United States
Environmental Protection
Agency
Office of
Radiation Programs
Las Vegas, Nevada 89114
ORP/EAD-77-3
March 1977
Radiation
sizEPA
Technical Note
An Analysis of
Radar Exposure in the
San Francisco Area
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Technical Note
ORP-EAD 77-3
AN ANALYSIS OF RADAR EXPOSURE IN THE SAN FRANCISCO AREA
Richard A. Tell
March 1977
U.S. Environmental Protection Agency
Office of Radiation Programs
Electromagnetic Radiation Analysis Branch
P.O. Box 15027
Las Vegas, Nevada 89114
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DISCLAIMER
This report has been reviewed by the Office of Radiation Programs -
Las Vegas Facility, U.S. Environmental Protection Agency, and approved
for publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for their use.
ii
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PREFACE
The Office of Radiation Programs of the U.S. Environmental Protection
Agency carries out a national program designed to evaluate population
exposure to ionizing and nonionizing radiation, and to promote development
of controls necessary to protect the public health and safety. This
report describes an analysis of radar measurements performed and reported
on by the Institute for Telecommunications, Department of Commerce.
This analysis addresses the microwave exposure aspects of radars to the
general populace. Readers of this report are encouraged to inform the
Office of Radiation Programs of any omissions or errors. Comments or
requests for further information are also invited.
Floyd L. Gal pin, Director
Environmental Analysis Division
Office of Radiation Programs
m
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CONTENTS
Page
DISCLAIMER tt
PREFACE *t*
LIST OF TABLES IV
ACKNOWLEDGMENTS Vlt
AN ANALYSIS OF RADAR EXPOSURE IN THE 1
SAN FRANCISCO AREA
Introduction and Description of Data Base 1
Antenna Corrections and Procedures 1
Results 4
Summary and Discussion 8
REFERENCES 10
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LIST OF TABLES
Number Page
1 Antenna Aperature Calibration for ASN-116A 2
Cavity Backed Spiral - Linear Polarization
2 Radar Exposure - Palo Alto 5
3 Radar Exposure - Bernal Heights 6
4 Radar Exposure - Mt. Diablo (2700-2900 MHz Only) 7
5 Summary of All Antenna Patterns and Radar 9
Spectra Measurements
vt
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ACKNOWLEDGMENTS
The author wishes to acknowledge the cooperation of the Office of
Telecommunications Policy in providing access to the radar measurement
data contained in the ITS report analyzed in this report.
The author would also like to extend his grateful appreciation to
Mr. Bob Mathison, Radio Spectrum Occupancy Group Leader, Institute for
Telecommunications Sciences, Office of Telecommunications, Boulder,
Colorado for his cooperation and assistance in interpretation of data
contained in the San Francisco area radar report.
Special thanks are given to Mrs. Lois McAllister for her diligent
efforts in the typing of this manuscript.
Vll
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AN ANALYSIS OF RADAR EXPOSURE IN THE SAN FRANCISCO AREA
Introduction and Description of Data Base
The Institute for Telecommunications Sciences (ITS), Department of
Commerce, Boulder, Colorado conducts a program of determining spectrum
usage in the major radar bands in various metropolitan areas. This anal-
ysis is based on measurement data contained within the ITS report on San
Francisco area measurements, OT/ITS Control Number 05150 (1). The data was
taken during the period June-August 1975 and includes measurements in the
1030 radar beacon band (interrogators), and the 1215-1400 MHz, 2700-3700
MHz, 5250-5925 MHz, and 8500-10,500 MHz radar bands. The intention of this
report is to assess exposure intensities from the radars observed and
reported on in the ITS report. The ITS report format indicates only the
signal power delivered to the receiver (in actuality, the power delivered
by the receiving antenna to the transmission line connecting the antenna to
the receiver). Thus, it was necessary to obtain from ITS information on
antenna apertures as a function of frequency to allow correction of the
reported data and consequent interpretation of absolute field intensities.
For the purpose of this report all field intensities are defined in terms
of power densities.
Antenna Corrections and Procedures
Graphs were provided by ITS showing antenna aperture vs. frequency for
the different antenna systems employed during the radar measurements. The
two principal antenna systems used consisted of cavity backed spirals (CBS)
and a 1 meter diameter steerable parabolic dish. The CBS antenna system
was composed of 4 pairs of CBS antennas, one right hand circular!ly polar-
ized and the other left hand circularily polarized, each pair oriented in
one of four quandrants, north, east, south, and west. Each CBS antenna has
a 3 dB beam width of 70-90 degrees which assures that signals from any
direction will be detected with essentially uniform gain. In practice,
spectral measurements were made with the antennas looking at each quadrant
to ensure capture of the radar signals arriving from any direction.
For each of the major radar bands, the aperture of the ASN-116A CBS
antenna was determined from the ITS information and a single value was
identified as being appropriate for use throughout the given band. Table 1
shows the aperture values as used for the analysis in this report. Total
variation of aperture across any of the four bands is no greater than
approximately 1 dB.
The steerable 1 meter diameter dish exhibits a nearly constant aper-
ture across the entire 1-10.5 GHz band of 10.5 dB>l m2. The aperture of
this antenna varies only from -10.0 dB>l m2 at 1 GHz to -11.2 dB>l m2 at
1
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ro
Table 1. ANTENNA APERTURE CALIBRATION FOR ASN-116A CAVITY BACKED SPIRAL
LINEAR POLARIZATION
FREQ. BAND (MHz) APERTURE (dB>l m2) APERTURE (dB>l cm2} APERTURE (cm2)
1260-1338 -25.6 14.4M4 27.5
2720-3062 -29.0 11.0^11 12.6
5386-5660 -32.2 7.8^8 6.0
8618-9450 -36.2 3.8^4 2.4
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10.5 GHz. All antenna calibration data used was for the case of linear
polarization. According to ITS personnel most radars observed and reported
on in their report were predominantly linearly polarized.
The data correctional procedure consisted of applying the antenna
aperture to the received power as shown in the ITS data in the following
manner:
P (dBm) + 3 dB-A (dB?>l cm2} - y(dB) -R (dB) = S (dBm/cm2) where
P => received power in dBm as reported by ITS
3 dB = correction factor for angle of arrival
A = antenna aperature in (dB>l cm2)
S = exposure power density in (dBm/cm2)
Y = transmitter duty factor (dB)
R = antenna effective duty factor due to rotation (dB)
The 3 dB correction factor is used since it was assumed that the signals
detected could be due to arrival from a direction corresponding to the 3 dB
point on the receiving antenna's pattern. The factor R, the antenna's
effective duty factor due to rotation, was a measured parameter in many
cases but for the purposes of this analysis an assumed value of -22 dB was
applied to all of the data. This value corresponds closely with measured
values on other antennas and is on the conservative side in that it will
probably overestimate the actual averaging effect of the antenna's rotation.
The value of -22 dB was arrived at by examining the statistical antenna
patterns in the ITS report. In the event that the transmitter's duty cycle
was not known, a value of -30 dB was used.
The procedure used in extracting measurement data from the ITS report
consisted of examining each radar spectrum shown and identifying the maxi-
mum level signal observed from each radar shown, depending on which direc-
tion the radar was strongest. Three main sites were used in the San
Francisco area for general radar spectrum measurements; Palo Alto, Bernal
Heights, and Mt. Diablo. A relatively large number of radars were detected
at each site. For this analysis, all detectable radars were used in deter-
mining exposure.
The ITS measurement system is very sensitive and revealed the presence
of a relatively large number of radar signals; most of these signals were
quite weak, however. The following chart shows the number of radars
detected in each band at each location and subsequently used for exposure
determination.
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Number of Radars Detected
Freq?»nc^ Range Pal° Alto Bernal Heights Mt. Diablo
(MHz)
1260-1338
2729-3062
5386-5660
8618-9450
2
13
10
21
3
28
4
16
N/A
8
N/A
N/A
u j M ^' Diabl° S1'te tne only band monitored was the 2700-3900 MHz
band. No radars were seen above 9.5 GHz at any of the measurement sites
and many of the radars seen in the 8500-9500 MHz band were aircraft
weather radars from airborne aircraft transiting the general area.
Each radar measurement used in the analysis was corrected as indicated
above yielding an average power density (averaged due to transmitter duty
cycle and antenna rotational duty factor). On the basis of these average
power densities a table was compiled showing the sources contributing most
to the overall radar exposure at each of the above three sites in order of
decreasing average power density.
Results:
*u *Tab]S 2 Pr0Yjdes these exposure results for the Palo Alto site showing
P °,COntbut°S to the over a11 exposure. The last ranked source
n , .
? I in-t e top ranked source- Total exposure for the site was
x 10 yw/cm2 or -65.7 dBm/cm2. The first three sources account for
greater than 99 percent of the total of 2.7 x 10-" yW/cm2. Columns are
shown for SRK (the peak pulse power density), SavxMTR (the average power
density corrected for transmitter duty cycle), and SavANT (the average
power density corrected for both transmitter and antenna rotational duty
\*J\f I CO •
+ +. 3 P;;oyides a similar description of the over-all radar exposure
at the Bernal Heights site where the total exposure from the top 10 source
contributors was 1.1 x 10- 3 uW/cm2. At this site the first five sources
account for greater than 97 per cent of the total and the 10th ranked
source was 26 dB down from the highest intensity source.
Table 4 provides the exposure results for the 2700-2900 MHz radar
measurements at the Mt. Diablo site. Accumulative exposure from the eiqht
radars observed there was 2.6 x 10- s yW/cm2. In this case the first three
sources account for greater than 95 per cent of the total for this band.
In addition to the general spectrum measurements made at Palo Alto,
Bernal Heights, and Mt. Diablo, special measurements were made at a number
4
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Table 2. RADAR EXPOSURE - PALO ALTO
RANKED IN ORDER OF DECREASING AVERAGE POWER DENSITYA/
Name
ASR-7
ASR-5
FPS-107
FPS-90
ARSR-1 E
<£/
T
I
B
G
Total
Freq. (MHz)
2729
2750
1310
2738
1338
8970-9000
9392
9239
8673
5837
Power Density
SpK (dBm/cm2)
-17
-17
-28
-35
-37
-40
-41
-46
-44
-44
-13.7
S.v (dBm/cm2)
MVXMTR
-47
-47
-56
-67
-69
-70
-72
-73
-75
-79
-43.7
Sflu (dBm/cm2 )£/
MVANT
-69
-69
-78
-89
-91
-92
-94
-95
-97
-101
-65.7
SAV (vW/.
MVANT
1.3x10""
l.SxlO'"
1.6xlO~5
1.3x10"
7.9xlO"7
6.3xlO"?
4.0x10"
3.2xlO"7
2.0xlO"?
7.9xlO"8
2.7x10""
A/The average power density is defined here to be the peak power density corrected for transmitter
duty cycle and antenna rotational duty cycle.
B/No transmitter duty cycle information was available so a duty cycle of -30 dB was assumed.
C_/ The Antenna rotational duty cycle was assumed to be -22 dB in all cases.
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Table 3. RADAR EXPOSURE - BERNAL HEIGHTS
RANKED IN ORDER OF DECREASING AVERAGE POWER DENSITY^/
Name
FPS-107
ASR-7
C
FPS-107
I
MPN-11D
M
ASR-5
d/
ARSR-1E
Total
Freq. (MHz)
1260
2729
5665-5812
1310
9364
2798
9406
2750
8930-9500
1338
Power Density
SpK (dBm/cm2)
-13
-13
-13
-20
-19
-30
-32
-33
-35
-35
-7.6 (174
yW/cm2 )
S.v (dBm/cm2)
MVXMTR
-41
-43
-48
-43
-49
-61
-62
-63
-65
-67
-37.5 (0.18
yW/cm2) '
S.v (dBm/cm2 )C/
AVANT
-63
-65
-70
-70
-71
-83
-84
-85
-87
-39
-59.5
SAV (PW/
MVANT
5.0x10""
3.2x10""
1.0x10""
1.0x10""
7.9xlO"5
5.0xlO"6
4.0x10"
3.2x10"
2.0xlO"6
1.3xlO~6
1.1x10"
cm2)
n /
-The average power density is defined here to be the peak power density corrected for transmitter
duty cycle and antenna rotational duty cycle.
—^No transmitter duty cycle information was available so a duty cycle of -30 db was assumed.
— The antenna rotational duty cycle was assumed to be -22 dB in all cases.
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Table 4. RADAR EXPOSURE - MT. DIABLO (2700-2900 MHZ ONLY)
RANKED IN ORDER OF DECREASING AVERAGE POWER DENSITY^/
Name
(dBm/cm2)
Density yW/cm2)
SAU (dBm/cm2)
MVXMTR
10"3 yW/cm2)
>AV
ANT
MPS-14
ASR-7
FPN-55^/
ASR-4
ASR-5
ASR-5
FPN-47
WRS-57
'otal Power
-24.0
-30.5
-35.0
-38.0
-42.0
-48.5
-49.5
-52.0
Density -22.6 (5.5
-55.6
-60.7
-65.0
-68.2
-72.3
-78.8
-79.5
-83.8
-53.3 (4.2x
-77.6
-82.7
-87.0
-90.2
-99.3
-100.8
-101.5
-105.8
-75.8
'ANT
(yW/cm2)
1.7x10"
5.4x10"
2.0x10"
9.5x10"
1.2x10"
8.3x10"
7.1x10"
2.6x10'
2.6x10'
A/
-The average power density is'defined to be the peak power density corrected for transmitter duty
B/cycle and antenna rotational duty cycle.
£yNo transmitter duty cycle information was available so a duty cycle of -30 dB was assumed.
-'The antenna rotational duty cycle was assumed to be -22 dB in all cases.
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of other locations for the purpose of determining the characteristic
emission spectra of various radars and to determine the radars transmitting
antenna pattern. From these measurements, exposure values were also deter-
mined by appropriate correction procedures. In these cases, distances to
the radars were determined by ITS. Table 5 presents the results of these
measurements, listed in order of increasing distance from the radar being
studied. This table provides information about the maximum observed power
densities for various radars at distances ranging from immediately next to
the radar to 147.7 km. No value greater than 2.0 x 10~5 yW/cm2 for a
single radar was seen regardless of the closeness to the source.
Summary and Discussion
This report has analyzed the measurements reported in the ITS San
Francisco radar report in terms of resulting microwave exposure. Radar
exposure, determined at the Palo Alto Site was 2.7 x 10-11 yW/cm2 and at the
Bernal Heights site 1.1 x 10-3 yW/cm2 for the top 10 contributing sources
at each location. Exposure in the 2700-2900 MHz band at the Mt. Diablo
site was 2.6 x 1Q-5 yW/cm2. These values are generally equal to or lower
than commonly existing radio-frequency fields from signals in the broadcast
service on the basis of past EPA measurements. Based on an analysis of EPA
measurement data at 72 sites in four major east coast cities only 4 sites
had total exposures (broadcast plus land mobile bands) which were as low
as the maximum average radar exposure found from the ITS radar data in San
Francisco. For these 72 sites a median total exposure of 0.03 yW/cm2 was
found. Certainly, ambient RF fields many times greater than these values
are commonly found in the environment near radio and television broadcast-
ing installations. The ITS San Francisco radar report indicates that time
averaged power density levels from the observed radars are well below the
present guideline for occupational microwave exposure of 10 mW/cm2 (3).
An additional factor is involved with radar exposure in that if one is
not close to line of sight (LOS) transmission to the radar, signal levels
will be significantly reduced. It should be pointed out that the three
sites mentioned above were chosen on the basis of maximizing the number of
radars which would be LOS from each point. In fact, if the distance between
the chosen monitoring point and the strongest radar had been shortened, the
measured level may have decreased because of intervening terrain obstacles.
in general, it appears that the total exposure is predominated by a few
sources with other detectable radars adding very little.
If one closely approaches a radar, however, it is entirely possible
that the resulting ambient field from the radar will exceed the exposure
due to other types of sources, e.g., the broadcast service. Based on what
is seen in these results, though not conclusive by any means, it seems as
though the contention that radars are not a major perturbation of the
ambient electromagnetic radiation exposure picture, on the average, is
correct. On the average means at randomly picked locations in a metro-
politan area.
The results of the other ITS radar reports should be analyzed to
determine conformity with these conclusions.'
8
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Table 5. SUMMARY OF ALL ANTENNA PATTERN AND RADAR SPECTRA MEASUREMENTS
Name
FPN-55^/
ASR-5
MPN-11
WSR-57R/
FPN-55|/
FPN-55&-'
ASR-7
ASR-7
ASR-5
ASR-7
c/
FPS-90
ARSR-1 E
ARSR-1 E
ARSR-1 E
ASR-7
ASR-7
FPS-90
ASR-5
ASR-5
ASR-5 R/
MPN-13^
c/
FPS-107
WSR-57
WSR-57
Dist. (km)
Next to
Next to
Near
1.0
1.2
1.2
12.2
14.4
14.4
17.5
22.2
25.4
27.4
29.2
29.2
33.4
36.5
38.4
48.6
50.2
50.2
68.6
68.4
68.7
87.4
147.7
SpK (dBm/cm2)
+ 0.5
- 1.5
+ 0.5
+ 1.5
+ 5.1
- 0.5
-41.2
-19.8
-20.5
-38.0
-24.8
- 5.5
-66.5
-19.6
-22.5
-21.2
-54.3
-25.5
-54.6
-70. G
-51.0
-66.9
-32.7
-36.5
-55.7
-69.9
SAV (dBm/cm2)
AVXMTR
-29.5
-31.8
-27.7
-30.3
-24.9
-30.5
-71.4
-50.1
-50.8
-68.2
-53.2
-37.1
-98.0
-51.1
-54.0
-51.4
-84.5
-57.1
-84.9
-101.1
-82.1
-99.9
-61.1
-64.9
-87.5
-101.7
S»y (dBm/cm
MVANT
-51.5
-53.8
-49.7
-57.3
-46.9
-52.5
-93.4
-72.1
-72.8
-90.2
-75.2
-59.1
-120.0
-73.1
-76.0
-73.4
-106.5
-79.1
-106.9
-123.1
-104.1
-121.9
-33.1
-86.0
-109.5
-123.7
/ flu \uw/cm ) —
HVANT
7.1x10*3
4.2x10*2
1.1x10*3
5.9x10*2
2.0x10*3
5.6xlO"7
4.6xlO"5
6.2xlO~5
5.2xlO"7
9.5xlO"5
3.0x10*3
1.2xlO"9
1.0x10*5
4.9xlO"5
2.5xlO"5
4.6xlO"8
2.2xlO"s
1.2x10*8
2.0xlO"10
4.9xlO"8
3.9xlO"10
6.5xlO"6
4.9xlO"6
2.0x10*8
— P
4!3xlO"10
-'Average power density is defined as the peak power density corrected for transmitting duty cycle
and antenna rotational duty cycle. Antenna duty cycle is assumed to be -22 dB.
-'Duty cycle of -30 dB assumed for transmitter.
C/Unidentified source.
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REFERENCES
1. Mathison, R.J., J.D. Smilley, and Y.S. Lawrence, Measurement Report
on Radar Operations in San Francisco, California and Vicinity,
June 1975-August 1975, OT/ITS Control Number 05150.
2. Janes, D.E., R.A. Tell, T.W. Athey, and N. N. Hankin, Radio-Frequency
Radiation Levels in Urban Areas, presented in Session AB-4A, Microwave
Measurements and Exposure Systems, Series on Biological Effects, USNC/URSI
Meeting, Amherst, MA, October 10-15, 1976.
3. Department of Labor Occupational Safety and Health Administration -
Title 29 Code of Federal Regulations 1926.54 and Title 29 Code of
Federal Regulations 1910.97.
10
CU. S. GOVERNMENT PRINTING OFFICE: 1977-784-886
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TECHNICAL REPORT DATA .
(Please read Instructions on the reverse before completing)
1. REPORT NO.
ORP-EAD 77-3
3. RECIPIENT'S ACCESSIONING.
4. TITLE AND SUBTITLE
An Analysis of Radar Exposure in the San Francisco
Area
5. REPORT DATE
March 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Richard A. Tell
8. PERFORMIf
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Radiation Programs
P.O. Box 15027
Las Vegas, Nevada 89114
1O. PROGRAM ELEMENT NC
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
13, TYPE OF REPORT
14, SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This renort provides an analysis of ambient microwave field intensities produced by
Sdar eauipmen? in thfs™ Francisco area. The original data on which this report
radar equipment in tne ort prepared by the Institute for Telecommunication
Sciences f TsfDeparmen? ofcl^rll, BoulLr, Colorado. System, characteristics
Heists site 1 1x10 5mW/m2 for the top 10 contributing radars at each location.
value! are generally equal to o? lower than commonly existing radio-frequency
from sSmlf in the broadcast service on the basis of past EPA measurements.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/GrOUJ
Radar, nonionizing radiation, microwave
exposure, field intensity
18. DISTRIBUTION STATEMENT
Release Unlimited
19. SECURITY CLASS (ThisReport)
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
22. PRICE
EPA Form 2220-1 (9-73)
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