Radar apparatus for detecting a direction of a center of a target

A radar apparatus of an automotive vehicle includes a radar unit which radiates an electromagnetic wave to a target in a forward direction of the vehicle and receives reflection beams from the target to detect the target. A scanning control unit performs a beam scanning of the radar unit to the target so that the reflection beams during the beam scanning are received. A center direction determining unit detects a distribution pattern of the received reflection beams with respect to respective scanning angles of the radar unit, performs a similarity approximation of the distribution pattern by using an antenna directional gain pattern of the radar unit to produce an approximated distribution pattern, and determines a direction of a center of the target based on a peak of the approximated distribution pattern.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention generally relates to a scanning radar apparatus, and 
more particularly to a scanning radar apparatus of an automotive vehicle 
which detects a direction of a center of a target, such as an advancing 
vehicle, by receiving reflection beams from the target. 
(2) Description of the Related Art 
In recent years, several types of radar devices for use in automotive 
vehicle have been developed in order to provide increased stability and 
operability of the automotive vehicle. The radar devices are capable of 
detecting a relative distance between a target (such as an advancing 
vehicle) and the vehicle, and a relative velocity of the target to a 
vehicle speed of the vehicle. 
Japanese Laid-Open Patent Application No. 4-158293 teaches a radar 
apparatus which is one of the above-mentioned types. The radar apparatus 
utilizes a radar unit radiating a laser beam in order to detect a target 
such as an advancing vehicle in a forward direction of the radar 
apparatus. 
To make use of the radar apparatus of the above publication, reflectors are 
mounted at a right-side rear end and a left-side rear end of the advancing 
vehicle. The radar apparatus receives reflection laser beams reflected off 
the reflectors of the advancing vehicle (the target). The radar apparatus 
detects a distance of each of the reflectors by measuring the time for the 
radiation laser beam to return to the radar apparatus after it has been 
reflected off the advancing vehicle. When the distances of the reflectors 
are detected to be the same, the radar apparatus determines a center 
scanning angle of the radar unit for a center of the advancing vehicle by 
detecting a mid-point between two scanning angles for the reflectors. 
Another type is a radar apparatus utilizing a radar unit radiating an 
extremely high frequency (EHF) electromagnetic wave in order to detect the 
target. However, in a case of the radar apparatus of this type, the radar 
apparatus receive reflection radar beams containing noises from the 
reflectors of the advancing vehicle, and the reflection of the radiation 
radar beam on the advancing vehicle is not uniform. 
It is difficult for the above-mentioned radar apparatus to accurately 
detect a position of an end of the advancing vehicle by measuring the time 
for the radiation radar beam to return to the radar apparatus after it has 
been reflected off the advancing vehicle. It is practically impossible for 
the above-mentioned radar apparatus to determine a center scanning angle 
of the radar unit for a center of the advancing vehicle by detecting a 
mid-point between two scanning angles for the reflectors as in the 
laser-beam radar apparatus. 
Therefore, when the conventional radar apparatus utilizing the radar unit 
radiating the EHF electromagnetic wave is used, it is difficult to 
accurately detect the direction of the center of the target. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an improved radar 
apparatus in which the above-described problems are eliminated. 
Another object of the present invention is to provide a radar apparatus of 
an automotive vehicle which accurately detects a direction of a center of 
a target in a forward direction of the vehicle by performing a similarity 
approximation using an antenna directional gain pattern of a radar unit. 
Still another object of the present invention is to provide a radar 
apparatus of an automotive vehicle which accurately detects individual 
targets in a forward direction of the vehicle by separately processing the 
data of received reflection signals related to one target from the data 
related to another when a plurality of adjacent targets are running in 
parallel in the forward direction of the vehicle. 
A further object of the present invention is to provide a radar apparatus 
of an automotive vehicle which easily and accurately detects individual 
targets in a forward direction of the vehicle by separately performing a 
pairing of the data of received reflection signals related to one target 
and a pairing of the data of received reflection signals related to 
another target when a plurality of targets in the forward direction of the 
vehicle are detected. 
The above-mentioned objects of the present invention are achieved by a 
radar apparatus which includes: a radar unit which radiates an 
electromagnetic wave to a target in a forward direction of the vehicle and 
receives reflection beams from the target to detect the target; a scanning 
control unit which performs a beam scanning of the radar unit to the 
target so that the reflection beams during the beam scanning are received; 
and a center direction determining unit which detects a distribution 
pattern of the received reflection beams with respect to respective 
scanning angles of the radar unit, performs a similarity approximation of 
the distribution pattern by using an antenna directional gain pattern of 
the radar unit to produce an approximated distribution pattern, and 
determines a direction of a center of the target based on a peak of the 
approximated distribution pattern. 
The radar apparatus of the present invention can determine a direction of a 
center of the target by performing the similarity approximation even when 
the reflection of the radiation beam on the target is not uniform and 
noises are superimposed in the received reflection beams. Accordingly, it 
is possible for the radar apparatus of the present invention to accurately 
detect the direction of the center of the target for a center scanning 
angle of the radar unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A description will now be given of the preferred embodiments of the present 
invention with reference to the accompanying drawings. 
FIG. 2 shows a radar apparatus in one embodiment of the present invention. 
This radar apparatus is installed on an automotive vehicle. 
Referring to FIG. 2, the radar apparatus of the present embodiment 
comprises a yaw rate sensor 10, an electronic control unit (ECU) 11, a 
radar scanning controller 12, a vehicle speed sensor 13 and a radar unit 
14. The radar apparatus of the present embodiment further includes an 
alarm unit 15. 
The yaw rate sensor 10 generates a yaw rate signal indicative of a measured 
yaw rate of the vehicle by using an acceleration sensor having a 
piezoelectric element, and supplies the yaw rate signal to the ECU 11. 
The vehicle speed sensor 13 generates a vehicle speed signal indicative of 
a measured vehicle speed of the vehicle, and supplies the vehicle speed 
signal to the ECU 11. 
The ECU 11 receives the vehicle speed signal from the vehicle speed sensor 
13. The ECU 11 receives the yaw rate signal from the yaw rate sensor 10. 
The ECU 11 performs a filtering of the received yaw rate signal and 
determines a yaw rate signal after the filtering is performed. The ECU 11 
determines a measured radius of curvature of a present path along which 
the vehicle is presently running, by using the determined yaw rate signal 
and the vehicle speed signal. 
By using the measured radius of curvature of the present path, the ECU 11 
is capable of providing an estimated radius of curvature of a following 
path along which the vehicle is about to run at a following time. 
Further, the ECU 11 generates a scanning angle signal indicative of a 
scanning angle of the radar unit 14, and supplies the scanning angle 
signal to the radar scanning controller 12. The radar unit 14 is 
controlled by the radar scanning controller 12 so that a beam radiation 
axis of the radar unit 14 is moved to the target in accordance with the 
scanning angle signal from the ECU 11. Accordingly, the ECU 11 controls 
the radar unit 14 in accordance with the scanning angle signal through the 
radar scanning controller 12. 
The radar unit 14 of the present embodiment is a 
frequency-modulation-continuous-wave (FMCW) radar unit which radiates an 
extremely high frequency (EHF) electromagnetic wave as a radiation beam to 
a target in a forward direction of the vehicle. A beam scanning of the 
radar unit 14 to the target is performed under the control of the radar 
scanning controller 12 by moving the radiation beam of the radar unit 14 
across the target from the left to the right of the target on the plane of 
a horizontal forward running direction of the vehicle. 
The radar unit 14 supplies signals indicative of results of the detection 
of the target to the ECU 10. These signals are generated by the radar unit 
14 by receiving reflection beams after the radiation beam has been 
reflected off the target. In response to the signals from the radar unit 
14, the ECU 10 is capable of determining a relative distance between the 
target and the vehicle and a relative velocity of the target relative to 
the vehicle speed of the vehicle. 
As described above, the ECU 11 determines, in response to the received 
reflection beams, the relative distance and the relative velocity related 
to the target. By using the relative distance and the relative velocity, 
the ECU 11 detects whether the vehicle is in a dangerous condition with 
respect to the target. When it is determined that the vehicle is in a 
dangerous condition, the ECU 11 switches ON the alarm unit 15 in order to 
provide a warning of the dangerous condition to a vehicle operator. 
FIG. 3 shows a center direction determining procedure which is executed by 
the ECU 11 of the radar apparatus in FIG. 2 by using the yaw rate sensor 
10, the vehicle speed sensor 13, the radar unit 14, and the radar scanning 
controller 12. This procedure is repeatedly executed by the ECU 11 at 
intervals of a predetermined time. 
Referring to FIG. 3, the ECU 11, at step S10, allows the radar scanning 
controller 12 to perform the beam scanning of the radar unit 14 to the 
target. The beam scanning is performed under the control of the radar 
scanning controller 12 by moving the radiation beam of the radar unit 14 
across the target from the left to the right of the target on the plane of 
the horizontal forward running direction of the vehicle. 
The ECU 11, at step S12, detects a distribution pattern of received 
reflection beams with respect to respective scanning angles (.theta.) of 
the radar unit 14, based on the reflection beams received from the target. 
When the relative distances and the relative velocities related to the 
received reflection beams are detected to be the same, the ECU 11 obtains 
a plotting of the distribution pattern of the received reflection beams 
with respect to the respective scanning angles of the radar unit 14. 
FIG. 4 shows a beam scanning of the radar unit 14 to a target 20, which is 
performed by the radar scanning controller 12. In FIG. 4, the radar 
scanning controller 12 moves the radiation beam of the radar unit 14 
across the target 20 from the left to the right on the plane of the 
horizontal forward running direction of the vehicle. A scanning angle of 
the radar unit 14 is an angle between a direction of the beam radiation 
axis of the radar unit 14 and the horizontal forward running direction of 
the vehicle. This angle is changed during the beam scanning. 
During the beam scanning in FIG. 4, the beam radiation axis of the radar 
unit 14 is moved relative to the forward running direction of the vehicle 
across the target 20 from a left-side rear end of the target 20 to a 
right-side rear end of the target 20. Detection of the received reflection 
beams from the target 20 starts when the beam radiation axis of the radar 
unit 14 is at a first scanning angle .theta.1 for the left-side rear end, 
and the detection of the received reflection beams ends when the beams 
radiation axis of the radar unit 14 is at a second scanning angle .theta.2 
for the right-side rear end. 
FIG. 5 shows an ideal distribution pattern of received reflection beams in 
which no noise is superimposed. The distribution pattern of the received 
reflection beams in FIG. 5 is obtained if the beam scanning of the radar 
unit 14 is performed and the reflection of the radiation beam on the 
target 20 is ideal. However, the limits of a beam scanning range when 
detecting the target in an actual case are not clear, and the reflection 
of the radiation beam on the target in such a case is not uniform and it 
is complicated. 
FIG. 6 shows an actual distribution pattern of received reflection beams in 
which noises are superimposed. The distribution pattern of the received 
reflection beams in FIG. 6 is obtained in an actual case. As shown, the 
received reflection beams in the actual case contains noises superimposed 
therein due to the non-uniform reflection on the target. 
Referring back to FIG. 3, after the step S12 is performed, step S14 
performs a smoothing of the distribution pattern of the received 
reflection beams. Influences of the noises in the actual distribution 
pattern are reduced by this smoothing. 
After the step S14 is performed, step S16 performs a similarity 
approximation of the distribution pattern by using an antenna directional 
gain pattern of the radar unit 14. FIG. 7 shows the antenna directional 
gain pattern for the respective scanning angles of the radar unit 14. FIG. 
8 shows a similarity approximation of the distribution pattern in FIG. 6 
using the antenna directional gain pattern in FIG. 7. 
As shown in FIG. 8, when the similarity approximation is performed, an 
approximated distribution pattern is produced from the distribution 
pattern of the received reflection beams after the smoothing, so that it 
is overlaid over the antenna directional gain pattern. Respective 
correlations of the approximated distribution pattern and the antenna 
directional gain pattern when the scanning angle .theta. is changed from 
the first scanning angle .theta.1 for the left-side rear end of the target 
20 to the second scanning angle .theta.2 for the right-side rear end of 
the target 20 are calculated by the ECU 11. 
After the step S16 is performed, step S18 determines a direction of a 
center of the target 20 for a center scanning angle (.theta.c) of the 
radar unit 14. As shown in FIG. 8, the direction of the center of the 
target 20 is determined based on a peak of the approximated distribution 
pattern. Based on the direction of the center of the target 20, the ECU 10 
generates a signal indicating the direction of the center of the target 10 
for the center scanning angle (.theta.c) of the radar unit 14. 
Even when the reflection of the radiation beam on the target is not uniform 
and noises are superimposed in the received reflection beams, a 
correspondence between the distribution pattern of the received reflection 
beams and the antenna directional gain pattern can be detected in the 
above manner. 
Accordingly, the radar apparatus of the present embodiment can determine 
the direction of the center of the target by performing the above 
similarity approximation. It is possible for the radar apparatus of the 
present embodiment to accurately detect the direction of the center of the 
target for the center scanning angle .theta.c of the radar unit. 
After the step S18 is performed, step S20 detects whether the vehicle is 
presently running along a curved path. The ECU 11 determines a radius (R1) 
of curvature of a present path along which the vehicle is presently 
running, by using a measured yaw rate signal (YAW) from the yaw rate 
sensor 10 and a measured vehicle speed signal (SPD) from the vehicle speed 
sensor 12. The radius R1 of curvature of the present path is determined in 
accordance with the equation: R1=SPD/YAW. That is, the radius R1 of 
curvature of the present path is calculated by dividing the measured 
vehicle speed SPD by the measured yaw rate YAW. By comparing the 
determined radius R1 of curvature of the present path with a predetermined 
reference value, the ECU 11 detects whether the vehicle is presently 
running along a curved path. 
When the radius R1 of curvature of the present path is above the 
predetermined reference value, it is determined that the vehicle is not 
presently running along a curved path. At this time, the ECU 11 generates 
a signal indicating the determined center scanning angle .theta.c (the 
step S18) in order to detect a direction of the center of the target. 
Further, steps S26 and S28 which will be described later are performed by 
the ECU 11. The center direction determining procedure in FIG. 3 ends 
after the steps S26 and S28 are performed. 
On the other hand, when the radius R1 of curvature of the present path is 
below the predetermined reference value, it is determined that the vehicle 
is presently running along a curved path. 
When the result at the step S20 is affirmative (the vehicle is presently 
running along a curved path), step S22 is performed by the ECU 11. Step 
S22 detects whether a beam scanning range .theta.w of the target is below 
a reference range value (=2.theta.vh). This discrimination is made to 
determine whether the beam radiation axis of the radar unit 14 directed to 
the target when the center scanning angle is determined at the step S18 is 
excessively slanting with respect to the horizontal forward running 
direction of the vehicle. 
The ECU 11 at the step S22 determines the beam scanning range .theta.w of 
the target by a difference between a lower limit of the scanning angle in 
the level of the received reflection beams which is above a threshold 
value and an upper limit of the scanning angle .delta. in the level of the 
received reflection beams which is above the threshold value. 
The above reference range value 2.theta.vh is determined by the following 
equation. 
EQU 2.theta.vh=2.multidot.tan.sup.-1 (W/2.multidot.L) 
where L is the measured relative distance of the target and W is a width of 
the target. The width W of the target (the advancing vehicle) in the 
present case is about 2 meter. According to the above equation, the value 
of .theta.vh, or 1/2 of the reference range value, corresponds to a beam 
scanning range of the radar unit 14 for 1/2 of the width of the advancing 
vehicle. 
FIG. 9 shows a case in which a vehicle 25 is running along a curved path 
and a target 30 in the curve path is detected by the radar apparatus of 
the vehicle 25. 
In the case of FIG. 9, the beam radiation axis of the radar unit 14 
directed to the target 30 is excessively slanting with respect to the 
horizontal forward running direction of the vehicle. FIG. 10A shows a 
distribution pattern of received reflection beams obtained in the slanting 
case of FIG. 9. The level of the received reflection beams in the slanting 
case of FIG. 9 is the maximum when the beam radiation axis of the radar 
unit 14 is directed to the left-side rear end of the target 30 as shown in 
FIG. 10A. 
FIG. 10B shows a distribution pattern of received reflection beams obtained 
in a normal case in which the beam radiation axis of the radar unit 14 
directed to the target 30 accords with the horizontal forward running 
direction of the vehicle. 
As shown, a beam scanning range .theta.w1 of the target 30 in the slanting 
case of FIG. 10A is smaller than a beam scanning range .theta.w2 in the 
normal case of FIG. 10B. The above reference range value 2.theta.vh used 
at the step S22 is defined by an estimated value of the beam scanning 
range .theta.w2 in the normal case. Accordingly, when the vehicle 25 is 
running along the curved path and the beam scanning range .theta.w of the 
target is below the reference range value 2.theta.vh, it is necessary to 
correct the center scanning angle .theta.c determined at the step S18. 
When the result at the step S22 is affirmative 
(.theta.w.ltoreq.2.theta.vh), step S24 is performed by the ECU 11. Step 
S24 determines a corrected center scanning angle .theta.c so as to 
eliminate an offset of the center scanning angle .theta.c which is 
produced at the step S18 in the slanting case. 
FIG. 10C shows a correction of a center scanning angle in the case of FIG. 
9. As shown in FIG. 10C, the corrected center scanning angle .theta.c is 
calculated by addition of a tentatively determined center scanning angle 
for the mid-point of the lower limit "A1" and the upper limit "A2" and the 
value of .theta.vh (which is equal to 1/2 of the reference range value 
corresponding to the beam scanning range of the radar unit 14 for 1/2 of 
the width of the target). That is, the corrected center scanning angle 
.theta.c in the case of FIG. 9 is determined at the step S24 by the 
following equation. 
EQU .theta.c=(A1+A2)/2+.theta.vh 
where A1 is the lower limit of the scanning angle, A2 is the upper limit of 
the scanning angle, and .theta.vh is equal to 1/2 of the reference range 
value of the radar unit 14. 
Referring back to FIG. 3, after the step S24 is performed, step S26 is 
performed by the ECU 11. 
On the other hand, when the result at the step S22 is negative 
(.theta.w&gt;2.theta.vh), the step S26 is performed and the step S24 (the 
correction of the center scanning angle) is not performed. At this time, 
the ECU 11 generates a signal indicating the determined center scanning 
angle .theta.c (the step S18) in order to detect a direction of the center 
of the target. 
As described above, when the vehicle is running along a curved path and the 
beam radiation axis of the radar unit directed to the target is slanting 
with respect to the forward direction of the vehicle, the radar apparatus 
of the present embodiment can eliminate the offset of the center scanning 
angle .theta.c which is determined in the slanting case. Accordingly, it 
is possible for the present embodiment to accurately detect the center 
scanning angle .theta.c of the radar unit for the center of the target in 
the slanting case also. 
Step S26 detects whether the center scanning angle .theta.c, which is 
determined at the step S18 or the step S24, meets the following conditions 
. 
EQU .theta.cv-.theta.vh&lt;.theta.c&lt;.theta.cv+.theta.vh .theta.cv=sin.sup.-1 
(L/2.multidot.R1) 
where .theta.cv is a center scanning angle for a center of a roadway lane 
of the vehicle, L is the measured relative distance of the target, and R1 
is the radius of curvature of the present path. When the above conditions 
are met by the center scanning angle .theta.c, it is determined that the 
target is in the roadway lane which is the same as that of the vehicle. 
After the step S26 is performed, step S28 is performed by the ECU 11. Step 
S28 detects whether the vehicle is in a dangerous condition with respect 
to the target, by receiving the relative distance and the relative 
velocity related to the target. When it is determined that the vehicle is 
in a dangerous condition, the ECU 11 switches ON the alarm unit 15 in 
order to provide a warning of the dangerous condition to a vehicle 
operator. After the step S28 is performed, the center direction 
determining procedure in FIG. 3 ends. 
FIG. 1A shows a radar apparatus according to a basic concept of the present 
invention. The basic concept of the present invention is already apparent 
from the foregoing description of the above embodiment. As shown in FIG. 
1A, the radar apparatus includes a radar unit 16, a scanning control unit 
17, and a center direction determining unit 18. 
The radar unit 16 is constructed by the radar unit 14 of the 
above-described embodiment in FIG. 2. The radar unit 16 radiates an 
electromagnetic wave to a target in a forward direction of a vehicle and 
receives reflection beams from the target to detect the target. 
The scanning control unit 17 is constructed by the radar scanning 
controller 12 of the above embodiment in FIG. 2 and the step S10 of the 
center direction determining procedure executed by the ECU 11. The 
scanning control unit 17 performs a beam scanning of the radar unit 16 to 
the target so that the reflection beams during the beam scanning are 
received. 
The center direction determining unit 18 is constructed by the steps S12 
through S18 in the center direction determining procedure executed by the 
ECU 11. The center direction determining unit 18 detects a distribution 
pattern of the received reflection beams with respect to respective 
scanning angles of the radar unit 16. The determining unit 18 performs a 
similarity approximation of the distribution pattern by using an antenna 
directional gain pattern of the radar unit 16 to produce an approximated 
distribution pattern. The determining unit 18 determines a center scanning 
angle of the radar unit 16 for a center of the target by a scanning angle 
of the approximated distribution pattern corresponding to a peak of the 
antenna directional gain pattern. 
Further, FIG. 1B shows a radar apparatus according to another basic concept 
of the present invention. This basic concept of the invention is also 
apparent from the foregoing description of the above embodiment. As shown 
in FIG. 1B, this radar apparatus includes a correcting unit 19 in addition 
to the units 16, 17 and 18 in FIG. 1A. In FIG. 1B, the elements which are 
the same as corresponding elements in FIG. 1A are designated by the same 
reference numerals, and a description thereof will be omitted. 
Referring to FIG. 1B, the correcting unit 19 is constructed by the steps 
S20 through S24 in the center direction determining procedure executed by 
the ECU 11. The correcting unit 19 determines a corrected center scanning 
angle from a reference range value corresponding to a beam scanning range 
of the radar unit 16 for a width of the target, and from a scanning angle 
of the radar unit 16 corresponding to a mid-point of lower and upper 
limits of the scanning angle in the distribution pattern, when the vehicle 
is running along a curved path and the beam scanning range is below the 
reference range value. 
Further, the correcting unit 19 in FIG. 1B includes a unit for detecting 
whether the vehicle is running along a curved path, by comparing a radius 
of curvature of a present path along which the vehicle is presently 
running with a predetermined reference value. The radius of curvature is 
determined by using a measured yaw rate and a measured vehicle speed. 
Further, the correcting unit 19 includes a unit for detecting whether a 
beam radiation axis of the radar unit 16 directed to the target is 
slanting with respect to the forward direction of the vehicle. 
Next, FIG. 11 shows a radar apparatus in another embodiment of the present 
invention. 
Referring to FIG. 11, the radar apparatus is controlled by a radar control 
unit 110 and a vehicle control unit 112 which are two separate electronic 
control units (ECU). This radar apparatus is installed on an automotive 
vehicle. 
A steering angle sensor 114, a yaw rate sensor 116, and a vehicle speed 
sensor 118 are connected to inputs of the radar control unit (ECU) 110. 
The steering angle sensor 114 generates a signal indicative of a steering 
angle of a steering wheel (not shown) of the vehicle. The yaw rate sensor 
116 generates a signal proportional to an angular velocity of the vehicle 
about a center of gravity of the vehicle. The vehicle speed sensor 118 
generates a signal indicative of a vehicle speed of the vehicle. 
The radar control unit (ECU) 110 is capable of providing an estimated 
radius of a turning circle of the vehicle by receiving these signals from 
the steering angle sensor 114, the yaw rate sensor 116 and the vehicle 
speed sensor 118. 
A radar unit 120 is connected to an input of the radar control unit 110. An 
output of the radar control unit 110 is connected to a scanning controller 
122. 
The radar unit 120 of the present embodiment is a 
frequency-modulation-continuous-wave (FMCW) radar unit which radiates an 
extremely high 10 frequency (EHF) electromagnetic wave as the radiation 
beam to a target in a forward direction of the vehicle. The radar unit 120 
has a rotating shaft 120a on which an antenna of the radar unit 120 is 
rotatably supported. By rotating the radar unit 120 on the rotating shaft 
120a, the beam radiation axis of the radar unit 120 is changed. 
A moving mechanism 124 is engaged with the radar unit 120 to move the beam 
radiation axis of the radar unit 120. The operation of the moving 
mechanism 124 is performed by the scanning controller 122 through a 
feedback control. A scanning angle signal (.theta.) output from the radar 
control unit 110 is supplied to the scanning controller 122. The scanning 
controller 122 feedback-controls the moving mechanism 124 to move the beam 
radiation axis of the radar unit 120 so that a scanning angle of the radar 
unit 120 is adjusted to be in accordance with a scanning angle indicated 
by the scanning angle signal (.theta.). 
The radar control unit 110 controls a beam scanning of the radar unit 120 
to the target through the scanning controller 122 by increasing or 
decreasing the scanning angle (.theta.) at a given period of time. By 
moving the radiation beam of the radar unit 120 across the target from the 
left to the right of the target on the plane of the horizontal forward 
running direction of the vehicle, the beam scanning of the radar unit 120 
is carried out. 
Signals related to the received reflection beams from the target are 
supplied from the radar unit 120 to the radar control unit 110. In 
response to these signals, the radar control unit (ECU) 110 detects the 
target in the forward direction of the vehicle. The results of the 
detection of the target are supplied from the radar control unit 110 to 
the vehicle control unit (ECU) 112. 
An alarm unit 126, a brake unit 128, and a throttle valve 130 are connected 
to outputs of the vehicle control unit 112. When the vehicle is detected 
to be in a dangerous condition with respect the target, the vehicle 
control unit 112 switches ON the alarm unit 126, controls the brake unit 
128, and/or controls the throttle valve 130, in order to provide a warning 
of the dangerous condition to a vehicle operator and decelerate the 
vehicle for safety. 
FIG. 12 shows a construction of the radar control unit (ECU) 110 of the 
radar apparatus in FIG. 11. 
The radar control unit 110 is essentially made up of a microcomputer. As 
shown in FIG. 12, the radar control unit 110 comprises a scanning angle 
determining part 132, a radar signal processing part 134, and a target 
recognition part 136. 
The scanning angle determining part 132 determines a scanning angle of the 
radar unit 120, and supplies a scanning angle signal indicating the 
scanning angle to the scanning controller 122 as described above. In the 
scanning angle determining part 132, the scanning angle (.theta.) 
indicated by the supplied scanning angle signal is changed in synchronism 
with a control timing of the radar signal processing part 134. 
When any target is detected as a result of the beam scanning of the radar 
unit 120, the radar signal processing part 134 receives signals of the 
reflection beams of the target from the radar unit 120. In response to 
these signals, the radar signal processing part 134 determines a relative 
distance between the target and the and the vehicle and a relative 
velocity of the target to the vehicle speed of the vehicle. Data of the 
relative distance and the relative velocity related to each of a plurality 
of targets, and correlations between such data and respective scanning 
angles with respect to each of the targets are generated by the radar 
signal processing part 134, and they are supplied to the target 
recognition part 136. A construction of the radar signal processing part 
134 will be described later with reference to FIG. 13. 
When the relative distances, the relative velocities, and the correlations 
for the respective targets from the radar signal processing part 134 are 
received, the target recognition part 136 generates a set of groups of 
recognition data, each group of the recognition data related to the 
relative distance, the relative velocity and the correlations of the same 
target. The target recognition part 136 provides an estimated radius (R) 
of the turning circle of the vehicle based on the signals output from the 
steering angle sensor 114, the yaw rate sensor 116 and the vehicle speed 
sensor 118, as described above. 
The radar apparatus of the present embodiment is characterized by the 
target recognition part 136 which separately generates each of groups of 
the recognition data of the relative distances, the relative velocities, 
and the correlations to the respective scanning angles, by using the 
estimated radius (R) of the turning circle of the vehicle, which are 
separated from each other for one of the targets being detected. 
FIG. 13 shows a construction of the radar signal processing part 134 in 
FIG. 12. As shown in FIG. 13, a radiation antenna 120b and a receiving 
antenna 120c are included in the radar unit 120. The radar signal 
processing part 134 comprises a carrier generator 138, frequency 
modulation circuit 140, a modulation voltage generator 142, and a 
directional coupler 144. These elements constitute a beam radiation 
portion of the FMCW radar unit. An output of the directional coupler 144 
is connected to the radiation antenna 120b of the radar unit 120. 
The carrier generator 138 generates a carrier signal having a given 
frequency, and supplies this signal to the frequency modulation circuit 
140. 
The modulation voltage generator 142 generates a modulation signal whose 
amplitude is varied in a triangular form, and supplies this signal to the 
frequency modulation circuit 140. 
The frequency modulation circuit 140 performs a frequency modulation of the 
carrier signal output from the carrier generator 138 in accordance with 
the triangular-form modulation signal output from the modulation voltage 
generator 142. Thus, a modulated signal is generated at an output of the 
frequency modulation circuit 140. 
FIG. 14A shows waveforms of radiation and reflection signals of the radar 
signal processing part 134 in FIG. 13. The waveform of the radiation 
signal indicated by a solid line in FIG. 14A shows a change in the 
frequency of the modulated signal at the output of the frequency 
modulation circuit 140. At a result of the above-mentioned frequency 
modulation, the modulated signal is generated at the output of the 
frequency modulation circuit 140. 
As shown in FIG. 14A, the frequency of this modulated signal (the radiation 
signal) is varied in a triangular form. A frequency change width of the 
radiation signal is indicated by "dF", and a modulation frequency of the 
radiation signal is indicated by "fm" (fm=1/T where T is a period of the 
amplitude change of the signal output by the modulation voltage generator 
142). The modulated signal output from the frequency modulation circuit 
140 is supplied to the radiation antenna 120b via the directional coupler 
144, and this signal is supplied to a mixer 146 (which will be described 
later) via the directional coupler 144. 
The radiation signal (the above modulated signal) supplied to the radiation 
antenna 120b is radiated as the radiation beams by the radar unit 120 to a 
target in a forward direction of the vehicle in accordance with the 
scanning angle signal (.theta.). When there is the target in the forward 
direction of the vehicle, reflection signals which are reflection beams 
after the radiation beam has been reflected off the target are received at 
the receiving antenna 120c of the radar unit 120. 
The receiving antenna 120c is connected to an input of the mixer 146. The 
radar signal processing part 134 comprises the mixer 146, an amplifier 
148, a filter 150, and a fast-Fourier-transform (FFT) circuit 152. These 
elements and the radar unit 120 constitute a beam receiving portion of the 
FMCW radar unit. In response to the reflection signals supplied from the 
receiving antenna 120c, the radar signal processing part 134 generates the 
data of the relative distance and the relative velocity related to the 
target, through the radar signal processing. 
The waveforms of reflection signals indicated by a dotted line and a 
one-dot chain line in FIG. 14A show changes of the frequencies of the 
reflection signals supplied from the receiving antenna 120c to the mixer 
146. 
The mixer 146 performs a mixing of the radiation signal from the 
directional coupler 144 and the reflection signals from the receiving 
antenna 120c, and generates beat signals at an output of the mixer 146 as 
a result of the mixing. Changes of the frequencies of the beat signals at 
the output of the mixer 146 are in accordance with the differences between 
the radiation signal frequency and the reflection signal frequencies. 
FIG. 14B shows waveforms of the beat signals generated in the radar signal 
processing part 134 in FIG. 13. Hereinafter, as shown in FIGS. 14A and 
14B, a frequency of a beat signal generated at an "up period" during which 
the frequency of the radiation signal is increasing is called an 
up-frequency "fup", and a frequency of a beat signal generated at a "down 
period" during which the frequency of the radiation signal is decreasing 
is called a down-frequency "fdwn". 
The beat signals generated at the output of the mixer 146 are supplied to 
the filter 150 after they have been amplified by the amplifier 148. The 
beat signals from the amplifier 148 are separated by the filter 150 into 
the beat signals of the up periods and the beat signals of the down 
periods. These beat signals at the output of the filter 150 are separately 
supplied to the FFT circuit 152. 
Thus, the FFT circuit 152 determines a power spectrum of the up-frequency 
for the beat signals of the up periods through the fast Fourier transform, 
and determines a power spectrum of the down-frequency for the beat signals 
of the down periods through the fast Fourier transform. 
FIG. 15A shows the spectrum level of the up-frequency determined by the FFT 
circuit 152 for the beat signals of the up periods when two targets in the 
scanning range of the radar unit 120 are detected. FIG. 15B shows the 
spectrum level of the down-frequency determined by the FFT circuit 152 for 
the beat signals of the down periods in the same case. 
In a case in which there are a plurality of targets in the scanning range 
of the radar unit 120, different reflection signals from the individual 
targets are received at the receiving antenna 120c. Different beat signals 
for the respective reflection signals of the targets are generated at the 
output of the mixer 146. Consequently, the spectrum level of the 
up-frequency determined by the FFT circuit 152 has a plurality of peaks, 
such as "FMu1" and "FMu2" in FIG. 15A, and the spectrum level of the 
down-frequency determined by the FFT circuit 152 has a plurality of peaks, 
such as "FMd1" and "FMd2" in FIG. 15B. 
Generally, there is a phase difference between the radiation signal output 
by the radiation antenna 120b and the reflection signal received by the 
receiving antenna 120c, and this phase difference is proportional to the 
time for the signals to be transmitted over the distance between the 
vehicle and the target. 
When the relative velocity of the target is zero (the speed of the target 
is equal to the vehicle speed of the vehicle), no Doppler shift of the 
frequency of the reflection signal takes place. The waveform of the 
reflection signal in this case which shows the change of the frequency of 
the reflection signal supplied to the mixer 146 is as indicated by the 
one-dot chain line in FIG. 14A. As shown, the waveform of the reflection 
signal in this case (the one-dot chain line) is described by translating 
the waveform of the radiation signal (the solid line) in a direction 
parallel to the time axis "t". 
Therefore, when the relative velocity of the target is zero, the 
up-frequency fup of the beat signal is the same as the down-frequency fdwn 
of the beat signal (fup=fdwn), which is indicated by the one-dot chain 
line in FIG. 14B. Each value of the up-frequency fup and the 
down-frequency fdwn in the present case is proportional to the relative 
distance between the target and the vehicle. 
On the other hand, when the relative velocity (Vr) of the target is greater 
or smaller than zero (the target moves away from the vehicle or the 
vehicle approaches the target), a Doppler shift of the frequency of the 
reflection signal proportional to the relative velocity Vr takes place. 
For example, when the relative velocity Vr is smaller than zero, the 
frequency of the reflection signal in this case is shifted to a frequency 
higher than the frequency of the radiation signal due to the Doppler 
shift. 
Since the Doppler shift occurs in the present case, the waveform of the 
reflection signal which shows the change of the frequency of the 
reflection signal supplied to the mixer 146 is that indicated by the 
dotted line in FIG. 14A. As shown, the waveform of the reflection signal 
in this case (the dotted line) is described by translating the waveform of 
the radiation signal (the solid line) both in a direction parallel to the 
time axis "t" and in a direction parallel to the frequency axis "f". 
When the relative velocity Vr is smaller than zero and the frequency of the 
reflection signal is shifted to the higher frequency as in FIG. 14A, the 
up-frequency fup of the beat signal is reduced and the down-frequency fdwn 
of the beat signal is enlarged, which is indicated by the dotted line in 
FIG. 14B. Each value of the up-frequency fup and the down-frequency fdwn 
in the present case contains a Doppler shift component which is 
superimposed in the beat signal. 
In the present case, an average of the up-frequency and the down-frequency 
is determined by 
EQU fr=(fup+fdwn)/2 (1) 
By obtaining the average fr by the above Equation (1), the Doppler shift 
components of the up-frequency fup and the down-frequency fdwn in the 
average fr are canceled by each other. It is possible to obtain the 
average fr of the up-frequency and the down-frequency which is 
proportional to the relative distance between the target and the vehicle 
since it contains no Doppler shift component. 
Further, in the present case, a value fd of 1/2 of a difference between the 
up-frequency fup and the down-frequency fdwn is determined by 
EQU fd=(fdwn-fup)/2 (2) 
By obtaining the value fd by the above Equation (2), an average of the sum 
of the Doppler shift components of the up-frequency fup and the 
down-frequency fdwn is determined. It is possible to obtain the value fd 
which is equivalent to the Doppler shift component of each of the 
up-frequency and the down-frequency due to the relative velocity of the 
target. 
In the present embodiment, the following relationships are met, supposing 
that a target in the scanning range of the radar unit 120 is detected, the 
relative distance of the target being indicated by L, and the relative 
velocity of the target being indicated by Vr. 
EQU fr=4fm.multidot.dF.multidot.L/c (3) 
EQU fd=2Vr.multidot.fo/c (4) 
where fo is a central frequency of the modulation signal output by the 
modulation voltage generator 142, fm is a frequency of the modulated 
signal output by the frequency modulation circuit 140, dF is the frequency 
change width of the modulated signal, and c is the travel speed of the 
electromagnetic wave. 
Therefore, if the peaks of the spectrum levels of the up-frequency and the 
down-frequency of the beat signals are determined by the FFT circuit 152, 
the values of the "fr" and the "fd" can be obtained by using the above 
Equations (1) and (2). Further, the values of the relative distance L and 
the relative velocity Vr related to the target can be obtained by 
substituting the values of the "fr" and the "fd" into the above Equations 
(3) and (4). 
As described above, the moving mechanism 124 is feedback-controlled by the 
scanning controller 122 to move the beam radiation axis of the radar unit 
120, so that the scanning angle of the radar unit 120 is adjusted to be in 
accordance with the scanning angle signal (.theta.) output from the radar 
control unit 110. 
FIG. 16 shows a range of the beam scanning of the radar unit 120, which is 
predetermined on a vehicle 54 in which the radar apparatus of the present 
embodiment in FIG. 11 is incorporated. 
Referring to FIG. 16, when the beam scanning of the radar unit 120 to the 
target is performed, the radiation beam of the radar unit 120 is moved by 
the scanning controller 122 across the target from the left to the right 
or vice versa on the plane of the horizontal forward running direction of 
the vehicle 54. As described above, the scanning angle (.theta.) of the 
radar unit 120 is the angle between the direction of the beam radiation 
axis of the radar unit 120 and the horizontal forward running direction of 
the vehicle 54. As shown in FIG. 16, the scanning angle (.theta.) is 
changed from -10.degree. to +10.degree. or vice versa during the beam 
scanning of the radar unit 120, and the horizontal forward running 
direction of the vehicle 54 accords with the direction of the scanning 
angle 0.degree.. The scanning angle .theta. is negative (or smaller than 
zero) when the radiation beam of the radar unit 120 covers a range on the 
left side of the target, and the scanning angle .theta. is positive (or 
greater than zero) when the radiation beam of the radar unit 120 covers a 
range on the right side of the target. 
FIG. 17 shows a relationship between the frequency f of the radiation 
signal and the scanning angle .theta. of the radar unit 120 in FIG. 11. As 
described above, the scanning angle .theta. supplied by the scanning angle 
determining part 132 is changed in synchronism with the control timing of 
the radar signal processing part 134. 
More specifically, in the radar apparatus of the present embodiment, the 
scanning angle .theta. is changed by 0.5.degree. when the frequency f of 
the radiation signal is changed for one period. In addition, in the radar 
apparatus of the present embodiment, the beam scanning of the radar unit 
120 during which the scanning angle .theta. is changed from -10.degree. to 
+10.degree. or vice versa is repetitively performed for every 100 
milliseconds (msec). 
In the radar control unit 110 of the present embodiment, the calculations 
of the values of the "fr" and the "fd" using the above Equations (1) and 
(2) and the calculations of the values of the relative distance L and the 
relative velocity Vr related to the target by using the values of the "fr" 
and the "fd" and the above Equations (3) and (4) are repetitively carried 
out each time the scanning angle .theta. is changed by 0.5.degree. for 
every 2.5 msec. Also, the beam scanning of the radar unit 120 is 
repetitively carried out through the scanning controller 122 each time the 
scanning angle .theta. is changed by 0.5.degree.. 
Accordingly, in the present embodiment, the range of the beam scanning of 
the radar unit 120 in FIG. 16 (in which the scanning angle .theta. is 
changed from -10.degree. to +10.degree.) is divided into forty 
subsections, the calculated values of the "fr" and the "fd" and the 
calculated values of the relative distance L and the relative velocity Vr 
related to the target are obtained for each subsection (corresponding to 
2.5 msec) of the beam scanning of the radar unit 120. Thus, in the present 
embodiment, for every 100 msec during which the beam scanning of the radar 
unit 120 to the target is completed, forty sets of the peaks of the 
spectrum levels of the up-frequency and the down-frequency (as in FIGS. 
15A and 15B), corresponding to respective forty scanning angles .theta., 
are determined by the FFT circuit 152, and forty sets of the calculated 
values of the "fr" and the "fd" and the calculated values of the relative 
distance L and the relative velocity Vr related to the target, 
corresponding to the respective forty sets of the peaks, are obtained by 
the radar signal processing part 134. These calculated values which are 
related to the respective scanning angles .theta. are supplied from the 
radar signal processing part 134 to the target recognition part 136. 
FIG. 18 shows a case in which two targets T1 and T2 (which are advancing 
vehicles) are separately running with a distance along a straight path in 
a forward direction of the vehicle 54. In FIG. 18, the target T1 is 
running forwardly in a roadway lane which is the same as a roadway lane of 
the vehicle 54. The target T2 is running forwardly in a roadway lane which 
is different from and adjacent to the roadway lane of the vehicle 54, and 
the target T2 is advancing forward from the target T1. 
FIG. 19 shows data of received reflection signals at the input of the 
target recognition part 136 of the radar apparatus on the vehicle 54, in 
the case of FIG. 18. The data of the received reflection signals in FIG. 
19 includes a plurality of plots of the relationship between the scanning 
angle (.theta.) and the relative distance (L) related to each of the 
target T1 and the target T2. 
As shown in FIG. 19, a group of plots of the data of the received 
reflection signals related to the target T2 gathers in an area in which 
the relative distance L is large. A different group of plots of the data 
of the received reflection signals related to the target T1 gathers in a 
separate area in which the relative distance L is small. In the present 
case, as shown in FIG. 19, it is possible to easily distinguish the group 
of the plots related to the target T2 and the group of the plots related 
to the target T1 with respect to each of the relative distance L and the 
relative velocity Vr. 
FIG. 20 shows a case in which two adjacent targets T1 and T2 (which are 
advancing vehicles) are running in parallel along a straight path in the 
forward direction of the vehicle 54. There is no substantial distance 
between the target T1 and the target T2 along the straight path. In FIG. 
20, the target T1 is running forwardly in the roadway lane which is the 
same as the roadway lane of the vehicle 54. The target T2 is running 
forwardly in the adjacent roadway lane which is different from to the 
roadway lane of the vehicle 54. In the present case, the target T1 and the 
target T2 are advancing in parallel forward from the vehicle 54. 
FIG. 21 shows data of received reflection beams at the input of the target 
recognition part 136 of the radar apparatus on the vehicle 54, in the case 
of FIG. 20. The data of the received reflection signals in FIG. 21 
includes a plurality of plots of the relationship between the scanning 
angle (.theta.) and the relative distance (L) related to both the target 
T1 and the target T2. 
As shown in FIG. 21, a group of plots of the data of the received 
reflection signals related to the target T2 and a group of plots of the 
data of the received reflection signals related to the target T1 gather in 
a single area in which the respective relative distances L are 
substantially the same. In the present case, as shown in FIG. 21, it is 
difficult to distinguish the group of the plots related to the target T2 
and the group of the plots related to the target T1 with respect to each 
of the relative distance L and the relative velocity Vr. 
The radar apparatus of the present embodiment is characterized by the 
target recognition part 136 which allows the radar control unit 110 to 
easily distinguish the group of the recognition data related to the target 
T2 and the group of the recognition data related to the target T1 with 
respect to each of the relative distance L and the relative velocity Vr, 
even in the case of FIGS. 20 and 21. 
FIG. 22 shows a control procedure performed by the target recognition part 
136 of the radar control unit (ECU) 110 in FIG. 12. This control procedure 
is performed in order to achieve the above-mentioned function of the 
target recognition part 136. The control procedure in FIG. 22 is started 
for every 100 msec needed for one beam scanning of the radar unit 120 to 
be performed by changing the scanning angle .theta. from -10.degree. to 
+10.degree. or vice versa. 
When the control procedure in FIG. 22 is started, the target recognition 
part 136 of the ECU 110, at step S40, detects whether a target in the 
roadway lane which is the same as that of the vehicle 54 has been detected 
at a preceding cycle of the control procedure. 
The radar apparatus of the present embodiment can determine the relative 
distance L of the target to the vehicle 56 if a target in the scanning 
range of the radar unit 120 in the forward direction of the vehicle 56 is 
detected. The determination as to whether the target is in the roadway 
lane which is the same as that of the vehicle 54 is performed at the step 
S40 as follows. 
FIG. 23 shows a scanning range of the radar unit 120 when the vehicle 54 
and a target 56 are separately running along a straight path with a 
relative distance L between the vehicle 54 and the target 56. If the 
forward direction of the target 56 accords with the forward direction of 
the vehicle 54, the scanning angle .theta. of the radar unit 120 meets the 
following condition: 
EQU -tan.sup.-1 (W/2L).ltoreq..theta..ltoreq.tan.sup.-1 (W/2L) 
where L is the relative distance between the vehicle 54 and the target 56, 
and W is a width of the target 56. 
AS previously described, the value of .theta.vh (which is 1/2 of the 
reference range value) corresponds to the beam scanning range of the radar 
unit 120 for 1/2 of the width W of the target. 
FIG. 24 shows a case in which the vehicle 54 and the target 56 are running 
in the same lane along a curved path with a relative distance L between 
the vehicle 54 and the target 56. A radius R of curvature of the curved 
path and the relative distance of the target 56 are determined by the 
radar apparatus of the present embodiment. The determination as to whether 
the target 56 is in the roadway lane which is the same as that of the 
vehicle 54 is performed depending on whether the center scanning angle 
.theta.c of the radar unit 120 for the center of the target 56 meets the 
following conditions: 
EQU .theta.cv-K.multidot..theta.vh&lt;.theta.c&lt;.theta.cv+K.multidot..theta.vh(5) 
where K is a predetermined coefficient of the radar apparatus. 
Referring back to FIG. 22, when the result at the step S40 is affirmative, 
it is determined that the target 56 in the roadway lane which is the same 
as that of the vehicle 54 has been detected at the preceding cycle of the 
control procedure. At this time, step S41 is performed next. 
On the other hand, when the result at the step S40 is negative, it is 
determined that the target 56 in the roadway lane which is the same as 
that of the vehicle 54 has not been detected at the preceding cycle of the 
control procedure. At this time, step S46 is performed next, and steps S41 
through S45 are not performed. 
Step S41 detects whether the recognition data related to the target 56 in 
the scanning range of the radar unit 120 in which the target 56 has been 
detected at the preceding cycle is detected at the present cycle. 
When no recognition data related to the target 56 in the scanning range of 
the radar unit 120 is detected at the present cycle (the result at the 
step S41 is negative), it is determined that the target 56, previously 
detected to be in the roadway lane of the vehicle 54, has been moved to a 
different roadway lane. At this time, step S46 is performed next, and 
steps S42 through S45 are not performed. 
When the result at the step S41 is affirmative, it is determined that the 
recognition data related to the target 56 in the scanning range of the 
radar unit 120 in which the target 56 has been detected at the preceding 
cycle is detected at the present cycle. At this time, step S42 is 
performed next. 
Step S42 detects whether the relative distance L of the target 56 presently 
determined at the present cycle is approximate to the relative distance L 
of the target 56 previously determined at the preceding cycle. As 
described above, the control procedure of FIG. 22 is performed for every 
100 msec. When the relative distance L of the target 56 presently 
determined at the present cycle is considerably different from the 
relative distance L of the target 56 previously determined at the 
preceding cycle, it is determined that the recognition data of the target 
56 presently detected at the present cycle is defective. 
Therefore, when the result at the step S42 is negative, it is determined 
that the recognition data of the target 56 presently detected at the 
present cycle is defective. At this time, step S46 is performed next, and 
steps S43 through S45 are not performed. 
On the other hand, when the result at the step S42 is affirmative, it is 
determined that the relative distance L of the target 56 presently 
determined at the present cycle is correct. At this time, step S43 is 
performed next. Step S43 detects whether the range of the scanning angle 
of the radar unit 120 presently detected at the present cycle is 
considerably greater than the range of the scanning angle of the radar 
unit 120 previously detected at the preceding cycle. 
When the result at the step S43 is affirmative, it is determined that 
another target has presently moved into or approached a roadway lane 
adjacent to the roadway lane of the target 56 in the range of the scanning 
angle of the radar unit 120 previously detected at the preceding cycle. 
Because of the above change, a group of plots of the data of the received 
reflection signals related to the other target and a group of plots of the 
data of the received reflection signals related to the target 56 may 
gather in a single area in which the relative distances L are 
substantially the same. At this time, step S44 is performed next. 
Step S44 reads out the group of the plots of the data of the received 
reflection signals related to the target 56 in the range of the scanning 
angle previously detected preferential to that in the range of the 
scanning angle presently detected. After the step S44 is performed, step 
S46 is performed. 
On the other hand, when the result at the step S43 is negative, it is 
determined that the range of the scanning angle presently detected at the 
present cycle is not considerably greater than the range of the scanning 
angle previously detected at the preceding cycle. At this time, step S45 
is performed next. Step S45 reads out the group of the plots of the data 
of the received reflection signals in the range of the scanning angle 
presently detected at the present cycle. After the step S45 is performed, 
step S46 is performed. 
Step S46 reads out the group of the plots of the data of the received 
reflection signals related to another target which is detected to be in 
another roadway lane which is different from the roadway lane of the 
vehicle 54. 
After the step S46 is performed, step S47 is performed. Step S47 stores all 
the groups of the plots of the read-out data of the received reflection 
signals in a memory of the target recognition part 136 of the radar 
control unit (ECU) 110. 
After the step S47 is performed, step S48 is performed. Step S48 calculates 
the values of the relative distances L and the relative velocities Vr 
related to the targets from the stored data for each of the groups of the 
plots. 
In the above-described embodiment, it is possible to accurately detect 
individual targets in a forward direction of the vehicle by separately 
processing the data of received reflection signals related to one target 
from the data related to another even when two or more targets are 
adjacent to each other and running in parallel in the forward direction of 
the vehicle. 
Next, FIG. 25 shows a radar apparatus in a further embodiment of the 
present invention. In FIG. 25, the elements which are the same as 
corresponding elements in FIG. 11 are designated by the same reference 
numerals, and a description thereof will be omitted. 
Referring to FIG. 25, the radar apparatus of the present embodiment 
includes a radar control unit 210 which is an electronic control unit 
(ECU) for controlling the radar apparatus including the scanning 
controller 122 and the radar unit 120. This radar apparatus is installed 
on an automotive vehicle. 
The radar control unit 210 of the present embodiment has a construction 
which is essentially the same as the construction of the radar control 
unit 110 shown in FIG. 12. This radar control unit 210 comprises the 
scanning angle determining part 132, the radar signal processing part 134 
and the target recognition part 136 which are the same as those of the 
radar control unit 110 previously described with reference to FIG. 12. 
The results of the detection of targets from the radar control unit 210 are 
supplied to the vehicle control unit (ECU) 112. Similarly to the vehicle 
control unit 112 in FIG. 11, the alarm unit 126, the brake unit 128 and 
the throttle valve 130 are connected to outputs of the vehicle control 
unit 112 of the present embodiment. These units provide a warning of a 
dangerous condition to a vehicle operator and decelerates the vehicle for 
safety. 
The radar apparatus of the present embodiment is characterized by the radar 
control unit 210 which carries out a control procedure. This control 
procedure will be described later. 
The radar signal processing part 134 of the present embodiment has a 
construction which is essentially the same as that of the radar signal 
processing part 134 shown in FIG. 13. This radar signal processing part 
134 comprises the carrier generator 136, the frequency modulation circuit 
140, the modulation voltage generator 142, the directional coupler 144, 
the mixer 146, the amplifier 148, the filter 150 and the FFT circuit 152 
which are the same as those of the radar signal processing part 134 
previously described with reference to FIG. 13. 
In the present embodiment, when the spectrum level peaks of the 
up-frequency and the down-frequency of the beat signals as shown in 
FIGS.15A and 15B are determined by the FFT circuit 152 of the radar 
control unit 210, a pairing of the peaks FMu1 and FMd1 is performed so 
that the values of the relative distance L and the relative velocity Vr 
related to one target can be obtained by using the above Equations 
(1)-(4). Further, a pairing of the peaks FMu2 and FMd2 is performed, and 
the values of the relative distance L and the relative velocity Vr related 
to another target can be obtained by using the above Equations (1)-(4). 
As previously described with reference to FIGS.16 and 17, in the present 
embodiment, the entire range of the beam scanning of the radar unit 120 in 
FIG. 16 is divided into forty subsections, the calculated values of the 
relative distance L and the relative velocity Vr related to one target are 
obtained for each subsection (corresponding to 2.5 msec). In the present 
embodiment, for every 100 msec during which the beam scanning of the radar 
unit 120 is performed, forty sets of the spectrum level peaks of the 
up-frequency and the down-frequency, corresponding to respective forty 
scanning angles .theta., are determined by the FFT circuit 152, and forty 
sets of the calculated values of the relative distance L and the relative 
velocity Vr related to the target are obtained by the radar signal 
processing part 134. These calculated values which are related to the 
respective scanning angles .theta. are supplied from the radar signal 
processing part 134 to the target recognition part 136. 
FIG. 26 shows a beam scanning of the radar unit 120 to two targets 50 and 
52 in the forward direction of the vehicle. The target 50 is a fixed pole 
on a roadway in the forward direction of the vehicle. The target 52 is an 
advancing vehicle running along the roadway in the forward direction of 
the vehicle. 
As described above, a set of the spectrum level peaks of the up-frequency 
and the down-frequency is determined for a range of the scanning angle 
.theta. corresponding to one subsection is determined. In FIG. 26, 
boundary lines of each range of the scanning angle for one subsection are 
indicated by solid lines, and a pair of boundary lines of a width of 
electromagnetic waves for the beam scanning directed to one subsection are 
indicated by dotted lines. 
In FIG. 26, when the beam radiation axis of the radar unit 120 is moved 
from the leftmost boundary line to the next boundary line for one 
subsection (corresponding to a 0.5.degree. change in the scanning angle 
.theta.), a range of the beam scanning indicated by "C1" is performed. 
Further, when the beam radiation axis of the radar unit 120 is moved for a 
further 0.5.degree. change in the scanning angle .theta., adjacent ranges 
of the beam scanning indicated by "C2", "C3" and "C4" are subsequently 
performed. These ranges "C1" through "C4" of the beam scanning overlap the 
adjacent ones. If a target is located near a boundary line between two 
adjacent ranges of the beam scanning, it is possible that the spectrum 
level peaks of the up-frequency and the down-frequency related to the same 
target be determined from each data of the reflection signals detected in 
the two ranges of the beam scanning. 
In the beam scanning of FIG. 26, the target 50 is located near the boundary 
line between the range C1 and the range C2. The spectrum level peaks 
related to the target 50 are determined from each of the data of the 
reflection signals detected in the range C1 and the data of the reflection 
signals detected in the range C2. Further, the target 52 is located near 
the boundary line between the range C2 and the range C3, and the spectrum 
level peaks related to the target 52 are determined from each of the data 
of the reflection signals detected in the range C2 and the data of the 
reflection signals detected in the range C3. 
FIGS. 27A and 27B show spectrum levels of the up-frequency and the 
down-frequency determined for the range "C1" of the beam scanning in FIG. 
26. As shown in FIG. 27A, a spectrum level peak "Su50" of the up-frequency 
related to the target 50 is determined from the data of the reflection 
signals for the range C1. As shown in FIG. 27B, a spectrum level peak 
"Sd50" of the down-frequency related to the target 50 is determined from 
the data of the reflection signals for the range C1. Since the target 50 
is the fixed pole, the relative velocity between the vehicle and the 
target 50 is considerably great. The frequency of the peak Sd50 is 
considerably separated from the frequency of the peak Su50. 
FIGS. 28A and 28B show spectrum levels of the up-frequency and the 
down-frequency determined for the range "C2" of the beam scanning in FIG. 
26. As shown in FIG. 28A, a spectrum level peak "Su52" of the up-frequency 
related to the target 52 and the spectrum level peak Su50 are determined 
from the data of the reflection signals for the range C2. As shown in FIG. 
28B, a spectrum level peak "Sd52" of the down-frequency related to the 
target 52 and the spectrum level peak Sd50 are determined from the data of 
the reflection signals for the range C2. Since the target 52 is running in 
advance of the vehicle, the relative velocity between the vehicle and the 
target 52 is not considerably great. The difference between the frequency 
of the peak Su52 and the frequency of the peak Sd52 is relatively small. 
FIGS. 29A and 29B show spectrum levels of the up-frequency and the 
down-frequency determined for the range "C3" of the beam scanning in FIG. 
26. As shown in FIG. 29A, only the spectrum level peak Su52 of the 
up-frequency is determined from the data of the reflection signals for the 
range C3. As shown in FIG. 27B, only the spectrum level peak Sd52 of the 
down-frequency is determined from the data of the reflection signals for 
the range C3. 
FIGS. 30A and 30B show spectrum levels of the up-frequency and the 
down-frequency determined for the range "C4" of the beam scanning in FIG. 
26. As shown, no spectrum level peak is determined from the data of the 
reflection signals for the range C4. 
When a single set of the spectrum level peaks of the up-frequency and the 
down-frequency is determined as in the case of FIGS. 27A and 27B or FIGS. 
29A and 29B, the values of the relative distance L and the relative 
velocity Vr related to the target can be easily and accurately calculated 
by using the above Equations (1)-(4). 
However, a plurality of sets of the spectrum level peaks of the 
up-frequency and the down-frequency related to a plurality of targets are 
determined as in the case of FIGS. 28A and 29B, it is difficult to 
accurately calculate the values of the relative distance L and the 
relative velocity Vr related to each target. In order to easily obtain 
accurate values of the relative distance L and the relative velocity Vr 
for each target, it is necessary to suitably perform a pairing of the 
spectrum level peaks related to the target and a pairing of the spectrum 
level peaks related to another target. 
In the radar control unit 210 of the present embodiment, a pairing of the 
spectrum level peaks related to one target and a pairing of the spectrum 
level peaks related to another target are selectively performed based on 
the data of the scanning angle. 
FIGS. 31A and 31B show a control procedure which is performed by the radar 
control unit 210 of the radar apparatus in FIG. 25. This control procedure 
is performed in order to achieve the above-mentioned function of the radar 
control unit 210. The control procedure in FIGS. 31A and 31B is started 
for every 100 msec needed for one beam scanning of the radar unit 120 to 
be performed by changing the scanning angle .theta. from -10.degree. to 
+10.degree. or vice versa. 
Referring to FIG. 31A, the radar control unit 210, at step S60, increments 
a counter i (i.rarw.i+1). The counter i indicates a specific range of the 
beam scanning of the radar unit 120 for one of forty subsections. When the 
radar control unit 210 is in an initial condition, the counter i is reset 
to zero. 
After the step S60 is performed, step S61 detects whether the data of the 
reflection signals for the range "i" indicated by the counter i is input. 
When the inputting of the data is not completed, the result at the step S61 
is negative. At this time, the step S61 is repeated until the inputting of 
the data is completed. 
When the result at the step S61 is affirmative, step S62 is performed. Step 
S62 performs the radar signal processing of the data of the reflection 
signals for the range of the beam scanning so that the spectrum level 
peaks of the up-frequency and the down-frequency for that range are 
determined. 
After the step S62 is performed, step S63 is performed. Step S63 detects 
whether the number of peaks included in the spectrum level data for one of 
the up-frequency and the down-frequency is greater than one. 
When the result at the step S63 is negative, step S66 is performed and 
steps S64 and S65 are not performed. At this time, a single set of the 
spectrum level peaks of the up-frequency and the down-frequency can be 
easily and accurately determined as in the case of FIGS. 27A and 27B or 
FIGS. 29A and 29B. 
When the result at the step S63 is affirmative, step S64 is performed. At 
this time, a plurality of sets of the spectrum level peaks of the 
up-frequency and the down-frequency related to a plurality of targets are 
determined as in the case of FIGS. 28A and 28B. Step S64 performs a 
pairing of the spectrum level peaks related to the target and a pairing of 
the spectrum level peaks related to another target on the order of the 
frequency of each peak. 
After the step S64 is performed, step S65 detects whether a correlation 
factor of the spectrum level peaks of each set is above a threshold value 
.alpha.th. 
The correlation factor is determined based on the shape of the spectrum 
level chart for the spectrum level peaks of each pair. When the spectrum 
level peaks are related to the same target, the correlation factor is set 
at a relatively great value. On the other hand, when the spectrum level 
peaks are related to different targets, the correlation factor is set at a 
relatively small value. At this time, the result at the step S65 is 
negative. 
When the result at the step S65 is affirmative, it is determined that the 
pairings of the spectrum level peaks related to the plurality of targets 
are suitably performed. At this time, step S66 is performed. Step S66 
determines the values of the relative distance L and the relative velocity 
Vr related to each target, and stores the determined values of the 
relative distance L and the relative velocity Vr of the target and the 
value of the counter i (indicating the range of the beam scanning) related 
thereto in a memory of the radar control unit 210. 
When the result at the step S65 is negative, it is determined that the 
pairings of the spectrum level peaks related to the plurality of targets 
are not suitably performed. At this time, step S67 is performed. Step S67 
stores the data of the spectrum level peaks in one of unfixed-peak areas 
of the memory of the radar control unit 210. In this embodiment, the 
stored data at the step S67 includes the value of the counter i, the 
spectrum level peaks, and the frequencies of the spectrum level peaks. 
After the step S66 or the step S67 is performed, step S68 is performed. 
Step S68 detects whether the value of the counter i is above a 
predetermined value n. The predetermined value n indicates the final range 
of the beam scanning of the radar unit 120. 
When the result at the step S68 is negative, it is determined that the 
inputting of the data of reflection signals for all the ranges of the beam 
scanning is not completed. At this time, the above steps S60 through S67 
are repeated until the inputting of all the data is completed. 
When the result at the step S68 is affirmative, it is determined that the 
inputting of all the data is completed. At this time, step S69 is 
performed. Step S69 resets the counter i to zero (i.rarw.0). After the 
step S69 is performed, step S70 in FIG. 31B is performed. 
Referring to FIG. 31B, step S70 sets a counter j at an unfixed-peak area 
number. This unfixed-peak area number indicates the unfixed-peak area of 
the memory of the radar control unit 210 in which the data of the spectrum 
level peaks is stored at the step S67. The value of the counter j at the 
step S70 indicates a specific one of the unfixed-peak areas of the memory 
of the radar control unit 210. 
After the step S70 is performed, step S71 sets a counter k at the value 
(j-1). 
Step S72 detects whether the data of the spectrum level peaks stored in the 
unfixed-peak area indicated by the value of the counter k has been fixed 
to determine the values of the relative distance and the relative 
velocity. 
When the result at the step S72 is negative, it is determined that the data 
of the spectrum level peaks stored in the area "k" has not been fixed. At 
this time, step S73 is performed. Step S73 detects whether the value of 
the counter k is smaller than the value of the counter j. 
When the result at the step S73 is affirmative (k&lt;j), step S74 decrements 
the counter k (k.rarw.k-1). On the other hand, when the result at the step 
S73 is negative (k.gtoreq.j), step S75 increments the counter k 
(k.rarw.k+1). 
After the step S74 or the step S75 is performed, the above step S72 is 
repeated until it is determined that the data of the spectrum level peaks 
stored in the area "k" has been fixed. 
When the result at the step S72 is affirmative, it is determined that the 
data of the spectrum level peaks stored in the area "k" has been fixed. At 
this time, step S76 is performed. Step S76 detects whether the spectrum 
level peaks stored in the area "k" are the same as those stored in an 
adjacent unfixed-peak area of the memory which is adjacent to the area 
"k". 
When the result at the step S76 is affirmative, it is determined that the 
pairings of the spectrum level peaks are suitably performed based on the 
peaks in the adjacent area which are the same. At this time, step S78 is 
performed. 
On the other hand, when the result at the step S76 is negative, it is 
determined that the pairings of the spectrum level peaks in this case 
cannot be suitably performed. At this time, step S77 is performed. Step 
S77 sets the counter k at the value (j+1). After the step S77 is 
performed, the above step S72 is repeated. 
Step S78 performs the pairings of the spectrum level peaks related to the 
data in the area "k" based on the peaks in the adjacent area. Since the 
number of the peaks included in the data in the area "k" is reduced, the 
pairings of the spectrum level peaks are easily performed. 
After the step S78 is performed, step S79 is performed. Step S79 performs 
the pairings of the remaining spectrum level peaks in the data in the area 
"k" on the order of the frequency of each peak and by using the 
correlation factor as in the steps S64 through S67. 
After the step S79 is performed, step S80 is performed. Step S80 detects 
whether all the data of the spectrum level peaks stored in all the 
unfixed-peak areas of the memory have been fixed to determine the values 
of the relative distance and the relative velocity. 
When the result at the step S80 is negative, the steps S70 through S79 are 
repeated until all the data of the spectrum level peaks are fixed. On the 
other hand, when the result at the step S80 is affirmative, the control 
procedure of the radar control unit 210 at the present cycle ends. 
It is possible that the radar apparatus of the present embodiment easily 
and accurately detects individual targets in a forward direction of the 
vehicle by separately performing a pairing of the data of received 
reflection signals related to one target and a pairing of the data of 
received reflection signals related to another target when a plurality of 
targets in the forward direction of the vehicle are detected. By 
performing the steps S70 through S78, the radar control unit 210 can 
separately perform the pairings of the spectrum level peaks in the 
unfixed-peak areas related to the plurality of targets, so that the 
relative distance and the relative velocity of each of the targets can be 
easily and accurately determined. 
Further, the present invention is not limited to the above-described 
embodiments, and variations and modifications may be made according to the 
present invention.