EPA-5207 2-74-008
AN EVALUATION OF SELECTED SATELLITE
 COMMUNICATION SYSTEMS AS SOURCES OF
    ENVIRONMENTAL MICROWAVE RADIATION
  1
  m
 wm
   9

-------
An Evaluation of  Selected  Satellite Communication Systems
    as Sources of Environmental  Microwave  Radiation
                               *
                                  By
                            Norbert N. Hankin
                              December 1974
             U.S. ENVIRONMENTAL PROTECTION AGENCY
                      Office of Radiation Programs
                        Field Operations Division
                 Electromagnetic Radiation Analysis Branch
                         9100 Brookville Road
                      Silver Spring, Maryland 20910

-------
                                  FOREWORD
     The Office of Radiation Programs carries out a national  program designed
to evaluate the exposure of man to ionizing and nonionizing radiation, and to
promote the development of controls necessary to protect the  public health
and safety and assure environmental quality.

     Office of Radiation Programs technical reports allow comprehensive and
rapid publishing of the results of intramural and contract projects.  The
reports are distributed to State and local radiological  health offices,
Office of Radiation Programs technical  and advisory committees, universities,
laboratories, schools, the press, and other interested groups and individuals
These reports are also included in the collections of the Library of Congress
and the National Technical Information Service.

     I encourage readers of these reports to inform the Office of Radiation
Programs of any omissions or errors.  Your additional comments or requests
for further information are also solicited.
                                             W. D. Rowe, Ph.D.
                                      Deputy Assistant Administrator
                                          for Radiation Programs

-------
                             TABLE OF CONTENTS
Section 1  - Introduction

    Background 	  1
    Measurement Objectives 	  1

Section 2 - Satellite Communication System Earth Terminals

    General Description  	  2
    Source Identification  	  3
    Antenna Characteristics  .  .  	  6
    Use of a Model in the Calculation of Satellite
    Communication Earth Terminal  Characteristics 	  7

Section 3   Satellite Communication System Measurements

    System Description 	 14
        AN/TSC-54	22
        LET	24
        AN/MSC-60	24
    Satellite Communication Systems Measurements 	 24
        Instrumentation Description  ..... 	 32
        Measurement Results	37

Section 4 - Discussion and Evaluation

    Measurement Considerations 	 39
    Evaluation of Model Applicability  	 42
    Anticipated Environmental Levels of Power Density for
    Simulated Satellite Communication Systems  	 45
    Anticipated Environmental Levels of Power Density for
    Selected Systems 	 46
    Potential Hazard Evaluation  	 48
    ECAC as a Resource in the Identification and Evaluation
    of Potentially Hazardous Sources 	 53

Section 5 - Conclusions and Summary	54

Acknowledgments  	 56

References	58

-------
                               LIST OF FIGURES
                                                                      Page
 1.  Cassegrain Antenna  ........... 	 ....  8
 2.  Radiation Zones for Paraboloidal  Reflectors ...........  9
 3.  Antenna Gain vs.  Wavelength ..............  	 15
 4.  Near Field Extent vs.  Wavelength  (Diameters:   1  to 20 feet)  ... 16
 5.  Near Field Extent vs.  Wavelength  (Diameters:  30 to 120 feet)  .   . 17
 6.  On-Axis Near Field Power Density  vs.  Antenna  Diameter ...... 18
 7.  Far Field Power Density/On-Axis Near  Field Power Density vs.
     Distance from Antenna/Near Field  Extent 	 19
 8.  Intermediate Field Power Density/On-Axis Near Field Power
     Density vs. Distance from Antenna/Near Field  Extent .  .   	 20
 9A and 9B.  AN/TSC-54 Antenna Array .........  	 23
10A. LET Geodesic Housing  ......... 	  ... 25
10B. Rear View of LET Antenna in Housing ............... 25
11A and 11B.  AN/MSC-60 Satellite Communication Earth Terminal .... 26
11C and 11D.  Close-up Views of AN/MSC-60  Antenna	27
12.  Other Satellite Communication System  Earth Terminals at
     Ft. Detrick		28
13.  Geometry for On-Axis Power Density Measurements 	 31
14.  Staircase Location for LET Near Field Measurement 	 33
15.  Measurement of AN/TSC-54 Near Field Power Density 	 33
16.  Measurement of AN/MSC-60 Near Field Power Density 	 34
17.  Possible Method of Identification of  Satellite Communication
     Systems 	  .....  	 51
                                      VI

-------
                               LIST  OF  TABLES
                                                                      Page

 1.   Ranking  of Sources  by EIRP	5

 2.   Paraboloidal  Antenna Characteristics   	  21

 3.   Summary  of Pertinent Characteristics  for  Selected

     Satellite Communication Systems 	  29

 4.   Measurement Geometry and Instrumentation   	  .....  31

 5.   NARDA Isotropic Probe Characteristics 	  36

 6.   Results  of On-axis  Power Density Measurements  	  .  .  38

 7.   Comparison of Measured and Calculated Values of

     On-Axis  Power Density 	  45

 8.   Anticipated Characteristics of  Simulated  Satellite

     Communication Systems 	  47

 9.   Anticipated Characteristics of  Selected  Satellite

     Communication Systems 	  49

10.   Hazards  Evaluation  Summary  	  57

-------
                                ABSTRACT
     Selected satellite communication (SATCOM)  systems are evaluated
analytically and, for some of these systems,  through measurement of the
microwave radiation power densities generated by them.  The evaluation
is directed toward assessing the radiation exposure hazards which exist
for specific systems and generally for SATCOM systems as a class of high
power nonionizing radiation source.  The paper  includes determinations
of anticipated maximum power density levels as  functions of distance from
the source, a description of the analytical method used, and the results
of measurements of the power densities produced by certain SATCOM systems,
Included also is a discussion of potential  hazard analysis and its uses
in identifying systems which may constitute environmental  hazards.
                                   VI 1 1

-------
         AN EVALUATION OF SELECTED SATELLITE COMMUNICATION SYSTEMS
               AS SOURCES OF ENVIRONMENTAL MICROWAVE RADIATION

                          Section 1  - Introduction

Background

     The U.S. Environmental Protection Agency supports a field operations

group to obtain data on the levels of existing environmental  radiation, to

determine any change in the radiological quality of the environment, to

identify sources of radiation and their contributions to environmental

levels, to provide data for estimating population exposure to ionizing  and

nonionizing radiation, and to determine if environmental radiation levels

are within established guidelines and standards.  This report evaluates

some selected satellite communication systems, a category of microwave

emitting source with the potential for significant environmental exposure.

This evaluation and others concerning specific source types and the general

ambient environment will be used together with the results of biological

effects studies to determine the need to establish guidelines for environ-

mental exposure to nonionizing radiation.

Measurement Objectives

     Satellite communication systems, evaluated on the basis of effective

isotropic radiated power, are the most powerful continuous wave (CW) sources

of environmental microwave radiation.  The determination, by measurement, of

the environmental radiation levels generated by certain of these sources has

several different objectives, the primary ones being:

     (1) to determine actual environmental radiation levels (power density)

as a function of distance from the system antenna,

-------
                                      2
     (2)  to determine the applicability  of a model,  using known system
characteristics in predicting  power density as a function of distance from
the source, by comparing measured and predicted levels,  and
     (3)  to evaluate the potential  of a  source to produce hazardous environ-
mental  radiation levels.
     Other important objectives may be realized through  use of the results
of the measurements performed, i.e., (1)  identification  of other factors
which may be involved in affecting the sources contributions to environmental
levels, e.g., the procedures used in system operation,  system power losses
which occur before power is introduced into the antenna  system, and the
effect of reflections from structures on  power density  levels in the environ-
ment; (2) determination of the most significant criteria which can be used
to identify sources having the potential  for creating significant radiation
levels, and to rank these sources relative to each other; and (3) evaluation
of the contents of the source  inventory  used to identify sources which may
be involved in an environmental situation under investigation, or have the
potential for significant contribution to environmental  radiation levels.
        Section 2 - Satellite  Communication System Earth Terminals
General Description
     Satellite communication system earth terminals, as  a source type, have the
greatest potential for creating hazardous environmental  situations in that
significant power densities may exist at greater distances from the antenna
than would be possible for other types of radiating  systems.  They have the
potential for irradiating a particular region of the environment for long
periods of time while tracking satellites in various earth orbits out to

-------
                                      3
geostationary (synchronous) orbits at a height of 22,300 miles above earth.
     The antenna diameter and maximum transmitter power are characteristics
of particular interest from an environmental aspect.  The need to transmit
power over large distances determines the transmitter power to be used with
an antenna whose diameter has been determined usually on the basis of
reception requirements.  Generally, as systems are required to provide high
data transmission rates at increasing distances, the earth terminal  trans-
mitter power and antenna diameter increase.  It is the combination of high
transmitter power and antenna diameter that is responsible for producing a
region of significant power density which may extend over very large
distances.
Source Identification
     Characterization of the environment, either analytically or through
measurement, requires identification of the radiating sources which con-
tribute to that environment.  These sources must be identified in order to
determine how many there are, where they are, and how they may affect the
environment.  In addition it is desirable to rank the sources to determine
their potential relative environmental importance.  Sources were identified
for EPA through the use of a computerized inventory of sources operated by
the Electromagnetic Compatibility Analysis Center (ECAC) located in Annapolis,
Maryland.
     The ECAC data base contains an inventory of transmitting sources and
their characteristics, and includes all U.S. equipment, both military and
civilian, common carrier microwave equipment, and all FCC licensed equipment
except for amateur and citizens bands.  The sorting criterion, used in the

-------
search of the inventory,  was effective isotropic radiated power (EIRP).*

This system characteristic is the product of the antenna gain and the

transmitter power.   The sources of interest include both non-pulsed (CW)

systems and pulsed  (radar) systems.  Computer listings of unclassified

sources were derived for  both source categories (]_).   The CW sources were

ranked in the order of decreasing EIRP.   The listing  includes all CW sources

whose EIRP is greater than or equal  to 1  megawatt (106 watts).   Other

source characteristics resident in the ECAC data files were included in the

computer printout in order to provide additional information on the character-

istics of these systems.   Twenty of the  most powerful CW systems identified

are listed in table 1 (2).  They are all  satellite communication earth

terminals.  On the  basis  of these results, selected systems in  the category

of satellite communication earth terminals were studied, analytically and

through measurement.

     Since the date of the inventory sort yielding the results  of table 1

(July 1972) other powerful sources have  been constructed and are now in

operation.  A search of the current ECAC source inventory would result in a

rearrangement of the source ranking presented in table 1, and include several

sources which did not previously exist.   One of the new sources which would
*
 Effective isotropic radiated power is defined as the hypothetical total
 power which a non-isotropic source of EM radiation would be required to
 radiate isotropically (assuming it to be a point source of radiation) so
 that the power radiated per unit solid angle would be the same as that
 actually radiated.   EIRP is obtained by multiplying the power radiated by
 a source by its antenna gain characteristic, gain being a measure of the
 antenna's directivity,  or concentration of radiation, and ideally equiva-
 lent to the ratio of 4ir to the solid angle subtended at the source by its
 collimated beam.

-------
                                  Table  1

                         Ranking of Sources  by  EIRP
                                Frequency                      Average
Rank         Location             (MHz)            Use          EIRP  (GW)

                                               Satellite
  1      Westford, MA              7748       Communication       31.6
  2     Lakehurst, NJ             8004             "             20.0
  3     Roberts, CA               7985             "             20.0
  4     Rosman, NC                5925             "             11.3
  5     Paumalu, HI               5925             "              7.9
  6     Jamesburg, CA             5925             "              7.9
  7     Etam, WV                  5925             "              7.9
  8     Brewster, WA              5925             "              7.9
  9     Andover, ME               5925             "              7.9
 10     Bartlett, AK              5925             "              7.9
 11      Archer City, TX            217             "              6.4
 12     Mojave Desert, CA         5985             "              6.4
 13     Pt. Loma, CA              7997             "              5.0
 14     Helemano, HI              7990             "              5.0
 15     Ft. Monmouth, NJ          7990             "              5.0
 16     Brandywine, MD            7986             "              5.0
 17     Camp Parks, CA            7990             "              5.0
 18     Wildwood, AK              7986             "              5.0
 19     Floyd Test Annex, NY      7986             "              5.0
 20     Elgin, IL                 8004             "              5.0
 144 CW unclassified sources have average EIRP's  of  1  MW  or  greater.

    79 nonpulsed, classified emitters,  none  had an EIRP greater  than
     GW.
Of
5.0 GW.

-------
                                      6



be included was the subject of a  measurement and evaluation discussed  in



this paper.  In addition,  several  other  sources  have become operable,  and the



transmission characteristics for  the  Mars  and Venus  communication systems at



Goldstone, California are  presented  in another section  of this paper.



     The initial  selection of effective  isotropic radiated power as the



criterion used in identifying and  ranking  sources resulted because EIRP is



a characteristic  commonly  used in  describing the power  radiating capability



of an antenna and transmitter system.  The system characteristics used in



calculating EIRP; i.e.,  antenna gain  and transmitter power, are entered



directly into the ECAC data inventory.



     These systems, identified on  the basis of selection  by EIRP, have a



functional requirement to  communicate with earth orbiting satellites and



possess a capability to  produce significant radiation levels at great



distances.  This  illustrates, at  least qualitatively, a degree of applica-



bility of EIRP in identifying categories of sources  potentially capable of



producing the most hazardous exposure situations; i.e., existence of



relatively high power density at  considerable distances from the source.



     Therefore, if it is desired  to  perform measurements  relating directly



to high power CW  sources with the greatest potential  for  creating hazardous



environmental situations,  satellite  communication systems provided the logical



first choice for  evaluation.



Antenna Characteristics



     The satellite communication  systems which are studied analytically and



by measurement, and most of the systems  listed in table 1, have paraboloidal



antennas with a Cassegrain design.  In the Cassegrain geometry, power  is



introduced to the antenna  from the primary radiating source (power feed)

-------
                                      7
located at the vertex of the paraboloidal reflector.  The radiation is
incident on a small hyperboloidal subreflector located between the vertex
and the focus of the antenna (figure  1).  Radiation from the power feed is
reflected from the subreflector, illuminates the main reflector as if it
had originated at the focus, and is then collimated.
     The Cassegrain antenna has advantages relative to a system which has
the power input at the focus; i.e., the very low-noise microwave receiving
preamplifier and the transmitter power amplifier are located immediately
behind the antenna resulting in lower  transmission  line loss and noise
which may interfere with the reception of transmissions from satellites
which operate at much lower transmitter powers than the earth situated
systems.  In addition, spillover radiation from the power source is
directed toward space resulting in a  lower antenna  noise temperature.
     The systems which have been studied all transmit and receive circularly
polarized microwave radiation.  The polarization generally is right-hand
for transmission and left-hand for reception.
Use of a Model  in the Calculation of Satellite Communication Earth Terminal
Characteristics
     An empirical  model  was selected which allows the characteristics of
satellite communication (SATCOM)  earth terminals to be calculated for use
in evaluations  of hazards (_3).   This model applies to antennas (reflectors)
that are circular cross section paraboloids, a characteristic of almost all
large SATCOM systems,  and calculates the on-axis power density at any
distance from the antenna as a  function of antenna diameter, radiation wave-
length,  and  transmitter power.

-------
                                                           PARABOLOID


                                                          FOCAL  POINT
                                                     HYPERBOLOID

                                                     SUBREFLECTOR
PARABOLOID

REFLECTOR
                                                                                        H
                                                                                        30
                                                                                        >
                                                                                        z
                                                                                        en
m
D

03
m
                                                                                                CO
                             Geometric Relationship Between Antenna Feed, Subreflector, and

                             Main Reflector In a Conventional Cassegraln Design
                              Figure 1  Cassegrain  Antenna

-------
      The  on-axis  radiation  field  characteristics  for  circular  cross-section

 paraboloidal  antennas  can be  described  using  figure 2.*  The maximum value

 of power  density  at  any  given distance  from the antenna exists on the

 antenna axis.   In the  near  field  of  an  antenna the magnitude of the power

 density oscillates with  distance,  however, the maximum value of the on-axis

 power density,  Wnf,  is constant over the  extent of the near field, and the

 beam  is collimated so  that  most of the  power  is contained in a region having

 approximately  the diameter  of the  reflector.
Wnf = 4nP/A
              5.66A
              -RI -
         Near Field
                                  = Wnf(R/R.)
Wff = 2 Wnf(R/R,)
                                                                     -2

         Rl =
                   Intermediate Field
Far Field
            Figure 2  Radiation Zones for Paraboloidal Reflectors
     *The model used in defining the extent of the various regions and the
magnitudes of the on-axis power density which exist in these regions were
developed by the U.S. Army Environmental Hygiene Agency (3j.

-------
                                     10
     The value of the maximum on-axis near field power density, Wnf, is
given by eq.(1):
                                 ii   -  4np                              m
                                 Wnf -  -£-                              U;

where
     P = total power radiated by the power feed
     A = cross sectional  area of antenna
     n = antenna efficiency
The efficiency of the antenna (4) is the ratio of the power radiated into
the main beam to the total power fed into the antenna system, and is the
product of two factors:
     1) the fraction of the total feed  power incident on the reflector
     2) the efficiency of the reflector in concentrating the available
        energy into the peak of the main beam.
The efficiencies of circular paraboloidal antennas in concentrating the
available energy into the peak of the main beam typically range from 0.50
to 0.75 depending upon the method used  in irradiating the hyperboloidal
subreflector.
     The maximum on-axis near field power density for a circular paraboloidal
antenna expressed in terms of antenna diameter, D, using eq.(l) and A = ^2
is
                                W f = 16nP                              (2)
                                wnf   ^02                               {*•>

     An  important characteristic of high power sources, in addition to the
maximum power density which can be generated, is the extent of the  near
field; i.e., the distance from the antenna over which the power density can

-------
                                     11
be a maximum before it begins to decrease with distance.  This parameter
and the maximum power density in the near field determine the value of the
on-axis power density at any distance from the antenna.  The extent of the
near field, R-j , is given as eq. (3).

                                                                        (3)
                                                                        (6)
                                   " 5.66X
where X is the wavelength of the transmitted radiation and is expressed in
the same units as the antenna diameter.
     The far field of the antenna is the region in which the beam diverges
and the power density in the far field decreases inversely as the square
of the distance from the antenna.  The far field on-axis power density,
Wff, can be expressed relative to Wnf by
                           W       / D  -2
where the distance from the antenna, R, must be at least as great as 2R-] .
     The intermediate field region is a transition region between the near
and far fields in which the power density decreases inversely with distance.
The transition from one region to another is continuous, and this is taken
into account in the model; the on-axis power density, in each region, being
equal at the "transition boundary."  The on-axis power density in the
intermediate field, W.., can be expressed as
where R, the distance from the antenna, lies in the interval between the end
of the near field region and the beginning of the far field region.

-------
                                     12

     The on-axis radiation field characteristics which have been described

were determined empirically  (_3) and yield the maximum power density, as a

function of distance, of which the system may be capable.  This constitutes

an assessment of the potential of the source for creation of a hazardous

exposure situation.

     A frequent occurrence in evaluating the potential hazard situation

created by a specific source, is the lack of information regarding antenna

diameter and efficiency.  However, if another characteristic, antenna gain,

is available, and the antenna is known  to be a circular paraboloid, the

antenna diameter may be approximated assuming r\ to be 0.50.  The antenna

gain is a measure of the directivity (collimation) of a reflector as com-

pared to an isotropic radiator and may  be expressed (4) as
where Ae is the effective area of the antenna.


     For the specific case of a circular paraboloidal  reflector the


expression for aperture gain becomes

                                     /  \2
                                j-\ __  | 7TLJ I
                                     \ A /
                                     \  /

     The gain is generally expressed in  dB,  and is then defined
                             G - 10 log
(8)
     The effective isotropic radiated power (EIRP) ,  previously described as the

basis for the identification of sources in the order of decreasing potential

hazard from the ECAC inventory, is commonly used also in describing satellite

communication earth terminals.   The value is related to the antenna gain and

-------
                                      13

radiated  power  capability  of  the  system by

                                EIRP  =  G-P                               (9)
where P = maximum power capability of the system, including losses of power
which occur  before  power is fed into  the antenna, and  the value used for G
is  the absolute gain.
     A simple computer program has been written which  calculates the various
pertinent characteristics  for circular  paraboloidal antennas and plots these
characteristics  on  a cathode  ray  tube (CRT).  The display may represent
characteristics  for one or several antenna diameters.  A printout of the
numerical values of the characteristics may also be obtained on a CRT dis-
play or in a teletype printout.
     The  calculations performed include:  (1) gain (dB) as a function of
wavelength for  various antenna diameters and for any specified antenna
efficiency (using eq. 7),  (2) the extent of the near field region as a
function  of wavelength for various antenna diameters (eq. 3 ), (3) the
maximum (on-axis) near field  power density as a function of antenna diameter
for 1 kW  of  transmitter power for any specified antenna efficiency (from eq.
2), (4) a dimensionless presentation  of the ratio of the far field on-
axis power density  to the  near field  on-axis power density as a function of
the ratio of the distance  from the antenna to the extent of the near field
(eq. 4),  and (5) a  dimensionless  plot of the on-axis intermediate field power
density to the  on-axis near field power density as a function of the ratio
of the distance  from the antenna  to the extent of the  near field (eq. 5).
The latter two  curves allow rapid predictions of on-axis power density
during measurements at locations in the far and intermediate fields.

-------
                                      14




     Displays of these characteristics,  generated by a Varian  ADAPTS mini-



computer system, are presented in figures 3 to 8.  An example  of a listing



of characteristics displayed on the CRT  is shown in table 2.   Characteristics



can be displayed for paraboloidal systems over a range of diameters of 1  to



200 feet and a wavelength range of 1  to  60 cm.



     These mathematical expressions and  the resulting graphical  displays



characterize the pertinent characteristics and generally describe the on-



axis power density as a function of distance in terms of the  near field on-



axis maximum power density and the near  field extent for antennas used in



satellite communication system earth  terminals.





        Section 3 - Satellite Communication System Measurements



System Description



     Measurements were made of environmental power densities  produced by



three high power, large diameter, satellite communication earth  terminals



located at Fort Monmouth, New Jersey  and  Fort Detrick, Maryland.  An



invitation extended by the U.S. Army  Environmental Hygiene Agency to join



them in hazards evaluation studies at these locations provided the oppor-



tunity to study the radiation characteristics of the satellite communication



systems located there.  These systems were operated in accordance with



directions furnished by the personnel performing the measurements in order



to evaluate them with respect to their potential hazards; the



systems were not operated under normal operational procedures.



     The systems studied were the AN/TSC-54 and the Lincoln Experimental



Terminal, both located at Fort Monmouth,  and the AN/MSC-60 located at Fort



Detrick.  The characteristics for these  systems are summarized in table 3.

-------
GRIN

    190
    78
    38

    28


    10

    e
                  16   19   20   25   38  35   40   45

                               WflVELENQTM  

                     Figure 3  Antenna Gain vs. Wavelength

-------
lit  i
let  e
           5    10   15   29   25    30   35   40   45   50   55   66
                             WflVELENGTH 
-------
1ft  4
tet  3
                18   15   28   25   3d   35   40
                             MflVEUENGTH  
-------
     let 4

 POWER
 DENSI TV

     let 2
     lit i
     let e
     iet-1
                    \
   P =  1
                                                   kW
                                                                                 co
                         40
120
                    60     80      108

                  REFLECTOR  DIflM  (FT)

Figure 6  On-Axis Near Field Power Density vs. Antenna Diameter
140
160

-------
i
    Figure  7   Far Field  Power Density/On-Axis  Near  Field  Power  Density  vs.
                    Distance  from Antenna/Near Field  Extent

-------
wa/wi
          i
          i
          5
           i
i. i   i.


1. 3   i. 4
i, 6   i.
                                                                        1>
1.  9   2
                                                                                                ro
                                                                                                O
     Figure 8  Intermediate  Field Power Density/On-Axis Near Field  Power Density vs,
                         Distance from Antenna/Near Field Extent

-------
                                Table 2

                    Paraboloidal Antenna Characteristics
DlflM(FT)


   6©
WflVELENGTH
                      1
                      2
                      3
                      4
                      5
                      6
                      7
                      8
                      9
                      18
                      13
                      26
                      29
                      38
                      35
                      48
                      45
                      38
                      55
                      68
QfllNCDB)
Ri(CM)
72. 1769
66. 1762
62. 6343
68. 1356
58. 1974
56. 6137
53. 2747
54. 1149
53. 8918
52. 1766
48. 6548
46. 1559
44. 2177
42. 6341
41. 2951
48. 1353
39. 1122
38 197
37. 3692
36. 6134
596992
2954i31
196967
147725
116180
96463. 8
84414. 7
73862. 7
65655. 8
59898 2
39393. 4
29545. 1
23636 1
19696. 7
16882 9
14772. 5
13131. 1
11818
18743. 6
9848. 36
WKHW/CMt2>


   761372

-------
                                       22




     The AN/TSC-54 comprises items  28 through 33 in the ECAC identification



(1) of the most powerful  CW sources,  ranked on the basis of decreasing EIRP.



The LET studied at Ft.  Monmouth,  an earth terminal used to communicate with



an experimental communication satellite developed by the Lincoln Laboratories,



was not identified in the ECAC source listings.



     The system studied at Ft. Detrick, Maryland, the AN/MSC-60, had



recently been constructed, was in the system calibration stage,  and was not



yet considered operational.  Its  EIRP,  5.0xl09 W, makes it one of the most



powerful in the U.S.  with respect to  EIRP (refer to table 1).



     A system located at Ft. Monmouth,  an AN/MSC-46, is listed in table 1



among the systems having the highest  EIRP values.  In fact, the  systems



numbered 13 through 20 are all examples of an AN/MSC-46 satellite communica-



tion system.  It was  one of the systems to be studied, but unfortunately was



not operational at that time.



     AN/TSC-54



     The AN/TSC-54 satellite communication terminal  is a part  of the Defense



Satellite Communication System.  The  system is transportable by  air or



vehicle, and provides the capability  for tracking a near synchronous orbit



communications satellite and for  transmitting voice and teletypewriter



communications through satellites to  other communication facilities.  It



transmits in the frequency range  from 7.9 to 8.4 GHz, and receives satellite



transmission in the 7.25-7.75 GHz range.



     The antenna consists of an array of four 10-foot diameter parabolic



reflectors, each having a special high efficiency power feed in a Cassegrain



geometry.  Figures 9a and 9b are  photographs of the antenna.  The overall



reflective surface area is approximately equal to that of a single 18-foot



diameter reflector.

-------
                                     23
 9A
                                              ....... .
9B
                 Figures 9A and 9B  AN/TSC-54 Antenna  Array

-------
                                      24
     LET
     The Lincoln Experimental  Terminal  has  a  15-foot diameter  parabolic
reflector.  The transmitter has  a  maximum power output of 2.5  kW and trans-
mits over a frequency range of 7.9 to  8.4 GHz.   The antenna is sheltered in
a weather-proof geodesic housing (figures lOa and  lOb).
     AN/MSC-60
     The AN/MSC-60 satellite communication  system  is considered a heavy
transportable earth terminal.   The antenna  has  a 60 foot diameter and uses a
Cassegrain geometry.   The system,  used for  communication with  satellites
in synchronous orbit (at a height  of 22,300 miles), has  three
transmitters, one high power (8  kW maximum) and two low  power  (3 kW maximum),
using only one at a time.  The maximum EIRP for the system (taking into
account a 3 dB power loss occurring in the  waveguide and swivel  joints)  is
5.0x10  W at a transmitting frequency  of  7.9  GHz.   The system  is shown in
figures lla and lib.   Close-up photographs  of the  antenna are  presented  in
figures lie and lid.
     As a matter of interest,  two  other extremely  powerful, 60-foot diameter
systems are under construction at  Ft.  Detrick.   These systems  are located
within 1000 ft. of the AN/MSC-60.   The photograph  showing these systems,
figure 12, was taken from the  AN/MSC-60 site.
Satellite Communication Systems  Measurements
     The power density, using  a  known  transmitter  power, was measured for each
of the systems on the reflector  axis at a location in the near field and
also, where possible, at a point on-axis  as far from the antenna, as
practical.  Due to the height  of the antenna  axis  above  ground, the limita-
tions on the minimum elevation angle to which each of the antennas could be

-------

                      25
       Figure 10A  LET Geodesic Housing
Figure 10B  LET Antenna (Rear View)  In Housing

-------
11A
11B
 Figures  11A  and  11B   AN/MSC-60  Satellite  Communication  Earth  Terminal

-------
                             27

Figures 11C and 11D  Close-up Views  of the  AN/MSC-60 Antenna

-------
                        28
Figure 12   Satellite  Communication  Earth  Terminals
      under Construction  at  Fort  Detrick,  Md.

-------
                                      29
                                  Table 3

                  Summary of Pertinent Characteristics for
                  Selected Satellite Communication Systems
Antenna
  Type
  Diameter (ft)
  Aperture Efficiency
  Gain (dB)
  1/2 Power Beamwidth (deg)
  Polarization of Trans-
    mitted radiation
  Height from center of
    antenna to ground (ft)
                                 LET
Cassegrain
 15
.50
 48
.58

 RHC
Frequency (GHz)

System EIRP (109 W)
        AN/TSC-54

Cloverleaf Array Using
 4 Modified Cassegrain
        Reflectors
          18 (eff)
         .75
          52
         .5

          RHC
Transmitter power output (kW)
(Maximum)                      2.5
 7.9-8.4

.161
          8.0

          7.9-8.4

          1.27
         .63*
AN/MSC-60

Cassegrain
 60
.50
 61
 RHC

 63


 8.0

 7.9-8.4

 10.0
 5.0*
*Includes 3 dB power loss in waveguide and swivel joints.

-------
                                      30




oriented, and the means available to elevate personnel  and instrumentation



to the system axis, the number of locations at which measurements can be



made is severely restricted.   For the measurements of the LET and AN/TSC-54



systems at Ft. Monmouth, the  only practical way for personnel to reach the



height at which the maximum power density could be measured was to use



buildings to which access was possible.   A "cherry picker" was available for



the measurements of the AN/MSC-60 system at Ft. Detrick, however, the number



of locations at which it could be situated was limited  because of structures



and streets in the area, and  the availability of suitable ground which could



provide a stable base.



     In all measurements, the antenna is oriented so as to illuminate the



measuring instrumentation, and the maximum power density is found by moving



the instrumentation until the maximum reading is obtained.



     The geometry for the measurements is generally illustrated in figure



13.  The information specifying the distances, elevation angle, and detector



used for each measurement is  given in table 4.



     The on-axis power density generated by the LET system was measured at



two locations:  one in the near field, on a metal staircase on the outside



of a building with a brick exterior; the second measurement in the inter-



mediate field at the second story window of a wooden building.  The loca-



tion for the near field power density measurement is shown in figure 14.



     The measurement of the near field maximum power density generated by



the AN/TSC-54 system was the only on-axis measurement attempted.  The



system's operating personnel  limit the minimum elevation angle to 7.5° to



avoid any possibility of creating a potentially hazardous exposure situation,

-------
                                  31
Antenna
                                                                Detector
     Figure 13  Geometry for On-Axis Power Density Measurements
                               Table 4



              Measurement Geometry and Instrumentation
System
LET
LET
AN/TSC-54
AN/MSC-60
AN/MSC-60
R (ft)
^200
•^600
50
60
360
9 (deg)
•\4
0.3
7.5
0
0
hi (ft)
15
15
16
63
63
h2 (ft)
^28
•v-18
^22
63
63
Instrumentation
Narda 8323 probe
HP 432A power meter,
AEL APN101A antenna
Narda 8321 probe
Narda 8321 probe
Narda 8321 probe

-------
                                     32




and for this reason the measurement could be performed only on the roof of



the wooden building which housed the transmitters and electronic systems of



the AN/TSC-54.   Figure 15 illustrates the actual  measurement in progress.



     The on-axis power density measurement of the microwave radiation



transmitted by the 60-foot diameter reflector of  the AN/MSC-60 was possible



only with the use of a "cherry picker" which elevated the measurement



personnel and instrumentation to the height of the center of the antenna for



an elevation angle of 0°.  The fiberglass basket  could accommodate two



persons and their hand-held instruments.   The antenna was oriented so as to



direct its radiation at the basket, and  then the  "cherry picker" boom was



moved and the basket oriented in order to intercept the on-axis beam.



     The extent of the near field for this antenna, 1.6x10-3 m, made it



impossible to measure power density beyond the near field.   Measurements



were made at two different locations with respect to the antenna, but both



were in the near field.  The antenna and  measuring personnel  are shown in



figure 16.



     Instrumentation Description



     The instrument primarily used in performing  these measurements was the



NARDA 8300 which employs the model 8321  broadband isotropic probe for



measurements of power density <20 mH/cm2  and the  8323 broadband isotropic



probe for measurements of power density  >20 mW/cm2.  The Hewlett Packard



power meter, model 432A, with calibrated  thermistor mount and calibrated



antenna, sensitive to the frequency emitted by each satellite communication



system, was used in one of the measurements (see  table 4).

-------
                             33
Figure 14  Staircase Location for LET Near  Field  Measurement
Figure 15  Measurement of AN/TSC-54 Near Field Power Density

-------
                              34
Figure 16  Measurement of AN/MSC-60 Near Field  Power Density

-------
                                     35




     The NARDA broadband isotropic monitor responds to the electric field



component of radiation, in the frequency range of 300 MHz to 18 GHz, with



equal sensitivity over all polarizations and direction of propagation, and



can measure the power density accurately in the near and far field.  This



isotropic response characteristic is derived from the probe design employing



thin film resistive thermocouple dipoles arrayed in three mutually



perpendicular planes.



     The HP-432A power meter uses a log periodic antenna as the radiation



sensor.  The antenna must be oriented to maximize the signal generated by



the detected radiation.  The maximum signal measured must be multiplied by



a factor of 2 in order to correct for the measurement of power density for



the circularly polarized radiation radiated by the satellite communication



systems measured; or measurements of power density must be made in two



orthogonal directions and then added.



     The characteristics of an instrument using the HP-432A power meter



depend to a great degree on the antenna used to detect RF or ywave



radiation.  The meter displays the power in the RF or ywave field which was



detected by an antenna having a specified cross-section and efficiency.



The 432A has 7 ranges of sensitivity from 10 uW to 10 mW.



     The characteristics of the NARDA 8300 with the 8321 and 8323 isotropic



probes are presented in table 5 (5).

-------
                                    36
                                  Table  5

                  NARDA Isotropic  Probe  Characteristics
  Frequency range (GHz)
  Power reading ranges
    (full  scale)
  Frequency sensitivity  (dB)
    1  to 12 GHz
    0.85 to 16 GHz
    0.30 to 18 GHz
  Isotropic responses

  Accuracy
  Overload threshold
    CW (mW/cm2}
    Peak (W/cm2)
  Power source
  Weight
8321
0.3 to 18
2 mW/cm2 &
20 mW/cm2
8323
0.3 to 18
10 mW/cm2 J
100 mW/cm2
+0.5                     +0.5
+0.5 to -1               +0.5 to -1
+0.5 to -3               +0.5 to -3
+0.5 dB from energy incident in any
direction (excluding handle)
+3% of full  scale

100                      300
20                       60
battery                  battery
4 pounds including carrying case
     A problem which existed in the NARDA probes,  especially the more

sensitive 8321, was the effect of static  charge  buildup  on  the 4-inch dia-

meter sphere of foamed polystyrene which  contains  the probe elements.   The

amount of static charge present causes  deflection  of the meter indicator

above the zero level, and may be responsible for inaccuracies in low-level

power density readings, observed in field measurements,  of  ^+0.8 dB at 2
     o
mW/cm .   The amount of static charge varies  continuously and cannot be

accurately compensated for by the zero  control.   It appears possible to

have up to ^+2 dB maximum error in measured  power  density for the most

sensitive scale.  The manufacturer has  recently  eliminated  the static

charge buildup problem with a design change.

-------
                                     37
     Measurement Results



     The results of the measurements performed to determine the on-axis



power density levels generated by the three satellite communication system



earth terminals studied are presented in table 6.  The values of near field,



on-axis, power density predicted by the model are given for a transmitter



power of 1  kW.  In addition, the predicted on-axis power density levels at



the point of measurement are given for the actual transmitter power used.



The physical geometry and instrumentation involved are as presented in



figure  13 and table 4.



     The maximum on-axis near field, power density for each system was



calculated using eq 2, the antenna diameter, transmitter power used, and



antenna efficiencies of 0.50 for the LET and AN/MSC-60 systems and 0.75 for



the AN/TSC-54.  The only measurement of on-axis power density made beyond



the near field extent of an antenna was that for the LET at a distance of



l.SxlO2 m to l.SxlO2 m.  Equation 5 was used in calculating the expected



power density.  In addition, the near field extent was calculated for all



systems, using eq 3, because of its importance in the calculation of power



density variation with distance from the antenna at distances beyond the



near field.

-------
                                                  Table 6

                               Results of On-axis  Power Density Measurements

Diameter (ft)
Near Field Distance (m)
Predicted Maximum Near Field On-
Axis Power Density (mW/cm2) for
1 kW Transmitter Power
Transmitter Power (kW)
R, Distance from Antenna (m)
to Point of Measurement
o
Measured Power Density (mW/cm )
Predicted Power Density (mW/cm2)
at R
LET
15
9.3X101
12.2
2
1.5xl02
to
l.SxlO2
12
15.1
to
12.6
2
e.ixio1
50*
24.4
AN/TSC-54
18
(eff)
1.4xl02
12.7
1
1 .5X101
7
12.7
6.4**
AN/MSC-60
60
1.6xl03
.76
.38b
.500
l.SxlO1
^.3
.38
^.19**
6.7
l.SxlO1
^2.2
5.1
2.5**
6.0
1 .OxlO2
to
1.1x10^
^3
4.6
2.3**
                                                                                                          GO
                                                                                                          oo
 *Measurement performed on metal staircase (see figure 14).
**Includes a 3 dB loss of power into waveguide and swivel joints not originally known but
  discovered after an inquiry was made to operations personnel about the discrepancy
  between the measured values and those predicted.

-------
                                     39
                   Section 4 - Discussion and Evaluation
Measurement Considerations
     The measurement procedure used in performing an on-site measurement of
potentially hazardous environmental levels of power density requires that
the system must be operated in a manner consistent with good safety
practices which consider the system characteristics, so that the transmitter
power, antenna orientation, and system activation be under the control  of
the persons performing the measurement.
     The determination of the procedure used in measuring the power densities
generated by any given satellite communications system involves:  a calcula-
tion of the environmental power density levels generated by the system based
on reflector and transmitter characteristics, knowledge of the distances
from the centerline of the reflector to ground for the minimum elevation
angle of the system at possible measurement locations, location of structures
in the vicinity of the system, a need to avoid the exposure of persons other
than personnel involved in measurements, provisions for the means to elevate
personnel and equipment to the proper height above ground for the measure-
ment, and the need for a reliable communication link between measurement
personnel and the system operators.
     The calculation of maximum near field power density (on-axis) per kW
transmitter power and near field extent specifies the transmitter powers
(other than maximum) to be used during a measurement of system characteristics
and the distances at which measurements may be considered.  The selection of
measurement locations also involves consideration of the minimum antenna
elevation angle possible, the need to avoid exposure to other persons, the
location of structures and the associated effects due to reflection of

-------
                                     40





radiation, terrain characteristics which affect the height above ground at



which it may be necessary to locate measurement personnel, and the avail-



ability of a means to reach that height.



     As antenna diameters increase, and therefore the near field extent also



increases, it becomes more impractical  to measure power density beyond the



near field for elevation angles significantly greater than zero degrees.



     The initial analysis used in the selection of systems to be investigated,



and the preliminary determination of instrumentation needs and measurement



procedure was based upon the data residing in the ECAC information inventory



and the use of an idealized model.  However, there are factors which could



modify this analysis and impose other requirements which must be satisfied.



After an initial evaluation has been made, complete and accurate character-



istics of the identified systems should be obtained.  Recent system modifi-



cations, i.e., transmitter power capability, may not have been included in



the data obtained from ECAC.



     The data resident in the ECAC information inventory includes the site



location, system frequency, transmitter power, antenna or system gain,



antenna diameter, system nomenclature,  antenna height above ground, a



qualitative description of the terrain, and the name of the operating agency.



However, there is much information which could be of use, does not exist in



the data file, and must be obtained from the persons operating the source



prior to a measurement.  This information concerns power losses which occur



between the transmitter and the antenna, the coupling efficiency between the



antenna feed and reflector, the minimum antenna elevation angle, and the



normal operating power of the transmitter.  The maximum power capability of



a transmitter and its usual operational power may be much different, however,

-------
                                     41





the maximum transmitter power should be used in evaluating a system as a



potential  hazard prior to its measurement.



     The source must be operated with particular considerations being given



to safety so that the personnel performing measurements are not exposed to



excessive levels of radiation and that exposure of persons not involved in



the measurement be avoided.  Thus an understanding of the measurement pro-



cedure and purpose by the satellite communication system operators is



extremely important, as is a reliable system for communication between the



measurement personnel and the system operators.  This direct communication



link and the source operator's knowledge of the measurement procedure



facilitates the measurement and results in knowing all of the pertinent



source operating characteristics at the time of each measurement.



     The instrumentation used to measure the power density from satellite



communication systems under less than ideal conditions (from a roof-top or



"cherry picker" basket) must not only have the necessary sensitivity over



the desired frequency range, but must be portable, lightweight, physically



small, extremely reliable, battery powered, thermally stable, and easily



read.  The effect of various weather conditions on the operation of an



instrument must be considered in determining its suitability during the



measurement.



     An important requirement is that the measured power density be directly



indicated by the instrument so that possible complications affecting the



measurement may be immediately obvious instead of being detected at a  later



time.  This requirement also serves to protect both the measurement



personnel and instrumentation from possible exposure  to excessive or



hazardous levels which could be accidentally produced.

-------
                                     42
Evaluation of Model  Applicability
     The model used in predicting characteristics and on-axis power density
levels for satellite communication systems earth terminals having circular
paraboloidal reflectors cannot be entirely validated by the measurements
reported because relatively few measurements were made, and of these, none
were made in the far field.  However, the results obtained, table 6, lend
support to the use of the model for predicting on-axis power density.
     If the on-site measurements agree with the anticipated values derived
through use of the model within the expected measurement accuracy of the
instrumentation used, the model can be used for preliminary determinations
of maximum on-axis power density at any distance from the antenna for
satellite communication systems.  If all  sources of instrument error would
add to produce the maximum possible error, deviations between measured and
actual power densities of up to ^40%, are possible.  A difference of 30%
between measured and power densities predicted by the model would be
acceptable.
     There are certain complicating factors not taken into account which
will cause the predictions based on the model  to deviate from the actual
on-site measurements.  These complications include the effect on power
density of interfering structures, and the power losses which occur before
power is introduced to the antenna system.  In addition, there is a possible
degradation in antenna gain due to geometrical considerations, but this
latter factor is infrequently encountered since most systems have undergone
rigorous testing prior to operation.  However, it is conceivable that
deviations from the idealized antenna geometry can occur, especially for
systems which are assembled in the field, i.e., the smaller transportable
systems.

-------
                                     43


     The effect of  interfering  structures and the discrepancy between

system transmitter power and the power fed to the antenna were demonstrated

in the satellite communication system measurements.   The effect of inter-

fering  structures on measured power density was seen in one of the LET

system measurements.  The near field measurement of power density yielded
                           o
a  maximum value of 50 mW/cnr as compared to a maximum theoretical  value of
          o
24.4 mW/cm^ for the transmitter power used.  The measurement was made on

the metal staircase shown in figure 15 and undoubtedly the high value of

power density was due to reflected radiation interfering constructively with

incident radiation.  While this measurement has no value as far as confirm-

ing the validity of the model, it is a fine example of the potential  effect

of structures having good reflective characteristics.

     The predicted system characteristics, including near field power

density, for the AN/MSC-60 system had been determined on the basis of the

antenna diameter and an assumed aperture efficiency of .50.  During the

measurements, it was noticed that the predicted values of on-axis, maximum

near field power density were a factor of ^2 greater than the measured

values of power densities significantly greater than zero; i.e., 2.2 and 3
     The discrepancy was pointed out by the system operators as being due

to a 3 dB power loss in the waveguide and swivel joints of the system.  This

power loss is typical of large systems where the antenna is massive and the

distance between the transmitter and antenna power feed is relatively large.

     The near field measurement of power density produced by the AN/TSC-54

system yielded a maximum value of ^7 mW/cm^ as compared to an anticipated

-------
                                     44




value of 6.4 mW/cm2, based on the assumption that the power losses incurred



prior to the antenna power feed is 3 dB and confirmed by persons having



experience with this system.



     System documentation and ECAC data do not necessarily provide



information describing the power loss which occurs in waveguide and swivel



joints, but may only specify maximum transmitter power and antenna gain from



which a theoretical maximum EIRP may be calculated.   The maximum on-axis



power density should be calculated using known values of antenna power or



including the effect of power losses between transmitter and antenna.



     The results of the satellite communication systems measurements lend



support to the use of the model for calculation of on-axis maximum power



density in the near and intermediate field for the initial hazard evaluation



of these systems.   Unfortunately, because of the limited number of systems



measured and the difficulty in placing personnel and instrumentation at the



antenna axis during the on-site hazards surveys performed, only three near



field measurements and one intermediate field measurements were possible.



     The extensive near field region associated with the AN/MSC-60 system



and the minimum elevation angle of 7.5° possible for the AN/TSC-54 system



made it impractical  to  make measurements beyond the near field for these



antennas.  The definition of near field extent cannot be substantiated



because the model  based calculation of near field extent is much greater



than the actual separation distance involved in the measurement.  The valid



LET system measurement was made at approximately the transition region



between the intermediate and far fields as defined by the model.



     The comparisons between the measured values of on-axis power density



and the calculated values of maximum on-axis power density, based upon the

-------
                                      45


model  are  given  in  table  7.   The  AN/MSC-60 measurement made with a

transmitter  power  of  .5  kW  (table 6)  must be  disregarded  because of  the

inherent inaccuracy of the  isotropic  probe at the  low end of  its most

sensitive  scale.   Static  charge buildup  effects can add significantly to

small  indicated  readings.   Measurements  of low power densities whose value

is within  an  order  of magnitude of inherent inaccuracies  in instrument

performance,  show  large  percent errors for relatively small deviations.


                                    Table 7

  Comparison  of  Measured  and  Calculated  Values of  On-Axis Power Density

                      LET              AN/MSC-60      AN/TSC-54

Measured Power
Density (mW/cm2)      12               %2.2   ^3      7

Calculated Power
Density (mW/cm2)      15.1 to  12.6     2.5     2.3    6.4

% difference          26 to  5          14      23     9


     The agreement  shown  supports  the use of  the USAEHA model  for initial

hazards evaluations of satellite  communication systems in the near and

intermediate  fields.  More measurements are needed to validate the model

in these regions and  in the far field, but in  order to illustrate the ideas

considered in the remainder of this report, the model will be used.

Anticipated Environmental Levels of Power Density for Simulated Satellite

Communication Systems

     The mathematical  model  previously described has been used to determine

expected characteristics  of various diameter circular paraboloidal  reflectors

assuming 5 kW transmitter power.   This combination of antenna and transmitter

-------
                                     46
simulates satellite communication system earth terminals.   The characteristics
are determined using realistic aperture efficiencies, transmitted wavelengths,
and system power losses which occur between the transmitter and antenna feed.
     These anticipated characteristics are presented in table 8 for reflector
diameters which range from 15 feet to 100 feet.  The gain, maximum on-axis
near field power density, EIRP, and distances at which on-axis power density
would reach selected levels have been calculated for two typical  aperture
efficiencies for antenna diameters where they may apply.
     While these systems are simulated, they represent approximations to some
satellite communication systems which are in use so far as antenna diameters
are concerned.  Transmitter power capability for actual systems may be
different than the 5 kW selected for the illustration being as low as 1 kW
for some tasks, however, this value may be typical  for the power output of
transmitters during usual system operation.
     The contents of table 8 generally identify potentially hazardous systems
directly from their maximum near field power densities and the distance
intervals (with respect to antenna location) over which power densities
exceed a selected threshold.  The values in the table show magnitudes of
expected maximum near field power density, for a given transmitter power and
wavelength, and that the power density levels close to the antenna (in its
near field) are more hazardous for smaller diameter antennas even though the
EIRP increases with antenna diameter.  However, the distances over which
levels exceed a selected threshold increase with diameter, but generally not
at the rate shown by EIRP.
Anticipated Environmental Levels of Power Density for Selected Systems
     Calculations have been made, for the expected characteristics of

-------
                                                    Table 8

               Anticipated  Characteristics  of Simulated Satellite  Communication Systems
Antenna
Diameter
(ft)
15
20
30
40
60
90
100
i
.5
.75
.5
.75
.5
.75
.5
.75
.5
.5
.5
Gain*
(dB)
48.1
49.8
50.6
52.4
54.1
55.9
56.6
58.4
60.1
63.7
64.6
Maximum Near Field Near
Power Density Field
(mW/cm2)** 5 kW Distance*
Transmitter Power (m)
60.9
91.4
34.3
51.4
7.61
11.4
4.28
6.42
1.90
0.846
0.685
9.23x10
1.64xl02
3.69xl02
6.57xl02
1.48xl03
3.32xl03
4.10xl03
EIRP
(109 W)
PT-G P-G
1 **
0.32
0.48
0.57
0.87
1.28
1.94
2.28
3.44
5.11
11.7
14.4
_
_
0.64
0.97
1.14
1.72
2.56
5.86
7.2
Distance (m
10 mW/cm2
3.20x10
3.95xl02
4.25xl02
5.27xl02
4.21xl02
-
-
-
-
) from Antenna for Power Densities of:
1 mW/cm2 100 yW/cm2 10 uW/cm2
l.OlxlO3
1.25xl03
1.34xl03
1.67x103
1.44xl03
1.76xl03
1.92xl03
2.36xl03
2.82x103
-
-
3. 20x1 O3
3. 95x1 O3
4.25xl03
5. 27x1 O3
4.55xl03
5. 58x1 03
6. 08x1 03
7.45xl03
9.13xl03
1.37xl04
1.52xl04
l.OlxlO4
1 .25xl04
1.34xl04
1.67xl04
1 .44xl04
1.76xl04
1.92xl04
2.36xl04
2. 89x1 O4
4. 32x1 O4
4. 80x1 O4
 *Assuming 4 cm ywave radiation  transmission.
**3  dB loss between transmitter  and power  feed for reflectors with  diameters >30 ft.

-------
                                     48





several  existing satellite communication systems operating at maximum



transmitter power.   In each case,  the distances from the antenna at which



power densities of 10 mW/cm^, 1  mW/crrr, 100 pW/cm^, and 10 yW/cirr are



expected have been determined.   The results are given in table 9.



     The points of interest are, that for these systems having antenna



diameters which vary from 15 feet  to 210 feet, the near field, RI,  increases



from approximately 100 meters to almost 6x10-3 meters.  With the exception of



the Intelsat system, the on-axis near field power densities,  Wnf, are



significant relative to 10 mW/cm^.   Examination of the distances from the



antenna  at which various on-axis power densities occur, shows the increase



in the spatial  extent, over which  significant power densities exist,  as the



antenna  diameter and near field  extent increase.



     The larger systems are included in the list of CW sources having the



highest  values  of EIRP with the  exceptions of the AN/MSC-60 and the two



deep space communication systems.   These more recent arrivals would not be



expected to appear in the ECAC  listing.



Potential Hazard Evaluation



     A potential hazard evaluation assesses the potential  of a source of



radiation to produce a hazardous exposure level relative to a defined thres-



hold for some selected exposure criterion.  Potentially hazardous sources may



be identified through an examination of the ECAC inventory.  The inventoried



sources  may be evaluated relative  to one another and assigned a priority for



further examination.



     An  initial evaluation of the potential hazards of an individual



satellite communication system may be performed by determining its worst

-------
                                                      Table  9

                  Anticipated Characteristics of  Selected Satellite Communication Systems
System
LET**
AN/TSC-54**
AN/MSC-46
AN/MSC-60**
AN/FSC-9
Intelsat
Goldstone
Venus***
Goldstone
Mars***
Antenna
Diameter
(ft)
15
18(eff)
40
60
60
97
85
210
(cm)
3.7
3.7
3.7
3.7
3.7
4.8
12.6
12.6
Gain
(dB)
48.8
52.1
57.3
60.8
60.8
62.7
53.8
61.9
PT
(kW)
2.5
8
10
8
20
5
450
450
EIRP
(109 W)
P*G
.189
.651
2.68
4.82
12.0
4.68
54.0
348
On)
9.98x10
1.44xl02
7-lOxlO2
1.60xl03
i.eoxio3
3.22xl03
9.43xl02
5. 76x1 O3
wnf (max)
(mW/cm2)
30.4
50.8
8.56
3.04
7.61
.728
97.3
16.8
Distance (m) from Antenna
for Power Densities of:
10 mW/cm2
2.46xl02
4. 58x1 O2
-
-
-
-
4.16xl03
9. 68x1 O3
1 mW/cm^
7.79xl02
1.45xl03
2. 94x1 O3
3. 94x1 O3
6. 23x1 O3
-
1.32xl04
3.34xl04
100 uW/crrr
2.46xl03
4. 58x1 O3
9. 29x1 O3
1.25xl04
1.97xl04
1.23xl04
4.16xl04
1.06xl05
10 yW/cm^
7.79xl03
1.45xl04
2.9xl04
3. 94x1 O4
6. 23x1 O4
3. 88x1 O4
1.32xl05
3. 34x1 O5
  *Includes a 3 dB loss  of power into waveguide and swivel joints.
 **Systems measured.
***These  are not satellite communication  systems, but systems which are used to communicate with space vehicles on  planetary
   exploration missions.

-------
                                      50





case (on-axis) power density capability and the distance from the system at



which the power density may equal  a selected threshold value of interest.



Simplified models exist which can  calculate reasonably well  the significant



radiation characteristics of a source from basic characteristics; i.e., the



reflector diameter, radiation frequency, aperture efficiency, and the maximum



power which can be introduced into the antenna system for subsequent radiation



into space.



     If the potential  hazard evaluation of satellite communication system



were carried further to include other factors, i.e., operational  procedures



and site characteristics, power density produced at any location  relative to



the source would be predicted with greater accuracy.  However, these factors



are difficult to incorporate into  calculations and they may be the factors



responsible for significant differences between measured and calculated



radiation field characteristics.  In addition, biological effects information



is inadequate for quantitative biological effects hazard analysis.  The



analysis depends on the power density at which effects occur and  their



frequency dependence, the exposure time, and the characteristic and distribu-



tion of the exposed population.



     A simple illustration of the  technique of applying a selected threshold



value in a potential hazard evaluation of the inventoried satellite communi-



cation systems treated in this paper is presented in a graphic display (figure



17).  Sources whose on-axis power  density is greater than any imposed thres-



hold are identified and their near field distances are immediately available



for use in further analysis.

-------
                                       51
OJ
 e
 o

 1
 to
 c
 0)
 o

 1-4
 0)
 3
 o
    10
 cfl
 0)
 2
    10'
     -1
   10
                                   • TSC-54
                                 LET
                                                        GOLDSTONE

                                                          VENUS
                                                                  GOLDSTONE

                                                                    MARS
                                                    •MSC-46
                                                              'FSC-9
                                                              MSC-60
                                                                    • INTELSAT
                                                        I
      10
                               102                      10*


                             Near Field Distance  (m)
Figure 17  Possible Method of  Identification of Satellite Communication Systems

-------
                                      52





     Once this initial identification has been made, the sources can be



comparatively ranked using chosen criteria.  One method of comparing sources



is based upon the distance from the source at which a selected on-axis power



density exists.  The results shown in table 9 can be used.  Another method



can be based upon the on-axis power density which exists at a selected



distance from the source.  It must be remembered that these evaluations do



not take frequency, power density, and exposure time into account; they are



based upon a model used for calculational purposes and assume a threshold



value for power density.



     Procedures which can be used to perform these evaluations for systems



using modified circular paraboloidal reflectors and other types of antennas



are available, although more complex, so that the evaluation techniques can



be applied more generally.



     The factors which must be considered in a realistic evaluation of the



potential environmental hazard of any particular system include the trans-



mitter power used in its regular operation (generally much less than the



maximum possible), the procedures employed in system operation, the distance



between the center of the antenna and ground, terrain characteristics, the



minimum elevation angle of the antenna below which the system cannot operate,



and the distribution of population within the area for which power density



equals or exceeds the selected threshold level.



     The operational transmitter power may not equal the transmitter power



capability, resulting in power densities produced during operation which



are less than the maximum possible.  The power densities vary directly as

-------
                                     53




transmitter power, so that if Pj (used)/Pj (max) =0.1, the power densities



produced will  be one-tenth of that calculated for use of maximum transmitter



power.



     Many satellite communication systems cannot operate at elevation angles



less than a specified angle relative to horizontal.  The knowledge of that



angle and other system and site characteristics; i.e., terrain features,



antenna height above ground, population distribution, location and height of



structures, and sidelobe radiation characteristics of the antenna, will



realistically determine the possibility for exposure of persons within a



radius for which the power density exceeds or equals the threshold level.



     A system may produce significant power densities, and still not con-



stitute a hazard if there is no possibility for exposure.



      It is apparent that measurements of existing radiation levels are



necessary to a realistic hazard evaluation.  A potential hazard evaluation



may be most useful in identifying those systems to be studied by measure-



ment, to assist in assigning a priority to them for a more intensive



evaluation, and to analytically determine radiation characteristics for a



specified source.  However, it is necessary to quantitatively measure the



environmental  levels of power density in a realistic evaluation due to the



difficulty of incorporating into an analytical evaluation the factors which



may significantly affect the results.



ECAC as a Resource in the Identification and Evaluation of Potentially



Hazardous Sources



     The value of potential hazard evaluations depends on the quality of



the information which resides in the computerized data inventory.  The

-------
                                     54
Electromagnetic Compatibility Analysis Center has the most extensive
inventory of sources containing most of the system characteristics
required, but the quality of the information is not always consistent.  The
organizations operating the systems have the responsibility to provide
accurate information to ECAC but there are inaccuracies and inconsistencies.
     The effective radiated power determined by ECAC and used in ranking
sources, usually the maximum EIRP for the systems considered, uses the
maximum transmitter power capability and, in many cases, the theoretical
system gain, not the actual system gain.  EIRP may be reported as defined
in eq.  (9), but usually as G-Pj, where Pj is the maximum output power
capability of the transmitter.   EIRP reported in this manner may be a
factor of two greater than that which includes losses in the system.
     The extent to which the ranking of systems would be affected by
inclusion of actual system gain characteristics needs to be determined, but
the effectiveness in identifying sources or categories of sources according
to their potential for creating potentially hazardous environmental radia-
tion levels may not be affected.
                    Section 5 - Conclusions and Summary
     This study applies in general to the concept of potential hazard
evaluations involving sources of environmental microwave radiation, and
specifically to satellite communication earth terminals.  The general con-
clusions reached are that:
     1) In general, satellite communication systems, operated in accordance
with prescribed system operational procedures, should not constitute a
thermal effects hazard.  The possibility of exposure of persons (not

-------
                                     55



employed in system operation) should be extremely small  because radiation



is directed generally upward.  The avoidance of population exposure is



intended, as indicated by the minimum elevation angles specified.   Certain



satellite communication systems, if operated improperly, can create thermally



hazardous situations due to the large on-axis power densities which can be



produced at great distances from the antennas.



     2) Models exist which predict, under ideal conditions, maximum on-axis



near field power density, and appear to be applicable in defining  the



intermediate and far field zones and on-axis power density as a function



of distance from the antenna.



     3) The calculated values of on-axis near field power density,  near



field extent, and on-axis power density as a function of distance  from the



source can be applied to a method for potential hazard evaluation.   A



selected power density threshold can be used as a basis  for the identifica-



tion of potentially hazardous systems, assigning a relative ranking to them,



and in the initial evaluation of a system with regard to its potential as



a source of hazardous exposure levels.



     4) Effective isotropic radiated power is not the most directly



applicable characteristic to be used in the potential hazard evaluation.



Small diameter antennas, having lower gain characteristics, can produce



greater on-axis near field power densities, for equal transmitter  powers



and radiation wavelengths than larger diameter systems.



     5) A more realistic hazards evaluation will include other criteria



defining the exposure problem in addition to power density; i.e.,  the



population exposed and the exposure duration.

-------
                                     56

     6) A true hazard evaluation will  not be possible until effects are
identified, thresholds defined,  and the relationships between the degree
of effect to radiation frequency, power density, and exposure as a
function of time are known.
     7) Nonthermal effects hazard evaluations would give greater importance
to the off-axis power density characteristics of satellite communication
systems.
     8) A potential hazard evaluation procedure can be used to identify
those systems to which priority can be assigned for a more realistic hazard
evaluation.  Factors exist which significantly affect the results of an
analytical evaluation, and make measurement a necessary part of a realistic
hazard evaluation.
     The requirements and uses for hazard evaluations are summarized in
table 10.
Acknowledgments
     I wish to express my appreciation to Colonel  James E. Anderson and
John Taylor for making possible my participation in the U.S. Army Environ-
mental Hygiene Agency radiation protection surveys at Fort Monmouth, New
Jersey and Fort  Detrick,  Maryland.  I am particularly grateful to Marcus
Dieterle and Arthur Riggs for their cooperation and efforts in coordinating
the investigations at Fort Monmouth and Fort Detrick so that my interest in
satellite communication system earth terminals could be satisfied, and to
Charles Hicks, Captain Robert Fenlason, and Francis Rura for their coopera-
tion, assistance, and good humor in helping to make the experience useful
and thoroughly enjoyable.

-------
                                                 Table 10



                                         Hazards Evaluation Summary



Potential Hazard Evaluation:



     1.   Used to identify potentially hazardous sources on the basis of a selected power density threshold



     2.   Systems can be ranked according to selected criteria



     3.   Uses existing simplified models to calculate:



             near, intermediate, and far field regions



             power density  (on-axis) vs. distance from source



Realistic Hazard Evaluation requires:



     1.   Quantitative identification of biological  effects; i.e.,  determining for each effect           ^



             a.  dependence upon frequency, power density, exposure time



             b.  threshold  values



     2.   Knowledge of the population exposed, including



             a.  unique characteristics



             b.  distribution



     3.   Measurement of significant radiation field characteristics for those sources  identified;  i.e.,



             power density  as a function of frequency and time.

-------
                                     58


                                References
(]_)  Electromagnetic Compatibility Analysis Center.   Metropolitan Radiation
    Hazards II.   ECAC-PR-72-034,  ECAC,  Annapolis,  Maryland,  1972.

(2J  Tell,  R.A.   Environmental  Nonionizing Radiation Exposure:   A Preliminary
    Analysis of  the Problem and  Continuing Work within EPA.   Session Pro-
    ceedings:   Environmental  Exposure to  Nonionizing Radiation, U.S. Environ-
    mental  Protection Agency,  Hashington, DC,  1973.

(3j  U.S.  Army Environmental  Hygiene  Agency.   Laser and Microwave Hazards -
    Course  Manual.   USAEHA,  Aberdeen Proving  Grounds,  Maryland (current).

(4)  Silver, S.   Microwave  Antenna Theory  and  Design.   Dover  Publications,
    Inc.,  New York, 1965.

(5j  Narda  Microwave Corporation.   Operation and Maintenance  Manual  for
    Broadband  Isotropic  Radiation Monitor.  NMC,  Plainview,  New York,  1972.

-------
                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
1. REPORT NO.
 EPA-520/2-74-008
                                                           3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
 AN EVALUATION OF SELECTED SATELLITE COMMUNICATION
 SYSTEMS AS SOURCES  OF  ENVIRONMENTAL MICROWAVE  RADIATION
                       5. REPORT DATE
                        December 1974;  Issuing  date
                       6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)

 Norbert N. Hankin
                                                           8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
 Electromagnetic  Radiation Analysis Branch
 9100 Brookville  Road
 Silver Spring, MD   20910
                                                            10. PROGRAM ELEMENT NO.
                       11. CONTRACT/GRANT NO.
 12. SPONSORING AGENCY NAME AND ADDRESS
 Field Operations  Division
 Office of Radiation  Programs
 Environmental Protection Agency
 401  M Street, SW.  Washington, DC
                       13. TYPE OF REPORT AND PERIOD COVERED
                        Final
                       14. SPONSORING AGENCY CODE
20460
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT

     Selected satellite  communication  (SATCOM)  systems are evaluated analytically and,
 for some of these  systems,  through measurement of the microwave radiation  power
 densities generated  by  them.   The evaluation  is  directed toward assessing  the  radia-
 tion exposure hazards which exist for specific systems and generally for SATCOM
 systems as a class of high  power nonionizing  radiation source.  The paper  includes
 determinations of  anticipated maximum power density levels as functions of distance
 from the source, a description of the analytical  method used, and the  results  of
 measurements of the  power densities produced  by  certain SATCOM systems.  Included also
 is a discussion of potential  hazard analysis  and  its uses in identifying systems which
 may constitute environmental  hazards.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.IDENTIFIERS/OPEN ENDED TERMS  C.  COSATI Field/Group
      Environment; microwave; nonionizing
 radiation; power densities;  satellite
 communication.
18. DISTRIBUTION STATEMENT
 Release to public
          19. SECURITY CLASS (This Report)
            Unclassified
                                                                         21. NO. OF PAGES
                                              20. SECURITY CLASS (This page)
                                                Unclassified
                                                                         22. PRICE
EPA Form 2220-1 (9-73)

-------