Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Radar mounted on and controls land vehicle
Reexamination Certificate
2000-05-23
2002-04-09
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Radar mounted on and controls land vehicle
C342S104000, C342S107000, C342S118000, C342S128000, C342S147000, C342S157000, C342S158000, C342S195000, C342S196000
Reexamination Certificate
active
06369748
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radar system mounted on a vehicle, which is suitable for use as a car-to-car distance measuring system for a vehicle.
2. Description of the Related Art
This type of known radar system may be an FMCW (Frequency Modulated Continuous Wave) radar system downsized by use of a transmit-receive shared antenna, of which a mountability on an automobile is thereby enhanced.
FIG. 5
is a block diagram showing a configuration of the conventional FMCW radar system.
Referring to
FIG. 5
, there are shown an oscillator
1
, a power divider
2
, a transmitting amplifier
3
, a circulator
4
, a transmit-receive shared antenna
5
including a horn antenna
51
and a reflection mirror antenna
52
, a target object
6
, a receiving amplifier
7
, a mixer
8
, a filter
9
, an AGC (Automatic Gain Control) amplifier
10
, an AD (Analog-to-Digital) converter
11
, a signal processor
12
, an antenna scan motor
13
for deflecting a transmitting direction and a receiving direction of the transmit-receive shared antenna
5
on the basis of an output given from the signal processor
12
, and an handle angle sensor
14
.
Next, an operation of the thus constructed prior art radar system mounted on the vehicle will be explained.
The signal processor
12
outputs a linear voltage signal for a frequency modulation. With this frequency modulation voltage signal, the oscillator
1
generates frequency-modulated electromagnetic waves. The power divider
2
divides the electromagnetic wave into two groups of electromagnetic waves. One group of electromagnetic waves are inputted to the mixer
8
, while the other group of electromagnetic waves, after being amplified by the transmitting amplifier
3
, arrive at the transmit-receive shared antenna
5
via the circulator
4
and are outputted into the air space from this antenna
5
.
The electromagnetic waves outputted into the air space from the transmit-receive shared antenna
5
, are reflected by the target object
6
and inputted back to the transmit-receive shared antenna
5
with a delay time Td with respect to the transmitting electromagnetic waves. Further, if the target object
6
has a relative velocity, the receiving electromagnetic waves are inputted to the transmit-receive shared antenna
5
with a Doppler shift Fd with respect to the transmitting electromagnetic waves. The electromagnetic waves received by the transmit-receive shared antenna
5
are, after being amplified by the receiving amplifier
7
, mixed with the transmitting electromagnetic waves by the mixer
8
, thereby outputting beat signals corresponding to the delay time Td and the Doppler shift Fd. The obtained beat signals are transmitted through the filter
9
and, after being amplified by the AGC amplifier
10
, inputted to the AD converter
11
. The signal processor
12
calculates a relative velocity and a relative distance to the target object
6
from the beat signals.
Next, a method by which the signal processor
12
calculates the relative velocity and the relative distance to the target object
6
, will be put into discussion.
FIG. 6
is an explanatory diagram showing one example of calculating the relative distance and the relative velocity by use of the radar system mounted on the vehicle.
Referring to
FIG. 6
, the transmitting signal is frequency-modulated with a frequency sweep bandwidth B at a modulation cycle Tm. The receiving signal has the delay time Td till the transmitting signal is inputted to the transmit-receive shared antenna
5
since the transmitting signals have been reflected by the target object
6
existing at, e.g., a distance R. Further, if the target object
6
has a relative velocity, the receiving signal is Doppler-shifted by a frequency fd with respect to the transmitting signal.
In this case, the mixer
8
outputs, as beat signals, a frequency difference Fbu between the transmitting signal and the receiving signal when the frequency rises, and a frequency difference Fbd between the transmitting signal and the receiving signal when the frequency lowers. The signal processor
12
takes in those beat signal as pieces of data via the A/D converter
11
, and executes an FFT (Fast Fourier Transformation) process on these pieces of data, thereby obtaining the frequency differences Fbu, Fbd and receiving intensities Mu, Md. The receiving intensities Mu, Md of the frequency differences Fbu, Fbd are generally the same, and hence an average value M thereof is given such as M=Mu=Md.
The relative distance R and the relative velocity V of the target object
6
are given by the following formula
R
=
TmC
4
B
(
Fbu
+
Fbd
)
,
V
=
λ
4
(
Fbu
-
Fbd
)
(
1
)
where Fbu, Fbd are the frequency differences, B is the frequency sweep bandwidth, Tm is the modulation cycle, C is the light velocity (=3.0×10
8
m/s), and &lgr; is the wavelength of the carrier wave (&lgr;=4.0×10
−3
m, if the carrier wave basic frequency F
o
=77 GHz).
Further, if a plurality of target objects
6
exist, the frequency differences Fbu, Fbd of the same object are elected from the plurality of frequency differences Fbu between the transmitting signals and the receiving signals when the frequencies rise, and the plurality of frequency differences Fbd between the transmitting signals and the receiving signals when the frequencies lower, and the relative distance R and the relative velocity V are obtained from the formula (1).
Given next is an explanation of a method by which the signal processor
12
calculates a direction of the target object
6
from the receiving intensity M.
For instance, Japanese Examined Patent Publication No. Hei 7-20016 discloses typical systems such as a mono-pulse system, a sequential lobing system and a conical scan system as conventional methods of calculating the direction. The sequential lobing system among those systems is herein described.
The signal processor
12
measures a relative distance, a relative velocity and a receiving intensity M
1
in a predetermined direction &thgr;1, and thereafter operates the antenna scan motor
13
to make a shift to a next direction &thgr;2. The signal processor
12
similarly measures a relative distance, a relative velocity and a receiving intensity M
2
. Data about the same relative distance and relative velocity are chosen among pieces of detection data in the plurality of directions, and an angle can be measured basically from a relationship in magnitude between the receiving intensity M
1
and the receiving intensity M
2
.
To be more specific, a sum pattern S(&thgr;) and a difference pattern D(&thgr;) are obtained from antenna beam patterns B
1
(&thgr;), B
2
(&thgr;) in the predetermined two directions &thgr;1, &thgr;2 by the following formulae (2) and (3):
S(&thgr;)=B
1
(&thgr;)+B
2
(&thgr;) (2)
D(&thgr;)=B
1
(&thgr;)−B
2
(&thgr;) (3)
Next, a discriminator DS(&thgr;) shown in the following formula (4), which is standardized by the sum pattern S(&thgr;), is obtained.
DS(&thgr;)=D(&thgr;)/S(&thgr;) (4)
Subsequently, the discriminator DS(&thgr;) shows a relationship of simple increment or simple decrement with the measured angle value &thgr; within a half-value width &thgr;s of the sum pattern S(&thgr;).
An angle &thgr;n at which a central angle &thgr;o in the predetermined two directions &thgr;1, &thgr;2 is standardized by the half-value width &thgr;s of the sum pattern S(&thgr;), is given by the following formula (5). An inclination k of the discriminator DS(&thgr;) in the vicinity of &thgr;n=0, is given by the following formula (6).
&thgr;n=(&thgr;−&thgr;o)/&thgr;s (5)
k=DS(&thgr;)/&thgr;n (6)
Furthermore, the discriminator DS obtained by observation from the receiving intensities M
1
and M
2
is obtained from the following formula (7):
DS=(M
1
−M
2
)/(M
1
+M
2
) (7)
Hence, the measured angle value &thgr; can be obtained b
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