Development of 26 GHz-band UWB Radar for Automobiles
Kei Takahashi *, and Yasushi Aoyagi *Taking the opportunity of the easing of regulations by Federal Communications
Commission (FCC) in the United States in Feb 14, 2002, UWB (Ultra WideBand) radio systems are being actively considered in the fields of communications and ITS(Intelligent Transport Systems). For an application of a UWB technology in the ITS field, SRRs
(Short-Range Radar) for automobiles using quasi-millimeter-wave band (24 GHz-29 GHz) thatare applied to monitoring sensors for automobile surroundings have been being considered 1).
Furukawa Electric has developed a 26 GHz band UWB Radar for automobiles which leaking
signals of a radar carrier (hereinafter called carrier leakage) was considerably reduced in order
to meet the world’s radio wave regulations. While the size is small enough to be mounted insideautomobile bumpers, a distance resolution and a detection capability less than 15 cm are alsoachieved applying features of the UWB technology. In addition, because a qualification for theradio experimental test station was given for the developed item by the Ministry of Internal Affairs
and Communications, it became possible to mount this radar in an actual vehicle and to conduct
evaluation experiments of radio propagations and detection performances while moving thevehicle. In this paper, the legislative aspects of UWB radars and details of the developed radar
will be reported.

ABSTRACT1.

INTRODUCTION

18,00016,00014,00012,00010,000
8,000
6,000
4,000
2,000
0
1945

Death toll

Number of accidents

Number of injuries

Number of accidents / injuries(Ten thousand cases/Ten thousand persons)

Death toll (Person)

Currently, governments, automobile manufacturers andparts manufacturers are going all out to promote thedevelopment of safety technologies in order to decrease
the number of traffic casualty toll. In Japan, as shown in
Figure 1, the number of deaths tends to decrease
because of the spread of passive safety technologies(crash safety technologies: air-bag and shoulder harness). However, the number of traffic accidents and injuries are still at a high level, therefore, expectations are
becoming higher for active safety technologies which prevent accidents before they happen (preventive safety
technologies: pre-crash system, lane change assist, blindspot detection, anti-lock brake system (ABS)).
140
120
100
80
60
40
20
1955

1965

1975

1985

1995

2005

0
2015

1. Until 1959, minor accidents (injuries fewer than 8 days, property damages less than
20,000 yen) are not included.
2. Until 1965, property damages are included in the number of accidents.
3. Until 1971, Okinawa prefecture is not included.

Figure 1

2)

Transition of the number of traffic accidents .

* R&D Center of Advanced Automotive & Electronics.,
		 RF Technology Center, R&D Div.

In order to achieve these active safety technologies,
monitoring sensors for automobile surroundings which
sense dangers of crashing into human or other automobiles before anything happens are important 3). There arevarious types of monitoring sensors for automobile surroundings such as a radio wave type, an optical type, asonic wave type and a camera type. The features of various types of sensors are shown in Table 1. UWB radars
can be expected to detect ranges with a high resolution
up to 30 m and to be applied not only to an active safety
technology, but also to a parking assistance and to aheadway control in a traffic jam.
Table 1

Monitoring sensors for automobile surroundings.

UWB Millimeter- Laser UltrasonicInfraredradar wave radar radar -wave sensor Camera camera
Point-blank detection (-2 m) ◦
△
△
◦
◦
◦
Close/intermediate range
◦
◦
◦
×
◦
◦
detection (-30 m)
Capability/method

Long range (-150 m)
Distance resolution(less than 30 cm)
Angle detection range(more than ±30°)
Relative velocity direct
detection
Weather resistance(mist / rain / snow)
Detection at night(darkness)

×

◦

◦

×

×

◦

◦

×

◦

×

×

×

◦

×

×

△

◦

◦

◦

◦

×

×

×

×

◦

◦

×

×

×

◦

◦

◦

◦

◦

×

◦

◦: Suitable △: Avairable ×: Not avairable

1: This comparative table is an example.
2: The capabilities of the UWB radar are based on which our company developed.

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Development of a 26 GHz-band UWB Radar for Automobiles

In this paper, the position of the 26 GHz band UWB
radar in the administration of radio waves will be introduced. Moreover, the principle and the composition of the
distance measurement, the angle measurement and therelative velocity measurement of the radar which
Furukawa Electric developed will be explained. Also, thespectrum of the transmitter pulse, the distance measurement, the angle measurement, the relative velocity measurement and the in-vehicle evaluation results will be reported.

2.

The position and the legislative trend of
the 26 GHz UWB radar

The 26 GHz band, which Furukawa Electric is developing,is becoming a common band for the UWB radar which, inthe long term, will be operated in the world (Japan, theUnited States and Europe). However, regulations areslightly different depending on the regions. For instance,
while Europe and the United States are based on a radiometric measurement, Japan is premised on a regulation
by output power not including antenna gain (antenna terminal regulation). While contributing to build up the technical standards by taking part in a domestic legislation,
Furukawa Electric advanced technology developments.
As a result, along with the enhancement of the understandings of the various regulations, we developed aradar which is available in every region. In this chapter,
regulations on the 26 GHz band, the contents and thetrends of the regulations in the world will be introduced.
2.1 Europe and the United Stated
In the United States, FCC started out the legislation of
UWB in 1998 and two standards are instituted at present.
The limitation in the elevation direction radiation level ofthe 24 GHz band will be tightened in stages by 2013. The
26 GHz band is positioned as a band which is available
perpetually and without any restriction. These regulations
are shown in Table 2.
In Europe, legislation was started according to e-Safety
vision SEC (2003) 963 proposed in the European
Parliament on September 15, 2003. Two regulations (the79 GHz band and the 24 GHz band) are instituted at present. The 24 GHz band is due to expire in June 2013. The
26 GHz band is under discussion, and almost the same
regulation as FCC04-285 in the United States is due to be

Table 2

instituted in March 2010 if all goes smoothly. The abstractof the European regulations are shown in Table 3.
Because the regulation values of the 26 GHz are underdiscussion, possible conditions are described.
2.2 Japan
Legislative actions in Japan started at the end of
December 2006 in the UWB radar task group set up in the
UWB Radio Systems Committee of the Information andCommunications Technology Sub-Council of theInformation and Communication Council of the Ministry ofInternal Affairs and Communications and deliberations
on quasi-millimeter-wave bands have started. Meetings
were set up per passive interference systems (Ad-hoc
interference examinations) which had been stated at a
public hearing conducted by the Ministry of Internal
Affairs and Communications in April 2007. Discussions
have been held based on the interference examination
model and the calculated results being proposed by thebusinesses which promote the legislation of the UWB
radars (hereinafter called promoter). Interference examinations were completed in September 2009 and revision
procedures of the ministerial ordinance will be completedby March 2010. If all goes smoothly, the operation of theradars will be available in April. Both the 24 GHz bandand the 26 GHz band regulations are instituted, and the
24 GHz band regulation is due to expire in December
2016. The abstract is shown in Table 4.
The EIRP regulation value is based on a case when theantenna gain is 0 dBi, and actually, it is premised on theantenna terminal regulation, not on the radiometric measurement.
Those listed below also have to be considered.
• An immediate interference examination and an appropriate countermeasure have to be taken when the operational condition of the passive interference system ischanged or a new passive interference system appears
in the future.
• Mainly businesses seek a solution when an unexpectedinterference which was not expected in the examination
occurs.
In Japan, the millimeter-wave UWB radar is called “highresolution radar” to which the exclusive wave band isassigned. And the different regulation from quasi-millimeter-wave band is in discussion.

Radio regulation in USA.

24 GHz band
22 GHz - 29 GHz (1st Report and Order)

26 GHz band
23.12 GHz - 29 GHz (2nd Report and Order)

Time of introduction

February 2002

December 2004

Average power (EIRP)Less than－41.3 dBm/MHz←

Peak power (EIRP)Less than 0 dBm/50 MHz←

PurposeRadar for automobiles

←

None

None

Frequency band

Expiration dateSpecial conditions

・There is a limitation in the elevation direction radiation level of・it is ruled in Section 15.252 which governs general qualification
the radiation forbidden band (23.6 - 24.0 GHz).
unnecessary stations.
・It is ruled in Subpart F which governs the UWB wireless stations. ・Radio wave emissions in the 23.6-24 GHz bands are less than・Center frequency and maximum output frequency are more than
−61.3 dBm/MHz.
24.075 GHz.
	There is no rule about radiation level in elevation directions.

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Development of a 26 GHz-band UWB Radar for Automobiles

Table 3Frequency band
Time of introduction
Average power (EIRP)
Peak power (EIRP)
PurposeExpiration dateSpecial conditions

Radio regulation in Europe.

79 GHz band77 GHz - 81 GHz

24 GHz band
22 GHz - 26.65 GHz

26 GHz band (assumption)
24.25 GHz - 29 GHz

July 2004

January 2005

March 2010 (approximately)Less than −3 dBm/MHz

Less than −41.3 dBm/MHz

Less than −41.3 dBm/MHz

Less than 55 dBm

Less than 0 dBm/50 MHz←

Radar for automobiles

←

←

None

June 2013

None

None

・There is a limitation in the elevation direction radiation level of the radiation forbidden band (23.6-24.0 GHz).
・A radar auto-off function has to be
mounted in the neighborhood of radio
observatories.
・The allowable diffusion rate is 7%.

None

Table 4

Radio regulation in Japan.

24 GHz band
22 GHz - 24.25 GHz

26 GHz band
24.25 GHz - 29 GHz

Time of operation

April 2010 (approximately)

April 2010 (approximately)

Average power (EIRP)Less than －41.3 dBm/MHz

Less than －41.3 dBm/MHz

Peak power (EIRP)Less than 0 dBm/50 MHz←

PurposeRadar for automobiles←

December 2016

None

Frequency band

Expiration date

2.3 Other countries
Currently, UWB radars are approved in about 60 countries in
the world. The 24 GHz band is approved in Canada,
Singapore, countries which are affiliated with CEPT
(Switzerland, Russia, etc), South Africa, Australia and Mexico.
Moreover, an approval for the 79 GHz was added in
Singapore. The 26 GHz is likely to be deliberated andapproved in the future in each country as a permanently
usable band, in accordance with the regulation in Japan,
Europe and the United States in the same way as the 24
GHz band.

3.

①A signal is transmitted from the radar②It is reflected on the target
time

Distance: R (ｍ)③The radar receives reflected signal propagation time
time

Propagation time: T (ｓ)OVERVIEW OF THE UWB RADAR

Figure 2

3.1 Distance measuring method
The time of flight (TOF) method is adopted as a distancemeasuring method of the radar. In the TOF method,
shown in Figure 2, a distance measurement is done by
the amount time required to go through the following;
first, a transmitter pulse is discharged from the radar, thetransmitter pulse reflects on the target and then it isreceived by the radar.
The distance R (m) is defined by the following formulausing the transmitter pulse propagation time T (s) and the8speed of light c (m/s) (=2.998×10 ).

R=

cT
2

（m）

Principle of TOF.

The distance resolution ΔL is defined by the following
formula if the radiation time of the radio wave isτ
because the UWB radars emit ultra-short pulse.

ΔL =

cτ
（m）
2

(2)

A distance resolution around 15 cm is required forshort-range radars and to enhance the distance resolution, a signal with a narrower pulse width has to be transmitted. The necessary frequency bandwidth W (Hz) totransmit this signal is defined by the following formula.

(1)
W=

2
（Hz）
τ

(3)

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Development of a 26 GHz-band UWB Radar for Automobiles

If ΔL=0.15 m, τ=1 ns and W=2 GHz.
It means an ultra wideband frequency band from several
hundred MHz to several GHz is required. That is, a UWB
has to be used as a necessary component of a highly
accurate radar 5).
3.2 Angle measuring method
For an angle measuring method which detects Doppler
directly, the signal switch method using Σ (sum pattern)
and Δ (delta pattern), which is based on the phase comparison mono-pulse method, is adopted.
The phase comparison mono-pulse method is a method where the phase difference of the signals received byeach antenna is detected and converted into angles byusing two different types of antenna patterns. Although
the signal processing has to be done in parallel in the
mono-pulse method, the control which shifts patterns by
the time-sharing was done in consideration of the circuitsizes and the data spread.
The principle will be explained below using Figure 3.
Now, the angular difference θ between the antenna's
central angle and the target becomes the ideal angle.
In this method, the phase difference is detected as theratio of the amplitude of both antenna patterns: Σ/Δ(indicated as A in the Figure). The Angle is calculated byobtaining the angle conversion table beforehand whichcorresponds a one-to-one to this amplitude ratio.6)

Δ

Δ/Σ

θ

Σ

A
θ

quency of the transmitting pulse signal is f 0 (Hz) and the
speed of light is c (m/s), the relative velocity v (m/s)
between the radar and the target is defined by the following formula.

Δf

v=

2f 0

Figure 3(4)①A pulse signal (Frequency: f0 (Hz)) is transmitted from the radar.
②It is reflected on the target.
time

Target with the relative
velocity v (m/s)③The radar detects the received signal band
In fact, only the amplitude
values indicated by red
circles are detected.
→The Doppler frequency( : ∆ f (Hz)) is measured.
time

Figure 4

Relative velocity detection method.

3.4 Radar composition and specifications
The radar composition is shown in Figure 5, the appearance is shown is Figure 6, and the specifications are shownin Table 5. The antenna and the RF circuit were integrated,
thereby a small size (110 mm×75 mm×25 mm) which ismounted in automobile bumpers including the control circuit was achieved.

Angle（°）
Antenna pattern×c（m/s ）AntennaAngle table

Transmission
ANT

RF circuit

Principle of phase comparison mono-pulse system.

Reception
ANT1

Switching circuit
Transmitting
circuit

3.3 Relative velocity detection method
The pulse Doppler method which detects Doppler directly,is adopted as a relative velocity detection method. As
shown in Figure 4, when a target with the relative velocity
is detected, signals whose pulse are amplitude-modulated by their Doppler frequency (sinusoidal waves indicatedby blue lines in the Figure) are detected (in fact, only
amplitude values of the received signals indicated by red
circles in the Figure). Pulse signals are emitted continuously and the Doppler frequency is measured by theenvelope curve of the received signals’ amplitude values.
If the measured Doppler frequency is Δf (Hz), the fre-Control circuit

User

Connector

Figure 5

Reception
ANT2

Power
SourceCan

Receiving
circuit

Data processing
department
・Department of transmit
and receive control
・Frequency analysis
・Object detection process
・Tracking process, etc.

Block diagram of the developed radar.

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Development of a 26 GHz-band UWB Radar for Automobiles

Table 6

Conditions of target detection.

Distancemeasurement

Item+10 dBsm

Distance

Specifications of the radar.

Item

Specifications

Radar method

Coherent pulse Doppler radar

Frequency

300 cm20 cm

0°－60° - 60°

－

700
600
500
400
300
200
100
0

26 GHz band

Distance resolution±60°

Relative velocity resolution

3.5 The UWB radar radiometer measurement
The measurement result of the developed UWB radar's
antenna terminal power is shown in Figure 7. It showsthat the radar doesn't exceed the regulation value (a redline in Figure 7) which is planned to be legislated inJapan. Moreover, it is confirmed that there is no carrierleakage in this radar.

700

Test result of distance measurement.

20
15
10
5
0
−5
−10
−15
−45 −30 −15−54

Figure 9

24.25

29

Frequency（GHz）
Note) The expected maximum gain of the used transmission antenna is 9 dB.

Figure 7

600

Figure 8 shows the result that the target placed in thefront direction of the radar moving by 7.5 cm was detected by the radar. It shows that the target detection and the
distance measurement were conducted accurately in therange of extremely close (7 cm) -700 cm from the radar.

−20
−60

−41.3
−44

0

200
300
400
500
Distance of Target (cm)+8 - +16 VDC
CAN and UART (switching)
110 mm×75 mm×25 mm※not including projection

Detected angle error（°）

Size

100

Figure 8

1.38 m/s

Power specification
Communication standard

00.15 mDetection angle

Spectrum of transmit signal（dBm/MHz）

Detected Distance of Target (cm)

Table 5

Metal pole

+5 dBsm

7 cm - 700 cm

Detection angle

Appearance of the developed radar.

Relative velocity
measurement

Corner reflector

TargetFigure 6

Anglemeasurement

Spectrum of transmit pulse.

The detection results of the distance measurement, theangle measurement, the relative velocity measurement,
and the detection conditions are shown below.

015Angle（°）

30

45

60

Test result of angle measurement.

Figure 9 shows the result of the angle measurement
error in the direction of the radar. The blue lines in the
Figure indicate the specifications of this radar's angle
measurement error. If an angle is detected in the range of±60° from the center of the radar, the target is detectedwith an angle error ±5° in the range of ±45° and with anangle error ±15° in the range of more than ±45°.

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Development of a 26 GHz-band UWB Radar for Automobiles

4.
Reﬂection from bumper
Moving target
Receivingstrength

distance

city detection

Test result of relative velo

Figure 10 Test result of detected relative velocity.

Figure 10 shows the evaluation result when an automobile with the radar (inside the rear bumper) approached
the extremely close range (20 cm) of a metal pole. The
metal pole, as an object with the relative velocity in the
distance of 20 cm, was detected without an influence ofthe reflection from the bumper (distance: 0 cm, relative
velocity: 0 m/s).
Also, the result of capability evaluation of the UWB
radar mounted to an automobile is shown in Figure 11.
With respect to the object detected by the radar, theimage figure (hereinafter called radar chart figure) viewed
from the sky is shown in the upper side of the screen andthe actual landscape figure is shown in the lower side of
the screen. In the radar chart figure, 1 scale indicates 1 m
and the point marked by a yellow circle indicates themounting location of the radar. The parts marked by redboxes in the radar chart figure and in the landscape figure
are associated. It means that obstacles in the field of viewof the radar can be detected accurately.

IN CONCLUSION

In this paper, the development result of the 26 GHz band
UWB radar and each country's position on the radio wave
control over quasi-millimeter-wave band including 26 GHz
were introduced. We were successful in adapting to theradio wave controls around the world by reducing the carrier leakage by a large margin with our unique circuit
technology. In addition, a qualification for the radio experimental test station of the developed item was given by the
Ministry of Internal Affairs and Communications and theemission measuring result was reported. Not only evaluating at a resting state but also conducting evaluation
experiments of a radio wave propagation and a sensing
capability in a running vehicle on which the radar ismounted became possible.
In the future, taking advantage of the know-how and thedetection data obtained through experiments, we would
like to improve driving assistance and comfort by developing more reliable products, thereby contributing to the
reduction of the number of traffic accidents and injuries.

REFERENCES
1) “Development of Ultra Wideband Radio System for Short-Range
Applications,” Furukawa Review No.30, (2006).
2) “Fatalities from traffic accidents in 2008,” Data of the National
Police Agency Traffic Bureau, (2009, in Japanese).
3) “Regulatory Status of Quasi-Millimeter wave Short-Range Radarfor Automobile in Japan,” IEICE technical report 108 (339) pp.49-52
20081204, (2008).
4) “Abstract of the UWB Radio Systems Committee of the Informationa n d C o m m u n i c a t i o n s Te c h n o l o g y S u b - C o u n c i l o f t h eTelecommunications Council Report (Draft)” “Technical Conditionsof UWB Radar Systems,” the Telecommunications Council, (2009,
in Japanese).
5) “Measurement Techniques on 26 GHz Ultra-wideband Short Range
Radar,” IEICE technical report vol. 105, no. 365, WBS2005-46, pp.
43-48, (2005)
6) “Development of SSR Mode S and Experiments on Surveillance,”
SANE, Space, Aeronautical and Navigational Electronics, 96 (205)pp.1-8 19960726, (1999).

Figure 11 Test result of the UWB radar mounted to an automobile.

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