Special Issue

Automobile Electronics

Development of 24 GHz-band High Resolution Multi-Mode Radar
Daisuke Inoue*, Kei Takahashi*, Hiroyasu Yano*,Noritaka Murofushi*, Sadao Matsushima*, Takashi Iijima*

In recent years, Advanced Driver Assistance System (ADAS), which has sensor
devices mounted and avoids vehicle accidents by detecting objects in surroundings, started to be popular. Using the radar technology and detecting attenuation characteristics based on the weather and the Doppler Effect of the radio waves make possible the higher more reliable sensing over the sensing based on cameras and lasers. For this reason, it isexpected that the demand will increase more and more in the future. Furukawa Electric hasdeveloped the multi-mode radar, based on pulse method radar which is in compliance with radio
equipments specified for low power radio stations or for mobile detection sensors and is suitablefor various applications. Since this radar is compact, has a lot of flexibility in mounting on vehicles and can be mounted inside the bumpers, it is suitable to various applications such as afront side monitoring and a rear side monitoring. Here, we introduce its development concept,
its fundamental performances and its considerations for mounting on vehicles.

ABSTRACT1.

INTRODUCTION

Automobile safety technologies for decreasing fatalities
from traffic accidents are classified roughly as preventive
safety technologies and as crash safety technologies.
For the crash safety technologies, the development of
the technologies such as a seat-belt or an air-bag is mainly advanced. In recent years, the development of the preventive safety technologies is advanced with the progressin electronics technologies, and various sensors such as
laser radars, millimeter-wave radars and image sensors
are commercialized to date. The sensors already put into
production are assumed to be applied for the systems
which are designed to reduce and prevent head-on collisions or rear-end accidents.
Here, we recently created a new concept for the development from the analysis of the events and the characteristics of each accident pattern and from the condition of
the types of road shape extracted from the database of
the number of traffic accidents in Japan, and wedesigned and developed the new sensor which meets
this concept.

2.

THE CONCEPT OF THE DEVELOPMENT2.1 The Required Performances
Based on, “The classification of the events and the characteristics of each accident pattern in Japan” shown in“The conditions of occurrence of traffic accidents”, theaccidents between vehicles account for more than 80%
and, in particular the accidents of cars having bumped
into each other and those which turned to right/left have ahigh percentage. The accidents between vehicles andpedestrian walking across the street have also a high percentage. In addition, based on “The classification of theconditions and the characteristics of the types of roadshape in the database of the number of traffic accidents
in Japan” shown in “The conditions of occurrence of traffic accidents”, it can be confirmed that more than half ofthe traffic accidents occur at intersections1). Therefore, wehave developed a sensor for the systems which reduce
the accidents of cars having bumped into each other andthose which turned to right/left at intersections. The typical requirements for each application are shown in Table
1 and 2.

Table 1Requirements to avoid the accident of cars having
bumped into each other.
ItemValue

Unit

Main detection
targetVehicle−Detection direction

Front side of vehicle−

View angle

60deg.

Detection distance

50m

Relative velocity

60km/h* Automotive System & Device Laboratories,
Research & Development Division

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9Development of 24 GHz-band High Resolution Multi-Mode Radar

Table 2Requirements to avoid the accident of cars turning toright/left.
Item

Value

Unit

Main detection
targetHuman−

Detection direction

Front side of vehicle−

View angle

120deg.

Detection distance

30m

Relative velocity

60km/h

2.2 SpecificationsFor the sensor that realizes the required performances ofthe system reducing accidents of cars having bumped
into each other and those which turned to right/left, weselect a radio wave type radar in consideration of its
mounting positions. The specification of the multi-mode
radar which can be applicable to various applications isshown in Table 3. Since there are radars which use millimeter-wave (76 GHz band, 79 GHz band) or quasi-millimeter wave (24–29 GHz band), we decided to develop
the radar with the quasi-millimeter wave ISM band (24.05–24.25 GHz)2) from the viewpoints of cost and detection
distance.
Table 3

RadomeMain board

ShieldcaseSubboard

Base
plate

Figure 1 The radar configuration.

The shape of the developed radar is shown in Figure 2.
The projected area is within 100 mm squares including
the bracket fixing unit and the connector unit for the connection to the power supply/CAN (Control area network),
and the thickness is 25 mm, so that it achieves the sizethat can be mounted easy in the limited space in thebumpers.

Specification of the 24 GHz-band high resolution multimode radar.
ItemValue

Unit

Modulation method

Pulse−Frequency band

24.05–24.25

GHz

Minimum detection distance0m

Maximum detection distance72m

Horizontal angle range

120deg.

Size

100 x 100 x 30mm

2.3 Radar Configuration and Characteristics
The radar configuration is shown in Figure 1. The antennas, the quasi-millimeter module and the signal processing section are placed on both sides of the main board.
The power supply unit is placed on the sub-board. Aradome, the main board, a shielding case, the sub-board
and a base plate are stacked to configure the radar. Theradar has a waterproof construction because it will bemounted in the bumpers.

Figure 2 The shape of the radar.

The basic block diagram of the radar with a monopulse
method is shown in the Figure 3. The main high frequency components consist of a local oscillator, a power divider which divides the signals from the oscillator into thetransmission line and into the reception line, a switch forthe transmission line, a transmission antenna, reception
antennas, a selector switch for the reception antennas, a
low-noise amplifier and a down converter mixer. There arealso the control/signal processing unit and the power
supply/communication unit. The angle measurement isdone by the configuration of one antenna for the transmission and two antennas for the reception.

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Development of 24 GHz-band High Resolution Multi-Mode Radar

Oscillator

SwitchSplitter

Reception
SwitchLNA

Mixer

Control / signal processing unit

Transmission8070
Detecting distance (m)Quasi-millimeter module

Power supply / communication unit

Antennas

60
50
4030
20
100024Time (sec.)

68Figure 3 The block diagram of the radar.

Figure 4 An automobile’s detection performance.

Next, we describe its performance. In the transmission
circuit, the switch in the transmission line is opened/closed by the signal which is time-adjusted in the control/
signal processing unit, and the transmission pulse signal
is generated. The signal which is reflected on the target isreceived by two reception antennas. With the selector
switch of the reception antennas, the signal from either
reception antenna is selectively transferred to a low-noise
amplifier. After amplification at the low-noise amplifier, theRF signal is converted to the base band signal at thedown converter mixer and then converted to the digitalvalue by the analog-to-digital (A/D) converter in the control/signal processing unit. The digital signal will have atarget detection decision after averaging and Fast Fourier
Transform (FFT) processing. The processing after the target detection decision will be discussed in another paper.
2.4 The Basic Performance of the Radar
Figure 4 shows the detection performance which showsthe event when a vehicle (sedan) is approaching to theradar with respect to its detecting distance and its time. It
is found that the radar starts detecting a vehicleapproaching from far at the distance of 72 m (time 0 sec.)
and keeps detecting until the distance of 0 m (time 6sec.). In the immediate vicinity of the radar, the target isdetected at several distances at same time. This isbecause that there are multiple reflection points on thevehicle. This data has no signal processing after target
detection decisions, so that the improvements in the target number of identifications and in the positional accuracy will be possible by the signal processing of the application. From this data, the radar has the detection performance of 50 m or more toward a vehicle, and it can beconfirmed that the radar meets the requirements shownin Table 1 to avoid the accident of cars having bumped
into each other and a maximum detection distance shownin Table 3.

Next, a pedestrian (adult male) detection performanceis shown in Figure 5. This figure shows the measurement
results of the event where a pedestrian gets away andthen comes close in front of the radar, with respect to its
detecting distance and its time. It is found that the radar isdetecting a pedestrian who starts to walk from the immediate vicinity of the radar (2 m) and keeps detecting until
the distance of 38 m(time 24 sec.). From the above, it canbe confirmed that the radar has a detection distance of 30m or more toward a pedestrian and meets the requirements shown in Table 2 to avoid the accident of cars turning to right/left.

Detecting distance (m)60504030201000102030Time (sec.)

4050Figure 5 A pedestrian’s detection performance.

Next, the accuracy of the detected angle performanceof the radar is shown in Figure 6. If the angle is detectedin the range from the center of the radar to 120 deg., anaccuracy within ±1 deg. is achieved over the whole angle
range, and it can be confirmed that the radar meets therequirements shown in Table 2 to avoid the accident ofcars turning to right/left and the horizontal angle range
shown in Table 3.

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Development of 24 GHz-band High Resolution Multi-Mode RadarIn Figure 8, the emission patterns of the transmission/
reception antennas are shown when comparing:a. the radar itself
b. the plastic plate and the radar, andc. the plastic plate, the radar and metallic plate (correspond to Figure 7).
The existence of the vehicle structure behind of theradar contributes to the characteristics, and it is foundthat the structure out of the radiation direction has an
influence to the main direction of the radiation.

108Angle error (deg.)

6420-2-4-6-8-10-90 -75 -60 -45 -30 -15 0 15 30Angle (deg.)

456075 90

a. the radar itself
b. the plastic plate and the radarc. the plastic plate, the radar and metallic plate

CONSIDERATION OF VEHICLE MOUNTING

3.1 Analysis by the Electromagnetic Simulation
To reduce the degradation of the detection performances
and the risk of the false alarm of the radar under practicaloperating condition, the understanding and the designingof not only the characteristics of the radar itself but also
the ones under the condition that the radar mounted inbumpers is required. Although the quasi-millimeter wave
band is less influenced by the bumpers than the millimeter wave band, the influences in the characteristics of themounting on the vehicles are noticeable comparing to thecharacteristic of the radar itself.
With respect to the vehicle mounting consideration, theradiation direction of the radio wave, for example the electromagnetic field analysis with bumpers or emblems
mounted, is well-known. On the other hand, it is getting
obvious that structures out of the main radiation direction
may have contribution to the analysis.
3.2 Influences of Bumpers and Vehicles
Figure 7 shows the pattern of the electromagnetic analysis in the model where the bumper or structures of thevehicle around the radar are simplified as a flat plate.
Plastic plate

Metallic plate
Figure 7 EM simulation model.

-90-60-300Angle (deg.)

306090Figure 8 Radiation patterns.

Figure 9 shows the calculated results of the gains in thedirections of 45deg. and 60deg. from the radar front,
when the gap between the plastic plate in the front andthe radar of Figure 7 is changed.

60 deg. direction
45 deg. direction

Gain variation (dBi) 5 dB/div

3.

Gain (dBi) 10dB/div

Figure 6 Accuracy of the detected angle performance.

051015Gap (mm)202530Figure 9 Change of the radiation pattern by the gap to a bumper.

Figure 7 shows the electric field distribution when theradio wave emits from the transmission antenna, while
installing a plastic plate as a simulation of a bumper in thefront side of the radar and a metallic plate as a simulationof a vehicle in the rear side of the radar. In this result, theelectric field distribution can be seen not only between
the front side of the radar and the plastic plate but also
between the plastic plate and the metallic plate.

From the results so far, it is found that the position of
the radar greatly contributes to the characteristics when
the radar is mounted on a vehicle. The actual bumper
configuration has a curved surface and there are many
structures of the vehicle around the radar. Therefore theappropriate mounting condition can be easily found out
by downsizing and increasing the flexibility of the installaFurukawa Review, No. 442013

12Development of 24 GHz-band High Resolution Multi-Mode Radartion of the radar. Especially for the wide-coverage radar
which is discussed in here, it is necessary to give a goodconsideration with respect to the influence of the vehicle
structure and the mounting position and to design so asto reduce the influence of the mounting on the vehicle.

4.

CONCLUSION

We have developed a high-resolution multi-mode radar
which is compact as fitting inside of the bumpers and has
a wide-coverage. This radar is considered for the applications of monitoring front side and rear side of the vehicle.
We will pursue improving the performances of the radar
itself to improve safety furthermore and contribute to thedecreasing of fatalities from traffic accidents, and pursue
a size reduction and a cost reduction for expansion into
applicable types of vehicles.

REFERENCES
1) “The Conditions of Occurrence of Traffic Accidents in Japan in theFiscal Year 2012”, The Metropolitan Police Department
2) “Sensors for Detecting or Measuring Mobile Objects for Specified
Low Power Radio Station”, ARIB-STD-T73

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