Communications: directive radio wave systems and devices (e.g. – Determining distance – With frequency modulation
Reexamination Certificate
2001-12-04
2003-05-13
Lobo, Ian J. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining distance
With frequency modulation
C342S109000, C342S128000
Reexamination Certificate
active
06563454
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a radar apparatus which is mounted on an automobile and/or installed on a road facility so as to detect an object (obstacle and traveling vehicle) appeared on a road. That is, the present invention is related to an FM-CW radar apparatus for detecting a beat signal of an FM transmission signal wave, which is produced by a reflection wave reflected from an object, and for analyzing a frequency component of the beat signal so as to calculate both a distance and a velocity-of the object. More specifically, the present invention is directed to an FM-CW radar apparatus capable of reducing a measuring time duration by ½, required to detect an object in such a manner that both an FM modulation wave along a frequency-up direction and an FM modulation wave along a frequency-down direction are simultaneously transmitted, and then, beat frequency components with respect to the respective FM modulation waves are analyzed so as to calculate a distance and a velocity of an object.
2. Description of the Related Art
In general, as described in, for instance, Japanese Patent Application Laid-open No. 63-275976 (Japanese Patent No. 2550574), FM-CW type radar apparatus have be widely used as radar apparatus designed for automobiles.
FIG.
7
and
FIG. 8
are explanatory diagrams for explaining a basic idea of a conventional FM-CW radar apparatus. That is,
FIG. 7
represents a change in reception frequencies and a change in beat frequencies in the case that a signal is transmitted to a stationary object, whereas
FIG. 8
shows a change in reception frequencies and a change in beat frequencies in such a case that a signal is transmitted to a moving object.
In these drawings, transmission frequencies of transmission signals to objects (targets) which should be detected; reception frequencies of reflection signals reflected/received from the objects; and the respective beat frequencies “fbu” and “fbd” obtained when the signal is frequency-modulated along the up direction, and the signal is frequency-modulated along the down direction are represented in the form of waveforms as a relationship with respect to time “t”, respectively.
In
FIG. 7
, a carrier wave (FM modulation wave) having a center frequency “f
0
” is transmitted by way of an FM modulation method by which the carrier wave is repeatedly changed to a triangular shape.
A triangular-shaped wave indicated by a solid line in
FIG. 7
shows a relationship between the frequency of the transmission signal and the time “t”. Another triangular-shaped wave indicated by a broken line shows a relationship between a reception signal and the time “t”. This reception signal is reflected/received from, for example, an object located at a distance “R”. This triangular-shaped wave is delayed by such a time duration defined by that the transmission signal has been transmitted, and the reflection signal is received.
In this case, assuming now that frequencies of beat signals constructed of frequency differences between transmission signals and reception signals during frequency-up modulation and also frequency-down modulation are selected to be “fbu” and “fbd”, the respective beat frequencies “fbu” and “fbd” are expressed by the below-mentioned equation (1).
fbu=−fr
fbd=fr
(1)
It should be noted that in the above-described equation (1), symbol “fr” shows a beat frequency caused by a reflection signal which is reflected from a stationary object located at a distance of “R”. This beat frequency is given by the below-mentioned equation (2) by employing a repetition frequency “fm” of an FM signal (FM modulation wave), a frequency shift width “&Dgr;F” of the FM signal, and a light velocity “c”.
fr=
4×
R·fm·&Dgr;F/c
(2)
Based upon this equation (2), the distance “R” is calculated in accordance with the below-mentioned equation (3).
R=fr·c/
(4×
fm·&Dgr;F
) (3)
On the other hand, in the case that an object is moved, both a frequency change in transmission signals and a frequency change in reception signals with respect to time, which are caused by the Doppler effect, are as indicated in FIG.
8
.
In general, a Doppler frequency “fv” is given by the following equation (4).
fv=
2×
vr·f
0
/c
(4)
In this equation (4), symbol “vr” indicates a velocity (speed) of the object. This velocity “vr” of the object may be given by the below-mentioned equation (5).
vr=fv·c/
(2×
f
0 (5)
Also, in
FIG. 8
, the beat frequencies “fbu” and “fbd” which are caused by reflection signals reflected from such an object which is approached are defined based upon the below-mentioned equation (6), namely are equal to such values obtained by adding the Doppler frequency “fv” to the beat frequencies obtained in the case of the stationary object.
fbu=−fr+fv
fbd=fr+fv
(6)
In accordance with the above-described equation (6), both the Doppler frequency “fv” and the beat frequency “fr” are expressed based upon the below-mentioned equation (7).
fv=
(
fbd+fbu
)/2
fr=
(
fbd−fbu
)/2 (7)
The above-explained equation (7) is substituted for the above-mentioned equations (3) and (5), so that both the distance “R” of the object and the velocity “vr” of this object may be calculated by employing the measured beat frequencies “fbu” and “fbd” as follows.
R=
(
fbd−fbu
)·
c/
(8×
fm·&Dgr;F
)
vr=
(
fbd+fbu
)·
c/
(4×
f
0) (8)
In this case, resolution “&Dgr;v” of the velocity “vr” is determined based upon analyzable minimum frequencies of the beat frequencies “fd” and “fr”. Since the repetition frequency of the FM modulation wave is equal to “fm”, this resolution “&Dgr;v” of the velocity “vr” may be determined for either a frequency ascent time period or a frequency descent time period (=2×fm) one time.
In other words, the resolution “&Dgr;v” of the velocity “vr” may be expressed by the following equation (9).
&Dgr;v=fm·c/f
0 (9)
On the other hand, in the case that a plurality of objects are present on a road, a plurality of beat signals are produced during the frequency-up modulation and also during the frequency-down modulation, the total number of which correspond to the total number of these objects.
In this case, in order to detect only a specific object, a beat signal of the relevant object is selected from the plurality of beat signals. Then, both the distance “R” and the velocity “vr” of this specific object are calculated from the respective beat signals during both the frequency-up modulation and the frequency-down modulation.
In order to select a combination of beat signals, such data as magnitudes of signal components of these beat signals may be used as reference purposes.
In other words, such beat signals whose signal levels are substantially equal to each other are selected from signals obtained during the frequency-up modulation and the frequency-down modulation, and then, the selected beat signals are combined with each other.
On the other hand, while an interval control operation between successively-driven automobiles is carried out, such a fact is known. That is, a change in vehicle drive speeds rather than a change in the above-described intervals between the successively-driven vehicles may give a large influence to a comfortable driving condition.
As a consequence, in order that a vehicle speed of the own vehicle is smoothly controlled in response to a relative speed with respect to a preceding vehicle so as to improve such a comfortable driving condition, this relative speed should be measured in high resolution.
In the above-explained radar apparatus, as previously described, in order to improve the resolution “&Dgr;V” of the velocity “vr”, the repetition period of the modulation should be set to the longer repetition period.
However, when the repetition period is made longer, the data updating period is lower
Lobo Ian J.
Sughrue & Mion, PLLC
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