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.
                                      ii

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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
                                      iii

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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
                                      vi

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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
                                      -1-

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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.
                                      -2-

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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
                               -3-

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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.
                                      -4-

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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.
                                      -6-

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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.
                                      -7-

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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)
                                      -8-

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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.
                                      -9-

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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.)
                                      -10-

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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.
                                     -11-

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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.
                                      -12-

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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
                                     -13-

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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.
                                      -14-

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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
                                     -15-

-------
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-

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                                   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-

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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-

-------
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-

-------
        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-

-------
     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-

-------
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-

-------
                          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-

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                                 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

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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-

-------
     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-

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                             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

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   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.
                                     -72-

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Figure 15.  Measured 100 yW/cm2 Contours for 50- and 100-Watt
            Mobile Transmitters at 164.45 MHz
                               -73-

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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
                                      -74-

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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.
                                     -75-

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                             REFERENCES

AHPR82  Advance Hotice of Propoaed Recommendations (ANPR), 1982,
  "Federal Radiation Protection Guidance for Public Exposure to
  Radiofrequency Radiation," Federal Register 47. (247), pp. 57338-39.

At78  Athey T.W., Tell R.A., Hankin N.H., Lambdin D.L., Hantiply E.D.
  and Janes, D.E., 1978, "Radiofrequency Radiation Levels and
  Population Exposure in Urban Areas of the Eastern United States,"
  U.S. Environmental Protection Agency Report EPA 520/2-77-008
  (Silver Spring, MD).  NTIS Ho. PB 292855.

B184  Elder J.A. and Cahill D.F., 1984, "Biological Effects of
  Radiofrequency Radiation," U.S. Environmental Protection Agency
  Report EPA-600/8-83-026F (Research Triangle Park, NO.
  NTIS No. PB 85-120-848.

Ga85  Gailey P.O. and Tell R.A., 1985, "An Engineering Assessment of
  the Potential Impact of Federal Radiation Guidance on the AM, FM, and
  TV Broadcast Services," U.S. Environmental Protection Agency Report
  EPA 520/6-85-011 (Las Vegas, NV).  NTIS No. PB 85-245 868.

Ha74a  Hankin, N.N., (1974), "An Evaluation of Satellite Communication
  Systems as Sources of Environmental Microwave Radiation,"
  U.S. Environmental Protection Agency Report EPA 520-2-74-008,
  (Washington, D.C.).  NTIS No. PB 257 138/AS.

Ha74b  Hankin N.N., Tell R.A., and Janes D.E., 1974,  "Assessing the
  Potential for Exposure to Hazardous Levels of Microwave  Radiation
  from High Power  Sources," presented at the 1974 Health Physics
  Society Annual Meeting, Abstract in: Health Physics 27^.  633.
                                -76-

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Ha76a  Hankin N.N., Tell E.A.,  Athey T.W., and Janes D.E., 1976,  "High
  Power Radiofrequency and Microwave Radiation Sources, A Study of
  Relative Environmental Significance," in: Operational Health Physics,
  Proceedings of the Ninth Midyear Topical Symposium of the Health
  Physics Society (compiled by P.L. Carson, U.R. Hendee, and D.C.  Hunt),
  pp. 231-238, (Boulder, CO: Central Rocky Mountain Chapter, Health
  Physics Society).

Ha76b  Hankin N.N., 1976, "Radiation Characteristics of Traffic Radar
  Systems," U.S. Environmental Protection Agency Technical Note ORP/EAD
  76-1 (Silver Spring, MD).  NTIS No. PB 257077/AS.

Ha76c  Hankin N.N., 1976, "Task Description for the RF and Microwave
  Source Distribution Study," performed by the Electromagnetic
  Compatibility Analysis Center (Annapolis, MD) for the U.S.
  Environmental Protection Agency (Silver Spring, MD) under
  Interagency Agreement EPA-IAG-D-H518.

Ha76d  Hankin N.N., 1976 (January 19), Letter to John Sainsbury, Office
  of Federal Affairs (Seattle,  WA), and 1977 (June 23), Letter to
  to Lloyd Holme, Federal Aviation Administration (Kansas City, MO) on:
  Evaluation of the Environmental Impacts of Air Route Surveillance
  Radar Facilities, U.S. Environmental Protection Agency
  (Silver Spring, MD).

Ha77a  Hankin N.N., 1977, "Environmental Impact Analysis, Project PAVE
  PAWS-OTIS AFB, MA," U.S. Environmental Protection Agency unpublished
  report (Silver Spring, MD).

Ha77b  Hankin N.N., 1977 (July 29), Letter to Mr. and Mrs. R. Kepner on:
  Exposure from WON (AM) Radio, U.S. Environmental Protection Agency
  (Silver Spring, MD).

Ha78a  Hankin N.N., 1978 (November 9), Memo to Dr. G.A. Jacobson
  (EPA, Kansas City, MO) on: Exposures from an HF Radio Facility,
  Environmental Protection Agency (Silver Spring, MD).

                                -77-

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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
  Air Force Station," U.S. Environmental Protection Agency
  (Silver Spring, MD).

Ha79  Hankin N.N., 1979 (March 19), Letter to James Ward on: Analysis
  of Radars at the National Severe Storms Laboratory, U.S. Environmental
  Protection Agency (Silver Spring, MD).

Ha82  Hankin-N.N., 1982 (April 15), Letter to Don Chaney on: Analysis
  of Exposure from AVQ-10 Weather Radar, U.S. Environmental Protection
  Agency (Washington, D.C.).

Ha85  Hall C.H., 1985, "An Estimate of the Potential Costs of Guidelines
  Limiting Public Exposure to Radiofrequency Radiation from Lroadcast
  Sources" (Vol. 1 and 2), U.S. Environmental Protection Agency Report
  EPA 520/1-85-025 (Washington, D.C.).  NTIS No. PB 86-108-226.

Ja76  Janes D.E., Tell R.A., Athey T.W. and Hankin N.N., 1976,
  "Radiofrequency Radiation Levels in Urban Areas," Presented at
  the USNC-URSI Meeting, October 10-15, Amherst, MA.

Ja77a  Janes D.E., Tell R.A., Athey T.W. and Hankin N.H. , 1977,
  "Radiofrequency Radiation Levels in Urban Areas," Radio Science
  (Suppl. 12), pp. 49-56.

Ja/7fa  Janes D.E., Tell R.A., Athey T.W. and Hankin N.N., 19/7,
  "Nonionizing Radiation Exposure in Urban Areas of the United
  States," in:  Proceedings of the 4th International Congress of the
  International Radiation Protection Association (edited by C. Bresson),
  Int. Radiation Protection Assoc. 2, pp. 329-32.

Ja79a  Janes D.E., 1979, "Current Status of Environmental Findings," in:
  Proceedings of 10th Annual National Conference on Radiation Control,
  U.S. HEW Publication 79-8054 (Rockville, MD).
                                -78-

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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
  the Institute of Environmental Sciences, Institute of
  Environmental Sciences (Mt. Prospect, IL).

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,
  Education, and Welfare Report FDA 79-8080 (Rockville, MD).

Si65  Silvar S., 1965, "Microwave Antenna Theory and Design,"
  (Hew York, NY:  Dover Publications, Inc.).
                                -79-

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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.
                                 -80-

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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.
                                -81-

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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
                                ~83-     Region 5, Library (PL-12J)
                                         77 West Jackson Boulevard, 12th
                                         Chicago, »L  60604-3590

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