Communications: directive radio wave systems and devices (e.g. – Determining velocity – Combined with determining distance
Reexamination Certificate
1999-12-10
2002-05-07
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining velocity
Combined with determining distance
C342S104000, C342S115000, C342S118000, C342S128000, C342S175000, C342S192000, C342S195000, C342S196000
Reexamination Certificate
active
06384769
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a distance/speed measuring method for measuring distances/speeds of detected targets (objects), and also a radar apparatus with employment of this distance/speed measuring method. More specifically, the present invention is directed to such a distance/speed measuring method capable of detecting the targets to measure relative distances and relative speeds between these targets by using a frequency-modulated continuous wave (FMCW), and further directed to a radar apparatus using this distances/speeds measuring method.
2. Description of the Related Art
Radar systems with employment of frequency-modulated continuous waves (FMCWs) are known in this technical field. In this known radar system, a beat frequency “F
up
” of a modulating frequency ascent period and another beat frequency “F
dn
” of a modulating frequency descent period are measured as to a target (object). In this case, the beat frequency “F
up
” of the modulating frequency ascent period and the beat frequency “F
dn
” of the modulating frequency descent period are expressed by the below-mentioned formulae (1) and (2):
[formula 1]
F
up
=(2
B/CT
)·
R
−2
/&lgr;·V≡Fr−Fv
(1),
and
F
dn
=−(2
B/CT
)·
R
−2
/&lgr;·V≡−Fr−Fv
(2).
As a result, a target relative distance “R” may be calculated from F
up
−F
dn
, and also a target relative speed “V” may be calculated from F
up
+F
dn
based upon the following formulae (3) to (6). It should be noted that in these formulae, symbol “B” shows a frequency modulation width; symbol “C” denotes a light velocity; symbol “T” represents a modulation period; symbol “&lgr;” shows a wavelength of a radar carrier wave; symbol “Fr” denotes a distance frequency; and also symbol “Fv” indicates a speed frequency:
[formula 2]
Fr
=(F
up
−F
dn
)/2 (3),
Fv
=−(F
up
+F
dn
/2) (4),
R
=(
CT
/2
B
)·
Fr
(5),
and
V
=(&lgr;/2)·
Fv
(6).
In such a case that the targets are present, combinations among beat frequencies “F
up
(n)” and the beat frequencies “F
dn
(m)” corresponding to the respective targets must be sought as to the beat frequencies F
up
(i) (i=1 to N) which are detected in the modulating frequency ascent period, and further as to the beat frequencies F
dn
(i) (i=1 to M) which are detected in the modulating frequency descent period.
For example, in Japanese Patent Application Laid-open No Hei-7-49378 and Japanese Patent Application Laid-open No. Hei7-55926, with respect to the frequency spectra of the reception signals in each of the periods, which are calculated so as to obtain the beat frequencies, the combinations of the beat frequencies are determined by utilizing the relative amounts as to the spectrum shape near peaks. Also, in Japanese Patent Application Lain-open No. Hei-7-77575, as to the frequency spectrum calculated to obtain beat frequencies, the combinations of the beat frequencies are determined by utilizing the magnitude order of the respective power levels of the peaks.
However, in any of the above-explained conventional radar systems, the combinations of the beat frequencies are erroneously determined due to the adverse influences, namely the variations in the moving (mobile) target signals, and also the unnecessary signal components such as the noise signals. As a result, these erroneous combinations are outputted as the false targets.
In this case, if such a discrimination can be carried out between a target which has no speed difference with respect to this radar system and may be observed as a stationary target from this radar system (will be simply abbreviated as a “stationary target” hereinafter), and another target which has a speed difference with respect to the radar system and may be observed as a moving target (mobile object) from this radar system (will be simply abbreviated as a “moving target” hereinafter) among targets, then it is possible to reduce the appearance of the false targets caused by this erroneous combination.
For example, in Japanese Patent Application Laid-open No. 6-214017, Japanese Patent Application Laid-open No. 7-98376, and Japanese Patent Application Laid-open No. 7-191133, the power difference (see
FIG. 9C
) is calculated between the frequency spectrum of the modulating frequency ascent period (see
FIG. 9A
) and the frequency spectrum of the modulating frequency decent period (see FIG.
9
B). Then, such stationary targets whose frequencies become equal to each other both in the modulating frequency ascent and descent periods are canceled, and only the moving targets are employed so as to be sought as the combinations.
However, when moving targets are employed as the targets to be sought, there is a certain case that a beat frequency (see
FIG. 10A
) in a modulating frequency ascent period of a certain moving target becomes equal to another beat frequency (See
FIG. 10B
) in a modulating frequency descent period of another moving target. Accordingly, there is a problem in that no final target detection output can be produced (see FIG.
10
C).
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-explained problem, and therefore, has an object to provide a target distance/speed measuring method, and a radar apparatus with employment of such a target distance/speed measuring method capable of measuring a distance and a speed between the respective targets while discriminating a moving target from a stationary target among targets.
A target distance/speed measuring method, according to an aspect of the present invention, is characterized in that in such a method for measuring distances and speeds of each of targets by employing a frequency-modulated continuous wave based upon a seeking result of combinations between beat frequencies detected for the targets in a modulating frequency ascent period and the beat frequencies detected in a modulating frequency descent period with respect to each of the targets, since moving targets are discriminated from stationary targets by using reference specific frequencies which correspond to a detection result with respect to a reference spectrum obtained as a calculation result between a frequency spectrum in a modulating frequency ascent period and a frequency spectrum in a modulating frequency descent period, the distances and the speeds of the respective targets are measured while the targets are discriminated as the moving targets and the stationary targets.
Also, the target distance/speed measuring method is characterized in that the specific frequencies equal to a detection result with respect to a reference spectrum which has been obtained during one preceding measuring operation of a presently measured modulating frequency ascent period and a presently measured modulating frequency descent period are utilized as a reference with respect to a repeated modulating frequency ascent period and a repeated modulating frequency descent period.
Also, the target distance/speed measuring method is characterized in that the reference spectrum is obtained from an absolute value of a power difference between a frequency spectrum of a modulating frequency ascent period and a frequency spectrum of a modulating frequency descent period.
A radar apparatus, according to another aspect of the present invention, is characterized by comprising: transmitting means for transmitting a transmission wave of a continuous wave whose modulating frequency ascends or descends to a target; receiving means for receiving a reception wave reflected from the target; beat signal producing means for producing a beat signal having a frequency corresponding to a frequency difference between the transmission wave and the reception wave reflected from the target; fast Fourier-transform processing means for acquiring a frequency spectrum of the beat signal; beat frequency detecting means for detecting the frequencies
Kirimoto Tetsuo
Mitsumoto Masashi
Gregory Bernarr E.
Mitsubishi Denki & Kabushiki Kaisha
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