Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Radar mounted on and controls land vehicle
Reexamination Certificate
2003-05-13
2004-06-08
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Radar mounted on and controls land vehicle
C342S071000, C342S072000, C342S091000
Reexamination Certificate
active
06747592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radar system mounted on a vehicle for measuring a range rate, e.g. a relative velocity and a relative distance between the vehicle and a preceding vehicle, obstacle etc.
2. Description of Related Art
A radio radar using millimeter waves and other waves has been used for air-traffic control, meteorological observation because of low propagation loss and great propagation distance even in bad weathers, e.g. rains, fogs. Thanks to these merits, in collision prevention and safety fields of automobiles, a millimeter wave radar to measure a vehicular gap (relative distance; car-to-car distance) and a relative vehicle velocity between a preceding vehicle and the following vehicle (the vehicle with the radar system) is being researched, developed and commercialized these days. A radar system of a diplex Doppler type is disclosed as a typical one of radar modulation systems in Japanese Application Patent Laid-open Publication No. Sho 49-107491.
Referring to
FIG. 7
, this radar system modulates a signal output from a millimeter wave oscillator
101
into two time-sharing signals on frequencies f
1
and f
2
(the difference &Dgr;f: f
2
—f
1
) by a modulation signal
102
from a modulator
103
. These signals are transmitted by a transmit antenna
104
and reflect back when they meet a preceding vehicle
202
, and then they are received by a receive antenna
106
.
When there is some range rate (relative velocity) V between the preceding vehicle
202
and the millimeter wave radar system
100
b
of the following vehicle, Doppler frequencies fd
1
and fd
2
are caused in the reflected signals. As the result, the signals received by the receive antenna
106
have frequencies f
1
+fd
2
and f
2
+fd
2
. A mixer
108
turns these signals into time-shared signals (or intermediate frequency signals
107
hereinafter abbreviated as IF signals) respectively containing information of Doppler frequencies fd
1
and fd
2
. The IF signals
107
are amplified by an amplifier
109
and distributed to two low-pass filters (LPFs)
111
and
111
by a switch
110
which works in synchronism with the modulation signal
102
.
Referring to
FIG. 8
, a relationship between transmit signals and IF signals
107
is explained below. Transmit signals consist of two time-sharing signals on frequencies f
1
and f
2
. When the IF signals
107
pass through the mixer
108
, frequency components f
1
and f
2
of the transmit signals are removed from the received signal and the IF signals
107
respectively become signals containing information of Doppler frequencies. As already described above, the switch
110
works in synchronism with the modulation signal
102
to distribute the IF signals
107
containing information of Doppler frequencies fd
1
and fd
2
into a signal of Doppler frequency fd
1
and a signal of Doppler frequency fd
2
.
These Doppler signals are digitized by an A/D converter
112
, and transformed (analyzed) with FFT (Fast Fourier Transform) by a DSP (digital signal processor)
113
b
. With the FFT analysis, Doppler frequencies fd
1
, fd
2
and the phase differences &phgr;
1
, &phgr;
2
are obtained. The relative velocity V between the preceding vehicle
202
and the following vehicle (the vehicle having this radar system) is expressed by equation (1) or (2) below.
V=
(
C×fd
1
)/(2
×f
1
) (1)
or
V=
(
C×fd
2
)/(2
×f
2
) (2)
wherein
C is a signal ray (propagation) velocity.
Let's assume that fd
1
<<f
1
, fd
2
<<f
2
, and &Dgr;f<<f
1
. In this case, fd
1
can be approximately equal to fd
2
and the relative velocity V can be expressed by equation (3) below.
V≈
(
C×fd
1
)/(2
×f
0
) (3)
wherein
f
0
=(
f
1
+f
2
)/2
The relative distance R (range) between two cars can be expressed by equation (4) below.
R=C
×(&phgr;
1
−&phgr;
2
)/(4
&pgr;×&Dgr;f
) (4)
After computing the relative velocity V and the relative distance (vehicular gap; car-to-car distance) R, the DSP (digital signal processor)
113
b
send them to ACC (adaptive cruise control) unit
120
of the vehicle through a system microcomputer
115
b.
For example, as shown in
FIG. 2
, let assume that a preceding vehicle
202
runs before a vehicle
201
with this radar system, these velocities are respectively V
1
and V
2
, namely the relative velocity is (V
1
-V
2
), and the frequencies of Doppler signals are fd
1
and fd
2
.
FIG. 3
shows the result of the FFT analysis of the signals. In
FIG. 3
, a peak spectrum appears at the Doppler frequencies fd
1
and fd
2
on the Frequency axis. The relative velocity (V
1
-V
2
) and the relative distance R (DL in
FIG. 2
) between the preceding vehicle
202
and the following vehicle
201
can be obtained from this frequency information and the phase information as it is mentioned above.
This diplex Doppler type signal processing enables stable detection of a preceding vehicle without any complicated signal processing because it detects a spectrum corresponding to a preceding vehicle from the result of FFT analysis and we can get a relative velocity from the frequency information and a relative distance from the phase information simultaneously.
The above prior art has problems listed below.
For example, if the difference between the velocity V
1
of a vehicle
201
and the velocity V
2
of a preceding vehicle
202
as described referring to
FIG. 2
, that is, a relative velocity (V
1
-V
2
) is almost close to 0 and smaller than a minimum relative velocity that can be analyzed by the FFT, the frequency fd of the Doppler signal of the preceding vehicle
202
does not appear in the result of the FFT analysis as indicated in FIG.
9
.
In other words, if the relative velocity of the preceding vehicle
202
to the following vehicle
201
is very small, there is a problem that this radar system cannot detect (catch) a preceding vehicle.
SUMMARY OF THE INVENTION
The present invention has been created considering the above problems, and the object of the present invention is to provide a radar system which can detect a preceding vehicle (object) even when the range rate of the preceding vehicle relative to the vehicle equipped with this system is very small.
To accomplish the aforesaid object, the present invention is characterized by
a radar system comprising a transmit antenna for alternately transmitting two signals on different frequencies, a receive antenna for receiving signals which were transmitted from said transmit antenna and reflected back on the preceding object (e.g. vehicle, obstacle) when they met an object, a first digitizing means for sampling and digitizing respectively said received signals, and a first analyzing means for analyzing the frequencies of said digitized receive signals, extracting a peak spectrum, and computing a range rate of said object from the frequency of said peak spectrum;
wherein said radar system further comprises a second digitizing means for sampling and digitizing respectively said received signals, a second analyzing means for analyzing the frequencies of said receive signals digitized by said second analyzing means, extracting a peak spectrum, and computing a range rate of said object from the frequency of said peak spectrum, and an output means for outputting selectively either the range rate computed by said first analyzing means or the range rate computed by said second analyzing means; said first analyzing means stores, as a threshold, a frequency which is within an analyzable low frequency range and higher than a minimum analyzable frequency; said second digitizing means samples and digitizes said received signals at a higher sampling resolution than the sampling resolution of said first digitizing means so that said second analyzing means may be able to analyze frequencies below said threshold; and said first analyzing means causes said second digitizing means and said second analyzing means to work when sai
Alsomiri Isam
Tarcza Thomas H.
LandOfFree
Radar system for detecting relative velocity and relative... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Radar system for detecting relative velocity and relative..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radar system for detecting relative velocity and relative... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3355224