Fine Positioning Three-Dimensional Electric-Field Measurement

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 56, NO. 3, MAY 2007 1295

Fine Positioning Three-Dimensional Electric-FieldMeasurements in Automotive Environments

Yoshiaki Tarusawa,Member, IEEE, Sadayuki Nishiki, and Toshio Nojima, Member, IEEE

AbstractA fine positioning system is introduced that measuresthe 3-D electric-field space distributions around passenger carsthat are equipped with cellular radio antennas. The measurementsystem, which is constructed of nonmetallic materials to reducethe electric-field fluctuation that is caused by the manipulator,uses an air-motor mechanism that yields a field sensor spatialresolution of better than 10 mm. The uncertainty of the measuredelectric-field strength is estimated as 4 dB, i.e., variations arewithin 4 dB. Detailed electric-field distributions inside and outsidethe passenger car are derived for three antennas: a trunk-lidantenna, rear-window antenna, and roof antenna. The measure-ment results show that the electric-field strengths in the front

and back seats are less than 30 V/m when the antenna input isless than 1 W as the net power. Inside the car, the local peakof the field strength is higher by 2 and 4 dB for the trunk lidand roof antenna, respectively, and approximately 10 dB higherfor the rear-window antenna. The electric fields both inside andoutside the car do not exceed the Level 4 (30 V/m) specifica-tion, which is one of the immunity levels for electronic devicesdefined in the IEC electromagnetic-compatibility standard. Inaddition, the measured electric-field strengths are lower than thereference levels for human exposure to RF electromagnetic fields,which are recommended by the International Commission on Non-Ionizing Radiation Protection. At maximum, the field strength of30 V/m as a specially averaged value at the frequency of 900 MHzcorresponds to half of the whole body specific-absorption-ratebasic restriction of 0.08 W/kg with respect to specifications for

the general public, when assuming conservative estimates for themaximum coupling between the human body and the field. Thedifferences in the far-field distributions of the three antennasoutside the car are also estimated.

Index TermsElectromagnetic compatibility (EMC), land mo-bile radio cellular system, mobile antennas, radiation safety.

I. INTRODUCTION

ONE SIGNIFICANT trend in the automotive industry is

the rapid replacement of mechanical control systems

with their electric equivalents. Such systems may allow new

applications that can reduce the risk of collision, minimize

personal injury, protect the environment, improve fuel econ-omy, implement automatic cruise control, achieve effective

traffic control, and enhance comfort [1]. They utilize advanced

Manuscript received April 9, 2003; revised December 18, 2003, December22, 2005, April 6, 2006, May 22, 2006, and June 20, 2006. This work wassupported in part by the NTT DoCoMo, Inc., Japan. The review of this paperwas coordinated by Dr. K. Dandekar.

Y. Tarusawa is with the NTT DoCoMo, Inc., Yokosuka 239-8536, Japan(e-mail: [email protected]).

S. Nishiki is with the DoCoMo Mobile, Inc., Tokyo 104-0053, Japan.T. Nojima is with Hokkaido University, Sapporo 060-0814, Japan.Color versions of one or more of the figures in this paper are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TVT.2007.895540

microprocessors, radar, high-speed ICs, and signal processing

chips.

On the other hand, the use of mobile phones has rapidly

expanded in our daily lives over the last decade. Mobile

communication systems have evolved from analog-to-digital

technology. Recent digital mobile communication systems aim

to handle many types of information, as well as provide two-

way voice links. In the near future, it is greatly anticipated that

digital mobile communication systems will be linked to new

automotive-technology applications.

The reliability of these electronic systems is paramount froma safety standpoint. They increase the need to ensure electro-

magnetic compatibility (EMC) with the environment in which

they operate. An electromagnetic field that is excited from a

car-mounted radio antenna is a potential source of interference

to the electric devices in the car. Moreover, compliance with

the safety guidelines for human exposure to RF electromagnetic

fields must be confirmed [2]. Therefore, a detailed examination

of the electric-field distributions inside and outside actual cars

that are equipped with mobile radio antennas is essential.

The National Bureau of Standards measured the electric-

field-strength levels of different types of vehicles exposed to

mobile radio transmitters operating at frequencies under the

400-MHz band and broadcast stations [3]. A handy field sensorheld by an engineer was used to measure the field-strength

level. The number of measurement points inside and outside

an actual car was around 15. This report provides some guid-

ance to manufacturers regarding the field-strength levels their

electronic systems may encounter and establish susceptibility

test bounds.

McCoy et al. [4] estimated the field strengths in an envi-

ronment comprising a compact car with a quarter wavelength

band antenna input of approximately 100 W at frequencies of

146 and 460 MHz. The electric-field data from 20 points were

measured along a straight line across the backseat headrests

of the car. The measurement results showed that the specificabsorption rate (SAR) in the backseat satisfied the basic FCC

safety limits. Chouet al. [5] derived the SAR distributions in

human models standing near trunk- and roof-mounted mobile

antennas for an 835-MHz cellular system. Tanaka [6] assessed

the internal electric-field distribution in a car body by using a

1/15 scale car. The wire grid method [7] and the finite difference

time domain (FDTD) technique [8] have been applied to esti-

mate radiation patterns of antennas for FM broadcast receivers

and cellular radio systems. None of these studies, however,

derived the 3-D electric-field distribution inside and outside an

actual car that is equipped with a cellular radio antenna using

frequencies above the 900-MHz band.

0018-9545/$25.00 2007 IEEE


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1296 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 56, NO. 3, MAY 2007

Fig. 1. Configuration of 3-D scanner for E-field measurements. (a) Rear view. (b) Side view.

Section II describes our 3-D scanner that measures the

electric-field distributions inside and outside actual cars. Mea-

surements are conducted for a 900-MHz band radio antenna for

cellular communications. Section III discusses the measured

results as well as the maximum electric-field strength and

compliance with the safety guidelines for human exposure to

RF electromagnetic fields.

II. MEASUREMENT S YSTEM

A. Basic Design of 3-D Scanner

The scanner comprises a main frame, a subframe, and tworails. It has R-, L-, and H-axes to move the field sensor in threedimensions, as shown in Fig. 1. The frames must minimize the

disturbance to the electric field to the greatest extent possible

while offering sufficient torsional rigidity so that the field

sensors can be precisely and repeatability positioned. Steel and

fiberglass reinforced plastic (FRP) frames are typically used to

provide sufficient torsional rigidity. However, we must consider

that these materials disturb the electric field. The electric-field

fluctuations caused by the FRP and steel frames are estimated

as follows.

Fig. 2 shows that in this estimation model, a plane wave

is incident to a rectangular column whose cross section is S(millimeter) square and T (millimeter) thick. The reflectionof the incident wave from the rectangular column causes an

electric-field fluctuation. The electric field around the rectan-

gular column is calculated by using the FDTD technique. This

calculation assumes that the relative dielectric constant and the

loss tangent are 4 and 0.04 for FRP, respectively. The resistivity

of steel is taken to be 0 m. Fig. 3(a) shows the calculated

results of the electric-field fluctuation Ethat is defined by

E =EE0

whereEis the electric field along the direction perpendicular to

the rectangular column, andE0 is the electric field without therectangular column in units of decibels, respectively. From the

Fig. 2. Model for estimating the electric-field fluctuation caused by a plane-wave incident to a square column. It is assumed that the column length isinfinite.

viewpoint of estimating the EMC, the values of the electric-

field amplitude are compared. The electric-field fluctuation

Edepends on the function of the distance from the columnsurface, as described hereafter.

The steel column yields an electric fluctuation of higher than

4 dB at distances shorter than 500 mm from the surface of the

column even if the section is 150 mm. On the other hand, thefluctuations caused by the FRP are approximately 2 dB at

the surface of the column even if the section is greater than

150 mm. Based on this comparison between the steel and FRP

columns, FRP is selected in this paper. In the actual measured

field, it is considered that both the antenna and the body of the

car work as the RF source. The field cannot only be described

by the perpendicular incidence of a TEM wave. To estimate

the field fluctuation in this situation, the field is calculated in

terms of parameters, i.e., the angles of incidence and frequency

values, as shown in Fig. 3(b). At the of 90 and of 90, thefluctuation is at the maximum value of 2 dB. Fig. 3(c) shows

that the fluctuation increases with an increase in the frequency

in the range from 0.5 to 2 GHz; however, a drastic change in thefield fluctuations due to resonant phenomena is not found.


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TARUSAWAet al.: FINE POSITIONING THREE-DIMENSIONAL ELECTRIC-FIELD MEASUREMENTS 1297

Fig. 3. Calculated electric-field fluctuation caused by the square column.(a) Distance dependence. (b) Incident-angle dependence of 300 300-mm FRPcolumn. (c) Frequency dependence of 300 300-mm FRP column.

In addition to the plane-wave analysis, the electric-field fluc-

tuation is also estimated with respect to the near field excitedfrom a half-wave dipole antenna. Fig. 4(a) shows the estimation

model that comprises the FRP column and the dipole antenna.

The dipole antenna is set to do, which is longer than 22 mm,because the minimum distance between the car body (or the car

mounted antenna) and the column is maintained to longer than

100 mm in the actual measurement described in Section III. In

addition, the elements of the dipole antenna are set parallel to

the column surface. Fig. 4(b) shows the electric-field fluctuation

Eas a parameter ofdo andd1 at the frequency of 900 MHz.The Evalue is defined by E E0, where E is the electricfield along the direction, as shown in Fig. 4(a), and E0 isthe electric field (in decibels) without the column. On the

dipole antenna, the boundary between the near field and farfield is approximately 53 mm if it can be calculated by /2.

Fig. 4. Electric-field fluctuation caused by the square column in the near andfar fields of a dipole antenna. (a) Estimation model. (b) Calculated electric-fieldfluctuation.

Fig. 4(b) shows the calculated results where the estimated

electric-field fluctuation is less than 1 dB in both near andfar fields of the dipole antenna. In addition, the electric-field

fluctuation is greater than that of the other angle of the dipole

elements against the column surface.

From these estimations, the FRP columns with a cross sec-

tion of 300 mm are used to construct the main frame, and

the positioning repeatability is better than 10 mm. The FRP

mainframe parameters are set toS= 300mm (each side) withT = 5 mm. The subframe basically comprises FRP materialwithSvalue of 150 mm.

B. Design of Mechanical Driving System and Data

Acquisition System

Fig. 5 shows the scanner. The main frame and the subframe

are basically constructed from the FRP and rigid plastics to

minimize the electric-field fluctuations. Two field sensors are

mounted on the subframe via a flexible rack that provides

R-axis movement. The same isotropic electric-field sensorthat has three shorted monopoles was used for each of the

field sensors, as described in Section II-C. The subframe is

linked to the main frame by a plastic rack-and-pinion gear

assembly. The flexible rack and the pinion on the subframe

are driven by air motors with the maximum power of 0.1 hp

and the maximum torque of 3 kg cm. Fig. 6(a) shows the

air motor driving the flexible rack of the subframe. The mainframe rolls along two steel rails (H-axis) using eight steel


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TABLE IMEASUREMENT-SYSTEMSPECIFICATIONS

Fig. 9. Error of used field sensor due to capacitive coupling with metal plate.(a) Test configuration. (b) Calculated and measured electric field.

generated from a horn antenna at the frequency of 900 MHz.

The calculation of the electric field assumes that the aluminum

plate is a perfect electric conductor and that a transmission line

model is used. Fig. 9(b) shows the measured and calculated

values of the electric-field strength. The difference between the

measured and calculated field strength is approximately 1.5 dB,

at the distance of 50 mm where the position of the field sensor

is as near as possible to the aluminum plate. The amplitude

component of the electric field is considered in order to estimate

the EMC. With respect to each axis of the field sensor, the same

difference is found.

The field sensor is used in the near- and far-field regionsof the antenna. The error due to the near field is estimated

Fig. 10. Error of used field sensor in the near field excited by the dipoleantenna.

from the experiment of the electric-field measurement for the

900-MHz half wavelength dipole antenna, as shown in Fig. 10.

The electric field is also calculated by using the wire gridmethod, assuming a sinusoidal current distribution along the

wire of the dipole. The measured electric field is 2 dB lower

than that of the calculated value, at the distance of 15 cm.

Based on these results, the errors of the field sensor in the

near metal surface and that in the near field of the antenna are

estimated within 2 dB. The resulting electric-field strength

yields an uncertainty of 4 dB, including the electric-field

fluctuation of 2 dB that is caused by the rectangular FRP

columns that are used to construct the 3-D scanner, and 2 dB

from the error of the field sensor in the near metal surface and

the near field of antenna, as summarized in Table I. The IEC

Standard 62209-1 that defines the SAR measurement method

based on the electric-field sensor analyzes the measurementuncertainty [9]. According to this standard, the uncertainty of


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2 dB due to the boundary effect has a rectangular distribution.

The uncertainty of1 dB of the field sensor for the far field has

a normal distribution. Therefore, the resulting uncertainty can

be estimated using the confidence interval, which is defined by

the uncertainty estimation in Section 7 of the IEC Standard.

The scanner and the test car are grounded and are far

from buildings and industrial plants. The car engine and allelectronic devices except the transmitter are shut down during

the measurements. While the actual cellular systems have the

transmission power levels of less than 2 W, these measurements

used an antenna input of 10 W to ensure adequate signal-to-

noise ratios given by the electric-field sensors that are used.

Since the antenna input, as net power input, is defined by the

forward power minus the reverse power at the antenna input

port, the forward power and the reverse power are measured

by using a directional coupler and power sensors. The VSWR

at the antenna input port is held to under 1.5 during the

measurement.

III. MEASUREMENTR ESULTS

Electric-field measurements are performed using a passenger

car, which is a 1993 MAZDA CAPELLA. Detailed electric-

field distributions are derived for the three antennas: trunk-lid

antenna, rear-window antenna, and roof antenna. The transmis-

sion frequency lies in the 900-MHz band. The value of the

field strength shown in the following measurement results is

normalized by the antenna input of 1 W because the antenna

input is typically on the order of the value for a mobile radio

unit of a cellular system, and it is easy to calculate the field

strength when the antenna input is arbitrary. The measured

electric-field strength in the following measurement results

shows the root mean square of each field component. Three-

dimensional field-strength data are acquired using the proposed

measurement system. The data show that the maximum field

strength exists on the plane, including the radiation center

of the antenna. Consequently, the xy, xz, and yz planes,including the radiation center of the antenna, are selected to

estimate the EMC requirements in the orthogonal coordinate

system.

This paper provides a set of measurements for the electric

field inside and outside a vehicle that is equipped with three

different antennas. Even if the measurement results show only

three specific configurations that are related to three possible

antenna installations on a particular car model, they can beuseful for general recommendations regarding the installation

of antennas on vehicles for EMC.

A. Trunk-Lid Antenna

The trunk lid is a popular place to mount radio antennas. A

vertical space-diversity antenna is located 40 cm from the top

rear edge of the trunk lid. This antenna comprises two sleeve

elements aligned along the vertical axis, as shown as the simple

single pole in [10, Fig. 5]. In this configuration, the upper sleeve

element is used as a transmission and reception port while the

lower sleeve element is used only as a reception port.

The distribution of the electric-field strength is representedas contours based on the orthogonal coordinate axes converted

Fig. 11. Measured electric-field strength of the trunk-lid antenna in the xzplane at y = 120cm.

from theR-,L-, andH-axes. Figs. 1113 show the distributionof the electric-field distribution inside and outside the car. In

this paper, the unit for electric-field strength is decibelvolt

per meter in addition to volt per meter. The value of 1 V/m

is converted to 0 dBV/m (decibelvolt per meter), and 10 V/m

is converted to 20 dBV/m, respectively. At any location, the

electric-field strength at any antenna input power can be eas-ily calculated from these measured results because the field

strength is proportional to the square root of the antenna input

power. When the electric-field sensor scans inside or outside

the car, the scanning area of the field sensor is limited to 10 cm

from the surface. Since the field strength could not be measured

closer than 10 cm from the surface, the contours were extrapo-

lated based on the first-order prediction method.

Inside the car, the maximum field strength is 5 V/m

(14 dBV/m) in the vicinity of the rear window, and the strengths

in the front seat and that on the instrument board are less than

2.5 V/m (8 dBV/m) when the antenna input is 1 W. The rear

window included a heating wire for a defogger, and the frontseats have a metal frame. It is possible that the measured field

strength includes error due to the effect of the near metal.

From the estimation of uncertainty as mentioned in the previous

section, if it is assumed that the uncertainty of the measurement

system is 4 dB, the maximum field strength is 8 V/m in the

vicinity of the rear window and less than 4 V/m in the front seat

and on the instrument board. The local peak of the electric field

is 2 and 4 dB higher in the front and rear seats, respectively. The

IEC Standard (61000-4-3) that defines test and measurement

techniques for electromagnetic fields designates four immunity

levels for digital mobile radios [11]. If an electronic device

passes the immunity test for Level 4, which corresponds to

the field strength of 30 V/m, the field within the car cannotinfluence the electronic devices.


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Fig. 12. Measured electric-field strength of the trunk-lid antenna in theyzplane at x = 200cm.

Fig. 13. Measured electric-field strength of the trunk-lid antenna in thexyplane at z = 400cm.

For human exposure to RF electromagnetic fields, the In-

ternational Commission on Non-Ionizing Radiation Protection

(ICNRP) defines that the reference levels of electric fields are

obtained from the basic restriction derived from the whole

body average SAR [2]. The reference level is 41.1 V/m at the

frequency of 900 MHz and could be yielded at the SAR of

0.008 W/kg with respect to the specifications for the general

public when the maximum coupling between the human body

and the field is assumed. If the field strength of 30 V/m

as a specially averaged value is found in the field-strength

measurement, the SAR is half of the basic restriction value at

maximum using the most conservative simple estimation. This

is because the square of the ratio between the measured 30 V/m

and the reference level of 41.1 V/m is about 1/2. If a more

precise SAR is needed for the dosimetry of the human body, the

local SAR distribution and specially averaged value of the field

strength in the human body should be measured using the hu-

man body phantom, as described in [4]. However, the providedmaximum protection when the measured electric-field strength

is at maximum is lower than the reference level, although the

specially averaged value of the electric-field strength is not

estimated.

Outside the car, the distribution of the far-field strength can

be predicted from the details of the measured field distribution.

The metal rooftop of the car did not significantly block the elec-

tromagnetic field excited from the upper sleeve element. The

field strength is highest in the region up to a half wavelength

from the upper sleeve element of the antenna. At the rear and

the side edges of the trunk lid, the field strength is less than

13 V/m (22 dBV/m). On the other side of the body, however,

the field strength did not exceed Level 3 (10 V/m) when the

antenna input is 1 W. If it is assumed that the uncertainty of the

measurement system is 4 dB, the field strength is less than

20 V/m at the rear and side edges of the trunk lid, and the field

strength did not exceed Level 3 (10 V/m) on the other side of

the body. The field strength did not exceed the reference level

indicated by the ICNRP guidelines even at the rear or side edgesof the trunk lid.


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Fig. 14. Rear-window antenna for 900-MHz band cellular system.

B. Rear-Window Antenna

The rear window is a good place to mount antennas forsystems such as cellular radios and broadcast receivers because

it is an unused location. A rear-window antenna comprising

two vertical dipoles is mounted on the rear window using two

suction cups, as shown in Fig. 14. To achieve parallel space

diversity, one dipole is used as the transmission and reception

ports while the other dipole is used only as a reception port; the

dipoles are separated by 15 cm. The transmitted signal lays in

the 900-MHz band. Figs. 1517 show the measured results.

Inside the car, the field strength in the front seat (interior)

is up to 14 dB higher than that with the trunk-lid antenna.

The local peak of the electric field is approximately 10 dB

higher in the vicinity of the steering wheel, as shown in Fig. 13.The same point yields the maximum field strength of 13 V/m

(22 dBV/m) when the antenna input is 1 W. This means that

electronic devices that offer Level 3 immunity (10 V/m) may

suffer an interference due to the electric field within the car.

Since the steering wheel has a metal frame, it is possible that

the measured field strength includes error due to the effect of

the near metal. A Level 4 device (30 V/m) would not experience

interference even if it were assumed that the uncertainty of

the measurement system is 4 dB because the maximum field

strength is 20 V/m. For human exposure to RF electromagnetic

fields, the field strength did not exceed the reference level

defined in the ICNRP guidelines.

Outside the car, a comparison of the side views, as shown

in Figs. 12 and 16, shows that the field strength in the front

of the car with the rear-window antenna is less than that with

the trunk-lid antenna, because the metal rooftop and body act

as a shield and reflector. Along the sides of the body, the field

strength did not exceed Level 4 (30 V/m) even if it is assumed

that the uncertainty of the measurement system is 4 dB.

C. Roof Antenna

The roof can be used to mount a radio antenna. A whip

antenna with the electrical wavelength of 5/8 in the 900-MHz

band is clamped to the junction of the roof and a windowpane.This location is useful because the antenna is accessible, allow-

ing rapid mounting or removal of the antenna. Figs. 1820 show

the measured results.

Inside the car, the field strengths at the headrest of the front

seat range from 10 V/m (20 dBV/m) to 20 V/m (26 dBV/m)

when the antenna input is 1 W. Since the headrest has a metal

frame and is near the metal roof of the car body, it is possible

that the measured field strength includes error due to the effectof the near metal. If it is assumed that the uncertainty of the

measurement system is 4 dB, the field strength is from 16 to

32 V/m. Near the headrest of the front seat, the electric field

of Level 4 (30 V/m) is exceeded; however, the reference level

indicated by the ICNRP is not exceeded if the antenna input is

less than 1 W, even though the field strength is extremely high

within one-half wavelength from the antenna. The local peak

of the electric field is higher by 2 or 4 dB in the rear and front

seats, respectively, as shown in Fig. 19.

Outside the car, the maximum field strength along the side of

the body toward which the antenna is mounted is approximately

10 V/m (20 dBV/m). However, along the other side, a value

less than 3 V/m (10 dBV/m) is obtained. If it is assumed

that the uncertainty of the measurement system is 4 dB, the

field strengths are 16 V/m for the antenna-mounted side and

5 V/m for the other side. The field strength did not exceed the

reference level defined in the ICNRP guidelines.

IV. SUMMARY

A. Construction of 3-D Measurement System

A 3-D system for measuring the electric-field space distri-

bution around a passenger car was described. The measure-

ment system can position a field sensor with the positioningrepeatability of better than 10 mm; the system was carefully

designed using nonmetallic materials and air motors to reduce

the electric-field fluctuation caused by the manipulator system.

The electric-field fluctuation due to the rectangular FRP col-

umn was calculated using the FDTD method. The calculation

considered the plane wave with different angles of incidence

and frequency values to take into account the actual measured

field, and the measurement system using the rectangular FRP

column was designed to hold the electric fluctuation to under

2 dB. In addition to the field fluctuation due to the rectan-

gular FRP column, the error of the used field sensor due

to the capacitive coupling between the field sensor and the

metal surface was also experimentally estimated to be 2 dB.The resulting electric-field strength yielded an uncertainty of

4 dB, including the electric-field fluctuation of2 dB caused

by the rectangular FRP columns that are used to construct the

3-D scanner and 2 dB from the capacitive coupling.

The developed measurement system was used to deter-

mine the detailed electric-field distributions of three antennas

mounted on a passenger car: a trunk-lid antenna, rear-window

antenna, and roof antenna.

B. Electric Field Within the Car

In the front seat, the field strength of the rear-window antennawas up to 14 dB higher than that for the trunk-lid antenna.


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Fig. 15. Measured electric-field strength of the rear-window antenna in the xzplane at y = 120cm.

Fig. 16. Measured electric-field strength of the rear-window antenna in the yzplane at x = 200cm.

When the antenna input was under 1 W, the electric field of the

trunk-lid antenna was nearly equal or less than 10 V/m at any

point inside the car even if it was assumed that the uncertainty

of the measurement system was 4 dB. However, there were

local peaks; the field strength exceeded 10 V/m for the rear-

window antenna and the roof antenna. The local peak of the

field strength was approximately 10 dB higher (maximum). For

all three antennas assessed, Level 4 (30 V/m) devices would

not experience interference due to the electric fields within thecar. However, the field strength of the headrest close to the

roof antenna was 32 V/m at maximum if the uncertainty of the

measurement system was assumed to be 4 dB.

For the human exposure to RF electromagnetic field, the field

strength did not exceed the reference level shown in the ICNRP

guidelines.

C. Electric Field Outside the Car

The electric field exceeded Level 3 (10 V/m) on the sideof the body toward which the trunk lid or roof antenna was


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Fig. 19. Measured electric-field strength of the roof antenna in theyzplane at x = 200cm.

Fig. 20. Measured electric-field strength of the roof antenna in thexyplane at z = 50cm.

ACKNOWLEDGMENT

The authors would like to thank H. Nishio at NTT DoCoMo

Engineering Company for his support.

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(Frequency Range of 300 MHz to 3 GHz), International ElectrotechnicalCommision (IEC), Feb. 2005.

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Yoshiaki Tarusawa (M93) received the B.S. andM.S. degrees in electrical engineering from NihonUniversity, Tokyo, Japan, in 1982 and 1984, re-spectively, and the Ph.D. degree in electronics andinformation engineering from Hokkaido University,Sapporo, Japan, in 2005.

In 1984, he joined Yokosuka Electrical Commu-nication Laboratories, NTT, Yokosuka, Japan. Since

then, he has been engaged in the development ofmicrowave circuits, mobile radio equipment, andelectromagnetic-compatibility technologies for mo-

bile radio systems. He is currently an Executive Senior Research Engineer inWireless Laboratories, NTT DoCoMo, Inc., Yokosuka.

Dr. Tarusawa is a member of the Institute of Electronics, Information, andCommunication Engineers of Japan.

Sadayuki Nishiki received the B.S. degree in elec-tronic engineering from Tokyo University of Agri-culture and Technology, Tokyo, Japan, in 1976.

In 1976, he was with Yokosuka Electrical Com-munication Laboratories, NTT, Yokosuka, Japan.Since then, he has been engaged in the developmentof frequency synthesizer circuits and high-efficiencypower amplifier circuits for mobile radio system.From 1992 to 2003, he was engaged in the develop-ment of electromagnetic-compatibility technologiesand the maintenance of base station radio equipment

for NTT DoCoMo, Inc. Since 2003, he has been a Senior Manager in MobileMultimedia Business Planning Department, DoCoMo Mobile, Inc.

Mr. Nishiki is a member of the Institute of Electronics, Information, andCommunication Engineers of Japan.

Toshio Nojima (S73M74) received the B.E. de-gree in electrical engineering from Saitama Univer-sity, Saitama, Japan, in 1972, and the M.E. and Ph.D.degrees in electronic engineering from HokkaidoUniversity, Sapporo, Japan, in 1974 and 1988,respectively.

From 1974 to 1992,he waswith NipponTelegraphand Telephone (NTT) Communications Laborato-

ries, where he was engaged in the development ofmicrowave radio systems. From 1992 to 2001, hewas with NTT DoCoMo, Inc., where he was a Senior

Executive Research Engineer and conducted research on the radio safety issuesrelated to mobile radio systems. Since January of 2002, he has assumed theposition of Professor in the graduate school of Hokkaido University.

Dr. Nojima is a member of the Institute of Electrical Engineers of Japanand the Institute of Electronics, Information, and Communication Engineersof Japan.

Documents

Fine Positioning Three-Dimensional Electric-Field Measurement