NAT'L INST. OF STAND & TECH

AlllDb 3A723D

NBS

Publications

NBSIR 81-2225

Field Strength Measurements of

Speed Measuring Radar Units

R. C. Baird

R. L. Lewis

D. P. Kremer

S. B. Kilgore

NEW BOOK SHELF

Electromagnetic Fields Division

Center foi Electronics Division

Center for Electronics and Electrical Engineering

National Engineering Laboratory

U S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

Prepared by

Law Enforcement Standards Laboratory

Center for Consumer Product Technology

U S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

May 1981

QC

100

,U56

81-2225

1981

C,Z.

Prepared for National Highway Traffic Safety Administration

Department of Transportation

Washington, DC 20590

NATIONAL BUMMAV

OF FTANSAJU*

LI BEAST

JUL 2 0 1981

NBSIR 81-2225

FIELD STRENGTH MEASUREMENTS OF

SPEED MEASURING RADAR UNITS

/w/ R. C. Baird

R. L. Lewis

D. P. Kremer

S. B. Kilgore

Electromagnetic Fields Division

Center for Electronics Division

Center for Electronics and Electrical Engineering

National Engineering Laboratory

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

Prepared by

Law Enforcement Standards Laboratory

Center for Consumer Product Technology

U.S. Department of Commerce > National Bureau of Standards

Washington, DC 20234

May 1981

Prepared for National Highway Traffic Safety Administration

Department of Transportation

Washington, DC 20590

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
*u •

' X i’ . •»* « u

W »r r* 1 i

i

*

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ACKNOWLEDGMENTS

This report was prepared by the Law Enforcement Standards Laboratory of

the National Bureau of Standards under the direction of Marshall J. Treado,

Manager, Communications Systems Program and Lawrence K. Eliason, Chief of

LESL. Dr. R. C. Baird directed the experimental measurement program which

was carried out by R. L. Lev/is and D. P. Kremer during the task 1 free-space

measurement portion, and S. B. Kilgore during the task 2 vehicular

measurement portion. A. C. Newell also assisted in the development of the

measurement techniques. This project was sponsored by the National Highway

Traffic Safety Administration, Department of Transportation, under

Interagency Agreement DOT-IIS--7-01697 . The assistance of Ronald Engle and

Dr. James Frank, NHTSA Contract Technical Monitors, is gratefully

acknowledged

.

Foreword

The National Highway Traffic Safety Administration (NUTSA) is engaged in

a continuing effort to fulfill the objectives of the Highway Safety Act of

1968. Accordingly, NHTSA has a particular interest in devices used for

measuring vehicle speeds for law enforcement purposes. In August 1977 the

NHTSA entered into an interagency agreement, DOT-HS-7-01697 , with the

National Bureau of Standards (MBS) for the purpose of developing performance

standards and a qualified product list of speed measuring devices used for

law enforcement purposes.

Modification 7 to the interagency agreement, initiated in July 1979,

provided for the measurement of the strength of microwave fields surrounding

typical speed measuring radar devices, both in free space and in a typical

working environment. This research and testing has been performed by the

personnel of the Electromagnetic Fields Division under the cognizance of the

Law Enforcement Standards Laboratory (LESL) of NBS. The results are

included in this document.

Among the tasks performed by the LESL for the NHTSA is the preparation

of technical reports on the results of research and testing. This document

is one such report. Technical comments and suggestions are invited from

interested parties. They may be addressed to the authors, or to the

undersigned at the National Bureau of Standards, Washington, DC 20234.

Lawrence K. Eliason, Chief

Law Enforcement Standards Laboratory

iii
, . "
Contents

Page

Foreword 111

1. Introduction 1

2. Task 1 Measurements 2

2.1 General Approach ..... 2

2 . 2 Description of Measurement 3

2.3 Calibration of Measurement System 4 2.4 Measurement Procedures and Results 7

3. Task 2 Measurements 9

3.1 General Approach 9

3.2 Probes Used for the Vehicular Measurements 9

3.3 Measurement Procedures and Results 11

4. Discussion of Measurement Results for Tasks 1 and 2 15

5. Power Density Graphic Displays 16

Appendix A—References 59

v
; * .
FIELD STRENGTH MEASUREMENTS OF SPEED MEASURING RADAR UNITS

R. C. Baird, R. K. Lewis, D. P. Kremer , S. B. Kilgore*

National Bureau of Standards

Washington, DC 20234

The objective of this project was to measure the

microwave radiation emitted by speed measuring radar units to

obtain a data base for evaluating the potential radiation

hazards of these devices. Measurements were taken both in

free-space and with the radar units mounted in typical

operating positions inside or attached to a four-door sedan.

The free-space measurements were made at four different

distances to determine the field strength as a function of

distance from the radar units. Calibrated radiation level

probes were used to measure the field strength inside the

automobile and scan the interior volume of the four-door sedan

with particular attention to the driver and passenger

locations. Twenty-two radar units were involved, and the data

are presented in a power density format.

Key words: Doppler radar; field intensity; hazard; microwave

radiation; power density; radar unit; radiation level; speed

measuring radar.

1 . INTRODUCTION

The objective of this project was to accurately measure the microwave

radiation emitted by speed measuring radar units in order to obtain a data

base for evaluating the potential radiation hazards of such devices. To

meet this objective, the following two measurement tasks were undertaken.

Task 1. Free-Space Measurements : Direct measurements of the field strength

levels surrounding 20 different radar units were made in the laboratory

under approximate free-space conditions. In order to obtain data in the

side- and back-lobe regions as well as in the direction of the main beam,

measurements were made at selected points on an imaginary spherical surface

centered at the aperture of the radar unit. Further, measurements were made

at several distances in order to determine the field strength as a function

of distance from the radar units.

Task 2. Vehicular Measurements : The radar units were mounted inside or

attached to a four-door sedan in normal operational configurations.

Calibrated radiation level probes were used to measure the field strength

inside the automobile and to scan the entire interior volume of the vehicle,

with particular attention to the driver and passenger locations. This task

provided data on field strengths inside the automobile under simulated

operating conditions.

*Electromagnetic Fields Division, Center for Electronics and Electrical

Engineering.

1
2. TASK 1 MEASUREMENTS

2.1 General Approach

The purpose of this task was to measure the field intensity in the

region surrounding each radar unit and to determine and display the power

density as a function of direction and distance from the radar. The

measurements were performed at the National Bureau of Standards (NBS) nearfield scanning facility employing standard antenna measurement techniques.

The experimental arrangement and coordinate system are shown in figure

1. The radar was mounted on a model mount aimed at a small receiving

antenna (probe) , and aligned so that the aperture was in the x-y plane and

the direction of the main beam was along the z-axis which coincided with the

axis of the receiving probe. The radar was then rotated (scanned) a full

360° about the y-axis (0 rotation) and the received signal was recorded

at 5° intervals in 0. Next, the radar was rotated by 10° about its own axis

(<J> rotation) and the 0 scan was repeated. (Note that, as shown in figure 1,

the <j> -rotation axis coincides with the z axis for 0=0.) This process of

stepping in <J> and scanning in 0 was repeated until data had been obtained

over the entire measurement sphere enclosing the radar. The complete

process was repeated for several separation distances, d.

y

Figure 1. Experimental setup used for measuring electromagnetic

field strength in the vicinity of speed radar units.
The received power, P R, picked up by the probe was determined by means

of a calibrated receiving system. The power density, W, incident on the

receiving probe, was determined from the relation

A

2 G

In this equation, G is the gain of the probe and A is the free-space

wavelength of the energy emitted by the radar unit [1]

1 .

2.2 Description of Measurement System

The measurement system is shown schematically in figure 2 as connected

for power-density measurements. The signal generator, rotary-vane

attenuator (RVA) , thermistor, and power meter were only used in the

calibration process to be described later. The rest of the system

functioned as follows. The electromagnetic (EM) field emitted by the radar

was sampled by a small probe antenna. The probe output signal was detected

in the mixer and amplified and measured in the receiver. Finally, the

amplitude was digitized and recorded on magnetic tape for later computer

processing. A coaxial mixer was used for the X-Band measurements and a waveguide mixer was used at K-Band. The receiver used was a calibrated,

three -channe 1 , wide-band, phase-amplitude model.

Figure 2. Schematic diagram of measurement system used to determine

power density. As shown here, the system is connected

for measuring the probe output produced by an incident

electromagnetic field. The auxiliary antenna and

circuit provide a stable reference signal to which the

receiver is phase locked. A 1 mV7 calibrating signal

is established at point A by means of the calibrated

thermistor, power meter, and rotary-vane attenuator

(RVA)

.

1 Numbers in brackets refer to references in appendix A.

3
In order for the receiver to have sufficient sensitivity to detect the

weak signals existing in the side- and back-lobe regions, it must be phase

locked to the radar. Since it was not feasible to connect a cable to the

radar, the phase-lock signal was provided by means of an auxiliary antenna

and mixer which responded to the side-lobe energy radiated by the radar and

provided a constant signal for phase locking the receiver. Note that the

auxiliary antenna and mixer were mounted on the rotator (fig. 1) so that, as the radar was rotated in azimuth (0), the relative positions of the radar

and auxiliary antenna remained unchanged and the phase-lock signal remained

constant within +1.0 dB. As the radar was rotated in changes of as much

as +3 dB in the amplitude of the phase-lock signals were observed, due

mainTy to the change in polarization. However, the receiver remained locked

during these changes and, since the data were recorded only during 0 scans

with constant 4>, these changes of amplitude in the locking signal were of no

consequence. The auxiliary antenna was mounted below the probe and well out

of the main beam, so there was no significant interaction between them; that

is, the auxiliary antenna did not noticeably perturb the field measured by

the probe.

The auxiliary antenna used for the X-Band measurements was a broadband

conical spiral with Type N connector and it was connected to a coaxial

mixer. The K-Band auxiliary system consisted of a standard gain horn and

waveguide mixer.

2.3 Calibration of Measurement System

2.3.1 Calibration Procedure

Absolute calibration of the power density measurement equipment was

accomplished by means of the signal generator, attenuator, thermistor, and

power meter of figure 2. The signal generator provided a calibrating signal

of constant amplitude and frequency. The power of this signal at point A

was measured by the calibrated thermistor and power meter combination, and

accurate changes in this power level were accomplished by means of the RVA.

The procedure for carrying out the calibration was as follows.

The radar was set at 0=0 and <j>=0 , in which case the probe measures

the power in the main beam and the probe output signal was near a maximum

for that distance. Under these conditions the receiver amplitude was set at

00.00 dB. Next, the signal generator frequency was set equal to the radar

frequency and, with the RVA set at 0 dB, the signal generator amplitude was

adjusted so that the power meter indicated 1 mW. This means that 1 mW of

power was available at A if the thermistor and power meter had been

calibrated correctly and all mismatch effects taken into consideration.

The next step was to disconnect the auxiliary mixer from the auxiliary

antenna and connect the mixer to the signal generator as shown in figure 3.

This link provided the required phase-lock signal for the receiver. The

transmission line connecting the RVA to the thermistor was disconnected at A

and connected to the primary mixer at B in place of the probe (see fig. 3)

Following these connections, the RVA was adjusted until the receiver again

read approximately 00.00 dB. The attenuator reading was noted, along with

the offset from zero on the receiver. Finally, the circuits were

reconnected as in figure 2 to make sure that no significant drift occurred

during the calibration.

The above procedure determined the output power from the probe at B with

respect to 1 mW. In other words, if the final RVA setting was K dB and the

receiver offset was L dB, then the probe output signal would be (K+L) dB

below 1 mW. Eq (1) can then be used to calculate the incident on-axis power

density, and the power densities at all other points are known since they

were measured with respect to the on-axis value.

4
Mixer

Figure 3. Schematic diagram of measurement system as it is

connected for calibrating the probe output signal.

The 1 mW calibrating signal is inserted at B and

compared with the signal produced by the probe

antenna (see sec. 2,3.1 for details).

This calibration procedure was repeated at every measurement distance

used for each radar.

2.3.2 Estimated Measurement Accuracy

According to eq (1) , the accuracy of the measured power density depends

on how accurately the received power is determined by the calibration

procedure of the preceding section, and on how well Gp, the gain of the

probe, is known. The accuracy of the PR calibration depends, in turn, on the

accuracies of the attenuator, thermistor, power meter, and receiver. An

additional factor is the degree of repeatability associated with the

disconnection and connection of the transmission lines and probe at points A

and B of figures 2 and 3. Any amplitude drifts in system components or in

the radar itself will also affect the repeatability.

The RVA is a calibrated, precision laboratory standard with an uncertainty of less than +0.02 dB over the range 0 to 20 dB used for these

measurements. The thermistor mounts were calibrated to account for mismatch

effects, loss due to absorption within the mount but not in the thermistor

elements, and the dc-to-microwave substitution error. The estimated

uncertainty associated with the thermistor mount is +0.06 dB, and the

uncertainty of the power meter used with the thermistor mount is +0.13 dB.

The uncertainty due to non-linearity of the receiver is +0.04 dB.

The repeatability error was determined by repeating the procedure of

section 2.3.1 and observing any variations in the attenuator setting and

receiver readings. The final receiver reading, following reconnection of

the probe, was especially significant for indicating drift and flange

5
connection errors. The uncertainty due to non-repeatability was estimated

to be +0.20 dB.

The theoretical gain value of each probe at the frequency of interest

was used. These values are:

X-Band (10.53 GHz) 16.7 dB+0.3 dB

K-Band (24.15 GHz) 6.7 dB+0.3 dB

These gains could have been determined to within +0.1 dB by careful

calibration, but it was not considered worth the added effort and expense in

view of the other errors associated with the measurement. In addition,

there is undoubtedly some variation in the output of different radar units

of the same model, so there is not much to be gained by testing a particular

radar to such accuracy. A near-zone gain correction for the X-Band probe

was required at the closest separation distance and has been included in the

calculations

.

The errors associated with these measurements are summarized below:

Uncertainty

Source of error (in decibels)

Rotary-vane attenuator +0.02 dB

Thermistor mount +0.06 dB

Power meter +0.13 dB

Receiver non-linearity +0.04 dB

Connector repeatability and system drift +0.30 dB

Uncorrected mismatch error +0.10 dB

Probe antenna gain +0.30 dB

Total error sum: +0.95 dB

The listed errors are approximate worst-case values and, since the errors

are uncorrelated, the sum represents a conservative estimate for the total

error

.

Although an estimated error approaching +1 dB may seem rather high, it

should be noted that radiated power density Ts a particularly difficult

parameter to measure with high accuracy because of the many variables and

precise calibrations involved. In this case, the two largest sources of

error were associated with the gain of the probe antenna and with connector

repeatability and system drift. As has already been mentioned, the gain

uncertainty could be reduced to +0.10 dB by careful calibration, and the

repeatability could probably be improved to 0.10 to 0.15 dB through the use

of precision connectors. These improvements would result in an overall

error of approximately +0.5 dB, which is about the best one could expect.

However, considering the variability that exists among radar units of the

same type and the variable effects of the immediate operational radar

environment on the radiated field strength, the approximate +0.3 dB

improvement in accuracy did not justify the use of the more expensive and

time-consuming techniques required to achieve it.

6
2.4 Measurement Procedures and Results

2.4.1 Alignment and Measurements

The mounting arrangement is shown in figure 4. A ring mount was

constructed which clamped to the radar being measured. The ring mount was

attached to a tilt plate which was, in turn, attached to a translation

plate. The translation plate was bolted to the model mount. A handgun is

shown mounted in figure 4, but the same basic arrangement was used for all

the radars tested. Care was taken to assure that the radar aperture was

always well in front of the metal mounting ring to minimize perturbation of

the pattern by the mount.

Translation

Figure 4 . Mounting arrangement used to support radars so that

they could be properly aligned for radiated power

density measurements.

Although mechanical, optical, and electrical techniques for antenna

alignment were employed, the final test involved only electrical

measurements of the fields emitted by the test antenna. Proven methods were

used for the precise alignment of each radar. The objective was to assure

that the radar axis coincided with the 4> rotation axis of the model mount

and that for 0=0, the axes of the probe, radar, and model mount were all

coincident with the z-axis of the coordinate system of figure 1. Once this

was accomplished, the z-position of the radar was adjusted slightly by

moving the model mount with respect to the azimuth rotator until rotation in

8 produced minimal phase variations. This adjustment was done to place the

rotation axis at the phase center of the radar.

After the alignment was completed, a set of data was obtained by

rotating the radar 360° about the 0 axis, recording the field strength at 5°

intervals in 0 , and repeating the process for 10° increments in 4> until the

entire sphere was scanned. This procedure yielded data along the 10°

meridians of a sphere.

7
The total power density is the sum of the power densities associated

with two orthogonal field components. Therefore, at each measurement

distance, two complete scans must be performed, one for each component.

Since the probes were linearly polarized, they were oriented to respond to

the vertical component for one scan and then rotated 90° to respond to the

horizontal component for the second scan. The entire process was carried out

at four distances for each radar, the distances being 1, 3, 6, and 12 ft

(30, 91, 183, and 366 cm) for the X-Band radars and 1, 3, 6, and 10 ft (30,

91, 183, and 305 cm) for the K-Band radars. The largest K-Band distance was

restricted to 10 ft (305 cm) because the probe assembly was longer than the

X-Band probe and the overall distance available was limited by the length of

the rails on which the rotator was mounted. At the shortest distance, 12 in

(30 cm) , the rotation about the 6 axis was limited to the range -135° to

+135° in order to avoid hitting the probe antenna with the rear of the model

tower

.

2.4.2 Results

The power density values were obtained as follows. Results of the

calibration procedures described in section 2.3.1 were analyzed and used to

calculate the received power at the on-axis reference point, which we shall

call P^. The values of Pr obtained during the scanning process were measured

relative to this on-axis value. Once P^ had been calculated, the received

power in mW at each measurement point was determined and the corresponding

incident power density was then calculated by eq (1) , for each point. The

power densities for each component were summed to give the total power

density at each point. These calculations were performed using the NBS

computing facilities, and one of a variety of plotting routines was selected

to display the results in graphical form.

In order to determine the symmetry of typical radiation patterns,

contour plots like that in figure 10 (see sec. 5) were generated for

selected radars. Note that the beam possesses circular symmetry down to

about 23.4 dB below the peak (42 dB below 1 mW/cm 2 ). This symmetry is

typical of all the radars tested. Because of the uniformity between radar

units, it was decided not to provide contour plots for each distance for 20

radars

.

A graphical display which presents the power density information in a more useful form is the polar coordinate format used in figures 11 through

50. These graphs display the power density in mW/cm2 or dB with respect to

1 mW/cm2 as functions of the angle off axis and the distance from the radar.

Each figure has four curves, one for each measurement distance, and figures

were prepared for both the vertical (elevation) and horizontal (azimuth)

pattern cuts in order to display the effects of any significant asymmetries

which might exist. The vertical and horizontal planes are defined with

respect to the radars when mounted in their normal upright configurations

and pointed horizontally as in figure 1. The horizontal and vertical cuts

correspond to 4> =0 and 90° , respectively* In each figure the origin

corresponds to a power density of 10"5 mw/cin 2. The power density in dB

corresponding to a particular distance and elevation or azimuth angle (equal

to 6 for these principal plane cuts) is proportional to the length of the

radius vector from the origin to the point selected on the particular

distance curve. Therefore, the inner curve represents the smallest power

density and is for the largest distance from the radar. The strongest

fields are associated with the closest distance 12 in (30 cm) and are

plotted on the outer curve. This format provides a good visual

representation of the field patterns as viewed by an operator positioned

behind the radar and looking in the direction the radar is aimed.

The nomenclature used to identify the radars (X-l, K-l, etc.) is

identical to that used in task 2 so that results between tasks may be

compared if desired. Fourteen X-Band and six K-Band radar units were tested

during task 1 and 15 X-Band and seven K-Band radar units were tested during

task 2

.

8
3. TASK 2 MEASUREMENTS

3.1 General Approach

Since speed radar units are usually mounted on or inside an automobile,

a complete investigation of microwave radiation levels requires that

measurements be made inside the automobile under normal operating

conditions. By this means it is possible to observe any field enhancement

effects produced by the automobile enclosure. Each of the 22 radar units

tested was mounted in the positions in which it is normally used, and

calibrated field probes were used to measure the power density (mW/cm ) throughout the interior of the car, paying particular attention to regions

where the head and groin would be located.

3.2 Probes Used for the Vehicular Measurements

Two different probes were used for these measurements. An NBS Model

EDM-1C Electric Energy Density Meter was used for the measurements involving

the X-Band (10.525 GHz) radars. This NBS probe does not operate above XBand, so a commerical Electromagnetic Radiation Monitor was used for the KBand (24.15 GHz) measurements. The sensor antennas in both probes consisted

of three orthogonal dipoles in order to achieve isotropic response patterns.

The measurements are, therefore, quite insensitive to the orientation of the

probe with respect to the field being measured, as long as the probe handle

is not pointed toward the radiation source. The NBS probe uses diodes for

the detecting elements, while the commerical unit employs thermocouples.

Consequently, the NBS probe has greater sensitivity; its threshold response

being 0,001 mW/cm2

. With the commerical meter, the minimum detectable power

density was 0.01 mW/cm 2

. Both probes make use of high-resistance leads

between the sensor and metering unit to eliminate pickup by the leads which

would generate an error signal.

The meters were calibrated by the free-space standard-field method which

is illustrated in figure 5. The power density, W, at a point on the

transmitting axis at a distance d from the standard gain horn is given by

where PT

is the net power delivered to the horn and G is the effective gain

of the horn. The gain was determined in advance [2] and PT and d were

measured as part of the calibration procedure. The incident power Pi and

reflected power P r were monitored with the coupler sidearms, and PT = P^-Pr . When W had been determined at a particular point, the probe being calibrated

was placed at this same point in the known field and a probe correction

factor was obtained from the ratio of the actual power density to the

indicated power density.

The error in the basic calibration was estimated to be +0.5 dB (12%).

However, in actual use, additional uncertainties arose due to such things as

multipath effects, perturbation of the field by the operator, and the fact

that the probe was calibrated in a plane-wave field but was used in a more

complex field configuration. Taking all of these factors into consideration

resulted in an estimated overall measurement uncertainty of +1.0 dB (25%).

Although it may seem rather high, a +1.0 dB uncertainty Is very good for

electromagnetic field measurements performed in such a complicated

electromagnetic environment.

9
CO

10

Figure

5.

Diagram

of

the

basic

experimental

arrangement

required

for

the

free-space

standard-field

method

of

calibrating

microwave

hazard

meters.
3.3 Measurement Procedures and Results

Prior to making measurements inside the automobile, the power density in

the main beam, close to the aperture, was determined by holding the probe

directly in front of the aperture as shown in figure 6. These results are

listed in column 2 of table 1. The maximum power density radiated to the

sides and rear of each unit was also determined by moving the probe over the

surface of the unit as shown in figure 7 and observing the maximum

indication. These values are listed in column 3 of table 1.

Following the above tests, the radars were mounted in, on, or hand-held

in a four-door sedan in the various operating positions indicated by the

numbers in figure 8. In positions 1 and 2, the radars were hand-held and

aimed through the windshield. Position 5 is the common dashboard mount with

the radar aimed forward (fig. 9a) , and 5R is the same arrangement with the

radar aimed to the rear through the back window (fig. 9b). In positions 6

and 7 the radars were hand-held and aimed out the left and right front side

windows, respectively. For position 3, the radar was attached to the inside

of the right rear window and aimed forward through the windshield while, in

position 4 , the radar, was attached outside the left rear window and aimed

forward. In position 8, the radar was aimed to the rear through the back

window

.

Each radar unit was mounted in each of the positions in which it was

designed to operate, as indicated in column 4 of table 1. With the radar in

each position, the appropriate hazard probe was used to survey the field

intensity throughout the interior of the automobile. The maximum power

densities observed in the general regions occupied by the driver and three

passengers (locations A through D of fig. 8) are given in table 1, columns

5-8. These recorded values represent the maximum levels observed, that is,

there were no values of higher radiation intensity in locations other than

those whose power density values are listed in table 1.

Figure 6. Measurement of main-beam

power density in the

aperture region

.

Figure 7. Measurement of radiation

in the side- and backlobe regions.

11
Table 1. Results of vehicular power density measurements.

This table contains results of measurements of field intensities

produced by the various radar units inside an automobile. The radar code

numbers are given in the first column, with the K-Band units (24.15 GHz)

designated by K-l to K-7 and the X-Band units (10.525 GHz) by X-l to X-15.

Column 2 gives the power density in the aperture, and column 3 the maximum

power density in the back hemisphere. The mounting positions of column 4 correspond to the numbered positions of figure 8 as described in the text.

The interior vehicular data are given in columns 5 to 8 . Blank entries in

these columns mean that the field intensities were too low to read with the

meters used for these tests; i.e., the fields were <0.01 mW/cm2 for K-Band

and <0.001 mW/cmz for X-Band.

Maximum Maximum power density at positions

Aperture back-lobe A, B , C , and D of figure 8 Radar power power Radar (mVJ/cm 2

) code density density

(mW/cm^)

mounting

number (mW/cm position 2

) A B C D

K-l 1.97 <0.01 5

8 K-2 2.40 0.02 1

2

55Ra 0.01 0.01

8 K-3 2.27 <0.01 1

2

5 K-4 1.83 <0.01 1

2

5 K-5 0.25 <0.01 1

2

55R a

K-6 2.78 0.02 1

2

5 K-7 1.64 <0.01 1

2

5 X-l 0.55 <0.001 1 0.001

2

3 0.137 0.001 0.002 0.002

4 0.001

X-2 0.73 0.001 1 0.001 0.001

2

3 0.36 0.003 0.001 0.001

4 0.002

X-3 2.82 0.018 1 0.002 0.003 0.001

2 0.001 0.021 0.001 0.001

5 0.002 0.001 0.001

X-4 2.55 0.018 1 0.002 0.001 0.001

2 0.001 0.003 0.001 0.001

5 0.001 0.001 0.001

X-5 0.36 0.001 1

2

5 12
Table 1. Results of vehicular power density measurements (Continued)

Maximum Maximum power density at positions

Aperture back-lobe A, B , C, and D of figure 8 Radar power power Radar (mW/cm 2

) code density density mounting

number (mW/cm 2

) (mW/cm*

)

position A BCD

X-6 1.19 0.002 1

2

5

6

7 0.001

X-7 1.10 0.004 1 0.001

7

O 0.002 0.001

6 0.001 0.002

5 0.001 0.001

X-8 0.89 0.002 1

X-9 0.96

X-10 1.76

X-ll 0.46

X-12 0.59

X-13 0.93

0.004

0.008

0.001

0.005

0.003

1

7

2

6

1

7

2

6

5

1

7

26

5

5

1

2

5

67

0.001

0.001

0.001

0.001

0.001

X-14 0.48 0.001 1

2

5

6

7 X-15 2.29 0.018 1

25

6 0.002

7 0.002

Si Same location as radar mounting position 5 except that the radar is pointed

toward the rear of the vehicle.

13
ANGLES (in degrees)

e =50

<t> = 21

a =62

i/i =37

FRONT

Numbers are radar mounting positions.

Letters are seat positions.

Figure 8. Diagram showing the location of radar mounting

positions (1-8) , seat locations (A-D) , and

distances between selected radar positions and

seat locations used in describing field

intensity distributions inside the automobile.

14
a) k)

Figure 9. Typical dashboard mounting arrangement:

a) shows the radar pointing forward, and b)

shows the radar aimed to the rear through the

back window.

4. DISCUSSION OF MEASUREMENT RESULTS FOR TASKS 1 AND 2

It is not the purpose of this report to state what levels of

electromagnetic fields constitute a health hazard. Such issues are left to

those organizations and committees that have been established to perform and

interpret research on the biological effects of electromagnetic waves and to

set exposure limits based on the results of such research.

From the graphs of figures 11 through 50 one can obtain the expected

power density in any desired region of space. For example, from the

horizontal cut for X-l (fig. 11) , it is evident that, for distances greater

than ^2 in (30 cm) and for all angles, the power density is less than 0.2

mW/cm (-7 dB) . Another way of using the curves is to determine regions

where a specified power density such as 0.1 mW/cm 2 is not exceeded. From

figure 11, it is clear that the power density is less than 0.1 mW/cm 2 (-10

dB) at all angles for distances greater than about 36 in (91 cm) and also

for distances greater than 12 in (30 cm) if the angle is greater than

approximately +10° off axis. Similar determinations can be done for the

other radars using the appropriate graphs.

Section 1910.97 of the Occupational Safety and Health Act (OSHA)

contains a Radiation Protection Guide (RPG) which applies to exposure to

electromagnetic radiation at various frequencies. At frequencies of 10 MHz

to 100 GHz, the RPG allows exposure up to a power density of 10 mW/cm 2 over

any 0.1-h period, or up to a power density of 10 mW/cm 2 averaged over any

0.1-h period or more. Concurrently, a voluntary Radio Frequency Protection

Guide of 5 mW/cm2 for the 1500 MHz to 100 GHz frequency range is under

consideration for adoption by the American National Standards Institute.

Whether the power density exposure limit remains at 10 mW/cm 2 or is lowered

to 5 mW/cm 2

, the power densities measured at a 12 in (30 cm) distance from

the radars did not exceed either limit, even if operated continuously. The

I
K-Band radars tended toward higher powers and, since the antennas had more

gain than the X-Band antennas, it was not surprising to observe that the

power densities were generally higher for most K-Band units.

2 In fact, all

except K-5 had on-axis power densities of approximately 1 mW/cm at the 12

in (30 cm) distance. For comparison, the U.S.S.R. defines safe exposure

limits at 10 yW/cm 2 for a whole working day or exposure for not more than 15

or 20 min a day at 1 mW/cm 2 while wearing goggles [3].

The aperture power density for most of the units, measured in task 2 (col. 2 of table 1) is a significant fraction (25 to 50%) of the existing or proposed maximum permissible exposure levels. Based on the back-lobe data

(col. 3 of table 1) , one can conclude that all units are well-designed and

packaged to provide shielding from leakage and back radiation. There was

not a single case of reverse-hemisphere radiation of sufficient intensity to

cause concern. In most cases, the power densities were *

, or less, of

the exposure limit presently specified in the OSHA guide. 0 0

The data in columns 5 to 8 of table 1 indicate that the field levels

inside the car do not exceed 0.002 mW/cm2 for most radar positions. The

major exception occurs in the data for X-l and X-2 which show relatively

strong fields at location A when the radar is mounted in position 3. This

is to be expected since location A, the front seat passenger position, is

directly in the main beam for this situation. Note, however, that the field

strength recorded at the driver location is still low.

5. POWER DENSITY GRAPHIC DISPLAYS

The radiation pattern contour plot and power density polar coordinate

plots discussed earlier (figs. 11-50) are grouped in this section for the

convenience of the reader.

16
Figure 10. Power density contours for Radar X-4 at a distance of

2.1 m (82.5 in) from the antenna aperture. The view

directly toward the radar. Numerical values of the

contour lines indicate the number of decibels below

1 mW/cm . The peak, on -axis value is -18.6 dB (0.014

mW/cm^) , and the contour interval is 6 dB. The

angular distance off axis is proportional to the

radial distance from the center of the figure.

17
Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 11. Horizontal power patterns for Radar X-l obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm 2

, or dB with respect

to 1 w.W/cm , as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

18
rt

tyyTtftn

'WttLWg

'

Hwaarff

‘uo

»i

<wi

»tr»

VERTICAL CUT POWER DENSITY, RADAR X-l

Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 12. Vertical power patterns for Radar X-l obtained at four

distances from the aperture. Each curve displays the

total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

19
*C5TJ

It.W.M

hH

14

KT. I

US

Dj

UBWU

HIM WM

6HIM

M

Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 13. Horizontal power patterns for Radar -X-2 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cra2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

20
Kofi

—

incs

ai

it

Act.

ms

—

rawnemc

bissm

<&

ry

Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 14. Vertical power patterns for Radar X-2 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction of

the main beam.

I

I 21
i

t»

hvmiq

m

w

ffft

'

amt-w

—dm

•»»

ti

a»

with

»

lo-w

Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 15. Horizontal power patterns for Radar X-4 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm* , as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

22
Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 16 . Vertical power patterns for Radar X-4 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction of

the main beam.

23
Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 17. Horizontal power patterns for Radar X-5 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees with the direction of the main

beam.

24
Figure 18. Vertical power patterns for Radar X-5 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cra2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

25
Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 19. Horizontal power patterns for Radar X-6 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

26
Distances From Radar (Inches): A = 144, B = 72, C = 36, D - 12

Figure 20. Vertical power patterns for Radar X-6 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

27
Figure 21. Horizontal power patterns for Radar X-7 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cnr* , as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

28
Figure 22

.

Vertical power patterns for Radar X-7 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm* , as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

29
n'amw

atcn

tuck

Distances From Radar (Inches) : A 144, B 72, C 36, D 12

Figure 23. Horizontal power patterns for Radar X-8 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

30
Figure 24. Vertical power patterns for Radar X-8 obtained at four

distances from the aperture. Each curve displays the

total power density in mW/cm2

, or dB with respect to

1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction of

the main beam.

31
Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 25. Horizontal power patterns for Radar X-9 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

32
Figure 26. Vertical power patterns for Radar X-9 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cirr , as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

33
Figure 27. Horizontal power patterns for Radar X-10 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

34
Figure 28. Vertical power patterns for Radar X-10 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/crn2

, or dB with respect

to 1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

35
Figure 29. Horizontal power patterns for Radar X-ll obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2 , as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

36
Figure 30. Vertical power patterns for Radar X-ll obtained at

four distances from the aperture. F.ach curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

37
Distances From Radar (Inches): A - 144, B - 72, C - 36, D - 12

Figure 31. Horizontal power patterns for Radar X-12 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction of

the main beam.

38
Figure 32. Vertical power patterns for Radar

four distances from the aperture,

the total power density in mW/cm2

to 1 mW/cm2

, as a function of the

degrees. Zero degrees coincides

of the main beam.

X-12 obtained at

Each curve displays

, or dB with respect

elevation angle in

with the direction

39
Figure 33. Horizontal power patterns for Radar X-13 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction of

the main beam.

40
Figure 34

.

Vertical power patterns for Radar X-13 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the elevation angle

in degrees. Zero degrees coincides with the direction

in the main beam.

41
E'igure 35. Horizontal power patterns for Radar X-14 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction of

the main beam.

42
f

Figure 36. Vertical power patterns for Radar X-14 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the elevation angle in

degrees . Zero degrees coincides with the direction

of the main beam.

43
Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 37. Horizontal power patterns for Radar X-15 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm 2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

44
Distances From Radar (Inches): A = 144, B = 72, C = 36, D = 12

Figure 38. Vertical power patterns for Radar X-15 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

45
Figure 39. Horizontal power patterns for Radar K-l obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

46
Figure 40. Vertical power patterns for Radar K-l obtained at four

distances from the aperture. Each curve displays the

total power density in mW/cm2

, or dB with respect to

1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

47
Figure 41. Horizontal power patterns for Radar K-2 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

48
Figure 42. Vertical power patterns for Radar K-2 obtained at four

distances from the aperture. Each curve displays the

total power density in mW/cm2

, or dB with respect to

1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

49
.gure 43. Horizontal power patterns for Radar K-3 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

50
Figure 44. Vertical power patterns for Radar K-3 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm* , as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

51
Figure 45. Horizontal power patterns for Radar K-5 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction of

the main beam.

52
iv.ll.a

M

I

IK

Figure 46. Vertical power patterns for Radar K-5 obtained at four

distances from the aperture. Each curve displays the

total power density in mW/cm2

, or dB with respect to

1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction of

the main beam.

53
Figure 47. Horizontal power patterns for Radar K-7 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

54
Figure 48. Vertical power patterns for Radar K-7 obtained at four

distances from the aperture. Each curve displays the

total power density in mW/cm2

, or dB with respect to

1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

55
Figure 49. Horizontal power patterns for Radar K-8 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the azimuth angle in

degrees. Zero degrees coincides with the direction

of the main beam.

56
Figure 50. Vertical power patterns for Radar K-8 obtained at

four distances from the aperture. Each curve displays

the total power density in mW/cm2

, or dB with respect

to 1 mW/cm2

, as a function of the elevation angle in

degrees. Zero degrees coincides with the direction

of the main beam.

57
'

1

•

' >v •
Appendix A—References

[1] Silver* S. Microwave antenna theory and design. New York* NY: McGrawHill; 1949. 1-4.

[2] Newell* A. C. ; Baird* R. C. ; Hacker* P. F. Accurate measurement of

antenna gain and polarization at reduced distances by an extrapolation

technique. IEEE transactions on antennas and propagation. AP-21(4):

419-431; 1973 July.

[3] Baranski* S.; Czerski* P. Biological effects of microwaves.

Stroudsburg* PA: Dowden* Hutchinson and Ross* Inc.; 1976. 177.

59
U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report NoJ 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO.

SHEET (See instructions) NBSIR 81-2225 May 1981

4. TITLE AND SUBTITLE

Field Strength Measurements of Speed Measuring Radar Units

5. AUTHOR(S)

R. C. Baird, S. B. Kilgore, R. L. Lewis, D. P. Kremer

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No. DOT-HS-7-01697

8. Type of Report & Period Covered

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

National Highway Traffic Safety Administration

U.S. Department of Transportation

Washington, DC 20590

10.

SUPPLEMENTARY NOTES

Q2] Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here) The objective of this project was to measure the microwave

radiation emitted by speed measuring radar units to obtain a data base

for evaluating the potential radiation hazards of these devices.

Measurements were taken both in free-space and with the radar units

mounted in typical operating positions inside or attached to a fourdoor sedan. The free-space measurements were made at four different

distances to determine the field strength as a function of distance

from the radar units. Calibrated radiation level probes were used to

measure the field strength inside the automobile and scan the interior

volume of the four-door sedan with particular attention to the driver

and passenger locations. Twenty-two radar units were involved, and the

data are presented in a power density format.

12.

KEY WORDS (S/'x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Doppler radar; field intensity; hazard; microwave radiation; power

density; radar unit; radiation level; speed measuring radar.

13.

AVAILABILITY

| j Unlimited

[X] For Official Distribution. Do Not Release to NTIS

J Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

59

15. Price

USCOMM-DC 6043-P80

t4