U.S. patent application number 10/621617 was filed with the patent office on 2005-01-13 for radar apparatus.
This patent application is currently assigned to Fujitsu Ten Limited. Invention is credited to Isaji, Osamu.
Application Number | 20050007271 10/621617 |
Document ID | / |
Family ID | 19046650 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050007271 |
Kind Code |
A1 |
Isaji, Osamu |
January 13, 2005 |
Radar apparatus
Abstract
A modulation signal generation circuit performs frequency
modulation of a VCO with a triangular wave for operation as an
FM-CW radar. A signal processing circuit gives a modulation signal
for detection generated from the modulation signal generation
circuit to the VCO. A high-frequency signal subjected to frequency
modulation in the VCO is transmitted as a radio wave from a
transmission antenna and is reflected on a target and the reflected
radio wave is received at a reception antenna. The reception signal
and the high-frequency signal are mixed by a mixer to provide a
beat signal and frequency shift corresponding to a voltage V1 is
detected from the frequency of the beat signal. If the voltage V1
of the modulation signal for detection is switched, the frequency
shift corresponding to different voltage V1 can be provided and the
frequency modulation characteristic can be detected.
Inventors: |
Isaji, Osamu; (Kobe-shi,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Fujitsu Ten Limited
Kobe-shi
JP
|
Family ID: |
19046650 |
Appl. No.: |
10/621617 |
Filed: |
July 18, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10621617 |
Jul 18, 2003 |
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10192520 |
Jul 11, 2002 |
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6597308 |
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Current U.S.
Class: |
342/70 ; 342/109;
342/128; 342/174 |
Current CPC
Class: |
G01S 13/345 20130101;
G01S 7/35 20130101; G01S 13/931 20130101; G01S 2013/9329 20200101;
G01S 7/4008 20130101 |
Class at
Publication: |
342/070 ;
342/174; 342/128; 342/109 |
International
Class: |
G01S 013/42 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 11, 2001 |
JP |
2001-211314 |
Claims
What is claimed is:
1. A radar apparatus for performing frequency modulation of a
high-frequency signal, transmitting the frequency-modulated signal,
and receiving a reflected radio wave to detect a target, the radar
apparatus comprising: a high frequency generation section for
generating the high-frequency signal; a modulation signal
generation section for generating and giving a modulation signal to
the high frequency generation section to modulate the high
frequency signal; a mixing section for mixing the high-frequency
signal and the reception signal of the reflected radio wave; and a
signal processing section for controlling the modulation signal
generation section so as to give a modulation signal for detection
changing among a plurality of predetermined signal levels and
retained for a predetermined time for each signal level to the high
frequency generation section, detecting frequency of a differential
signal between the high-frequency signal and the reception signal,
inputted from the mixing section, and detecting a frequency
modulation characteristic of the high frequency generation section
based on the relationship between a signal level of the modulation
signal for detection and the frequency of the differential
signal.
2. The radar apparatus according to claim 1, further comprising a
modulation characteristic correction section for correcting the
modulation signal based on the frequency modulation characteristic
detected by the signal processing section so that the frequency
modulation characteristic is not placed out of a predetermined
normal range.
3. The radar apparatus according to claim 1, further comprising a
width calculation section for calculating frequency modulation
width, which is a difference between frequency of the differential
signal when the signal level of the modulation signal is the
maximum value and frequency of the differential signal when the
signal level is the minimum value based on the frequency modulation
characteristic detected by the signal processing section.
4. The radar apparatus according to claim 3, wherein the width
calculation section includes a counter for counting the frequency
of the difference.
5. The radar apparatus according to claim 3, further comprising a
width correction section for correcting the modulation signal based
on the frequency modulation width calculated by the width
calculation section so that the frequency modulation width has a
predetermined value.
6. The radar apparatus according to claim 2, wherein one of the
modulation characteristic correction section and the width
correction section performs the correction when the level of the
reception signal of the reflected radio wave is equal to or greater
than a predetermined level.
7. The radar apparatus according to claim 2, further comprising a
temperature detection section, wherein one of the modulation
characteristic correction section and the width correction section
performs the correction when a temperature detected by the
temperature detection section has a predetermined temperature.
8. The radar apparatus according to claim 2, wherein one of the
modulation characteristic correction section and the width
correction section performs the correction when a distance to the
target is in a predetermined distance range.
9. The radar apparatus according to claim 2, wherein one of the
modulation characteristic correction section and the width
correction section performs the correction when relative speed of
the target is in a predetermined speed range.
10. The radar apparatus according to claim 1, wherein the signal
processing section detects the frequency modulation characteristic
when an input level of the reflected radio wave from the target is
equal to or greater than a predetermined reference level at a
normal radar operation time.
11. The radar apparatus according to claim 1, wherein the signal
processing section detects the frequency modulation characteristic
when a distance to the target is in a predetermined distance
range.
12. The radar apparatus according to claim 1, wherein the signal
processing section detects the frequency modulation characteristic
just after detecting the target initially after a radar operation
starts and determines whether or not a normal modulation operation
for the high frequency generation section is performed.
13. The radar apparatus according to claim 1, further comprising a
reference signal source for generating a reference signal to
decrease a frequency with respect to the differential signal
between the high-frequency signal and the reception signal, the
differential signal inputted to the signal processing section from
the mixing section, wherein the signal processing section detects
the frequency modulation characteristic based on the inputted
differential signal with the frequency decreased by the reference
signal.
14. The radar apparatus according to claim 13, wherein the
reference signal source comprises: a basic signal generation
section for generating a basic signal, which is a source of the
reference signal; and a frequency division section for dividing the
frequency of the basic signal generated from the basic signal
generation section according to one of frequency dividing ratios
that can be switched to convert the basic signal into the reference
signal.
15. The radar apparatus according to claim 13, wherein the
reference signal source includes a plurality of reference signal
generation sections and selects one of the reference signal
generation sections to generate the reference signal.
16. The radar apparatus according to claim 13, wherein the
reference signal source comprises a signal arithmetic section for
generating the reference signal by performing arithmetic processing
according to a preset program.
17. The radar apparatus according to claim 13, wherein the
reference signal source supplies a clock signal for a signal
arithmetic processing to the signal processing section.
18. The radar apparatus according to claim 13, wherein a frequency
of the reference signal is set so that a difference from the
frequency of the reception signal from the target is within a beat
signal band at a time of a radar operation.
19. The radar apparatus according to claim 18, wherein the signal
processing section performs at least a part of processing of the
beat signal.
20. The radar apparatus according to claim 1, wherein the signal
processing section changes a predetermined time for holding a
signal level of the modulation signal for detection in response to
a distance to the target.
21. The radar apparatus according to claim 1, wherein the signal
processing section changes a predetermined time for holding a
signal level of the modulation signal for detection in response to
a relative speed of the target.
22. The radar apparatus according to claim 1, wherein the signal
processing section detects the frequency of the differential signal
between the high-frequency signal and the reception signal
considering a Doppler shift based on a relative speed of the
target.
Description
[0001] The present disclosure relates to the subject matter
contained in Japanese Patent Application No.2001-211314 filed on
July 11, which is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a radar apparatus using frequency
modulation (FM) such as an FM-CW system and in particular to
detection and correction of the frequency modulation characteristic
thereof.
[0004] 2. Description of the Related Art
[0005] Hitherto, an FM-CW system radar 1 having a basic
configuration as shown in FIG. 16 has been mainly installed in an
automobile for use to give a collision alarm, prevent or lighten a
collision, perform vehicle-to-vehicle control of auto cruise
control, drive a car, etc. FIG. 16(a) shows a schematic electric
configuration and FIG. 16(b) shows a modulation signal waveform.
Related arts to the FM-CW system radar are disclosed in
JP-A-5-40169, JP-A-7-55942, JP-A-8-327728, etc., for example.
JP-A-5-40169 discloses an art for using second frequency modulation
to improve the reception S/N ratio.
[0006] In the basic configuration of the FM-CW system radar 1, a
radio wave is transmitted from a transmission antenna 2 and the
reflected radio wave from a target, etc., is received at a
reception antenna 3, as shown in FIG. 16(a). A high-frequency
signal of a millimeter waveband generated from a VCO
(voltage-controlled oscillator) 4 is given to the transmission
antenna 2. A part of the high-frequency signal for exciting the
transmission antenna 2 from the VCO 4 branches from a coupler 5 and
is mixed with a reception signal from the reception antenna 3 by a
mixer 6. An output signal from the mixer 6 is selected through a
BPF (band-pass filter) 7 and is amplified by an amplifier 8. The
high-frequency signal generated from the VCO 4 is subjected to
frequency modulation in accordance with the voltage level of a
modulation signal given by a modulation signal generation circuit
9.
[0007] For example, in the FM-CW system radar 1 of a millimeter
waveband, a modulation signal shaped like a triangular wave of
about several hundred Hz as shown in FIG. 16(b) is used to generate
an FM wave with the maximum frequency shift amount being several
ten to several hundred MHz. As the modulation signal, a saw tooth
wave (chirp wave) may be used in some cases. If the frequency
modulation characteristic of the VCO 4 has good linearity relative
to change in the voltage level of the modulation signal, the
frequency of the high-frequency signal generated from the VCO 4
also changes linearly corresponding to FIG. 16(b). The frequency of
the reflected radio wave received at the reception antenna 3 is
delayed from the frequency of the high-frequency signal given to
the transmission antenna 2 as much as the time taken for the radio
wave to go and back at the distance to the target. If the
high-frequency signal whose frequency changes like a triangular
wave corresponding to FIG. 16(b) is generated from the VCO 4 and
the distance to the target is constant, the signal output from the
mixer 6 contains a beat signal component of a constant frequency
corresponding to the time taken for the radio wave to go and back
at the distance. The beat signal component is selected through the
BPF 7 and is amplified by the amplifier 8 and then can be input to
a signal processing circuit 10 for calculating the distance to the
target. When the distance to the target changes, the effect of
Doppler shift appears in the frequency of the beat signal and the
relative speed can also be calculated by the signal processing
circuit 10. Letting the frequency of the beat signal be fb, the
frequency depending on the distance be fx, and the frequency
depending on the relative speed be fd,
fb=fx.+-.td.
[0008] With the FM-CW system radar 1, the frequency modulation
characteristic in the VCO 4 has an importance effect on the
measurement accuracy. JP-A-7-55942 discloses an art for previously
measuring the frequency modulation characteristic of a
voltage-controlled oscillator for generating a high-frequency
signal of an FM-CW radar and making a correction with an inverse
function of the measured characteristic for improving linearity.
JP-A-8-327728 discloses an art for correcting a modulation signal
so that the frequency of a high-frequency signal generated in an
FM-CW radar apparatus changes like a triangular wave. JP-A-6-34756
discloses an art wherein the linearity of a voltage-controlled
oscillator for generating a high-frequency signal as a source of a
transmission radio wave in a radar transponder for transmitting a
frequency-modulated radio wave and responding upon reception of a
radio wave from a radar is corrected with data previously stored in
memory. However, the related arts do not give any direct
description as to how the frequency modulation characteristic is
measured.
[0009] FIG. 17 shows a schematic configuration for measuring the
frequency modulation characteristic and sensing whether or not
linearity is maintained in the FM-CW system radar 1 in the related
art shown in FIG. 16(a). Another signal source 11 is provided, the
high-frequency signal from the VCO 4 is branched by a coupler 12
and is mixed by a mixer 13 for down conversion, and the difference
from the frequency of the signal source 11 is counted by a counter
14. In addition to such down conversion, a method of counting the
frequency of the high-frequency signal from the VCO 4 is also
available.
[0010] The FM-CW system radar 1, etc., installed in a vehicle is
used in a hostile environment concerning vibration, temperature,
etc. Thus, if the linearity of the frequency modulation
characteristic is good at the initial stage, there is a possibility
of degradation while the radar is used. If the down converter
configuration as shown in FIG. 17 is adopted to install a
configuration for detecting the linearity of the frequency
modulation characteristic in the FM-CW system radar 1 itself, as
the signal source 11, the mixer 13, and the like, expensive
components for high frequencies of a millimeter waveband become
necessary. To count the frequency of the high-frequency signal from
the VCO 4, the millimeter waveband cannot directly be counted and
therefore a frequency divider needs to be used. However, the
frequency divider operating in the millimeter waveband is expensive
and as the frequency dividing ratio increases, the measurement
accuracy is degraded.
[0011] That is, if an attempt is made to detect and correct the
frequency modulation characteristic in the system in the related
art as shown in FIG. 17, the following problems are involved:
[0012] (1) The higher the transmission frequency, the higher the
costs of the components, such as a detector and a frequency
divider.
[0013] (2) The higher the transmission frequency, the larger the
frequency dividing ratio and the worse the measurement
accuracy.
BRIEF SUMMARY OF THE INVENTION
[0014] It is an object of the invention to provide a radar
apparatus that can detect and correct the frequency modulation
characteristic in a simple configuration at low costs.
[0015] According to the invention, there is provided a radar
apparatus for performing frequency modulation of a high-frequency
signal, transmitting the frequency-modulated signal, and receiving
a reflected radio wave to detect a target, the radar apparatus
including a high frequency generation section for generating the
high-frequency signal, a modulation signal generation section for
generating and giving a modulation signal to the high frequency
generation section to modulate the high frequency signal, a mixing
section for mixing the high-frequency signal and the reception
signal of the reflected radio wave, and a signal processing section
for controlling the modulation signal generation section so as to
give a modulation signal for detection changing among a plurality
of predetermined signal levels and retained for a predetermined
time for each signal level to the high frequency generation
section, detecting frequency of a differential signal between the
high-frequency signal and the reception signal, inputted from the
mixing section, and detecting a frequency modulation characteristic
of the high frequency generation section based on the relationship
between a signal level of the modulation signal for detection and
the frequency of the differential signal.
[0016] According to the invention, the radar apparatus for
performing frequency modulation of a high-frequency signal,
transmitting the frequency-modulated signal, and receiving a
reflected radio wave for detecting a target comprises the
modulation signal generation section, the mixing section, and the
signal processing section. The modulation signal generation section
generates a modulation signal whose change state can be controlled
and gives the signal to the high frequency generation section. The
mixing section mixes the high-frequency signal generated from the
high frequency generation section and the reception signal of the
reflected radio wave. The signal processing section controls the
modulation signal generation section so as to give modulation
signal for detection changing between a plurality of predetermined
signal levels and retained for a predetermined time for each signal
level to the high frequency generation section, inputs the signal
of the component of the difference between the high-frequency
signal and the reception signal from the mixing section, detects
the frequency, and detects the frequency modulation characteristic
of the high frequency generation section based on the relationship
between the signal level of the modulation signal for detection and
the frequency. The modulation signal for detection generated from
the modulation signal generation section is changed between a
plurality of predetermined signal levels and is mixed with the
reception signal from the target by the mixing section, the
frequency of the signal of the component of the difference is
detected, the relationship between the signal level of the
modulation signal for detection and the frequency is found, and the
frequency modulation characteristic of the high frequency
generation section can be detected. The reception signal can be
used as the high-frequency signal source to detect the frequency
modulation characteristic and the mixing section for reception can
also be shared, so that the frequency modulation characteristic can
be detected easily in the inexpensive configuration.
[0017] The invention provides the radar apparatus further including
a modulation characteristic correction section for correcting the
modulation signal based on the frequency modulation characteristic
detected by the signal processing section so that the frequency
modulation characteristic is not placed out of a predetermined
normal range.
[0018] According to the invention, the modulation signal is
corrected so that the frequency modulation characteristic that can
be detected easily in the inexpensive configuration is not placed
out of the predetermined normal range, so that the frequency
modulation characteristic can also be corrected easily in the
inexpensive configuration.
[0019] The invention provides the radar apparatus further including
a width calculation section for calculating frequency modulation
width, which is a difference between frequency of the differential
signal when the signal level of the modulation signal is the
maximum value and frequency of the differential signal when the
signal level is the minimum value based on the frequency modulation
characteristic detected by the signal processing section.
[0020] According to the invention, the frequency modulation width
of the difference between the frequency when the signal level of
the modulation signal is the maximum value and the frequency when
the signal level is the minimum value can be calculated based on
the frequency modulation characteristic detected as frequency
change between a plurality of signal levels.
[0021] In the radar apparatus of the invention, the width
calculation section includes a counter for counting the frequency
of the difference.
[0022] According to the invention, frequency change between a
plurality of signal levels is counted by the counter, so that
frequency change can be measured easily.
[0023] The invention provides the radar apparatus further including
a width correction section for correcting the modulation signal
based on the frequency modulation width calculated by the width
calculation section so that the frequency modulation width has a
predetermined value.
[0024] According to the invention, the frequency modulation width
of the frequency modulation characteristic can also be corrected to
the predetermined value. When the distance is calculated in the
signal processing section, a correction can also be made on the
arithmetic operations.
[0025] In the radar apparatus of the invention, one of the
modulation characteristic correction section and the width
correction section performs the correction when the level of the
reception signal of the reflected radio wave is equal to or greater
than a predetermined level.
[0026] According to the invention, if the level of the reception
signal is equal to or greater than the predetermined level, a
correction is made and thus can be made stably.
[0027] The invention provides the radar apparatus further including
further comprising a temperature detection section, in which one of
the modulation characteristic correction section and the width
correction section performs the correction when a temperature
detected by the temperature detection section has a predetermined
temperature.
[0028] According to the invention, if the frequency of the
high-frequency signal generated from the high frequency generation
section changes with the temperature, a correction is made if the
predetermined temperature of the temperature detection section is
reached, so that the effect of the temperature can be decreased and
the accuracy of the frequency modulation characteristic can be
enhanced.
[0029] In the radar apparatus of the invention, one of the
modulation characteristic correction section and the width
correction section performs the correction when a distance to the
target is in a predetermined distance range.
[0030] According to the invention, the distance range, etc., having
a high possibility that the signal level of the reception signal
will lower is placed out of the predetermined distance range,
whereby correction processing is not entered, so that accuracy
degradation of correction can be avoided.
[0031] In the radar apparatus of the invention, one of the
modulation characteristic correction section and the width
correction section performs the correction when relative speed of
the target is in a predetermined speed range.
[0032] According to the invention, the relative speed of the target
is considered and if the relative speed of the target is placed in
the predetermined speed range, a correction is made, so that the
accuracy of the correction can be enhanced.
[0033] In the radar apparatus of the invention, the signal
processing section detects the frequency modulation characteristic
when an input level of the reflected radio wave from the target is
equal to or greater than a predetermined reference level at a
normal radar operation time.
[0034] According to the invention, if the input level of the
reception signal is equal to or greater than the predetermined
reference level, the frequency modulation characteristic is
detected, so that the radar apparatus can concentrate attention on
usual target detection processing.
[0035] In the radar apparatus of the invention, the signal
processing section detects the frequency modulation characteristic
when a distance to the target is in a predetermined distance
range.
[0036] According to the invention, if the distance to the target is
out of the predetermined distance range, the frequency modulation
characteristic is not detected, so that the radar apparatus can
concentrate attention on usual target detection processing.
[0037] In the radar apparatus of the invention, wherein the signal
processing section detects the frequency modulation characteristic
just after detecting the target initially after a radar operation
starts and determines whether or not a normal modulation operation
for the high frequency generation section is performed.
[0038] According to the invention, if the target is detected
initially and it is made possible to receive the reflected radio
wave, whether or not the frequency modulation characteristic of the
high frequency modulation section is normal is determined, so that
occurrence of an anomaly can be found at an early stage if the
anomaly occurs.
[0039] The invention provides the radar apparatus further including
a reference signal source for generating a reference signal to
decrease a frequency with respect to the differential signal
between the high-frequency signal and the reception signal, the
differential signal inputted to the signal processing section from
the mixing section, in which the signal processing section detects
the frequency modulation characteristic based on the inputted
differential signal with the frequency decreased by the reference
signal.
[0040] According to the invention, for the component of the
difference between the high-frequency signal and the reception
signal provided by the mixing section, the reference signal
generated from the reference signal source is heterodyned and the
frequency is decreased, so that frequency measurement is
facilitated.
[0041] In the radar apparatus of the invention, the reference
signal source includes a basic signal generation section for
generating a basic signal, which is a source of the reference
signal, and a frequency division section for dividing the frequency
of the basic signal generated from the basic signal generation
section according to one of frequency dividing ratios that can be
switched to convert the basic signal into the reference signal.
[0042] According to the invention, the frequency dividing ratio of
the frequency division section is changed for switching the
frequency of the reference signal provided by dividing the
frequency of the basic signal generated from the basic signal
generation section, the frequency is lowered, and the frequency
measurement accuracy can be enhanced.
[0043] In the radar apparatus of the invention, the reference
signal source includes a plurality of reference signal generation
sections and selects one of the reference signal generation
sections to generate the reference signal.
[0044] According to the invention, a plurality of reference signal
generation section are switched for generating the reference signal
and the signal components provided by switching the reference
signal generation section are compared, whereby it is made possible
to determine the frequency to be measured, and the accuracy can be
enhanced.
[0045] In the radar apparatus of the invention, the reference
signal source comprises a signal arithmetic section for generating
the reference signal by performing arithmetic processing according
to a preset program.
[0046] According to the invention, the reference signal of the
frequency fitted for frequency measurement can be generated for
enhancing the measurement accuracy.
[0047] In the radar apparatus of the invention, the reference
signal source supplies a clock signal for a signal arithmetic
processing to the signal processing section.
[0048] According to the invention, generation of the reference
signal and clock signal supply to the signal processing section can
be conducted from the common reference signal source, so that space
saving and cost reduction are made possible.
[0049] In the radar apparatus of the invention, a frequency of the
reference signal is set so that a difference from the frequency of
the reception signal from the target is within a beat signal band
at a time of a radar operation.
[0050] According to the invention, the reference signal set within
the beat signal band is used, so that the band of the frequency of
the difference provided by heterodyning can be lowered for
enhancing the measurement accuracy.
[0051] In the radar apparatus of the invention, the signal
processing section performs at least a part of processing of the
beat signal.
[0052] According to the invention, the configuration is shared
between at least a part of beat signal processing and a part of
detection processing of the frequency modulation characteristic, so
that the whole configuration can be simplified and can be
implemented at low costs.
[0053] In the radar apparatus of the invention, the signal
processing section changes a predetermined time for holding a
signal level of the modulation signal for detection in response to
a distance to the target.
[0054] According to the invention, frequency modulation
characteristic detection can be optimized in response to the
distance to the target and the detection accuracy can be
enhanced.
[0055] In the radar apparatus of the invention, the signal
processing section changes a predetermined time for holding a
signal level of the modulation signal for detection in response to
a relative speed of the target.
[0056] According to the invention, the detection accuracy of the
frequency modulation characteristic can be enhanced considering the
relative speed with the target.
[0057] In the radar apparatus of the invention, the signal
processing section detects the frequency of the differential signal
between the high-frequency signal and the reception signal
considering a Doppler shift based on a relative speed of the
target.
[0058] According to the invention, if it is difficult to find out a
relatively still object when the radar is installed in an
automobile, etc., the frequency modulation characteristic can be
detected with good accuracy considering the Doppler shift.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] In the accompanying drawings:
[0060] FIG. 1(a) is a block diagram to show a schematic electric
configuration of an FM-CW system radar 21 of a first embodiment of
the invention, FIG. 1(b) is a waveform chart to show the waveform
of a modulation signal, and FIG. 1(c) is a waveform chart to show
the waveform of a modulation signal for detection;
[0061] FIGS. 2(a) to 2(c) are time charts to show the principle to
enable a frequency shift to be provided based on the modulation
signal for detection in the first embodiment of the invention;
[0062] FIG. 3 is a graph to show an example of the frequency
modulation characteristic of the VCO 24 in FIG. 1(a);
[0063] FIG. 4(a) is a waveform-chart of a modulation signal for
detection generated in a modulation signal generation circuit 29 in
FIG. 1 and FIG. 4(b) is a time chart of a beat signal provided;
[0064] FIG. 5(a) is a waveform chart of a modulation signal for
detection generated in the modulation signal generation circuit 29
in FIG. 1 and FIG. 5(b) is a time chart of a beat signal
provided;
[0065] FIG. 6 is a block diagram to show a schematic electric
configuration of an FM-CW system radar 31 of a second embodiment of
the invention;
[0066] FIG. 7 is a block diagram to show a schematic electric
configuration of an FM-CW system radar 41 of a third embodiment of
the invention;
[0067] FIG. 8 is a block diagram to show a partial electric
configuration of an FM-CW system radar 61 of a fourth embodiment of
the invention;
[0068] FIG. 9 is a block diagram to show a schematic electric
configuration of an FM-CW system radar 71 of a fifth embodiment of
the invention;
[0069] FIG. 10 is a flowchart to show a processing procedure in the
embodiments in FIGS. 8 and 9;
[0070] FIG. 11 is a block diagram to show a schematic electric
configuration of an FM-CW system radar 81 of a sixth embodiment of
the invention;
[0071] FIG. 12 is a block diagram to show the electric
configuration of a signal processing circuit 100 of an FM-CW system
radar of a seventh embodiment of the invention;
[0072] FIG. 13 is a block diagram to show a schematic electric
configuration of an FM-CW system radar 111 of an eighth embodiment
of the invention;
[0073] FIG. 14 is a block diagram to show a configuration example
of a signal source 12 in the embodiment in FIG. 13;
[0074] FIG. 15 is a block diagram to show a schematic electric
configuration of an FM-CW system radar 121 of a ninth embodiment of
the invention;
[0075] FIG. 16(a) is a block diagram to show a schematic electric
configuration of an FM-CW system radar 1 in a related art and
[0076] FIG. 16(b) is a waveform chart of a modulation signal;
and
[0077] FIG. 17 is a block diagram to show the electric
configuration to detect the frequency modulation characteristic in
the FM-CW system radar in FIG. 16.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0078] Referring now to the accompanying drawings, there are shown
preferred embodiments of the invention. Parts identical with or
similar to those described in advance are denoted by the same
reference numerals and will not be discussed again. A plurality of
embodiments can also be combined in a range in which they do not
overlap each other. Further, the common portions to those of the
preceding embodiments may not be discussed again.
[0079] FIG. 1(a) shows a schematic electric configuration of an
FM-CW system radar 21 of a first embodiment of the invention, FIG.
1(b) shows the waveform of a modulation signal, and FIG. 1(c) shows
the waveform of a modulation signal for detection. The FM-CW system
radar 21 of the embodiment has a basic configuration similar to
that of the FM-CW system radar 1 in the related art shown in FIG.
16(a). That is, it includes a transmission antenna 22, a reception
antenna 23, a VCO 24, a coupler 25, a mixer 26, a BPF 27, an
amplifier 28, a modulation signal generation circuit 29, and a
signal processing circuit 30. A radio wave is transmitted from the
transmission antenna 22 and the reflected radio wave from a target,
etc., is received at the reception antenna 23. A high-frequency
signal of a millimeter waveband generated from the VCO
(voltage-controlled oscillator) 24 is given to the transmission
antenna 22. A part of the high-frequency signal for exciting the
transmission antenna 22 from the VCO 24 branches from the coupler
25 and is mixed with a reception signal from the reception antenna
23 by the mixer 26. A beat signal in an output signal from the
mixer 26 is selected through the BPF (band-pass filter) 27 and is
amplified by the amplifier 28. The high-frequency signal generated
from the VCO 24 is subjected to frequency modulation in accordance
with the voltage level of a modulation signal given by the
modulation signal generation circuit 29. The beat signal is
processed by the signal processing circuit 30 for calculating the
distance to the target and the relative speed.
[0080] For example, in the FM-CW system radar 21 of a millimeter
waveband, a modulation signal shaped like a triangular wave of
several hundred Hz as shown in FIG. 1(b) is used to generate an FM
wave with the maximum frequency shift amount being several ten to
several hundred MHz. As the modulation signal, a saw tooth wave
(chirp wave) may be used in some cases. The normal operation of the
FM-CW system radar 21 is similar to that of the FM-CW system radar
1 in the related art shown in FIG. 16. In the embodiment, a
modulation signal for detection shaped like a rectangular wave
changing at voltage V1 as shown in FIG. 1(c) is given to the VCO 24
from the modulation signal generation circuit 29. Therefore, it is
made possible to sense whether or not the frequency modulation
characteristic of the VCO 24 has good linearity relative to change
in the voltage level of the modulation signal.
[0081] FIGS. 2(a) to 2(c) show the principle to provide the shift
component of frequency modulation corresponding to the modulation
signal for detection shaped like a rectangular wave shown in FIG.
1(c). From the VCO 24, frequency shift component .DELTA.F is
provided in response to change in voltage V1 as in FIG. 1(c). For
the frequency shift component .DELTA.F, at A point in FIG. 1(a), a
signal waveform as shown in FIG. 2(a) is provided and is almost the
same as the waveform transmitted from the transmission antenna 22.
At B point in FIG. 1(a) where the radio waves reflected on the
target is received at the reception antenna 23, the phase is
delayed as shown in FIG. 2(b) based on the propagation delay of the
radio wave. At C point on the output side of the mixer 26 as shown
in FIG. 1(a), a beat signal of frequency of .DELTA.F is provided
only for the time period of the propagation delay. If the relative
speed to the target is not zero, a Doppler shift component is also
contained, but is about several kHz. Since the frequency .DELTA.F
of the beat signal is several MHz to several 10 MHz, the effect of
the Doppler shift component is small.
[0082] FIG. 3 shows an example of the frequency modulation
characteristic in the VCO 24 in FIG. 1(a). The frequency shift
amount between the minimum value V1 of the lower limit voltage of
the modulation signal and the maximum value V2 of the upper limit
voltage is found by adding up frequency shift .DELTA.fn
corresponding to section voltage .DELTA.vn. As a method of changing
the voltage level between V1 and V2 to provide the modulation
signal for detection, it is possible to change the voltage level
(modulation signal for detection) stepwise as shown in FIG. 4 and
it is possible to change the pulse-like peak value as shown in FIG.
5.
[0083] FIG. 4(a) shows the waveform of the modulation signal for
detection changing stepwise and FIG; 4(b) shows the frequency shift
of the beat signal. FIG. 5(a) shows the waveform of the modulation
signal for detection changing like a pulse and FIG. 5(b) shows the
frequency shift of the beat signal. In the frequency shift in FIG.
4(b) corresponding to the stepwise voltage change in FIG. 4(a), the
modulation width is found by adding up the frequency shift
components as shown in expression (1) given below. For the voltage
change like a pulse as in FIG. 5(a), the last frequency shift
component shown in FIG. 5(b) is the added-up value. 1 Modulation
Width ( f ) = n = 1 m f n ( 1 )
[0084] In the embodiment, there is provided the FM-CW system radar
apparatus 21 in which a modulation signal shaped like a triangular
wave is given to the VCO 24 of a high-frequency generation section
to generate a high-frequency signal whose frequency changes and a
radio wave is transmitted from the transmission antenna 22 based on
the generated high-frequency signal and the, reflected radio wave
is received for detecting the target. The radar apparatus 21
includes the modulation signal generation circuit 29 of a
modulation signal generation section, the mixer 26 of a mixing
section, and the signal processing circuit 30 of a signal
processing section. The modulation signal generation circuit 29
generates a modulation signal for detection whose change state can
be controlled and gives the modulation signal to the VCO 24. The
mixer 26 mixes the high-frequency signal generated from the VCO 24
and the reception signal of the reflected radio wave. The signal
processing circuit 30 controls the modulation signal generation
circuit 29 so as to give the modulation signal for detection
changing among a plurality of predetermined signal levels and
retained for a predetermined time for each signal level to the VCO
24, as shown in FIG. 4(a), 5(a). The signal processing circuit 30
inputs the signal of the component of the difference between the
high-frequency signal and the reception signal from the mixer 26 to
detect the frequency, and detects the frequency modulation
characteristic of the VCO 24 based on the relationship between the
signal level of the modulation signal for detection and the
frequency. The reception signal is used as the high-frequency
signal source for frequency characteristic detection and the mixer
26 for reception can also be shared, so that the frequency
modulation characteristic can be detected easily in the inexpensive
configuration.
[0085] FIG. 6 shows a schematic electric configuration of an FM-CW
system radar 31 of a second embodiment of the invention. In the
second embodiment, a modulation signal correction circuit 32
corrects a modulation signal of a triangular wave, etc., generated
by a modulation signal generation circuit 29 and gives the
corrected modulation signal to a VCO 24. The modulation signal
correction circuit 32 corrects the modulation signal in accordance
with a correction signal given by a signal processing circuit 40.
The signal processing circuit 40 generates the correction signal so
that the frequency modulation characteristic detected in a similar
manner to that in the first embodiment is not placed out of a
predetermined normal range. For the frequency modulation
characteristic, the linearity indicating the linearity range and
the modulation width indicating the upper and lower limits are
corrected. To correct the linearity, a polygonal line circuit,
etc., can be used. To correct the modulation width, a gain control
amplifier, a variable attenuator, etc., can be used. The modulation
signal correction circuit 32 serves as a range correction section
if it makes a linearity correction; the modulation signal
correction circuit 32 serves as modulation characteristic
correction section if it corrects the modulation width.
[0086] FIG. 7 shows a schematic electric configuration of an FM-CW
system radar 41 of a third embodiment of the invention. In the
third embodiment, a modulation signal generation circuit 49
includes a D/A converter 42 for converting a digital signal
representing modulation data given by a signal processing circuit
50 into an analog signal to generate a modulation signal. The
signal processing circuit 50 detects the frequency modulation
characteristic in a similar manner to that in the first embodiment
and stores modulation data for correcting the detected
characteristic in an internal memory 51. In the third embodiment,
the memory 51 serves as a range correction section and a modulation
width correction section.
[0087] In the embodiments shown in FIGS. 6 and 7, the modulation
signal is corrected so that the frequency modulation characteristic
that can be detected easily in the inexpensive configuration is not
placed out of a predetermined normal range and thus the frequency
modulation characteristic can also be corrected easily in the
inexpensive configuration.
[0088] FIG. 8 shows a partial electric configuration of an FM-CW
system radar 61 of a fourth embodiment of the invention. In the
fourth embodiment, a beat signal output from an amplifier 28 is
converted into a digital signal by an A/D converter 62 and signal
level is obtained by a DSP (digital signal processor) 64 and FFT
processing 63 by a microcomputer. The FFT processing 63, which is
fast Fourier transform processing, is implemented as the program
operation of the DSP 64, etc. A signal processing circuit 70 of the
embodiment includes the A/D converter 62 and the DSP 64. The signal
level of the beat signal can be determined as to any reference
level.
[0089] FIG. 9 shows a partial electric configuration of an FM-CW
system radar 71 of a fifth embodiment of the invention. In the
fifth embodiment, a beat signal is detected by a detection circuit
74 and is compared with a reference signal by a comparator 75 for
determining signal level. To set the reference signal given to the
comparator 75, the beat signal is converted into a digital signal
by an A/D converter 72 and arithmetic processing is performed by a
microcomputer 73, a DSP, etc. A signal processing circuit 80 of the
embodiment includes the A/D converter 72 and the microcomputer
73.
[0090] FIG. 10 shows a processing procedure of detecting the
frequency modulation characteristic in response to the signal level
of a reception signal in the fourth and fifth embodiments
previously described with reference to FIGS. 8 and 9. The procedure
is started at step a0. At step a1, the beat signal level is
calculated as the usual FM-CW radar. At step a2, whether or not the
beat signal level is greater than a setup reference level is
determined. If it is determined that the beat signal level is
greater than the setup level, whether or not the frequency
modulation characteristic is to be detected is determined at step
a3. The frequency modulation characteristic may be detected, for
example, for the first detected target after the power is turned
on, and need not always be detected. If it is determined at step a3
that the frequency modulation characteristic is to be detected,
detection processing of the frequency modulation characteristic is
performed at step a4 in a similar manner to that in the first
embodiment. At a5, whether or not the detection result involves a
problem is determined. If the detection result involves a problem,
at step a6, correction processing is performed as in the second or
third embodiment or warning processing with an alarm, etc., is
performed. If it is not determined at step a2 that the beat signal
level is greater than the setup level, if it is not determined at
step a3 that the frequency modulation characteristic is to be
detected, or if it is not determined at step a5 that the detection
result involves a problem, normal FM-CW radar processing is
performed at step a7. When the input level of the reception signal
is equal to or greater than the predetermined reference level, a
correction is made and thus can be made stably.
[0091] If the target is detected initially and it is made possible
to receive the reflected radio wave at step a3, occurrence of an
anomaly can also be found at an early stage by determining whether
or not the frequency modulation characteristic of the VCO 24 is
normal.
[0092] FIG. 11 shows a schematic electric configuration of an FM-CW
system radar 81 of a sixth embodiment of the invention. In the
sixth embodiment, the temperature in the proximity, etc., of a VCO
24 is detected by a temperature sensor 82 such as a thermister and
if the frequency modulation characteristic of the VCO 24 changes
with the temperature, it is also made possible to make a correction
for each arbitrary temperature and the accuracy of the frequency
modulation characteristic can be enhanced. The temperature detected
by the temperature sensor 82 is given to a signal processing
circuit 90 and a correction can be made in a similar manner to that
in the embodiments previously described with reference to FIGS. 6,
7. A correction can also be made if the temperature detected by the
temperature sensor 82 as a temperature detection section becomes a
predetermined temperature when the frequency of a high-frequency
signal generated from the VCO 24 changes with the temperature,
since a correction is made if the predetermined temperature is
reached, so that the effect of the temperature can be decreased and
the accuracy of the frequency modulation characteristic can be
enhanced.
[0093] In the embodiments of the invention, preferably, if the
distance to the target is in the predetermined distance range, the
frequency modulation characteristic is detected and corrected
and/or if the relative speed of the target is in the predetermined
speed range, the frequency modulation characteristic is detected
and corrected. The distance range, etc, having a high possibility
that the signal level of the reception signal will lower is placed
out of the predetermined distance range, whereby detection
processing and correction processing are not entered at such a
distance, so that accuracy degradation of detection and correction
can be avoided. With regard to the relative speed, the relative
speed of the target is considered and if the relative speed of the
target is placed in the predetermined speed range, detection and
correction are executed, so that the accuracy can be enhanced.
[0094] FIG. 12 shows a partial electric configuration of a signal
processing circuit 100 of an FM-CW system radar of a seventh
embodiment of the invention. In the seventh embodiment, a beat
signal is converted into a digital signal by an A/D converter 102
and the digital signal is input to a microcomputer 103 in a similar
manner to that in the embodiment previously described with
reference to FIG. 9, and the frequency count result of a frequency
counter 104 is input to the microcomputer 103. Since the frequency
counter 104 is used, frequency measurement of the beat signal can
be conducted easily.
[0095] FIG. 13 shows a schematic electric configuration of an FM-CW
system radar 111 of an eighth embodiment of the invention. In the
eighth embodiment, a beat signal of the FM-CW system radar is mixed
with a reference signal generated from a signal source 112 by a
mixer 113 for heterodyning and further the frequency can be lowered
for facilitating frequency measurement. An output of the mixer 113
is selected through a BPF 114 and is amplified by an amplifier 115
and is fed into a signal processing circuit 120. The signal
processing circuit 120 detects and corrects the frequency
modulation characteristic in a similar manner to that in each
embodiment described above.
[0096] FIG. 14 shows an example of implementing the signal source
112 in the embodiment in FIG. 13. In FIG. 14(a), a changeover
switch 114, a frequency divider 115', and an oscillator 116 are
included. The oscillator 116 becomes a basic signal generation
section for generating a basic signal as a source of the reference
signal. The frequency divider 115' becomes a frequency division
section for dividing the frequency of the basic signal according to
one of frequency dividing ratios that can be switched by the
changeover switch 114 for converting the basic signal into the
reference signal. In FIG. 14(b), outputs of a plurality of
oscillators 117, 119, and 119 are switched by the changeover switch
114. In FIG. 14(c), the signal processing circuit 120 directly
generates the reference signal by performing program processing and
feeds the signal into the mixer 113. The reference signal and a
clock signal based on which the signal processing circuit 120
operates can be generated in common.
[0097] As shown in FIG. 14(a), if the frequency dividing ratio is
changed for switching the frequency of the reference signal
provided by dividing the frequency of the basic signal generated
from the basic signal generation section, the frequency measurement
accuracy can be enhanced. As shown in FIG. 14(b), if any of the
oscillator 117, 118, or 119 is selected for generating the
reference signal, it is made possible to determine the frequency to
be measured, and the accuracy can be enhanced. As shown in FIG.
14(c), if the reference signal is generated by performing
arithmetic processing following the preset program, the reference
signal of the frequency being suitable for frequency measurement
can be generated to enhance the measurement accuracy. If the
reference signal and the clock signal of the signal processing
circuit 120 are used as a common signal, the need for providing new
signal source 113 is eliminated and space saving and cost reduction
are made possible.
[0098] In the embodiment in FIG. 13, the frequency of the reference
signal is set so that the difference from the frequency of the
reception signal from the target becomes within the beat signal
band at the radar operation time. Since the reference signal set
within the beat signal band is used, the band of the frequency of
the difference provided by heterodyning can be lowered for
enhancing the measurement accuracy. In FIG. 13, the signal
processing circuit 120 performs at least apart of beat signal
processing in the FM-CW system radar. Since the configuration is
shared between at least a part of beat signal processing and a part
of detection processing of the frequency modulation characteristic
the whole configuration is simplified and can be implemented at low
costs.
[0099] FIG. 15 shows a schematic electric configuration of an FM-CW
system radar 121 of a ninth embodiment of the invention. In the
ninth embodiment, the concept disclosed as the second embodiment in
JP-A-5-40169 can be applied for enhancing the S/N ratio of a
reception signal. A beat signal is converted into a digital signal
by an A/D converter 122 and FFT processing 123 is performed by a
DSP 124, etc. A modulation signal is fed into a gate switch 126
from a signal source 125 for performing frequency modulation of a
reception signal. Then, the beat signal is provided by a mixer 26
and further is mixed with the modulation signal by a mixer 127 and
the resultant signal is detected. A signal processing circuit 130
of the embodiment includes the A/D converter 122 and the DSP
124.
[0100] In the embodiments described above, preferably the time (t1,
t2, t3, . . . , tn) taken for holding the voltage level in a
plurality of values in the range of V1 to V2 in the modulation
signal for detection shown in FIGS. 4(a) and 5(b) is changed in
response to the distance to the target and the relative speed.
Accordingly, frequency modulation characteristic detection can be
optimized in response to the distance to the target and the
relative speed and the detection accuracy can be enhanced.
[0101] Preferably, the signal processing circuit in each embodiment
detects the frequency of the beat signal component of the
difference between the high-frequency signal and the reception
signal considering the Doppler shift based on the relative speed of
the target. If it is difficult to find out a relatively still
object when the radar is installed in an automobile, etc., the
frequency modulation characteristic can be detected with good
accuracy considering the Doppler shift.
[0102] In the embodiments, the FM-CW system radars have been
described, but the invention can also be applied to radars if the
radars use frequency modulation.
[0103] As described above, according to the invention, the
reception signal from the target can be used to detect the
frequency modulation characteristic of the high frequency
generation section. The reception signal can be used as the
high-frequency signal source to detect the frequency modulation
characteristic and the mixing section for reception can also be
shared, so that the frequency modulation characteristic can be
detected easily in the inexpensive configuration.
[0104] According to the invention, the modulation signal is
corrected so that the frequency modulation characteristic is not
placed out of the predetermined normal range, so that the frequency
modulation characteristic can be corrected easily in the
inexpensive configuration.
[0105] According to the invention, the frequency modulation width
can be calculated from frequency change between a plurality of
signal levels.
[0106] According to the invention, frequency change is counted by
the counter, so that frequency change can be measured easily.
[0107] According to the invention, the frequency modulation width
of the frequency modulation characteristic can be corrected to the
predetermined value.
[0108] According to the invention, if the level of the reception
signal is equal to or greater than the predetermined level, a
stable correction can be made.
[0109] According to the invention, the effect of the temperature
can be decreased and the accuracy of the frequency modulation
characteristic can be enhanced.
[0110] According to the invention, if the distance to the target is
placed out of the appropriate range, correction processing is not
entered, so that accuracy degradation of correction can be
avoided.
[0111] According to the invention, the relative speed of the target
is considered and the accuracy of the correction can be enhanced.
For example, targets for generating high relative speed components,
such as a road side object and an incoming vehicle, are placed out
of the objects, the accuracy can be enhanced.
[0112] According to the invention, if the input level of the
reception signal is less than the predetermined reference level,
the radar apparatus can concentrate attention on usual target
detection processing. Whether or not detection processing of the
frequency modulation characteristic is to be performed is
determined based on the signal level at the usual radar operation
time, so that the number of detection processing times can be
decreased.
[0113] According to the invention, if the distance to the target is
out of the predetermined distance range, the radar apparatus can
concentrate attention on usual target detection processing.
[0114] According to the invention, if an anomaly occurs in the
frequency modulation characteristic of the high frequency
modulation section, it can be found at an early stage.
[0115] According to the invention, for the beat signal of the
component of the difference between the high-frequency signal and
the reception signal provided by the mixing section, the reference
signal generated from the reference signal source is heterodyned
and the frequency is decreased, so that frequency measurement of
the beat signal is facilitated.
[0116] According to the invention, a plurality of frequency
dividing ratios can be switched for lowering the frequency, and the
frequency measurement accuracy can be enhanced.
[0117] According to the invention, a plurality of reference signals
are switched and the signal components provided by switching the
reference signals are compared, whereby it is made possible to
determine the frequency to be measured, and the accuracy can be
enhanced.
[0118] According to the invention, the reference signal of the
frequency fitted for frequency measurement can be generated for
enhancing the measurement accuracy.
[0119] According to the invention, generation of the reference
signal and clock signal supply to the signal processing section can
be conducted in common and space saving and cost reduction are made
possible.
[0120] According to the invention, the reference signal set within
the beat signal band is used and the measurement accuracy can be
enhanced.
[0121] According to the invention, the configuration is shared
between at least a part of beat signal processing and a part of
detection processing of the frequency modulation characteristic,
the whole configuration can be simplified, the costs can be
reduced.
[0122] According to the invention, frequency modulation
characteristic detection can be optimized in response to the
distance to the target and the detection accuracy can be
enhanced.
[0123] According to the invention, the detection accuracy of the
frequency modulation characteristic can be enhanced considering the
relative speed with the target.
[0124] According to the invention, if it is difficult to find out a
relatively still object, the frequency modulation characteristic
can be detected with good accuracy considering the Doppler
shift.
* * * * *