.11
0.14
145.6
37.92
72.5
420-450
2.2
2.6
3.4
-20
4.8
-30
20
+3
Growth Option
1164.8
0.25
0.11
0.14
291.2
40.9
102
420-450
1.5
1.8
2.4
-20
3.3
-30
20
+3
-67-
-------
Table 19
PAVE PAWS ENVIRONMENTAL EXPOSURE CHARACTERISTICS
System Characteristics
Basic System
Growth System
Antenna area, on2
Aperture efficiency
Near-field extent, Rnf,
cm, (ft)
3.84 x 10«
.571
1.83 x 10*
(601)
7.59 x 10*
.573
3.62 x 10*
(1189)
Near-field on-axis time- 86.7 87.9
averaged power density,
Snf, mw/on2
Far field begins, .6D2/X 4.39 x 10* 8.69 x 10*
cm, (ft) (1442) (2854)
On-axis power density at 37.2 37.7
.6D2/\, mW/on2
First side lobe max. power .372 .377
density, mW/cm2
Second side lobe max. power .037 .038
density, fflM/on2
-68-
-------
Traffic Radars
Traffic radar systems are small portable units used by police (in both
moving or stationary modes) to determine the speed of vehicles relative to
that of the police vehicles in which the units are mounted. The system
operation is based on measuring the Doppler shift in the fundamental
frequency transmitted, the shift in frequency being directly related to the
relative velocity of the target vehicle and the microwave radiation source.
The systems analyzed emit radiation in a nonpulsed, continuous mode (Ha76b) .
Traffic radars are low-power devices, 0.1 W or less, using a conical
horn antenna for which the far field starts at distances of less than 2 feet
from the antenna for the radiation frequencies typically used. As a result,
traffic radars are incapable of producing environmental levels of microwave
radiation greater than 1 yW/cm* at distances at which a member of the
public would normally be exposed during the use of such systems. The
maximum power density produced, determined by calculation, is 3.6 mW/cm
and occurs at distances 9 centimeters (3.6 inches) or less from the
antenna. Exposure levels decrease rapidly at distances greater than 2 feet
from the antenna, where the maximum power density is less than 0.4
mW/cm . At a distance of 14 feet, the maximum exposure level is less
than 10 pW/cm and decreases to less than 1 yU/cma at 44 feet.
Vehicular shielding would further reduce the microwave radiation level
inside a vehicle. The occupants of a moving vehicle being irradiated by a
traffic radar are unlikely to be exposed to a power density as great as
MICROWAVE RADIO
Microwave radio systems are used for voice and video communications and
data transmission. They link transmitting and receiving points within
line-of-sight of each other. A series of transmitters and antennas can be
used for long-distance communications or data transfer and are commonly used
-69-
-------
in telephone communications. These microwave relay or point-to-point
systems are probably the most numerous of all RF emitting systems using
high-gain antennas. They are conspicuous on rooftops of tall buildings in
metropolitan areas or when mounted in clusters on tall support towers.
The antennas are high-gain, circular cross-section paraboloid
reflectors or conical horn reflectors and are highly collimating. The power
radiated is very low, generally ranging from less than 1 watt to 40 watts.
Persons are exposed to secondary side-lobe radiation in the far field, or at
far off-axis locations if exposure occurs at distances not yet in the far
field. Relative exposures are at least a factor of 10 less than
on-axis power densities at the same horizontal distance from the antenna.
Exposure estimates and system characteristics for some commonly used systems
are presented in Table 20. Results of a few measurements are included at
the end of the table. Estimated exposure power densities are well below
microwatt per square centimeter levels. Measured exposures are on the order
of or less than 10 3 yW/cm (PeSO).
MOBILE COMMUNICATIONS
Mobile communications equipment is in common use for both personal and
business applications. Measurements of electric and magnetic field
intensities in and around vehicles equipped with such systems have
been reported (La78, Te76e, Ru79). The greatest exposures typically
encountered by persons in and close to vehicles so equipped are summarized
here. The transmitter powers for these systems varied from 4 watts for
Citizens Band (CB) radios operating at 27.12 MHz to 35 to 100 watts for
systems using nominal frequencies of 37, 39, 41, 64, 150, 154, 450, and 458
MHz.
-70-
-------
table 20
CALCUlAltt) RA01AUON CHARAClERtSHCS OF SOME COMMONLY USED MICROWAVE RADIO SYSIEMS
Antenna
Diameter
(ft)
2
4
4
4
6
6
6
6
8
8
8
8
8
9.42
9.5
10
10
10
10
10
10
10
10
12
12
12
12
(m)
0.61
.22
.22
.22
.83
.83
.83
.83
2.44
2.44
2.44
2.44
2.44
2.87
2.90
3.05
3.05
3.05
3.05
3.05
3.05
3.05
3.05
3.66
3.66
3.66
3.66
Freq.
(GHz)
2.0
12.95
12.34
2.0
12.95
6.0
11.305
6.865
6.855
1.865
2.175
6.425
12.95
6.0
6.0
12.95
6.425
11.0
11.7
6.425
11.2
6.175
6.424
11.2
6.425
6.175
6.0
X
(on)
15
2.32
2.43
15
2.32
5.0
2.65
4.370
4.376
16.1
13.8
4.67
2.32
5.0
5.0
2.32
4.67
2.73
2.56
4.67
2.68
4.86
4.67
2.68
4.67
4.86
5.0
G
(dBi)
19.2
41.5
41.1
25.2
45.1
39.0
44.0
39.8
42.1
31.1
32.2
41.6
47.6
43.5
43.5
48.8
43.6
48.5
48.3
43.6
48.4
43.2
43.6
49.5
45.2
44.8
45.0
•W
(m)
0.62
16.0
15.3
2.48
36.1
16.7
31.5
19.1
34.0
9.24
10.8
31.8
64.2
41.2
41.9
100
49.7
85.2
90.6
49.7
86.7
47.8
49.7
125
71.6
68.8
66.9
(ft)
2.0
52.6
50.2
8.13
118
54.9
103
62.8
111
30.3
35.4
104
210
135
138
329
163
279
297
163
284
157
163
410
235
226
219
Rff
(m)
1.48
38.5
36.7
5.95
86.6
40.1
75.6
45.9
81.5
22.2
25.8
76.4
154
98.9
101
241
119
204
217
119
208
115
119
300
172
165
160
(ft)
4.88
126
120
19.5
284
132
248
151
267
72.8
84.8
251
505
324
330
789
392
671
713
392
683
376
392
983
564
542
527
n
(calc)
.51
.52
.52
.51
.53
.60
.54
.55
.53
.57
.54
.54
.53
.69
.68
.44
.55
.57
.48
.55
.54
.54
.54
.48
.55
.54
.60
P
(W)
10
1.58
.93
10
1.58
.60
1.19
.415
.195
.275
1.0
3.15
1.58
15.9
25.2
1.58
3.15
2.5
.12
10
18.3
25.6
40
1.5
10
14.7
20
Snf
(tiW/cm*)
6.99x10'
2.81x10*
1.65x10*
1.74x10*
1.27x10*
5.50x10
9.72x10
3.49x10
8.84
1.34x10
4.62x10
1.45x10*
7.14x10
6.78x10*
1.04x10*
3.86x10
9.41x10
7.87x10
3.18
2.99x10a
5.43x10a
7.55x10a
1.19x10*
2.76x10
2.08x10*
3.02x10*
4.56xlpa
10-3 Snf
(liW/cma)
6.99
0.28
0.16
1.74
0.127
0.055
0.097
0.035
0.0088
0.0134
0.046
0.145
0.071
0.68
1.04
0.039
0.094
0.079
0.003
0.299
0.54
0.76
1.19
0.028
0.21
0.302
0.456
NT3 S100)B
(|iM/cma)
6.6x10"4
1.8xUTa
9.5x10-
2.6x10-
4.1x10-
3.8x10-
2.4x10-
3.2x10-
2.5xMr
. 2.8x10-
1.3x10"
3.6x10-
4.6x10"
2.8x10"
4.3x10-
3.9x10"
4.7x10-
6.7x10'
2.9x10"
1.5x10"
4.7x10'
3.6x«r
5.9x10"
2.8x10-
1.5x10-
2.1x10-
3.0x10"
The following values were measured at ground level:
Antenna Dia. Freq. Power Density
(ft)
10
10
7
7
(m)
3.05
3.05
—
—
(GHz)
11.0
11.2
2.1
4.0
(tiW/on*)
2.0XKT3
1.1x10~3
1.0x10'*
6.2xMT4
within 300 ft. off to the side
100 ft. from antenna
less than 100 ft. from antenna
about 300 ft. from antenna
-------
The exposures depend greatly on antenna type, antenna location on the
vehicle, and the type of vehicle, as well as on transmitter power. All
systems can produce large electric fields very near the antennas.
However, the electric field strength decreases rapidly with distance from
the antenna and the systems transmit intermittently. Four-watt CB
systems can produce fields ranging from 225 V/m to 1,350 V/m at a
distance of 2 inches from the antenna. At a distance of 2 feet from the
antenna, 60 V/m fields can exist. The free space (plane-wave) equivalent
power density for 60 V/m is 0.95 mw/cma. Exposure to persons inside
or outside of vehicles generally would occur at greater distances so that
exposures are even lower.
The more powerful mobile communications systems can produce exposures
up to 200 V/m (10 mW/cm free space equivalent power density) near
the exterior surface of the vehicle and in the interior where the driver
and passengers are exposed. Measured 100 yW/cm power density
contours for 50- and 100-W transmitters are shown in Figure 15.
HAND-HELD RADIO
Hand-held radios are low-power devices having maximum output
transmitter powers of 5 watts. The systems are held close to the head in
normal use, creating the possibility that the antenna might be placed
close to the eyes. These systems normally operate with the same
frequencies as mobile communications systems. The electric fields at a
distance of 2 inches from the antenna have been measured to be 150 to
960 V/m (La78, Ru79). Exposures to the eye can be greater than 200 V/m.
At distances of 2 feet from the antenna, exposure fields of 40 V/m have
been found. The significance of these exposures to the user of the radio
is not known; exposure durations can vary from a few seconds to several
minutes during a single use interval. Whole-body-average specific
absorption rates are extremely small since the power radiated is so low.
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Figure 15. Measured 100 yW/cm2 Contours for 50- and 100-Watt
Mobile Transmitters at 164.45 MHz
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SECTION 5
SUMMARY
The information presented in this report has focused on exposure at
locations relatively close to the antennas of RF-emitting systems,
because it is at ouch locations that exposures of public health
significance night occur. All of the high-power source categories
discussed in this report are capable of producing on-axis power densities
on the order of or greater than 10 nU/cm . However, the normal
operation of most systems, with the exception of broadcast transmitters
and height-finder radars, makes it unlikely that people would be exposed
to time-averaged power densities above 10 iiW/cm*. Radio and
television broadcast systems generally use antennas with radiation
patterns designed to expose the public to the transmitted RF radiation;
RF radiation produced by these systems dominates the multisource,
multifrequency, general RF radiation environment to which everyone is
exposed.
It is estimated that over 99 percent of the population is continuously
exposed to levels not greater than 1 yW/cm for FM radio and tele-
vision frequencies between 54 and 806 MHz and less than 2.5 V/m for AM
radiofrequencies between 0.5 and 1.6 MHz. These population exposure
estimates represent exposures far from RF sources and exclude population
t
exposures for individuals living or working close to RF sources.
Measurements made close to broadcast transmitters, or at locations
where exposures to main-beam or near-ma in-beam radiation from broadcast
antennas occur, have found exposure power densities that range up to
10 mW/cm2. Ground-level exposures from AM transmitters have been
found to be as great as 300 V/m (electric field) and 9.0 A/m (magnetic
field). Measurements made inside high-rise office buildings, in or near
the main beams of nearby FM and TV transmitters, have shown exposure
levels of up to 97 yW/cm2. Measurements of the exposures at
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recreational areas on the roofs of high-rise buildings revealed AH
•lectric field intensities of 100 to 200 V/m and exposure from FM
transmitters of up to 375 vU/cm . Other measurements and observations
have shown that possibilities for exposure of these magnitudes are not
unusual and that although tha total number of parsons exposed is likely to
be relatively small, the extent of such exposures and tha size of the
population exposed ara yat to be determined.
Mobile communication systems and much lower powered hand-held radios
can produce exposures in excess of 200 V/m to the occupants of ft vehicle or
the system user. The possibility for exposures lasting more than a few
seconds exists usually only for the occupants of a vehicle equipped with a
mobile communication system or the user of a hand-held radio. Exposures at
distances of several feet are less than 20 V/m.
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Ha76a Hankin N.N., Tell E.A., Athey T.W., and Janes D.E., 1976, "High
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Ha78a Hankin N.N., 1978 (November 9), Memo to Dr. G.A. Jacobson
(EPA, Kansas City, MO) on: Exposures from an HF Radio Facility,
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Ha78b Hankin N.N., 1978 (April 14), Homo to B. Keene (EPA, Boston, MA)
on: "Summary of Results of the Impact Analysis for the North Truro
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Ha79 Hankin N.N., 1979 (March 19), Letter to James Ward on: Analysis
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Ha82 Hankin-N.N., 1982 (April 15), Letter to Don Chaney on: Analysis
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Ha85 Hall C.H., 1985, "An Estimate of the Potential Costs of Guidelines
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Ja76 Janes D.E., Tell R.A., Athey T.W. and Hankin N.N., 1976,
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Ja77a Janes D.E., Tell R.A., Athey T.W. and Hankin N.H. , 1977,
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Ja79b Janes D.E., 1979, "Moasurement of Leakage Emissions and Potential
Exposure Fields," Bull. H.Y. Acad. Ned. 55 (11), pp. 1021-1041.
JaBO Janes D.E., 1980, "Population Exposure to Radiowave Environments
in the United States," in: Life Cycle Problems and Environmental
Technology, Proceedings of the 26th Annual Technical Meeting of
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Jo68 Jordan E.G. and Balmain K.G., 1968, "Electromagnetic Waves and
Radiating Systems (Englewood Cliffs, NJ: Prentice-Hall, Inc.).
La78 Lambdin D.L., 1978, "An Investigation of Energy Densities in the
Vicinity of Vehicles with Mobile Communications Equipment and Near a
Hand-Held Walkie-talkie," U.S. Environmental Protection Agency
Technical Note ORP/EAD 79-2 (Las Vegas, HV). NTIS No. PB 298251.
\
Le85 Lewis R.L. and Newell A.C., 1985, "An Efficient and Accurate
Method for Calculating and Representing Power Density in the
Near-Zone of Microwave Antennas," National Bureau of Standards Report
NBSIR 85-3036 prepared for U.S. Environmental Protection Agency under
Interagency Agreement DW930145-01-1 (Boulder, CO).
Pe80 Peterson R.C. and Testagrossa P.A., 1980 (September 26),
Memorandum for Record on "Microwave Survey, Bell of Pennsylvania,
Eagleville and Neiffer Sites, Case 48078-7," Bell Laboratories
(Murray Hill, NJ).
Ru79 Ruggera P.S., 1979, "Measurements of Electromagnetic Fields in
the Close Proximity of CB antennas," U.S. Department of Health,
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(Hew York, NY: Dover Publications, Inc.).
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Te72 Tell R.A., 1972, "Broadcast Radiation: How Safe Is Safe?,"
IEEE Spectrum 9_, pp. 43-51.
Ta74a Tell R.A., Nelson J.C. and Hankin N.N., 1974, "HF Spectral
Activity in the Washington, D.C. Area," Radiat. Data Rep. 15,
pp. 549-58.
Te74b Tell R.A. and Hankin N.N., 1974, "Evaluation of the Environmental
Microwave Radiation Levels Outside of the Grumman ECU Site, Oalverton,
NY; August 26-27, 1974," U.S. Environmental Protection Agency
Unpublished Report.
Te74c Tell R.A. and Nelson J.C., 1974, "RF Pulse Spectral Measurements
in the Vicinity of Several ATC Radars," U.S. Environmental Protection
Agency Report EPA-520/1-74-005 (Washington, D.C.).
Te74d Tell R.A. and Nelson J.C., 1974, "Microwave Hazard Measurements
Near Various Aircraft Radars," Radiat. Data Rep. 15. pp. 161-79.
Te74e Tell R.A. and Nelson J.C., 1974, "Calculated Field Intensities
Near a High Power UHF Broadcast Installation," Radiat. Data Rep. 15,
pp. 401-410.
Te76a Tell R.A., Hankin N.N., Nelson J.C., Athey T.W. and Janes D.E.,
1976, "An Automated Measurement System for Determining Environmental
Radiofrequency Field Intensities: II," in: National Bureau 'of
Standards Special Publication 456, Measurements for the Sate Use of
Radiation (edited by S.P. Fivoainsky), pp. 203-213 (Washington, D.C.).
Te76b Tell R.A., 1976, "A Measurement of RF Field intensities
in the Immediate Vicinity of an FM Broadcast Station Antenna,"
U.S. Environmental Protection Agency Report ORP/EAD 76-2
(Silver Spring, MD), NTIS No. PB 257698/AS.
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Te76c Tell R.A., Hankin N.N. and Janes D.E., 1976, "Aircraft Radar
Measurement* in the Wear Field," in: Operational Health Physics,
Proceedings of the Ninth Midyear Topical Symposium of the Health
Physics Society (compiled by P.L. Carson, W.R. Hendee and D.C. Hunt)
pp. 239-246 (Boulder, CO. Central Rocky Mountain Chapter,
Health Physics Society).
Te76d Tell R.A. and Janes D.E., 1976, "Broadcast Radiation: A Second
Look," in: Biological Effects of Electromagnetic Waves, Selected
Papers of the USNC URSI (1975) Annual Meeting Vol. II, pp. 363-388
(Edited by C.C. Johnson and M.L. Shore), U.S. Department of Health,
Education, and Welfare Publication FDA 77-8010 (Rockville, MD).
GPO Order No. 017-015-001240.
Te76e Tell R.A. and O'Brien P.J., 1976, "Radiation Intensities Due
to Mobile Communications Systems," U.S. Environmental Protection
Agency Unpublished Report (Silver Spring, MD).
Te77a Tell R.A., 1977, "An Analysis of Radar Exposure in the San
Francisco Area," U.S. Environmental Protection Agency Report
ORP/EAD 77-3 (Las Vegas, NV).
Te77b Tell R.A. and O'Brien P.J., 1977, "An Investigation of Broadcast
Radiation Intensities at Mt. Wilson, California," U.S. Environmental
Protection Agency Report ORP/EAD 77-2 (Las Vegas, NV).
NTIS No. PB 275-40/AS.
Te78a Tell R.A. and Mantiply E.D., 1978, "Population Exposure to VHF
and UHF Broadcast Radiation in the United States," U.S. Environmental
Protection Agency Report ORP/EAD 78-5 (Las Vegas, NV).
Te78b Tell R.A. and Hankin N.N., 1978, "Measurements of Radiofrequency
Field Intensity in Buildings with Close Proximity to Broadcast
Stations," U.S. Environmental Protection Agency Report ORP/EAD 78-3
(Las Vegas, NV). NTIS No. PB 290944.
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Te78c Tell R.A., 1979, "Field Strength Measurements of Microwave Oven
Leakage at 915 MHz," IEEE Transactions on Electromagnetre
Compatibility EMC 20 (2), pp. 341-346.
! ,. ' •:
Te78d Tell R.A,., 1978, "Near-field Radiation Prop*r,V-« .of S*«nple
Linear Antennae with Applications to Radiofrequpncy Hazar** und
Broadcasting," U.*. Environmental Protection Agrncy Technical Hote
ORP/EAD 78-4 (Las Vegas, NV) . NTIS Ho. PB 292647.
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Te85a Tell R.A., 1985, "HF Radiation Measurements: The EPA Honolulu
Study,"" U.S. Environmental Protection Agency Unpublished Report
(Las Vegas, NV) Prepared for the Federal Communications Commission.
Te85b Tell R.A., 1985, "An Investigation of Radiofrequency Radiation
Exposure Levels on Cougar Mountain, Issaquah, Washington, May 6-10,
1985, "U.S.' -Environmental Protection Agency Unpublished Report
(Las Vegas, NV) Prepared for the Federal Communications Commission.
Wa76 Hang J. and Linthicum j., 1976, "RF Field Intensity Measurements
in Selected Broadcast Facilities," Federal Communications Commission
Report (Washington, D.C.).
U S Environmental Protection Af«ncy
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