U.S. patent application number 13/371020 was filed with the patent office on 2012-10-25 for multibeam radar apparatus for vehicle, multibeam radar method, and multibeam radar program.
This patent application is currently assigned to HONDA ELESYS CO., LTD.. Invention is credited to Hiroyuki Kamo, Junji Kanamoto, Yoshihiko KUWAHARA.
Application Number | 20120268314 13/371020 |
Document ID | / |
Family ID | 46972442 |
Filed Date | 2012-10-25 |
United States Patent
Application |
20120268314 |
Kind Code |
A1 |
KUWAHARA; Yoshihiko ; et
al. |
October 25, 2012 |
MULTIBEAM RADAR APPARATUS FOR VEHICLE, MULTIBEAM RADAR METHOD, AND
MULTIBEAM RADAR PROGRAM
Abstract
An on-board multibeam radar apparatus includes a plurality of
beam elements that constitute an antenna transmitting a
transmission wave and receiving an incoming wave being reflected
and arriving from a target in response to the transmission wave, a
control unit configured to select a beam element used for
transmission and reception out of the plurality of beam elements so
as to change a field of view, and a processing unit configured to
apply a Fourier transformation to beam element data which are data
of a received wave received through the beam element used for
transmission and reception selected by the control unit based on
the number of elements and the element interval of a desired
virtual array antenna so as to create virtual array data, and to
perform a predetermined process based on the created virtual array
data.
Inventors: |
KUWAHARA; Yoshihiko;
(Hamamatsu-shi, JP) ; Kanamoto; Junji;
(Yokohama-shi, JP) ; Kamo; Hiroyuki;
(Yokohama-shi, JP) |
Assignee: |
HONDA ELESYS CO., LTD.
Yokohama-shi
JP
NATIONAL UNIVERSITY CORPORATION SHIZUOKA UNIVERSITY
Shizuoka-shi
JP
|
Family ID: |
46972442 |
Appl. No.: |
13/371020 |
Filed: |
February 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61441828 |
Feb 11, 2011 |
|
|
|
Current U.S.
Class: |
342/147 ;
342/175; 342/374 |
Current CPC
Class: |
G01S 13/42 20130101;
G01S 13/48 20130101; G01S 13/931 20130101; G01S 3/74 20130101 |
Class at
Publication: |
342/147 ;
342/175; 342/374 |
International
Class: |
G01S 13/00 20060101
G01S013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2011 |
JP |
P2011-183054 |
Claims
1. An on-board multibeam radar apparatus comprising: a plurality of
beam elements that constitute an antenna transmitting a
transmission wave and receiving an incoming wave being reflected
and arriving from a target in response to the transmission wave; a
control unit configured to select a beam element used for
transmission and reception out of the plurality of beam elements so
as to change a field of view; and a processing unit configured to
apply a Fourier transformation to beam element data which are data
of a received wave received through the beam element used for
transmission and reception selected by the control unit based on
the number of elements and the element interval of a desired
virtual array antenna so as to create virtual array data, and to
perform a predetermined process based on the created virtual array
data.
2. The on-board multibeam radar apparatus according to claim 1,
wherein a switch is provided to the beam element of whose state is
switched between a state where the beam element is used for
transmission and reception and a state where the beam element is
not used for transmission and reception out of the plurality of
beam elements, and wherein the control unit is configured to select
the beam element used for transmission and reception to change the
field of view by switching the ON and OFF states of the switch.
3. The on-board multibeam radar apparatus according to claim 1,
wherein the beam element whose state is switched between a state
where the beam element is used for transmission and reception and a
state where the beam element is not used for transmission and
reception is abeam element selected from the side farthest from the
center out of the plurality of beam elements.
4. The on-board multibeam radar apparatus according to claim 1,
wherein the processing unit is configured to perform, as the
predetermined process, a process of detecting the azimuth of the
target based on the created virtual array data.
5. The on-board multibeam radar apparatus according to claim 1,
further comprising a lens that passes the transmission wave
transmitted from and the received wave received by the plurality of
beam elements, wherein the plurality of elements constituting the
virtual array antenna are arranged so that all the elements are
within an aperture of a virtual lens corresponding to the lens.
6. The on-board multibeam radar apparatus according to claim 1,
further comprising a lens that passes the transmission wave
transmitted from and the received wave received by the plurality of
beam elements, wherein the plurality of elements constituting the
virtual array antenna are arranged so that the width of an aperture
of a virtual lens corresponding to the lens is equal to the width
between the elements at both ends.
7. The on-board multibeam radar apparatus according to claim 1,
wherein the processing unit is configured to apply the Fourier
transformation to the beam element data at a searching incident
angle corresponding to the beam element data which is data of the
received wave received by the beam element used for transmission
and reception and selected by the control unit based on the number
of elements and the element interval of the desired virtual array
antenna and creates a steering vector used to detect an
azimuth.
8. The on-board multibeam radar apparatus according to claim 7,
wherein the processing unit is configured to apply a unitary
transformation to a correlation matrix based on the created virtual
array data, to apply a unitary transformation on the steering
vector, and to perform the predetermined process based on the
result of the unitary transformation.
9. A multibeam radar method comprising: causing a plurality of beam
elements constituting an antenna to transmit a transmission wave
and to receive an incoming wave being reflected and arriving from a
target in response to the transmission wave; causing a control unit
to select a beam element used for transmission and reception out of
the plurality of beam elements so as to change a field of view; and
causing a processing unit to apply a Fourier-transform to beam
element data which are data of a received wave received through the
beam element used for transmission and reception selected by the
control unit based on the number of elements and the element
interval of a desired virtual array antenna so as to create virtual
array data, and to perform a predetermined process based on the
created virtual array data.
10. A multibeam radar program causing a computer to perform: a step
of causing a plurality of beam elements constituting an antenna to
transmit a transmission wave and to receive an incoming wave being
reflected and arriving from a target in response to the
transmission wave; a step of causing a control unit to select a
beam element used for transmission and reception out of the
plurality of beam elements so as to change a field of view; and a
step of causing a processing unit to apply a Fourier transformation
to beam element data which are data of a received wave received
through the beam element used for transmission and reception
selected by the control unit based on the number of elements and
the element interval of a desired virtual array antenna so as to
create virtual array data, and to perform a predetermined process
based on the created virtual array data.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Non-provisional patent application of
U.S. Provisional Patent Application No. 61/441,828, filed Feb. 11,
2011, and claims priority on Japanese Patent Application No.
2011-183054, filed Aug. 24, 2011, the contents of which are
entirely incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an on-board multibeam radar
apparatus, a multibeam radar method, and a multibeam radar program,
which can detect a target using a reflected wave from the target in
response to a transmitted wave.
[0004] 2. Background Art
[0005] In recent years, on-board detection apparatuses measuring
the distance, the relative velocity, and the azimuth between a
vehicle and another vehicle (which is also referred to as a
reflecting object, an object, or a target) using a millimeter wave
radar or the like have been practically used. As on-board radars,
an FMCW (Frequency Modulated Continuous Wave) radar, a
multi-frequency CW (Continuous Wave) radar, a pulse radar, and the
like have been known.
[0006] In such on-board radars, a spectrum estimating method using
a high-resolution algorithm, such as an AR spectrum estimating
method (including a maximum entropy method or a linear prediction
method) and a MUSIC (MUltiple Signal Classification) method which
can achieve a high resolution with a small number of channels, has
been used as a signal processing technique of detecting the
direction of an arrival wave (a received wave) from a target (a
reflecting object) (see JP-A-2009-156582 (Patent Document 1) and
Japanese Patent No. 4098311).
[0007] Here, a multibeam radar apparatus (also referred to as a
beam space system) is known with respect to an electronic scanning
radar apparatus of an array antenna system (also referred to as an
element space system).
[0008] In recent years, dielectric lens antennas have been studied
for the multibeam system (for example, see Design of Multibeam
Dielectric Lens Antennas by Multiobjective Optimization/IEEE Trans.
AP Vol. 57 No. 1, pp. 57-63, 2009, Shizuoka University). Regarding
on-board multibeam radar apparatuses, radar apparatuses using a
dielectric lens antenna have been developed (for example, see
JP-T-2009-541725).
[0009] Since the multibeam system represented by a dielectric lens
antenna can embody high-gain/high-efficiency antennas more easily
than the array antenna system, it is easier to detect a target with
a small RCS (Radar Cross Section) even in environments with a low
SNR (Signal to Noise Ratio).
[0010] Depending on the shape of a lens or the arrangement of
primary feeds (primary radiators) and because of no grating lobe
occurring, it is possible to flexibly design multibeam radars with
various FOVs (Fields Of View) or various gain properties.
SUMMARY OF THE INVENTION
[0011] In recent years, in on-board radars using millimeter waves
or microwaves, there has been a need for the resolution of multiple
targets (a plurality of targets) present within the same
measurement point (for example, the same distance point or bin in
the FMCW type), the improvement in angle measurement accuracy, the
achievement of a plurality of detection functions with various FOVs
(Field Of View) and various resolutions using a single radar
apparatus, and the compatibility of the improvement in total
performance and the reduction in cost of a radar system.
[0012] In the conventional multibeam radar using a lens, there is a
merit in that it is possible to flexibly design a multibeam radar
with various FOVs or gain prperties depending on the shape of a
lens or the arrangement of beam elements. However, since the
angle-measuring method is basically of an amplitude monopulse type
method, it is necessary to reduce a beam width and to increase the
number of beams in order to improve angle measurement accuracy for
multiple targets present at the same measurement point. In
practice, the small beam width and the large number of beams are
limited from the viewpoint of structure and cost, and the
resolution or the angle measurement accuracy of multiple targets at
the same measurement point is also limited. In addition, because of
the increase in size of an apparatus, it is difficult to realize a
plurality of detection functions with various FOVs in a single
radar apparatus.
[0013] The present invention is made in consideration of such
circumstances, and an object thereof is to provide an on-board
multibeam radar apparatus, a multibeam radar method, and a
multibeam radar program, which can switch between various FOVs and
can detect a target with a high accuracy.
[0014] To achieve the above-mentioned object, according to a first
aspect of the invention, there is provided an on-board multibeam
radar apparatus including: a plurality of beam elements that
constitute an antenna transmitting a transmission wave and
receiving an incoming wave being reflected and arriving from a
target in response to the transmission wave; a control unit
configured to select a beam element used for transmission and
reception out of the plurality of beam elements so as to change a
field of view; and a processing unit configured to apply a Fourier
transformation to beam element data which are data of a received
wave received through the beam element used for transmission and
reception selected by the control unit based on the number of
elements and the element interval of a desired virtual array
antenna so as to create virtual array data, and to perform a
predetermined process based on the created virtual array data.
[0015] In the on-board multibeam radar apparatus, a switch may be
provided to the beam element of whose state is switched between a
state where the beam element is used for transmission and reception
and a state where the beam element is not used for transmission and
reception out of the plurality of beam elements, and the control
unit may be configured to select the beam element used for
transmission and reception to change the field of view by switching
the ON and OFF states of the switch.
[0016] In the on-board multibeam radar apparatus, the beam element
whose state is switched between a state where the beam element is
used for transmission and reception and a state where the beam
element is not used for transmission and reception may be a beam
element selected from the side farthest from the center out of the
plurality of beam elements.
[0017] In the on-board multibeam radar apparatus, the processing
unit may be configured to perform, as the predetermined process, a
process of detecting the azimuth of the target based on the created
virtual array data.
[0018] The on-board multibeam radar apparatus may further include a
lens that passes the transmission wave transmitted from and the
received wave received by the plurality of beam elements, and the
plurality of elements constituting the virtual array antenna may be
arranged so that all the elements are within an aperture of a
virtual lens corresponding to the lens.
[0019] The on-board multibeam radar apparatus may further include a
lens that passes the transmission wave transmitted from and the
received wave received by the plurality of beam elements, and the
plurality of elements constituting the virtual array antenna may be
arranged so that the width of an aperture of a virtual lens
corresponding to the lens is equal to the width between the
elements at both ends.
[0020] In the on-board multibeam radar apparatus, the processing
unit may be configured to apply the Fourier transformation to the
beam element data at a searching incident angle corresponding to
the beam element data which is data of the received wave received
by the beam element used for transmission and reception and
selected by the control unit based on the number of elements and
the element interval of the desired virtual array antenna and
creates a steering vector used to detect an azimuth.
[0021] In the on-board multibeam radar apparatus, the processing
unit may be configured to apply a unitary transformation to a
correlation matrix based on the created virtual array data, to
apply a unitary transformation to the steering vector, and to
perform the predetermined process based on the result of the
unitary transformation.
[0022] To achieve the above-mentioned object, according to a second
aspect of the invention, there is provided a multibeam radar method
including: causing a plurality of beam elements constituting an
antenna to transmit a transmission wave and to receive an incoming
wave being reflected and arriving from a target in response to the
transmission wave; causing a control unit to select a beam element
used for transmission and reception out of the plurality of beam
elements so as to change a field of view; and causing a processing
unit to apply a Fourier-transform to beam element data which are
data of a received wave received through the beam element used for
transmission and reception selected by the control unit based on
the number of elements and the element interval of a desired
virtual array antenna so as to create virtual array data, and to
perform a predetermined process based on the created virtual array
data.
[0023] To achieve the above-mentioned object, according to a third
aspect of the invention, there is provided a multibeam radar
program causing a computer to perform: a step of causing a
plurality of beam elements constituting an antenna to transmit a
transmission wave and to receive an incoming wave being reflected
and arriving from a target in response to the transmission wave; a
step of causing a control unit to select a beam element used for
transmission and reception out of the plurality of beam elements so
as to change a field of view; and a step of causing a processing
unit to apply a Fourier transformation to beam element data which
are data of a received wave received through the beam element used
for transmission and reception selected by the control unit based
on the number of elements and the element interval of a desired
virtual array antenna so as to create virtual array data, and to
perform a predetermined process based on the created virtual array
data.
[0024] According to the invention, it is possible to provide an
on-board multibeam radar apparatus, a multibeam radar method, and a
multibeam radar program, which can switch between various FOVs and
can detect a target with a high accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a block diagram illustrating the constitution of
an on-board multibeam radar apparatus according to a first
embodiment of the invention.
[0026] FIG. 2 is a block diagram illustrating a first
constitutional example of a signal processing unit of an FMCW
type.
[0027] FIG. 3 is a diagram illustrating the relationship between an
FMCW signal and a beat signal.
[0028] FIG. 4 is a diagram illustrating an example of the level of
a received signal from a target in an ascending region and a
descending region.
[0029] FIG. 5 is a graph illustrating the frequency resolution
result of a beat signal and shows beat frequencies (horizontal
axis) and peak values (vertical axis) thereof.
[0030] FIG. 6 is a block diagram illustrating a second
constitutional example of the signal processing unit of the FMCW
type.
[0031] FIG. 7 is a diagram schematically illustrating the flow of
processes performed by an azimuth detecting unit.
[0032] FIG. 8 is a flowchart illustrating an example of the flow of
processes performed by the azimuth detecting unit according to the
first embodiment of the invention.
[0033] FIG. 9 is a flowchart illustrating an example of the flow of
a MUSIC spectrum calculating process performed by the azimuth
detecting unit according to the first embodiment of the
invention.
[0034] FIG. 10 is a diagram illustrating an example where a
multibeam for detecting a distant target is formed.
[0035] FIG. 11 is a diagram illustrating an example where a
multibeam for detecting a near target is formed.
[0036] FIG. 12 is a flowchart illustrating an example of the flow
of an eigenvalue calculating process including a unitary
transformation of a correlation matrix, which is performed by an
azimuth detecting unit according to a second embodiment of the
invention.
[0037] FIG. 13 is a flowchart illustrating an example of the flow
of a MUSIC spectrum calculating process including a unitary
transformation of a steering vector, which is performed by the
azimuth detecting unit according to the second embodiment of the
invention.
[0038] FIG. 14 is a block diagram illustrating the constitution of
an on-board multibeam radar apparatus according to a third
embodiment of the invention.
[0039] FIG. 15 is a diagram illustrating an example where a
multibeam for detecting a distant target is formed.
[0040] FIG. 16 is a diagram illustrating an example where a
multibeam for detecting a near target is formed.
[0041] FIG. 17 is a flowchart illustrating an example of the flow
of processes performed by a control unit and an azimuth detecting
unit according to the third embodiment of the invention.
[0042] FIG. 18 is a diagram illustrating the principle of
estimating an arrival direction with an ultrahigh resolution using
a multibeam dielectric lens antenna.
[0043] FIG. 19 is a diagram illustrating horizontal beam
patterns.
[0044] FIG. 20 is a diagram illustrating an outline of a lens.
[0045] FIG. 21 is a diagram illustrating the relationship of the
SNR, the number of snapshots, and the resolution.
[0046] FIG. 22 is a diagram of a graph illustrating the
relationship of the SNR, the DUR, and the resolution.
[0047] FIG. 23 is a diagram illustrating an example of a MUSIC
spectrum.
[0048] FIG. 24 is a diagram illustrating an example of a MUSIC
spectrum.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
<Constitution of Multibeam Radar Apparatus>
[0049] FIG. 1 is a block diagram illustrating the constitution of
an on-board multibeam radar apparatus 101 according to a first
embodiment of the invention.
[0050] In the first embodiment, the invention is applied to a
millimeter wave radar of an FMCW type in a multibeam system using a
dielectric lens antenna.
[0051] As shown in FIG. 1, the multibeam radar apparatus 101
according to the first embodiment includes a dielectric lens 1, M
beam elements (antenna elements) 2-1 to 2-M which are plural
primary feeds, M directional couplers 3-1 to 3-M, M mixers 4-1 to
4-M, M filters 5-1 to 5-M, an SW (switch) 6, an ADC (A/D
(Analog-to-Digital) converter) 7, a signal processing unit 8, a
control unit 11, a VCO (Voltage Controlled Oscillator) 12, and a
distributor 13.
[0052] Here, M represents the number of beam elements 2-1 to
2-M.
[0053] The multibeam radar apparatus 101 according to the first
embodiment includes M amplifiers 21-1 to 21-M between the M
directional couplers 3-1 to 3-M and the M mixers 4-1 to 4-M,
includes an amplifier 22 between the SW 6 and the ADC 7, includes
an amplifier 23 between the control unit 11 and the VCO 12,
includes M amplifiers 24-1 to 24-M between the distributor 13 and
the M mixers 4-1 to 4-M, and includes M amplifiers 25-1 to 25-M
between the distributor 13 and the M directional couplers 3-1 to
3-M.
[0054] Here, in the first embodiment, the dielectric lens 1 and the
plurality of beam elements 2-1 to 2-M constitute an antenna
unit.
[0055] Multibeams capable of simultaneously being transmitted and
received are formed by the directional couplers 3-1 to 3-M
connected to the beam elements 2-1 to 2-M, respectively.
<First Constitutional Example of Signal Processing Unit>
[0056] FIG. 2 is a block diagram illustrating a first
constitutional example of the signal processing unit of an FMCW
type (described as a signal processing unit 8).
[0057] As shown in FIG. 2, the signal processing unit 8 according
to the first constitutional example of the first embodiment
includes a memory 51, a frequency resolving unit 52, a peak
detecting unit 53, a peak combining unit 54, a distance/velocity
detecting unit 55, a pair fixing unit 56, an azimuth detecting unit
57, and a target fixing unit 58.
<Operational Example of Multibeam Radar Apparatus 101 Including
Signal Processing Unit 8 According to First Constitutional
Example>
[0058] An example of the operation performed in the multibeam radar
apparatus 101 according to the first embodiment will be described
below.
[0059] The control unit 11 employs an FMCW system and outputs a
signal to the VCO 12 via the amplifier 23.
[0060] The VCO 12 outputs a CW signal (FMCW signal) having been
subjected to frequency modulation to the distributor 13 based on
the signal input from the control unit 11.
[0061] The distributor 13 divides the FMCW signal input from the
VCO 12 into two signals, outputs one divided signal to the
directional couplers 3-1 to 3-M via the amplifiers 25-1 to 25-M,
and outputs the other divided signal to the mixers 4-1 to 4-M via
the amplifiers 24-1 to 24-M.
[0062] The FMCW signal sent from the distributor 13 to the
directional couplers 3-1 to 3-M is sent to the beam elements 2-1 to
2-M via the directional couplers 3-1 to 3-M and is transmitted
(wirelessly transmitted) from the beam elements 2-1 to 2-M via the
dielectric lens 1.
[0063] This transmitted wave is returned as a reflected wave when
it is reflected by a target. In this case, the reflected wave is
received by the beam elements 2-1 to 2-M via the dielectric lens 1
and is input to the directional couplers 3-1 to 3-M.
[0064] The received wave (received reflected wave) is input to the
mixers 4-1 to 4-M from the directional couplers 3-1 to 3-M via the
amplifiers 21-1 to 21-M.
[0065] The mixers 4-1 to 4-M mix the received wave (received
signal) input from the respective directional couplers 3-1 to 3-M
and the FMCW signal (transmitted signal) input from the distributor
13 and outputs a beat signal as the resultant signal to the filters
5-1 to 5-M. Here, beat signals corresponding to the number of
elements (M) are generated.
[0066] The filters 5-1 to 5-M filter (band-limit) the beat signal
input from the mixers 4-1 to 4-M and output the band-limited signal
to the SW 6. Here, the beat signals input from the mixers 4-1 to
4-M to the filters 5-1 to 5-M correspond to beat signals of
channels (CH) 1 to M corresponding to the beam elements 2-1 to 2-M
and generated by the mixers 4-1 to 4-M.
[0067] Under the control of the control unit 11, the SW 6 performs
a switching operation and outputs the beat signals input from the M
filters 5-1 to 5-M to the ADC 7 via the amplifier 22. Specifically,
the SW 6 sequentially switches the beat signals of CH1 to CHM
corresponding to the beam elements 2-1 to 2-M and passing through
the filters 5-1 to 5-M in response to a sampling signal input from
the control unit 11 and outputs the beat signals to the ADC 7 via
the amplifier 22.
[0068] Under the control of the control unit 11, the ADC 7 A/D
converts the beat signals input from the SW 6 and outputs the
resultant signals to the signal processing unit 8. Specifically,
the ADC 7 A/D-converts the beat signals of CH1 to CHM, which are
input from the SW 6 in synchronization with the sampling signal,
corresponding to the beam elements 2-1 to 2-M in synchronization
with the sampling signal to convert analog signals into digital
signals and sequentially stores the digital signals in a waveform
storage area of the memory (the memory 51 shown in FIG. 2 or 6 in
the first embodiment) of the signal processing unit 8.
[0069] As a result, the received data (data of the beat signals)
for each beam element 2-1 to 2-M (for each CH) is sent to the
signal processing unit 8.
[0070] The control unit 11 controls the switching operation of the
SW 6. The control unit 11 controls the ADC 7. Specifically, the
control unit 11 outputs the sampling signal to the SW 6 and the ADC
7.
[0071] Here, the control unit 11 is constructed, for example, by a
microcomputer or the like and controls the whole multibeam radar
apparatus 101 shown in FIG. 1 based on a control program stored in
a ROM (Read Only Memory) not shown.
[0072] In the first embodiment, the dielectric lens 1, the beam
elements 2-1 to 2-M, the directional couplers 3-1 to 3-M, the
amplifiers 21-1 to 21-M, the mixers 4-1 to 4-M, the filters 5-1 to
5-M, the SW 6, the amplifier 22, and the ADC 7 constitute a
receiver unit.
[0073] In the first embodiment, the VCO 12 and the distributor 13
constitute a beat signal generating unit.
[0074] The operational example performed by the signal processing
unit 8 of the FMCW system according to the first constitutional
example of the first embodiment shown in FIG. 2 will be described
below.
[0075] The memory 51 stores the time-series data (the ascending
region and the descending region), which is obtained by performing
the A/D conversion on the received signal (beat signal) by the use
of the ADC 7, in the waveform storage area in a manner associated
with the beam elements 2-1 to 2-M. For example, when 256 pieces of
data are sampled from each of the ascending region and the
descending region, data pieces of 2.times.256.times.number of
elements are stored in the waveform storage area.
[0076] In this manner, the beat signals corresponding to CH of the
beam elements 2-1 to 2-M are stored in the memory 51.
[0077] The frequency resolving unit 52 transforms the beat signals
corresponding to the channels CH1 to CHM (the beam elements 2-1 to
2-M) into frequency components with a predetermined resolution, for
example, through the use of the Fourier transformation and thus
outputs frequency points indicating the beat frequencies and
complex data of the beat frequencies. For example, when each of the
ascending region and the descending region of each beam element 2-1
to 2-M has 256 sampled data pieces, the data pieces are transformed
to the beat frequencies as complex frequency-domain data for each
beam element 2-1 to 2-M, and 128 pieces of complex data (data
pieces of 2.times.128.times.number of elements) are generated for
each of the ascending region and the descending region. The beat
frequencies appear at the frequency points.
[0078] In this manner, the frequency resolving unit 52 transforms
the beat signals to a range of beat frequencies through the use of
the Fourier transformation for each CH of the beam elements 2-1 to
2-M.
[0079] Regarding the peak values of the intensity in the ascending
region and the descending region of a triangular wave at the
frequency-transformed beat frequencies, the peak detecting unit 53
detects the beat frequencies having a peak value greater than a
predetermined value (peak-detecting threshold value) from the peaks
of the signal intensity (or amplitude) using the complex data.
Accordingly, the presence of a target for each beat frequency is
detected and the target frequency is selected.
[0080] In this manner, the peak detecting unit 53 can detect the
peak value of each spectrum as the beat frequency, that is, the
presence of a target depending on the distance, by converting the
complex data for each beam element 2-1 to 2-M into a frequency
spectrum.
[0081] The peak combining unit 54 combines all the beat frequencies
of the ascending region and the descending region and the peak
values thereof in a matrix shape based on the beat frequencies and
the peak values thereof output from the peak detecting unit 53 for
each beam element, thus combines the beat frequencies of the
ascending region and the descending region, and sequentially
outputs the combinations to the distance/velocity detecting unit
55.
[0082] In the first embodiment, since such combination is performed
for each CH of the beam elements 2-1 to 2-M, the presence of a
target can be detected for each beam direction.
[0083] The distance/velocity detecting unit 55 calculates the
distance r from the target based on the values obtained by adding
the beat frequencies of the combinations of the ascending region
and the descending region sequentially input thereto.
[0084] The distance/velocity detecting unit 55 calculates the
relative velocity v based on the difference between the beat
frequencies of the combinations of the ascending region and the
descending region sequentially input thereto.
[0085] In the first embodiment, the calculations of the distance r
and the relative velocity v is performed for each CH of the beam
elements 2-1 to 2-M.
[0086] The pair fixing unit 56 creates a first pair table based on
the input distance r, the input relative velocity v, and the input
peak levels p.sub.u and p.sub.d of the ascending region and the
descending region for each CH, determines a suitable combination of
the peaks of the ascending region and the descending region for
each target, fixes the pair of peaks of the ascending region and
the descending region using a second pair table, and outputs a
target group number indicating the fixed distance r and the fixed
relative velocity v to the target fixing unit 58.
[0087] The first pair table is a table showing a matrix of the beat
frequencies of the ascending region and the descending region and
intersections of the matrix, that is, the distance and the relative
velocity in the combinations of the beat frequencies of the
ascending region and the descending region, in the peak combining
unit 54.
[0088] The second pair table is a table showing the distance, the
relative velocity, and the frequency point for each target group.
For example, in the second pair table, the distance, the relative
velocity, and the frequency point (the ascending region and/or the
descending region) are stored in manner associated with the target
group number.
[0089] The first pair table and the second pair table are stored,
for example, in the inner storage of the pair fixing unit 56.
[0090] The pair fixing unit 56 may employ a technique of selecting
the combination of the target groups preferentially using the
values predicted in the present detection cycle rather than the
distances r and the relative velocities v from and to the targets,
which are finally fixed, for example, in the preceding detection
cycle.
[0091] The pair fixing unit 56 sends the frequencies, of which a
pair is fixed, to the frequency resolving unit 52 for each CH.
[0092] The frequency resolving unit 52 having received the
frequencies outputs specific frequency point data (complex data) of
the beam elements 2-1 to 2-M (CH) used to estimate the azimuth (to
detect the azimuth) to the azimuth detecting unit 57. That is, when
a pair is present at a specific frequency point of any CH, the
specific frequency point data is used as the complex data used to
detect the azimuth by forming a set along with data at the same
frequency point of another CH.
[0093] Here, one of the ascending and the descending may be used as
the complex data, or both the ascending and the descending may be
used.
[0094] The azimuth detecting unit 57 performs a spectrum estimating
process using a high-resolution algorithm such as the MUSIC method
or the linear prediction method. The azimuth detecting unit 57
detects the azimuth of a corresponding target based on the result
of the spectrum estimation process and outputs the detected azimuth
to the target fixing unit 58.
[0095] At this time, in the first embodiment, the azimuth detecting
unit 57 applyies the Fourier transformation to the complex data
(beam element data) based on the a plurality of beam elements 2-1
to 2-M constituting an antenna to create complex data (virtual
array data) based on a plurality of virtual array elements
constituting a virtual array antenna and performs the spectrum
estimating process using a high-resolution algorithm such as the
MUSIC method or the linear prediction method.
[0096] In this manner, the azimuth detecting unit 57 performs the
process of estimating the azimuth of a target.
[0097] The target fixing unit 58 fixes a target based on the
distance r, the relative velocity v, and the frequency point output
from the pair fixing unit 56 and the azimuth of a target detected
by the azimuth detecting unit 57.
[0098] In this manner, the azimuth is determined along with the
distance r from the target and the relative velocity v, and the
target is fixed.
[0099] The principle of detecting the distance between the
multibeam radar apparatus 101 and a target, the relative velocity
therebetween, and the angle (azimuth) thereof, which is used in the
signal processing unit 8 according to the first embodiment, will be
described in brief below. Here, the FMCW system is assumed.
[0100] FIGS. 3 and 4 are graphs illustrating a state where a
transmitted signal 1001 is reflected by a target and a received
signal 1002 is input. In the examples of FIGS. 3 and 4, the number
of targets is 1.
[0101] FIG. 3 is a diagram illustrating the relationship between an
FMCW signal and a beat signal. Specifically, the relationship
between the transmitted signal and the time, the relationship
between the received signal and the time, and the relationship
between the beat signal and the time are shown. In FIG. 3, the
horizontal axis represents the time and the vertical axis
represents the frequency.
[0102] FIG. 4 is a diagram illustrating an example of the level of
the received signal from a target in the ascending (ascending
region) and the descending (descending region). Specifically, the
relationship between the received signal and the frequency in the
ascending region and the descending region is shown. In FIG. 4, the
horizontal axis represents the frequency and the vertical axis
represents the signal level (intensity).
[0103] FIG. 3 shows the transmitted signal 1001 obtained by
frequency-modulating a triangular wave signal generated by the
control unit 11 through the use of the VCO 12, the received signal
1002 received by causing a target to reflect the transmitted signal
1001, and the beat signal 1003 thereof.
[0104] In addition, FIG. 3 shows the ascending region 1004 and the
descending region 1005. FIG. 3 also shows the central frequency
f.sub.0, the modulation width .DELTA.f, and the modulation time
T.
[0105] As can be seen from FIG. 3, the received signal 1002 which
is a reflected wave from the target is received with a delay in a
right-hand direction (time delay direction) with respect to the
transmitted signal 1001 in proportion to the distance from the
target. The received signal 1002 is shifted in the vertical
direction (frequency direction) with respect to the transmitted
signal 1001 in proportion to the relative velocity to the
target.
[0106] When the beat signal 1003 acquired in FIG. 3 is
frequency-transformed (through the use of the Fourier
transformation, a DTC, a Hadamard transform, a wavelet transform,
or the like), one peak value is generated in each of the ascending
region and the descending region in the case of a single target, as
shown in FIG. 4.
[0107] Specifically, the ascending received signal 1011 has a peak
value at the frequency f.sub.u. The descending received signal 1012
has a peak value at the frequency f.sub.d.
[0108] The frequency resolving unit 52 performs a frequency
resolution on sampled data of the beat signals stored in the memory
51 in each of the ascending region (ascending) and the descending
region (descending) of a triangular wave at discrete times and
performs a frequency transformation, for example, through the use
of the Fourier transformation. That is, the frequency resolving
unit 52 decomposes the beat signals into beat frequencies having a
predetermined frequency bandwidth and calculates complex data based
on the beat signals decomposed for each beat frequency.
[0109] As a result, as shown in FIG. 4, a graph of signal levels
for the decomposed beat frequencies in the ascending region and the
descending region is obtained.
[0110] The peak detecting unit 53 detects the peak value from the
signal level for each beat frequency shown in FIG. 4 to detect the
presence of a target and outputs the beat frequencies f.sub.u and
f.sub.d (both the ascending region and the descending region) of
the peak values as target frequencies.
[0111] The distance/velocity detecting unit 55 calculates the
distance r through the use of Equation (1) based on the target
frequency f.sub.u of the ascending region and the target frequency
f.sub.d of the descending region which are input from the peak
combining unit 54.
r={C.times.T/(2.times..DELTA.f)}.times.{(f.sub.u+f.sub.d)/2}
(1)
[0112] The distance/velocity detecting unit 55 calculates the
relative velocity v through the use of Equation (2) based on the
target frequency f.sub.u of the ascending region and the target
frequency f.sub.d of the descending region which are input from the
peak combining unit 54.
v={C/(2.times.f.sub.0)}.times.{(f.sub.u-f.sub.d)/2} (2)
[0113] In Equations (1) and (2) of calculating the distance r and
the relative velocity v, C represents the light speed, .DELTA.f
represents the frequency modulation width of a triangular wave,
f.sub.0 represents the central frequency of the triangular wave, T
represents the modulation time (ascending region/descending
region), f.sub.u represents the target frequency of the ascending
region, and f.sub.d represents the target frequency of the
descending region.
[0114] FIG. 5 shows the result of the frequency resolution on the
beat signals and is a graph illustrating the beat frequencies and
the peak values thereof. In the graph shown in FIG. 5, the
horizontal axis represents the frequency point of a beat frequency
and the vertical axis represents the signal level (intensity).
[0115] Specifically, in a beat signal 1021 of a specific beam CH of
the ascending region, three beat frequencies f.sub.u1, f.sub.u2,
and f.sub.u3 having a peak value greater than a predetermined value
(peak-detecting threshold value) 1022 appear.
[0116] In a beat signal 1031 of a specific beam CH of the
descending region, three beat frequencies f.sub.d1, f.sub.d2, and
f.sub.d3 having a peak value greater than a predetermined value
(peak-detecting threshold value) 1032 appear.
[0117] In this manner, three targets are present in the distance
direction in this example.
[0118] The peak combining unit 54 combines all the beat frequencies
of the ascending region and the descending region and the peak
values thereof in a matrix shape based on the beat frequencies and
the peak values thereof output from the peak detecting unit 53 and
shown in FIG. 5, combines all the beat frequencies of the ascending
region and the descending region, and sequentially outputs the
combinations to the distance detecting unit 25 and the velocity
detecting unit 26.
<Second Constitutional Example and Operational Example of Signal
Processing Unit>
[0119] FIG. 6 is a block diagram illustrating a second
constitutional example of the signal processing unit of the FMCW
type (described as a signal processing unit 8a).
[0120] As shown in FIG. 6, the signal processing unit 8a according
to the second constitutional example of the first embodiment
includes a memory 51, a frequency resolving unit 52a, a peak
detecting unit 53a, an azimuth combining unit 57a, a peak combining
unit 54a, a distance/velocity detecting unit 55a, and a target
fixing unit 58a.
[0121] Here, the memory 51 is the same as shown in FIG. 2 and is
denoted by the same reference numeral as shown in FIG. 2.
[0122] In the constitution shown in FIG. 6, a pair is fixed after
an azimuth is detected both in the ascending region (rising region)
and the descending region (falling region) of a triangular wave in
the FMCW system.
[0123] The signal processing unit 8a shown in FIG. 6 estimates an
azimuth through the use of a high-resolution algorithm in the same
way as shown in FIG. 2. Differences from FIG. 2 will be described
below.
[0124] The frequency resolving unit 52a converts the beat signals
of the ascending region and the descending region into complex data
for each antenna and outputs the frequency points indicating the
beat frequencies and the complex data to the peak detecting unit
53a.
[0125] The frequency resolving unit 52a outputs the complex data of
the ascending region and the descending region to the azimuth
detecting unit 57a. The complex data is a target group (beat
frequencies having a peak in the ascending region and the
descending region) of each of the ascending region and the
descending region.
[0126] The peak detecting unit 53a detects the peak values of the
ascending region and the descending region and the frequency points
at which the peak values are present, and outputs the frequency
points to the frequency resolving unit 52a.
[0127] The azimuth detecting unit 57a performs a spectrum
estimating process through the use of a high-resolution algorithm
such as the MUSIC method or the linear prediction method. The
azimuth detecting unit 57a detects the azimuth of a corresponding
target based on the result of the spectrum estimating process.
[0128] At this time, in the first embodiment, the azimuth detecting
unit 57a applies Fourier transformation to the complex data (beam
element data) based on the plurality of beam elements 2-1 to 2-M
constituting an antenna to create complex data (virtual array data)
based on a plurality of virtual array elements constituting a
virtual array antenna and performs the spectrum estimating process
using a high-resolution algorithm such as the MUSIC method or the
linear prediction method.
[0129] The azimuth detecting unit 57a detects an angle .theta. for
each of the ascending region and the descending region and outputs
the detected angles as an azimuth table to the peak combining unit
54a.
[0130] Here, the azimuth table is a table used to combine the peaks
of the ascending region and the descending region.
[0131] Specifically, in the azimuth table of the ascending region,
angle 1, angle 2, . . . , and the frequency points f are correlated
with the target groups. For example, target group 1 is correlated
with t.sub.1.sub.--ang.sub.1 of angle 1, t.sub.1.sub.--ang.sub.2 of
angle 2, and the frequency point Target group 2 is correlated with
t.sub.2.sub.--ang.sub.1 of angle 1, t.sub.2.sub.--ang.sub.2 of
angle 2, and the frequency point f.sub.2. The same is true of the
subsequent target groups.
[0132] In the azimuth table of the descending region, angle 1,
angle 2, . . . , and the frequency points f are correlated with the
target groups. For example, target group 1 is correlated with
t.sub.1.sub.--ang.sub.1 of angle 1, t.sub.1.sub.--ang.sub.2 of
angle 2, and the frequency point f.sub.1. Target group 2 is
correlated with t.sub.2.sub.--ang.sub.1 of angle 1,
t.sub.2.sub.--ang.sub.2 of angle 2, and the frequency point
f.sub.2. The same is true of the subsequent target groups.
[0133] The peak combining unit 54a generates a combination having
the same angle using the information of the azimuth table output
from the azimuth detecting unit 57a and outputs the combinations of
beat frequencies of the ascending region and the descending region
to the distance/velocity detecting unit 55a.
[0134] The distance/velocity detecting unit 55a calculates the
distance r from the target based on the values obtained by adding
the beat frequencies of the combinations of the ascending region
and the descending region sequentially input thereto through the
use of Equation (1).
[0135] The distance/velocity detecting unit 55a calculates the
relative velocity v based on the difference between the beat
frequencies of the combinations of the ascending region and the
descending region sequentially input thereto through the use of
Equation (2).
[0136] Here, the distance/velocity detecting unit 55a calculates
the values of the distance and the relative velocity based on the
combinations of beat frequencies of the ascending region and the
descending region.
[0137] The target fixing unit 58a determines pairs of peaks of the
ascending region and the descending region and fixes a target.
[0138] In this manner, in the constitution shown in FIG. 6, unlike
the constitution shown in FIG. 2, the azimuth detecting unit 57a
first performs the azimuth estimation on the ascending region and
the descending region and pairs are then fixed as a result.
<Detailed Operation of Azimuth Detecting Unit>
[0139] The detailed operation performed by the azimuth detecting
unit 57 shown in FIG. 2 will be described below. The same is true
of the detailed operation performed by the azimuth detecting unit
57a shown in FIG. 6.
[0140] The principle of the invention, in the case of a multibeam
system, focuses on a Fourier transformation relationship between
the receiving pattern in the primary feeds and the distribution of
an antenna aperture (the distribution function of a wave source,
for example, a phase distribution function).
[0141] FIG. 7 is a diagram schematically illustrating the flow of
processes performed by the azimuth detecting unit 57.
[0142] Data transmitted and received via the plurality of beam
elements 2-1 to 2-M (CH) can be transformed into data transmitted
and received via a plurality of virtual array elements through the
use of the Fourier transformation 1101.
[0143] FIG. 7 shows a case where the number of beam elements 2-1 to
2-M (number of elements) is 5 (M=5) as an example of the first
feeds.
[0144] Beams 111-1 to 111-5 are transmitted and received via the
dielectric lens 1 through the five beam elements 2-1 to 2-5.
[0145] FIG. 7 shows a case where the number of virtual array
elements (virtual array elements) 112-1 to 112-9 (number of
elements) is 9 as an example of the virtual array elements.
[0146] In this case, all the virtual array elements 112-1 to 112-9
are arranged to be included in the lens aperture length (the same
aperture length as the dielectric lens 1) of a virtual dielectric
lens 1a equivalent to the dielectric lens 1.
[0147] In this case, a plurality of virtual array elements 112-1 to
112-9 is arranged at constant intervals.
[0148] Here, the inventor induced that when the elements are
arranged within the lens aperture length at the time of conversion
into data to be transmitted and received through the virtual array
elements as in this case, it is possible to form the virtual array
elements with any number of elements and any element interval.
[0149] By using the data to be transmitted and received through the
virtual array elements 112-1 to 112-M, it is possible to perform
the processes of a high-resolution algorithm, such as the MUSIC
method or the linear prediction method, or to form a beam with a
changed number of elements and element interval.
[0150] In a specific example, a graph 1111 indicating the
relationship between an azimuth angle (angle) and a spectrum
intensity is obtained through the use of a high-resolution
algorithm, and based on this, the angles of multiple targets can be
measured with a high resolution.
[0151] Therefore, when estimating an azimuth using a
high-resolution algorithm or a beam forming based on the calculated
virtual array element data, the azimuth detecting unit 57 according
to the first embodiment can flexibly set input data depending on
the processing situation of the high-resolution algorithm or the
beam forming pattern.
[0152] FIG. 8 is a flowchart illustrating the flow of processes
performed by the azimuth detecting unit 57. In this example, the
MUSIC method is used as a high-resolution algorithm.
[0153] The flow of processes in this flowchart is repeatedly
performed for each beat frequency point at which a target is
detected through a peak detection.
[0154] First, the azimuth detecting unit 57 reads the complex data
y (m) of the CH of a plurality of beam elements 2-1 to 2-M at one
of the beat frequencies which are extracted by the frequency
resolving unit 52 and at which a target is present (step S101).
[0155] The azimuth detecting unit 57 transforms the read complex
data y(m) of the CH of the plurality of beam elements 2-1 to 2-M
through the use of the Fourier transformation equation expressed by
Equation (3) to calculate virtual array data Y(n) (step S102).
Y ( n ) = 1 2 .pi. m = 1 M y ( m ) - j u ( m ) v ( n ) ( 3 )
##EQU00001##
[0156] Here, m=1 to M represents the number of a beam element, n
represents the number of a virtual array element, y(m) represents
m-th beam element data, Y(n) represents n-th virtual array data,
u(m)=2.pi. sin .theta..sub.m, .theta..sub.m represents the
direction the m-th multi beam, and v(n) represents the position of
the n-th virtual array element.
[0157] For example, the position v(n) of the m-th virtual array
element is expressed by v(n)=d.times.(n-1) using a predetermined
interval d.
[0158] As shown in Equation (3), the virtual array data Y(n) in
which the number of elements and the element interval are
arbitrarily set can be obtained from the beam element data y(m) by
the input of the actual multibeam direction .theta..sub.m and the
set position v(n) of the virtual array element.
[0159] In the processes of steps S103 to S107, the virtual array
data Y(n) calculated through the process of step S102 is processed
using the MUSIC method.
[0160] The MUSIC method is generally used and can employ various
known techniques (for example, refer to Patent Document 1 for the
details of the processes of steps S103 to S107). As shown in FIG.
9, a characterized process is performed in the first embodiment,
which is different from the related art.
[0161] Schematically, the azimuth detecting unit 57 creates a
correlation matrix (covariance matrix) (step S103).
[0162] Then, the azimuth detecting unit 57 performs an eigenvalue
decomposition process to calculate eigenvalues .lamda..sub.1,
.lamda..sub.2, .lamda..sub.3, . . . and eigenvectors e.sub.1,
e.sub.2, e.sub.3, . . . (step S104).
[0163] The azimuth detecting unit 57 estimates the order (step
S105).
[0164] The azimuth detecting unit 57 calculates a MUSIC spectrum
(step S106).
[0165] The azimuth detecting unit 57 detects the number of targets
and the angles (step S107).
[0166] FIG. 9 is a flowchart illustrating an example of the flow of
a MUSIC spectrum calculating process (the process of step S106
shown in FIG. 8) performed by the azimuth detecting unit 57.
[0167] In the MUSIC spectrum calculating process, the azimuth
detecting unit 57 first creates a steering vector a(n, .theta.) of
a virtual array (step S111). The steering vector a(n, .theta.) is
expressed by Equation (4).
a ( n , .theta. ) = 1 2 .pi. m = 1 M y ( m , .theta. ) - j u ( m )
v ( n ) ( 4 ) ##EQU00002##
[0168] Here, m=1 to M represents the number of a beam element, n
represents the number of a virtual array element, .theta.
represents a searching incident angle, y(m, .theta.) represents
m-th beam element data at the searching incident angle .theta.,
a(n, .theta.) represents the n-th steering vector at the searching
incident angle .theta., u(m)=2.pi. sin .theta..sub.m, .theta..sub.m
represents the direction the m-th multibeam, and v(n) represents
the position of the n-th virtual array element.
[0169] Then, the azimuth detecting unit 57 searches for the
orthogonality of the eigenvector in a noise subspace calculated
from the virtual array data Y(n) and the steering vector a(n,
.theta.) of a virtual array (step S112). In this process, the inner
product is used. Specifically, the calculation of the MUSIC method
expressed by Equation (5) is performed (for example, refer to
"Adaptive Antenna Technique", written by Nobuyoshi Kikuma and
published by Ohmsha Ltd., 2003 (Non-patent Document 1) for the
general MUSIC method).
P MUSIC ( .theta. ) = a H ( .theta. ) a ( .theta. ) a ( .theta. ) e
L + 1 H 2 + a ( .theta. ) e L + 2 H 2 + + a ( .theta. ) e K H 2 = a
H ( .theta. ) a ( .theta. ) a H ( .theta. ) E N E N H a ( .theta. )
( 5 ) ##EQU00003##
[0170] Here, .theta. represents a searching incident angle,
P.sub.MUSIC(.theta.) represents a MUSIC spectrum, a(.theta.)
represents a mode vector, e.sub.i represents the i-th eigenvector
(where i=L+1 to K), L+1 to K represent the number of a noise
subspace, K represents the number of elements, L represents the
number of arrival waves (plane waves), EN=[e.sub.L+1, . . . ,
e.sub.K], and H on the right-handed shoulder represents a complex
conjugate transpose (Hermitian transpose).
[0171] In this manner, the azimuth detecting unit 57 acquires the
MUSIC spectrum P.sub.MUSIC(.theta.) (step S113).
[0172] Specifically, as shown in FIG. 7, the graph 1111
illustrating the relationship between the azimuth angle (angle) and
the spectrum intensity can be acquired through the use of a
high-resolution algorithm and the angles of multiple targets can be
measured with a high resolution on the basis thereof.
[0173] In the first embodiment, as expressed by Equation (4), the
steering vector a(n, .theta.) is created (calculated) by the input
of the actual multibeam direction .theta..sub.m and the set
position v(n) of the virtual array element, similarly to the
creation (calculation) of the virtual array data Y(n) expressed by
Equation (3). The first embodiment is characterized by this
point.
[0174] Accordingly, in the first embodiment, the steering vector
a(n, .theta.) capable of searching for the orthogonality to the
virtual array data Y(n) can be created. The azimuth estimation of
the virtual array data Y(n) cannot be performed using the steering
vector created from general linear array data.
<Example of Arrangement of Virtual Array Elements>
[0175] An example of the arrangement of virtual array elements will
be described below.
[0176] For example, it is assumed that the number of virtual array
elements is N. The plurality of virtual array elements 1 to N is
arranged in an array shape at intervals d. An arrival wave
(incident wave, that is, the reflected wave from a target in
response to the transmitted wave transmitted from the transmitting
antenna) from a target incident from the direction of angle .theta.
about an axis perpendicular to the plane on which the plurality of
virtual array elements 1 to N is input to the receiving antenna
including a plurality of virtual array elements 1 to N.
[0177] At this time, the arrival wave is received at the same angle
by the plurality of virtual array elements 1 to N.
[0178] A phase difference "d.times.sin .theta." calculated using
the same angle, for example, the angle .theta., and the interval d
between the antennas appears between the adjacent virtual array
elements 1 to N.
[0179] The angle .theta. can be detected, for example, through the
use of a signal process such as a beam forming process or a
high-resolution algorithm of additionally Fourier-transforming the
values, which are subjected to the frequency resolution in the time
direction for each of the virtual array elements 1 to N, in the
antenna direction using the phase difference.
[0180] Here, a phase difference based on the angle .theta. exists
in the complex data pieces for the virtual array elements 1 to N.
The absolute values (receiving intensities or amplitudes) of the
complex data pieces in the complex plane are equivalent to each
other.
<Example of Formation of Multibeam>
[0181] FIG. 10 is a diagram illustrating an example where a
multibeam for detecting a distant target is formed. In this
example, it is assumed that the number of beam elements (primary
feeds) 2-1 to 2-M is 5 (M=5).
[0182] In this example, the shape of the dielectric lens 1b
(corresponding to the dielectric lens 1 shown in FIG. 1) and the
positions of five beam elements 2-1 to 2-5 are determined to
realize a narrow FOV (Field Of View) 1205. Accordingly, beams
1201-1 to 1201-5 having a small beam width 1204 are formed.
[0183] By forming this narrow beam, for example, it is possible to
detect a target located at a distant position.
[0184] The azimuth of the target is estimated by transforming the
beam element data y(m) acquired through the five beam elements 2-1
to 2-5 to the virtual array data Y(n) through the use of the
Fourier transformation 1202 or transforming the beam element data
y(m, .theta.) at the searching incident angle to the steering
vector a(n, .theta.) through the use of the Fourier
transformation.
[0185] Here, virtual array elements having, for example, any number
of elements and any element interval can be used.
[0186] In this example, it is assumed that nine virtual array
elements 112-1 to 112-9 are linearly arranged at a constant
interval and it is also assumed that both ends of the virtual array
elements 112-1 to 112-9 are arranged to be included in the aperture
length of the dielectric lens 1b.
[0187] In the azimuth estimation, it is possible to detect the
azimuth (angle) of a target at a small angle with a high resolution
by using the virtual array data.
[0188] Specifically, the graph 1203 illustrating the relationship
between the azimuth angle (angle) and the spectrum intensity can be
acquired through the use of a high-resolution algorithm and the
angles of multiple targets can be measured with a high resolution
on the basis thereof.
[0189] Accordingly, it is possible to detect a target with a small
RCS such as a motorcycle.
[0190] FIG. 11 is a diagram illustrating an example where a
multibeam for detecting a near target is formed. In this example,
it is assumed that the number of beam elements (primary feeds) 2-1
to 2-M is 5 (M=5).
[0191] In this example, the shape of the dielectric lens 1c
(corresponding to the dielectric lens 1 shown in FIG. 1) and the
positions of five beam elements 2-1 to 2-5 are determined to
realize a wide FOV (Field Of View) 1215. Accordingly, beams 1211-1
to 1211-5 having a large beam width 1214 are formed.
[0192] By forming this wide beam, for example, it is possible to
detect a target located at a near position.
[0193] The azimuth of the target is estimated by transforming the
beam element data y(m) acquired through the five beam elements 2-1
to 2-5 to the virtual array data Y(n) through the use of the
Fourier transformation 1212 or transforming the beam element data
y(m, .theta.) at the searching incident angle to the steering
vector a(n, .theta.) through the use of the Fourier
transformation.
[0194] Here, virtual array elements having, for example, any number
of elements and any element interval can be used.
[0195] In this example, it is assumed that nine virtual array
elements 112-1 to 112-9 are linearly arranged at a constant
interval and it is also assumed that both ends of the virtual array
elements 112-1 to 112-9 are arranged to be included in the aperture
length of the dielectric lens 1c.
[0196] In the azimuth estimation, it is possible to detect the
azimuth (angle) of a target at a large angle with a high resolution
by using the virtual array data.
[0197] Specifically, the graph 1213 illustrating the relationship
between the azimuth angle (angle) and the spectrum intensity can be
acquired through the use of a high-resolution algorithm and the
angles of multiple targets can be measured with a high resolution
on the basis thereof.
[0198] Accordingly, it is possible to detect a target with a small
RCS such as a walker or a bicycle.
[0199] As shown in FIGS. 10 and 11, in the first embodiment, the
shape of the dielectric lens 1 or the positions of the primary
feeds (beam elements 2-1 to 2-M) are changed so as to realize an
application for a small angle (for example, for detecting a distant
target, .+-.10 deg) shown in FIG. 10 and to realize an application
for a large angle (for example, for detecting a near target, .+-.40
deg) shown in FIG. 11.
[0200] In the examples shown in FIGS. 10 and 11, the shapes (for
example, including the sizes) of the dielectric lenses 1b and 1c or
the arrangements of the plurality of beam elements 2-1 to 2-5 are
changed. The beam elements depart from the focal lengths of the
dielectric lenses 1b and 1c. The beam width is changed depending on
the arrangement of the dielectric lenses 1b and 1c and the
plurality of beam elements 2-1 to 2-5.
[0201] With the narrow beam, the FOV is in the range of the self
lane and both lanes thereof and, for example, it is possible to
detect or track another vehicle (vehicle or motorcycle). With the
wide beam, for example, it is possible to detect a walker, a
bicycle, or another vehicle at an intersection.
[0202] In the multibeam radar apparatus 101 according to the first
embodiment, since the high-resolution performance can be maintained
without interruption within the FOV, it is possible to cope with
the situation depending on the FOV. Therefore, it is possible to
arbitrarily set the FOV depending on the application or
specification of a radar.
[0203] In this manner, in the multibeam radar apparatus 101
according to the first embodiment, it is possible to perform a
high-resolution azimuth detection with a high gain and a high
efficiency characteristic based on a multibeam and regardless of a
small angle or a large angle.
Conclusion of First Embodiment
[0204] Although it has been stated in the first embodiment that the
FMCW system is exemplified as the radar system, the invention is
not limited to the radar system and the constitution according to
the first embodiment may be applied to another radar system.
[0205] Although it has been stated in the first embodiment that the
MUSIC method is exemplified as the high-resolution algorithm, the
constitution according to the first embodiment may be applied to
other techniques such as a linear prediction method or a beam
forming method. For example, it is possible to calculate an azimuth
angle (angle) using virtual array data and virtual array steering
vectors.
[0206] As described above, the multibeam radar apparatus 101
according to the first embodiment include Apparatus Constitution 1
to Apparatus Constitution 4 described below.
[0207] As Apparatus Constitution 1, the multibeam radar apparatus
101 according to the first embodiment performs the Fourier
transformation using the multibeam direction .theta..sub.m
expressed by Equation (3) from the data (beam element data y(m))
received through the beam elements 2-1 to 2-M and thus calculates
the virtual array data Y(n).
[0208] As Apparatus Constitution 2, the multibeam radar apparatus
101 according to the first embodiment acquires the virtual array
data with any number of elements and any element interval within
the aperture (length) of the dielectric lens 1 when performing the
process associated with Apparatus Constitution 1.
[0209] As Apparatus Constitution 3, the multibeam radar apparatus
101 according to the first embodiment creates the steering vector
a(n, .theta.) used to perform the azimuth estimation of the virtual
array data Y(n) through the use of the Fourier transformation using
the multibeam direction .theta..sub.m expressed by Equation (4),
similarly to the creation of the virtual array data Y(n). At this
time, the same number of elements and element interval used to
calculate the virtual array data Y(n) are used.
[0210] As Apparatus Constitution 4, the multibeam radar apparatus
101 according to the first embodiment performs a direction
estimating process through the use of a high-resolution algorithm,
such as the MUSIC method or the linear prediction method, or the
beam forming method using the virtual array data Y(n) and the
virtual array steering vector a(n, .theta.) acquired by Apparatus
Constitution 1 to Apparatus Constitution 3.
[0211] Since the multibeam radar apparatus 101 according to the
first embodiment has Apparatus Constitution 1 to Apparatus
Constitution 4, it is possible to perform a high-resolution
direction estimating operation without being affected by grating
lobes. In the multibeam radar apparatus 101 according to the first
embodiment, since data based on the number of array elements N and
the element interval d but not depending on the number of original
beam elements M is acquired, it is possible to flexibly set the
input data, for example, depending on the purpose or the processing
efficiency in the high-resolution algorithm or the beam forming
method, as an after-process. In the multibeam radar apparatus 101
according to the first embodiment, it is possible to form a small
beam width and a large number of beams with the increase in the
number of virtual array elements N in the beam forming.
[0212] Since the multibeam radar apparatus 101 according to the
first embodiment has Apparatus Constitution 3 and thus can create
the steering vector a(n, .theta.) for the virtual array data Y(n)
suitable for the actual multibeam antenna, it is possible to
appropriately perform the direction estimation.
[0213] Since the multibeam radar apparatus 101 according to the
first embodiment includes Apparatus Constitution 1 to Apparatus
Constitution 4 and thus can perform the direction estimation with a
high resolution, it is possible to reduce the number of beam
elements M, compared with the apparatuses according to the related
art measuring the angle using only the beam element data. Since the
arrangement interval of the beam elements (primary feeds) 2-1 to
2-M has a margin due to the reduction of the number of beam
elements M, it is possible to provide the primary feeds with a high
gain.
[0214] Since the multibeam radar apparatus 101 according to the
first embodiment includes Apparatus Constitution 1 to Apparatus
Constitution 4, it is possible to cope with various FOVs such as a
small-angle FOV and a large-angle FOV, regardless of the FOV. For
example, even in a radar (for example, in which the individual beam
width is increased to widen the direction) designed for the large
angle, since the angle can be measured with a high resolution even
with a small number of beam elements M, it is possible to form a
multibeam with a high resolution.
[0215] In this manner, in the multibeam radar apparatus 101
according to the first embodiment, it is possible to activate the
multibeam formation with a high gain and a high efficiency which is
a merit of the multibeam system and to markedly improve the
resolution of multiple targets and the angle measurement accuracy
at the same measurement point, compared with the related art.
[0216] Accordingly, in the multibeam radar apparatus 101 according
to the first embodiment, since the high separation capability and
the high resolution can be added to the multibeam system with a
high gain and a high efficiency, it is possible to better detect an
object with a small RCS such as a walker or a bicycle at a near
position (in the vicinity) and a motorcycle at a distance position,
for example, in application to an on-board radar.
[0217] Although it has been stated in the first embodiment that all
the virtual array elements are included within the lens aperture
length (the same aperture length as the dielectric lens 1) of the
virtual dielectric lens 1a equivalent to the dielectric lens 1, the
length (distance between both ends) of all the virtual array
elements when they are linearly arranged may be equal to or
substantially equal to the lens aperture length.
[0218] On the contrary, a constitution in which a plurality of
virtual array elements (for example, one or more elements at both
ends) are disposed out of the lens aperture length, that is, a
constitution in which all the virtual array elements are not
included in the lens aperture length, may be employed. This
constitution may be used.
[0219] Although it has been stated in the first embodiment that the
dielectric lens 1 is used, various other lenses may be used instead
of the dielectric lens 1.
[0220] Although it has been stated in the first embodiment that the
lens (the dielectric lens 1) is provided, a constitution using no
lens may be used. In this case, the multibeam transmission and
reception is performed through the use of the plurality of beam
elements 2-1 to 2-M without using the lens.
[0221] Regarding the number M of beam elements 2-1 to 2-M
constituting an antenna for transmission and reception, when
multiple targets are detected, it is possible to detect the targets
corresponding to only the number smaller by 1 than the number of
beam elements 2-1 to 2-M.
[0222] For example, in the examples shown in FIGS. 10 and 11, the
application to 5 element beams. However, the FOV (Field Of View),
the beam width, and the number of beam elements can be arbitrarily
set depending on the application or specification of a radar.
Particularly, in the multibeam system using a lens antenna, they
can be flexibly set depending on the shape of the lens and the
positions of the primary feeds (beam elements), which is desirable
for combination.
Second Embodiment
<Constitution Using Unitary Transformation>
[0223] In a second embodiment of the invention, the constitution
and operation different from those of the first embodiment will be
described in detail.
[0224] Specifically, the second embodiment is different from the
first embodiment, in that a MUSIC method of applying a unitary
transformation to virtual array data Y(n) and virtual array
steering vectors a(n, .theta.) is performed. Non-patent Document 1
(pp. 158-160) can be referred to for the unitary transformation
itself.
[0225] FIG. 12 is a flowchart illustrating an example of the flow
of an eigenvalue calculating process including the unitary
transformation of a correlation matrix, which is performed by the
azimuth detecting unit 57. The processes (the processes of steps
S121 to S123) shown in FIG. 12 correspond to the processes of steps
S103 to S104 shown in FIG. 8.
[0226] The azimuth detecting unit 57 creates a correlation matrix
(covariance matrix) R.sub.xx based on the virtual array data Y(n)
(step S121). This process corresponds to the process of step S103
shown in FIG. 8.
[0227] The azimuth detecting unit 57 converts an Hermitian matrix
into a real symmetric matrix through the use of the unitary
transformation (step S122).
[0228] Specifically, it is considered that a phase reference point
is set to the center of the array. Accordingly, conjugate
centrosymmetry is achieved.
[0229] In Equations (6) to (9), a unitary matrix
Q.sub.K(=.sub.Q2P+1) when the matrix order is odd (K=2P+1) is
expressed by Equation (6) and a unitary matrix Q.sub.K(=.sub.Q2P)
when the matrix order is even (K=2P) is expressed by Equation
(7).
[0230] In Equation (6), T on the right-hand shoulder represents the
transpose.
Q 2 P + 1 = 1 2 [ I P 0 j I P 0 T 2 0 T II P 0 - j II P ] ( 6 ) Q 2
P = 1 2 [ I P j I P II P - j II P ] ( 7 ) I P = [ 1 0 0 0 1 0 0 0 0
1 ] ( 8 ) II P = [ 0 0 1 0 1 0 1 0 0 ] ( 9 ) ##EQU00004##
[0231] A unitary transformation is expressed by Equation (10). In
Equation (10), only a real part is calculated.
[0232] Regarding the unitary matrix (complex orthogonal matrix)
Q.sub.K, Equation (11) is established using a unit matrix
I.sub.K.
[0233] In Equations (10) and (11), H on the right-hand shoulder
represents a complex conjugate transpose (Hermitian transpose).
R.sub.xx.sub.--.sub.u=Q.sub.K.sup.HR.sub.XXQ.sub.K (10)
[0234] (Calculation of Only Real Parts)
Q.sub.KQ.sub.K.sup.H=Q.sub.K.sup.HQ.sub.K=I.sub.K (11)
[0235] In the eigenvalue calculation according to the second
embodiment, the correlation matrix can be transformed to a real
correction matrix by applying the unitary transformation thereto.
Accordingly, the eigenvalue calculation of which the computational
load is the heaviest in the subsequent steps can be performed using
only real numbers, thereby greatly reducing the computational
load.
[0236] In this manner, by applying the unitary transformation
thereto, it is possible to reduce the computational load of the
eigenvalue calculation in the subsequent stage and thus to expect
the suppression of signal correlation. Accordingly, although the
eigenvalue calculation can be performed using complex numbers in
the subsequent stage without performing the transformation to a
real correlation matrix through the unitary transformation, it is
preferable that the transformation to a real correlation matrix
through the unitary transformation be performed.
[0237] The azimuth detecting unit 57 calculates eigenvalues
.lamda..sub.1, .lamda..sub.2, .lamda..sub.3, . . . and eigenvectors
e.sub.1, e.sub.2, e.sub.3, . . . by performing the real eigenvalue
decomposition (step S123).
[0238] Here, a characteristic equation for performing the
eigenvalue calculation is expressed by Equations (12) and (13).
R.sub.xx.sub.--.sub.e=.lamda.e (12)
|R.sub.xx.sub.--.sub.u-.lamda.I|=0 (13)
[0239] Any solution algorithm can be used for the eigenvalue
calculating process in addition to the direct solving of the
characteristic equation of Equation (13). For example, repeated
calculation type algorithms (convergence type algorithms) such as a
Jacobi method, a Householder method, and a QR method may be
employed.
[0240] FIG. 13 is a flowchart illustrating an example of the flow
of a MUSIC spectrum calculating process including the unitary
transformation of a steering vector, which is performed by the
azimuth detecting unit. The processes (the processes of steps S131
to S133) shown in FIG. 13 correspond to the processes (the process
of step S106 shown in FIG. 8) of steps S111 to S113 shown in FIG.
9.
[0241] In the MUSIC spectrum calculating process, the azimuth
detecting unit 57 creates a vector (the real steering vector of a
virtual array) d(.theta.) obtained by applying the unitary
transformation to the virtual array steering vector a(n, .theta.)
(step S131).
[0242] Specifically, it is considered that a phase reference point
is set to the center of the array. Accordingly, conjugate
centrosymmetry is achieved.
[0243] The rear steering vector d(.theta.) of the virtual array is
expressed by Equation (14). In Equation (14), only real parts are
calculated.
d(.theta.)=Q.sub.K.sup.Ha(n,.theta.) (14)
(Calculation of Only Real Parts)
[0244] Here, n represents the number of a virtual array element,
.theta. represents a searching incident angle, K represent the
number of elements, d(.theta.) represents the real steering vector
of a virtual array at the searching incident angle .theta., a(n,
.theta.) represents the n-th steering vector at the searching
incident angle .theta., and H on the right-handed shoulder
represents the complex conjugate transpose (Hermitian
transpose).
[0245] Then, the azimuth detecting unit 57 searches for the
orthogonality of the real eigenvector in a noise subspace
calculated from the virtual array data Y(n) and the real steering
vector d(.theta.) of a virtual array (step S132). In this process,
the inner product is used. Specifically, the calculation of the
MUSIC method expressed by Equation (15) is performed (for example,
refer to Non-patent Document 1 for the general MUSIC method).
P UM ( .theta. ) = d H ( .theta. ) d ( .theta. ) d ( .theta. ) e L
+ 1 H 2 + d ( .theta. ) e L + 2 H 2 + + d ( .theta. ) e K H 2 = d H
( .theta. ) d ( .theta. ) d H ( .theta. ) E N E N H d ( .theta. ) (
15 ) ##EQU00005##
[0246] Here, .theta. represents a searching incident angle,
P.sub.UM(.theta.) represents a MUSIC spectrum, d(.theta.)
represents a real steering vector, e.sub.i represents the i-th
eigenvector (where i=L+1 to K), L+1 to K represent the number of a
noise subspace, K represents the number of elements, L represents
the number of arrival waves (plane waves), E.sub.N=[e.sub.L+1, . .
. , e.sub.K], and H on the right-handed shoulder represents a
complex conjugate transpose (Hermitian transpose).
[0247] In this manner, the azimuth detecting unit 57 acquires the
MUSIC spectrum P.sub.UM(.theta.) through the use of the unitary
transformation (step S133).
[0248] Specifically, as shown in FIG. 7, the graph 1111
illustrating the relationship between the azimuth angle (angle) and
the spectrum intensity can be acquired through the use of the
high-resolution algorithm and the angles of multiple targets can be
measured with a high resolution on the basis thereof.
[0249] In this manner, in the second embodiment, the conjugate
centrosymmetry about the center of the virtual array is used. A
unitary transformation is applied to the correlation matrix based
on the virtual array data Y(n) by the use of Equation (10), and A
unitary transformation is applied to the virtual array steering
vector a(n, .theta.) by the use of Equation (14). The MUSIC
spectrum is calculated by Equation (15).
[0250] In the second embodiment, since the MUSIC method using the
unitary transformation can be carried out on the virtual array data
Y(n) and the virtual array steering vector a(n, .theta.), it is
possible to perform the eigenvalue decomposing process using a real
correlation matrix. Therefore, it is possible to achieve functional
advantages of a radar of reducing the computational load and more
performing the high-resolution process in the measurement point
direction of the radar (that is, more performing the MUSIC process
for each beat frequency) and to achieve the advantage of reducing
the apparatus cost.
Conclusion of Second Embodiment
[0251] As described above, the multibeam radar apparatus 101
according to the second embodiment includes Apparatus Constitution
5 described below.
[0252] As Apparatus Constitution 5, the multibeam radar apparatus
101 according to the second embodiment applies the unitary
transformation to the correlation matrix R.sub.xx based on the
virtual array data Y(n) and the virtual array steering vector a(n,
.theta.) using the conjugate centrosymmetry of the virtual array
and then performs the direction estimation, when performing the
direction estimation using the MUSIC method as a high-resolution
algorithm through the use of Apparatus Constitution 1 to Apparatus
Constitution 4.
[0253] Since the multibeam radar apparatus 101 according to the
second embodiment includes Apparatus Constitution 5 and thus can
perform the eigenvalue decomposing process using the real
correlation matrix, it is possible to achieve functional advantages
of reducing the computational load and more performing the
high-resolution process for each measurement point and to achieve
the advantage of reducing the apparatus cost.
Third Embodiment
<Constitutional Example of Multibeam Radar Apparatus>
[0254] FIG. 14 is a block diagram illustrating the constitution of
an on-board multibeam radar apparatus 102 according to a third
embodiment of the invention.
[0255] In the third embodiment, the invention is applied to an FMCW
type millimeter wave radar in a multibeam system using a dielectric
lens antenna. In the third embodiment, differences from the
multibeam radar apparatus 101 according to the first embodiment
shown in FIG. 1 will be described in detail and similarities
thereto will not be described or will be described in brief.
[0256] In the multibeam radar apparatus 102 shown in FIG. 14, the
same constituent parts as shown in FIG. 1 are denoted by the same
reference numerals.
[0257] In the third embodiment, it is assumed that the number M of
M beam elements (antenna elements) 2-1 to 2-M as a plurality of
primary feeds is 5.
[0258] As shown in FIG. 14, the multibeam radar apparatus 102
according to the third embodiment includes a dielectric lens 1, M
(=5) beam elements (antenna elements) 2-1 to 2-5 which are a
plurality of primary feeds, M (=5) directional couplers 3-1 to 3-5,
M (=5) mixers 4-1 to 4-5, M (=5) filters 5-1 to 5-5, an SW (switch)
6, an ADC (A/D (Analog-to-Digital) converter) 7, a signal
processing unit 8, a control unit 33, a VCO (Voltage Controlled
Oscillator) 12, and a distributor 13.
[0259] The multibeam radar apparatus 102 according to the third
embodiment includes M (=5) amplifiers 21-1 to 21-5 between the five
directional couplers 3-1 to 3-5 and the five mixers 4-1 to 4-5,
includes an amplifier 22 between the SW 6 and the ADC 7, includes
an amplifier 23 between the control unit 33 and the VCO 12, and
includes M (=5) amplifiers 24-1 to 24-5 between the distributor 13
and the five mixers 4-1 to 4-5.
[0260] The multibeam radar apparatus 102 according to the third
embodiment includes an SW (switch) 31 and an amplifier 25-1 in
series between the distributor 13 and the directional coupler 3-1
corresponding the beam element 2-1 at one end.
[0261] The multibeam radar apparatus 102 according to the third
embodiment includes an SW (switch) 32 and an amplifier 25-5 in
series between the distributor 13 and the directional coupler 3-5
corresponding the beam element 2-5 at the other end.
[0262] The multibeam radar apparatus 102 according to the third
embodiment includes three amplifiers 25-2 to 25-4 between the
distributor 13 and the directional couplers 3-2 to 3-4
corresponding the other (three close to the center) beam elements
2-2 to 2-4.
[0263] In the third embodiment, the dielectric lens 1 and the
plurality of beam elements 2-1 to 2-5 constitute an antenna
unit.
[0264] Multibeams capable of simultaneously being transmitted and
received are formed by the directional couplers 3-1 to 3-5
connected to the beam elements 2-1 to 2-5, respectively.
<First Constitutional Example and Second Constitutional Example
of Signal Processing Unit>
[0265] In the multibeam radar apparatus 102 according to the third
embodiment, similarly to the first embodiment, the FMCW type signal
processing unit 8 shown in FIG. 14 can employ the same constitution
as the first constitutional example shown in FIG. 2 or the same
constitution as the second constitutional example shown in FIG.
6.
[0266] In the third embodiment, a case where the constitution (for
example, the azimuth detecting unit 57) shown in FIG. 2 is employed
will be described. However, the same is true of the case where the
constitution (for example, the azimuth detecting unit 57a) shown in
FIG. 6 is employed.
<Points Similar to First Embodiment>
[0267] The multibeam radar apparatus 102 according to the third
embodiment has the constitution and operation similar to those
described in the first embodiment with reference to FIGS. 3, 4, 5,
7, 8, and 9.
<Operational Example of Multibeam Radar Apparatus 102 According
to Third Embodiment>
[0268] The multibeam radar apparatus 102 according to the third
embodiment includes SWs 31 and 32 in the lines between the
distributor 13 and the beam elements 2-1 and 2-5 at both ends, as a
structural difference from the multibeam radar apparatus 101
according to the first embodiment shown in FIG. 1.
[0269] The control unit 33 has a function of switching between the
ON and OFF states (enabled/disabled states) of the respective SWs
31 and 32.
[0270] In the third embodiment, when the respective SWs 31 and 32
are in the ON state, a signal flows in the corresponding line and
the transmission and reception using the corresponding beam
elements 2-1 and 2-5 is enabled. On the other hand, when the
respective SWs 31 and 32 are in the OFF state, a signal does not
flow in the corresponding lines and the transmission and reception
using the corresponding beam elements 2-1 and 2-5 is disabled.
[0271] The switching between the ON and OFF states of the SWs 31
and 32 by the control unit 33 may be automatically performed by the
control unit 33 of the multibeam radar apparatus 102, for example,
depending on a predetermined condition (for example, a program), or
may be performed when the control unit 33 detects a driver (user)
of the vehicle (for example, automobile) mounted with the multibeam
radar apparatus 102.
[0272] In the third embodiment, by providing the SWs 31 and 32 to
two beam elements 2-1 and 2-5 at both ends out of five beam
elements 2-1 to 2-5, it is possible to switch between a state where
all the five beam elements 2-1 to 2-5 are used for transmission and
reception and a state where only three beam elements 2-2 to 2-4
close to the center are used for transmission and reception.
Accordingly, in the third embodiment, it is possible to make the
variation of the FOV (Field of View) compatible with the
high-resolution detection.
<Formation of Multibeam>
[0273] It will be described below that the FOV is made to vary by
selecting the beam elements 2-1 to 2-5 to be used for transmission
and reception and a virtual array corresponding to the FOV is
formed to create virtual array data.
[0274] FIG. 15 is a diagram illustrating an example where a
multibeam for detecting a distant target is formed.
[0275] In this example, by turning off two SWs 31 and 32 so as to
realize a small-angle FOV (Field of View) 2004, two beam elements
2-1 and 2-5 on the outside are disabled out of five beam elements
2-1 to 2-5 and only three beam elements 2-2 to 2-4 close to the
center are used for transmission and reception. Accordingly, beams
2001-2 to 2001-4 are formed.
[0276] By forming this small-angle FOV 2004, for example, it is
possible to detect a target located at a distant position.
[0277] The azimuth of the target is estimated by transforming the
beam element data y(m) acquired through the three beam elements 2-2
to 2-4 to the virtual array data Y(n) through the use of the
Fourier transformation 2002 or transforming the beam element data
y(m, .theta.) at the searching incident angle to the steering
vector a(n, .theta.) through the use of the Fourier
transformation.
[0278] Here, virtual array elements having, for example, any number
of elements and any element interval can be used as the virtual
array elements.
[0279] In this example, it is assumed that five virtual array
elements 113-1 to 113-5 are linearly arranged at a constant
interval and it is also assumed that both ends of the virtual array
elements 113-1 to 113-5 are arranged to be included in the aperture
length of the dielectric lens 1.
[0280] In the azimuth estimation, it is possible to detect the
azimuth (angle) of a target at a small angle with a high resolution
by using the virtual array data.
[0281] Specifically, the graph 2003 illustrating the relationship
between the azimuth angle (angle) and the spectrum intensity can be
acquired through the use of a high-resolution algorithm and the
angles of multiple targets can be measured with a high resolution
on the basis thereof.
[0282] Accordingly, it is possible to detect a target with a small
RCS such as a motorcycle.
[0283] FIG. 16 is a diagram illustrating an example where a
multibeam for detecting a near target is formed.
[0284] In this example, by turning on two SWs 31 and 32 so as to
realize a large-angle FOV (Field of View) 2014, two beam elements
2-1 and 2-5 on the outside are enabled out of the five beam
elements 2-1 to 2-5 and all the'five beam elements 2-1 to 2-5 are
used for transmission and reception. Accordingly, beams 2011-1 to
2011-5 are formed.
[0285] By forming this large-angle beams, for example, it is
possible to detect a target located at a near position.
[0286] The azimuth of the target is estimated by transforming the
beam element data y(m) acquired through the five beam elements 2-1
to 2-5 to the virtual array data Y(n) through the use of the
Fourier transformation 2012 or transforming the beam element data
y(m, .theta.) at the searching incident angle to the steering
vector a(n, .theta.) through the use of the Fourier
transformation.
[0287] Here, virtual array elements having, for example, any number
of elements and any element interval can be used as the virtual
array elements.
[0288] In this example, it is assumed that seven virtual array
elements 114-1 to 114-7 are linearly arranged at a constant
interval and it is also assumed that both ends of the virtual array
elements 114-1 to 114-7 are arranged to be included in the aperture
length of the dielectric lens 1.
[0289] In the azimuth estimation, it is possible to detect the
azimuth (angle) of a target at a large angle with a high resolution
by using the virtual array data.
[0290] Specifically, the graph 2013 illustrating the relationship
between the azimuth angle (angle) and the spectrum intensity can be
acquired through the use of a high-resolution algorithm and the
angles of multiple targets can be measured with a high resolution
on the basis thereof.
[0291] Accordingly, it is possible to detect a target with a small
RCS such as a walker or a bicycle.
[0292] The number of targets which can be detected can be
increased.
[0293] As shown in FIGS. 15 and 16, in the third embodiment, the
beam elements 2-1 to 2-5 to be used for transmission and reception
are changed so as to realize an application for a small angle (for
example, for detecting a distant target, .+-.10 deg) shown in FIG.
15 and to realize an application for a large angle (for example,
for detecting a near target, .+-.40 deg) shown in FIG. 16.
[0294] With the narrow beam, the FOV is in the range of the self
lane and both lanes thereof and, for example, it is possible to
detect or track another vehicle (car or motorcycle). With the wide
beam, for example, it is possible to detect a walker, a bicycle, or
another vehicle at an intersection.
[0295] In the third embodiment, various types of virtual array data
can be created depending on the transmission and reception
states.
[0296] For example, as shown in FIG. 15, when a target at a distant
position is detected, only the beams of three elements close to the
Center are transmitted and received and the beams of the two
elements on the outside thereof are blocked by the SWs 31 and 32.
Accordingly, since narrow multibeams are formed, the resultant
virtual array data Y(n) can exclude the detection of an unnecessary
reflecting object in the extra range. Accordingly, this is suitable
for a high-speed tracking application in an on-board radar.
[0297] In this example, since the beams of three elements are
transmitted and received, two targets at the same measurement point
can be detected by the high-resolution detection using the virtual
array data Y(n), but the number of beam elements is preferably set
depending on the number of targets to be detected.
[0298] As shown in FIG. 16, when a target at a near position (in
the vicinity) is detected, the SWs 31 and 32 of the two beam
elements on the outside are turned on in addition to the
transmission and reception of the beams of the three elements close
to the center. Accordingly, since wide multibeams are formed, the
detection with a wide FOV is possible using the resultant virtual
array data Y(n). Since the beams of the five elements are
transmitted and received, four targets at the same measurement
point can be detected by the high-resolution detection using the
virtual array data Y(n), and thus the number of targets to be
detected can be increased. In this manner, since multiple targets
at near positions can be detected at a wide field of view, this is
suitable for a collision avoiding application in downtown suing an
on-board radar.
[0299] In this example, since the beams of five elements are
transmitted and received, four targets at the same measurement
point can be detected by the high-resolution detection using the
virtual array data Y(n); however, the number of beam elements is
preferably set depending on the number of targets to be
detected.
[0300] In the multibeam radar apparatus 102 according to the third
embodiment, since the high-resolution performance can be maintained
without interruption within the FOV, it is possible to cope with
the situation depending on the FOV. Therefore, it is possible to
arbitrarily set the FOV depending on the application or
specification of a radar.
[0301] In this manner, in the multibeam radar apparatus 102
according to the third embodiment, it is possible to perform a
high-resolution azimuth detection with a high gain and a high
efficiency characteristic based on multibeams and regardless of a
small angle or a large angle.
[0302] The resolution can be arbitrarily set in the example shown
in FIG. 15 and in the example shown in FIG. 16.
[0303] FIG. 17 is a flowchart illustrating the flow of processes
performed by the control unit 33 and the azimuth detecting unit 57.
In this example, the MUSIC method is used as a high-resolution
algorithm.
[0304] In the third embodiment, the control unit 33 changes the FOV
between a small angle and a large angle and the azimuth detecting
unit 57 detects an azimuth at the corresponding FOV.
[0305] Schematically, when the control unit 33 changes the FOV to
the small angle, the azimuth detecting unit 57 performs the process
of detecting a target through transmission and reception at a small
angle (for example, .+-.10 deg) (steps S201 to S208). When the
control unit 33 changes the FOV to the large angle, the azimuth
detecting unit 57 performs the process of detecting a target
through transmission and reception at the large angle (for example,
.+-.40 deg) (steps S211 to S218).
[0306] The flow of processes in the flowchart is repeatedly
performed for each beat frequency point at which a target of which
the peak is detected is present in each process at the small angle
and the large angle. In this manner, since the flow of processes is
performed for each target (for example, each of the targets) of
which the peak is detected in the measurement point direction, the
flow of processes is performed by the number of peaks (for example,
a plurality of times) at the small angle and the large angle.
[0307] Specific descriptions will be given below.
[0308] First, the control unit 33 enables the transmission and
reception using three beam elements 2-2 to 2-4 to change the FOV to
the small angle by switching the SWs 31 and 32 to the OFF state
(disabled state).
[0309] The azimuth detecting unit 57 reads the complex data y(m) of
CH of a plurality of beam elements 2-2 to 2-4 for one of the beat
frequencies at which a target is present and which is extracted by
the frequency resolving unit 52 (step S201). In this example, m=2,
3, and 4 is set.
[0310] The azimuth detecting unit 57 transforms the read complex
data y(m) of CH of a plurality of beam elements 2-2 to 2-4 through
the use of the same Fourier transformation equation as expressed by
Equation (3) and calculates virtual array data Y1(n1) (step S202).
In this example, n1=1, 2, 3, 4, and 5 is set.
[0311] As shown in Equation (3), the virtual array data Y1(n1) in
which the number of elements and the element interval are
arbitrarily is be obtained from the beam element data y(m) by the
input of the actual multibeam direction .theta..sub.m and the set
position v(n) of the virtual array element.
[0312] In the processes of steps S203 to S208, the virtual array
data Y1(n1) calculated through the process of step S202 is
processed using the MUSIC method.
[0313] The MUSIC method is generally used and can employ various
known techniques (for example, refer to Patent Document 1 for the
details of the processes of steps S203 to S208). As shown in FIG.
17, a characterized process is performed in the third embodiment,
which is from the related art.
[0314] Schematically, the azimuth detecting unit 57 creates a
correlation matrix (covariance matrix) (step S203).
[0315] Then, the azimuth detecting unit 57 performs an eigenvalue
decomposition process to calculate eigenvalues .lamda..sub.1,
.lamda..sub.2, .lamda..sub.3, . . . and eigenvectors e.sub.1,
e.sub.2, e.sub.3, . . . (step S204).
[0316] The azimuth detecting unit 57 estimates the order (step
S205).
[0317] In the MUSIC spectrum calculating process, the azimuth
detecting unit 57 first creates a steering vector a1(n1, .theta.1)
of a virtual array (step S206). The steering vector a1(n1,
.theta.1) is expressed in the same way as in Equation (4). In this
example, the searching incident angle .theta.1 is in the range of
-10 to +10 deg.
[0318] Subsequently, in the MUSIC spectrum calculating process, the
azimuth detecting unit 57 calculates a MUSIC spectrum (step
S207).
[0319] The azimuth detecting unit 57 detects the number of targets
at distant positions (at a small angle) and the angles (step
S208).
[0320] Then, the control unit 33 enables the transmission and
reception using five beam elements 2-1 to 2-5 to change the FOV to
the large angle by switching the SWs 31 and 32 to the ON state
(enabled state).
[0321] The azimuth detecting unit 57 reads the complex data y(m) of
CH of the plurality of beam elements 2-1 to 2-5 for one of the beat
frequencies at which a target is present and which is extracted by
the frequency resolving unit 52 (step S211). In this example, m=1,
2, 3, 4, and 5 is set.
[0322] The azimuth detecting unit 57 transforms the read complex
data y(m) of CH of the plurality of beam elements 2-1 to 2-5
through the use of the same Fourier transformation equation as
expressed by Equation (3) and calculates virtual array data Y2(n2)
(step S212). In this example, n2=1, 2, 3, 4, 5, 6, and 7 is
set.
[0323] As shown in Equation (3), the virtual array data Y2(n2) in
which the number of elements and the element interval are
arbitrarily is be obtained from the beam element data y(m) by the
input of the actual multibeam direction .theta..sub.m and the set
position v(n) of the virtual array element.
[0324] In the processes of steps S213 to S218, the virtual array
data Y2(n2) calculated through the process of step S212 is
processed using the MUSIC method.
[0325] The MUSIC method is generally used and can employ various
known techniques (for example, refer to Patent Document 1 for the
details of the processes of steps S213 to S218). As shown in FIG.
17, the characterized process is performed in the third embodiment,
which is from the related art.
[0326] Schematically, the azimuth detecting unit 57 creates a
correlation matrix (covariance matrix) (step S213).
[0327] Then, the azimuth detecting unit 57 performs an eigenvalue
decomposition process to calculate eigenvalues .lamda..sub.1,
.lamda..sub.2, .lamda..sub.3, . . . and eigenvectors e.sub.1,
e.sub.2, e.sub.3, . . . (step S214).
[0328] The azimuth detecting unit 57 estimates the order (step
S215).
[0329] In the MUSIC spectrum calculating process, the azimuth
detecting unit 57 first creates a steering vector a2(n2, .theta.2)
of a virtual array (step S216). The steering vector a2(n2,
.theta.2) is expressed in the same way as in Equation (4). In this
example, the searching incident angle .theta.2 is in the range of
-40 to +40 deg.
[0330] Subsequently, in the MUSIC spectrum calculating process, the
azimuth detecting unit 57 calculates a MUSIC spectrum (step
S217).
[0331] The azimuth detecting unit 57 detects the number of targets
at distant positions (at a small angle) and the angles (step
S218).
Conclusion of Third Embodiment
[0332] Although it has been stated in the third embodiment that the
FMCW system is exemplified as the radar system, the invention is
not limited to the radar system and the constitution according to
the third embodiment may be applied to another radar system.
[0333] Although it has been stated in the third embodiment that the
MUSIC method is exemplified as the high-resolution algorithm, the
constitution according to the third embodiment may be applied to
other techniques such as a linear prediction method or a beam
forming method. For example, it is possible to calculate an azimuth
angle (angle) using virtual array data and virtual array steering
vectors.
[0334] As described above, the multibeam radar apparatus 102
according to the third embodiment includes Apparatus Constitution 6
to Apparatus Constitution 8 described below.
[0335] As Apparatus Constitution 6, the multibeam radar apparatus
102 according to the third embodiment controls the transmission and
reception of the beam elements 2-1 to 2-5, combines arbitrary beam
elements out of the beam elements 2-1 to 2-5, and creates a
plurality of virtual array data Y1(n1) and Y2(n2), when creating
the virtual array data.
[0336] As Apparatus Constitution 7, the multibeam radar apparatus
102 according to the third embodiment creates steering vectors
a1(n1, .theta.1) and a2(n2, 82) corresponding to a plurality of
virtual array data Y1(n1) and Y2(n2) created through the
arrangement of beam elements under the control of transmission and
reception in Apparatus Constitution 6, as for the virtual array
steering vectors.
[0337] As Apparatus Constitution 8, the multibeam radar apparatus
102 according to the third embodiment uses a high-resolution
algorithm, such as the MUSIC method or the linear prediction
method, or the direction estimating process such as the beam
forming process by the use of the virtual array data Y1(n1) and
Y2(n2) and the virtual array steering vectors a1(n1, .theta.1) and
a2(n2, .theta.2) acquired through the use of Apparatus Constitution
6 to Apparatus Constitution 7.
[0338] Since the multibeam radar apparatus 102 according to the
third embodiment includes Apparatus Constitution 6 to Apparatus
Constitution 8, a plurality of virtual array data Y1(n1) and Y2(n2)
with various FOVs can be created by a single radar apparatus and it
can thus be applied to the detection of a target for different
purposes such as a small angle and a large angle. For example, a
small angle is set so as not to detect unnecessary reflecting
objects in an extra range when detecting a target at a distant
position, and a large angle is set so as to detect more targets
within the sample measurement point when detecting a target at a
near position (in the vicinity). That is, it is possible to enable
the detection control at a small angle and a large angle, thereby
achieving the simplicity of an apparatus and the superiority in
cost.
[0339] In the multibeam radar apparatus 102 according to the third
embodiment, since the resolution in the high-resolution process
using the plurality of virtual array data Y1(n1) and Y2(n2) can be
set to arbitrary value, it is possible to set an appropriate
resolution suitable for the small-angle/large-angle detection.
[0340] Accordingly, in the multibeam radar apparatus 102 according
to the third embodiment, since the high separation capability, the
high resolution capability, and the FOV changing function can be
added to the multibeam system with a high gain and a high
efficiency, it is possible to better detect an object with a small
RCS such as a walker or a bicycle nearby (in the vicinity) and a
motorcycle at a distance, for example, in application to on-board
radar.
[0341] In the multibeam radar apparatus 102 according to the third
embodiment, since it is possible to perform the azimuth detection
processes with various types (for example, two types) of FOVs by
the use of a signal apparatus, the processing result can be sent to
a vehicle control unit, for example, depending on the application.
For example, when an application of fixing a distant target and a
near target by switching between the distant detection and the near
detection within a control period of 100 ms and controlling both
the distant detection and the near detection is used; the azimuth
estimating processes at both a small angle and a large angle can be
performed in a period of 100 ms.
[0342] In this manner, in the multibeam radar apparatus 102
according to the third embodiment, it is possible to activate the
merits of the multibeam system (the multibeam formation with a high
gain and a high efficiency), to markedly improve the resolution of
multiple targets and the angle measurement accuracy at the same
measurement point, and to perform a plurality of detection
functions with various FOVs through the use of a single radar
apparatus.
[0343] Although it has been stated in the third embodiment that all
the virtual array elements are included within the lens aperture
length (the same aperture length as the dielectric lens 1) of the
virtual dielectric lens equivalent to the dielectric lens 1, the
length (distance between both ends) of all the virtual array
elements when they are linearly arranged may be equal to or
substantially equal to the lens aperture length.
[0344] On the contrary, a constitution in which a plurality of
virtual array elements (for example, one or more elements at both
ends) are disposed out of the lens aperture length, that is, a
constitution in which all the virtual array elements are not
included within the lens aperture length, may be employed. This
constitution may be used.
[0345] Although it has been stated in the third embodiment that the
dielectric lens 1 is used, various other lenses may be used instead
of the dielectric lens 1.
[0346] Although it has been stated in the third embodiment that the
lens (the dielectric lens 1) is provided, a constitution using no
lens may be used. In this case, the multibeam transmission and
reception is performed through the use of the plurality of beam
elements 2-1 to 2-M (M=5 in the third embodiment) without using the
lens.
[0347] Regarding the number M of beam elements 2-1 to 2-M
constituting an antenna for transmission and reception, when
multiple targets are detected, it is possible to detect the targets
corresponding to only the number (M-1) smaller by 1 than the number
of beam, elements 2-1 to 2-M.
[0348] Although it has been stated in the third embodiment that the
invention is applied to the five beam elements, the FOV (Field of
View) changing type, the beam width, the total number of beam
elements, the number of beam elements to be selected, selection of
the beam element on which the SW is povided to enable switching
between the ON and OFF states, and the like may be arbitrarily
determined depending on the application or specification of a
radar. Particularly, in the multibeam system using a lens antenna,
they can be flexibly set depending on the shape of the lens and the
positions of the primary feeds (beam elements), which is desirable
for combination.
[0349] For example, although it has been stated in the third
embodiment that the SW is provided to the beam elements from the
outermost beam element to the central beam element out of the
plurality of beam elements 2-1 to 2-M and the SW is not provided to
only the central beam element or the central beam element and the
beam elements close to the central beam element, a constitution in
which the SW may be provided to all the beam elements 2-1 to 2-M
may be used.
Fourth Embodiment
<Constitution Using Unitary Transformation>
[0350] In a fourth embodiment of the invention, the constitutions
and operations different from those of the third embodiment will be
described in detail.
[0351] Specifically, the fourth embodiment is different from the
third embodiment, in that the MUSIC method of applying a unitary
transformation to virtual array data Y1(n1) and Y2(n2), and to
virtual array steering vectors a1(n1, .theta.1) and a2(n2,
.theta.2).
[0352] Here, the constitution using the unitary transformation in
the fourth embodiment is the same as described in the second
embodiment.
[0353] The multibeam radar apparatus 102 according to the fourth
embodiment has the constitutions and operations similar to those
described with reference to FIGS. 12 and 13 in the second
embodiment.
Conclusion of Fourth Embodiment
[0354] As described above, the multibeam radar apparatus 102
according to the fourth embodiment includes Apparatus Constitution
9 described below.
[0355] As Apparatus Constitution 9, the multibeam radar apparatus
102 according to the fourth embodiment first applied the unitary
transformation to the correlation matrices and to the virtual array
steering vectors a1(n1, .theta.1) and a2(n2, .theta.2) based on the
virtual array data Y1(n1) and Y2(n2) using the conjugate
centrosymmetry of the virtual array and then perform the direction
estimation, when performing the direction estimation using the
MUSIC method as the high-resolution algorithm through the use of
Apparatus Constitution 6 to Apparatus Constitution 8.
[0356] Since the multibeam radar apparatus 102 according to the
fourth embodiment includes Apparatus Constitution 9 and thus can
perform the eigenvalue decomposing process on the real correlation
matrix, it is possible to reduce the computational load, to achieve
the advantage of reducing the computational load due to the
plurality of virtual array data Y1(n1) and Y2(n2) and the virtual
array steering vector a1(n1, .theta.1) and a2(n2, .theta.2), and to
reduce the apparatus cost.
[Description of Related Art]
[0357] The related art of the invention will be described
below.
[0358] For reference, the details of the related art is based on
the contents of "DOA Estimation with Super Resolution Capabilities
using Multi-beam Antenna of Dielectric Lens", Ide, Kuwabara
(Engineering Department of Shizuoka University), Kamo, and Kanemoto
(Honda Elesys Co., Ltd.), General Conference of Institute of
Electronics, Information and Communication Engineers, Fundamental
and Boundary Lecture Essays, pp. 261.
[0359] This related art may be used in the invention or may not be
used if not necessary.
[0360] Title: DOA Estimation with super resolution capabilities
using a multi-beam antenna of the dielectric lens
1. Introduction
[0361] The arrival direction estimation of an element space is
difficult to use under environments of a low gain of an antenna
element and a low SNR. The use of a beam space can be considered as
a solution thereto. The inventors applied the beam space to the
pre-process of removing unnecessary waves already [1]. The DOA
estimation with super resolution capabilities using a multibeam
dielectric lens antenna [2] will be reviewed.
2. Operational Principle
[0362] The operational principle is shown in FIG. 18. Horizontal
multibeams are generated by the dielectric lens. The aperture
distribution of the lens surface and the primary feed pattern have
the Fourier transformation relationship and the steering vector of
a virtual array antenna in the aperture distribution is created
from this relationship. The signal received through the primary
feed array is transformed to the output of the virtual array
antenna through the Fourier transformation. The covariance matrix
of the output of the virtual array antenna is estimated and the
arrival direction is estimated using the MUSIC method.
3. Simulation
[0363] A dielectric lens antenna generating horizontal multibeam
patterns of -30.degree., -15.degree., 0.degree., 15.degree., and
30.degree. was designed based on Document [1].
[0364] The primary feeds were approximated to a cos.sup.n .theta.
pattern (E face n=2, H face n=3) and the beam width was designed in
E face 6.degree. and H face 20.degree.. The resultant directivity,
the lens shape, and the focal position are shown in FIGS. 19 and
20. The number of elements of the virtual array antenna was set to
9 and two signals not correlated with each other were incident
thereon.
[0365] The minimum angular separation of the two signals was
estimated using the number of snapshots and the SNR as parameters.
The minimum angular separation when the number of snapshots was
fixed to 100 and the DUR (Desire and Undesire Ratio) of the
arriving signals was changed was estimated. The results are shown
in FIGS. 21 and 22. Examples of the MUSIC spectrum are shown in
FIGS. 23 and 24.
4. Conclusion
[0366] The super resolution capability in the arrival direction
estimation using the multibeam dielectric lens antenna and the
MUSIC method was checked through the use of a computer
simulation.
REFERENCES
[0367] [1] Japanese Patent No. 4098311 and Japanese Patent No.
4098318 [0368] [2] IEEE Trans. AP Vol. 57, No. 1, pp. 57-63,
2009
Explanation of FIGS. 18 to 24
[0369] FIG. 18 is a diagram illustrating the principle of the
arrival direction estimation with a super resolution using a
multibeam dielectric lens antenna.
[0370] Five beam elements 3001-1 to 3001-5 and five beams 3002-1 to
3002-5 are shown. As the result of the Fourier transformation 3003
thereof, a virtual dielectric lens 3004 and nine virtual array
elements 3005-1 to 3005-9 are shown.
[0371] FIG. 19 is a diagram illustrating horizontal beam
patterns.
[0372] In the graph, the horizontal axis represents the angle [deg]
and the vertical axis represents the gain [dB].
[0373] Five beam patterns 3011 to 3015 are shown.
[0374] FIG. 20 is a diagram illustrating the profile of a lens.
[0375] The profile of a lens 3021 is shown. Specifically,
x[.lamda.], y[.lamda.], and z[.lamda.] are shown.
[0376] FIG. 21 is a diagram illustrating the relationship of the
SNR, the number of snapshots, and the resolution.
[0377] The horizontal axis represents the SNR [dB] and the vertical
axis represents the resolution [degree].
[0378] FIG. 22 showing examples where the number of snapshots is
100, 10, and 2 is a diagram of a graph illustrating the
relationship of the SNR, the DUR, and the resolution.
[0379] In the graph, the horizontal axis represents the SNR [dB]
and the vertical axis represents the resolution [degree].
[0380] A graph line 3031 corresponding to the DUR of 3 dB, a graph
line 3032 corresponding to the DUR of 6 dB, and a graph line 3033
corresponding to the DUR of 10 dB are shown.
[0381] FIG. 23 is a diagram illustrating an example of the MUSIC
spectrum.
[0382] In this example, the angular separation is 2.degree.. In
addition, SNR=40 dB, number of snapshots=100, and DUR=0 dB are
set.
[0383] In the graph, the horizontal axis represents the angle [deg]
and the vertical axis represents the gain [dB].
[0384] A music spectrum 3041 is shown.
[0385] FIG. 24 is a diagram illustrating an example of the MUSIC
spectrum.
[0386] In this example, the angular separation is 4.degree.. In
addition, SNR=40 dB, number of snapshots=100, and DUR=0 dB are
set.
[0387] In the graph, the horizontal axis represents the angle [deg]
and the vertical axis represents the gain [dB].
[0388] A music spectrum 3051 is shown.
CONCLUSION OF EMBODIMENTS
[0389] It has been stated in the above-mentioned embodiments that
the multibeam radar apparatus 101 shown in FIG. 1 or the multibeam
radar apparatus 102 shown in FIG. 14 is provided as an on-board
radar apparatus to a vehicle or the like, the multibeam radar
apparatus may be provided to any other moving object.
[0390] Programs for realizing the functions of the control unit 11
or the signal processing unit 8 shown in FIG. 1 and the functions
of the control unit 33 or the signal processing unit 8 shown in
FIG. 14 may be recorded on a computer-readable recording medium and
the programs recorded on the recording medium may be read and
executed by a computer system to perform the processes. The
"computer system" includes an OS (Operating System) and hardware
such as peripherals. The "computer system" also includes a WWW
system having a homepage provision environment (or display
environment). The "computer-readable recording medium" includes a
portable medium such as a flexible disc, a magneto-optical disc, a
ROM, or a CD-ROM or a storage device such as a hard disk built in
the computer system. The "computer-readable recording medium" also
includes a device storing a program for a predetermined time, like
an internal volatile memory (RAM (Random Access Memory)) of a
computer system serving as a server or a client when the programs
are transmitted through a network such as the Internet or a
communication line such as a telephone line.
[0391] The programs may be transmitted from a computer system
having the programs stored in a storage device thereof or the like
to another computer system through a transmission medium or by
carrier waves in the transmission medium. The "transmission medium"
which transmits a program means a medium having a function of
transmitting information and examples thereof include a network
(communication network) such as the Internet and a communication
link (communication line) such as a telephone line. The program may
realize some of the above-described functions. The program may
realize the above-described functions in combination with a program
already recorded in a computer system, that is, the program may be
a differential file (differential program).
[0392] While the embodiments of the invention have been described
with reference the accompanying drawings, the specific
constitutions are not limited to the embodiments, and may include
other designs which do not depart from the concept of the
invention.
* * * * *