Patent Description:
When a target to be observed is a distant target that can be regarded as a point wave source, a reflected wave from the target does not have an angle width. In contrast, when the target to be observed is an adjacent target that cannot be regarded as the point wave source, the reflected wave from the target has the angle width.

When an angle measurement device that measures an angle of the adjacent target does not measure the angle of the target using the angle width of the reflected wave from the target, accuracy of measuring the angle of the target is deteriorated.

Non-Patent Literature <NUM> discloses an angle width estimating technology of estimating an angle width of a reflected wave from an adjacent target.

In the angle width estimating technology, a computer estimates the angle width of the reflected wave by executing the Capon method. The Capon method is a method of estimating the angle width that can be executed when a plurality of reception array signals at different sampling times is acquired by an array antenna.

<NPL>, discloses angular spread estimation using CAPON and MUSIC algorithms.

<NPL>, discloses angular spread estimation using a null in the direction of an access terminal.

<NPL>, XP011385922, discloses a method of direction estimation by rotating a notch in an antenna pattern.

<NPL>, discloses a directionally constrained minimization of power.

In the angle width estimating technology disclosed in Non-Patent Literature <NUM>, the computer cannot execute the Capon method unless a plurality of reception array signals is acquired. For this reason, there is a problem that the computer cannot estimate the angle width of the reflected wave unless a plurality of reception array signals is acquired.

The present disclosure has been achieved to solve the above-described problem, and an object thereof is to acquire an angle width estimation device and an angle width estimation method capable of estimating an angle width of a reflected wave from a target from one reception array signal.

According to the present disclosure, an angle width of a reflected wave from a target can be estimated from one reception array signal.

A mode for carrying out the present disclosure is hereinafter described with reference to the attached drawings in order to describe the present disclosure in further detail.

<FIG> is a configuration diagram illustrating a target angle measurement device including an angle width estimation device <NUM> according to a first embodiment.

<FIG> is a hardware configuration diagram illustrating hardware of a digital signal processing unit in the target angle measurement device illustrated in <FIG>.

The target angle measurement device illustrated in <FIG> is provided with a reflected wave receiving unit <NUM>, the angle width estimation device <NUM>, and a target angle measuring unit <NUM>.

The reflected wave receiving unit <NUM> is provided with reception antenna elements <NUM>-<NUM> to <NUM>-M and analog-to-digital converters (hereinafter referred to as "A/D converters") <NUM>-<NUM> to <NUM>-M. M is an integer equal to or larger than two.

The reflected wave receiving unit <NUM> receives a reflected wave from a target to be observed, and outputs a reception array signal rARE of the reflected wave to the angle width estimation device <NUM>. The reception array signal rARE of the reflected wave is a signal including a plurality of reception signals r<NUM> to rM output from the reception antenna elements <NUM>-<NUM> to <NUM>-M, respectively.

The target angle measurement device illustrated in <FIG> is not provided with a radio wave transmitting unit that emits a radio wave toward the target to be observed. Therefore, in the target angle measurement device illustrated in <FIG>, it is supposed that an external radio wave transmitting unit not illustrated emits the radio wave toward the target to be observed. However, this is merely an example, and the target angle measurement device illustrated in <FIG> may be provided with the radio wave transmitting unit.

The reception antenna elements <NUM>-<NUM> to <NUM>-M form a reception array antenna.

The reception antenna element <NUM>-m (m = <NUM>,. , M) receives the reflected wave from the target to be observed, and outputs the reception signal rm included in the reception array signal rARE of the reflected wave to the A/D converter <NUM>-m.

The A/D converter <NUM>-m converts the reception signal rm output from the reception antenna element <NUM>-m from an analog signal to a digital signal.

The A/D converter <NUM>-m outputs the digital signal to the angle width estimation device <NUM>, as the reception signal included in the reception array signal rARE.

In the target angle measurement device illustrated in <FIG>, a receiver that detects the reception signal rm output from the reception antenna element <NUM>-m is not illustrated. For example, a receiver may be mounted between the reception antenna element <NUM>-m and the A/D converter <NUM>-m, or the receiver may be included in the A/D converter <NUM>-m.

In the target angle measurement device illustrated in <FIG>, the reflected wave receiving unit <NUM> is provided with the reception array antenna including the reception antenna elements <NUM>-<NUM> to <NUM>-M. However, this is merely an example, and the reflected wave receiving unit <NUM> may be provided with an array microphone including a plurality of microphones or an array sensor including a plurality of radio wave sensors, in place of the reception array antenna. When the reflected wave receiving unit <NUM> is provided with the array microphone, the reflected wave is a sound wave. When the reflected wave receiving unit <NUM> is provided with the array sensor, the reflected wave is a radio wave.

The angle width estimation device <NUM> is provided with a beam forming unit <NUM> and an angle width estimating unit <NUM>.

The angle width estimation device <NUM> estimates an angle width of the reflected wave, by performing signal processing on the reception array signal rARE output from the reflected wave receiving unit <NUM>.

The beam forming unit <NUM> is provided with coherent integrating units <NUM>-<NUM> to <NUM>-M, pulse compressing units <NUM>-<NUM> to <NUM>-M, and a digital beam forming (DBF) unit <NUM>.

The beam forming unit <NUM> acquires one reception array signal rARE output from the reflected wave receiving unit <NUM>, and forms, from the one reception array signal rARE, a plurality of null beams having nulls in an arrival direction of the reflected wave, and having null widths which are widths of the nulls and different from each other.

In the target angle measurement device illustrated in <FIG>, for example, since a schematic position of the target to be observed is detected in advance, the beam forming unit <NUM> can form the null beam in the arrival direction of the reflected wave.

The coherent integrating unit <NUM>-m (m = <NUM>,. , M) is implemented by, for example, a coherent integrating circuit <NUM> illustrated in <FIG>.

The coherent integrating unit <NUM>-m performs coherent integration on the digital signal output from the A/D converter <NUM>-m, by performing, for example, fast Fourier transform (FFT) in a time direction, and outputs the signal after the coherent integration to the pulse compressing unit <NUM>-m.

The pulse compressing unit <NUM>-m (m = <NUM>,. , M) is implemented by, for example, a pulse compressing circuit <NUM> illustrated in <FIG>.

The pulse compressing unit <NUM>-m performs pulse compression on the signal after the coherent integration output from the coherent integrating unit <NUM>-m, and outputs the signal after the pulse compression to the DBF unit <NUM>.

The DBF unit <NUM> is implemented by a DBF circuit <NUM> illustrated in <FIG>, for example.

The DBF unit <NUM> is provided with a table 8a.

The table 8a stores a plurality of weights regarding the null beam formed by the DBF unit <NUM>. Because of the different weights, one or more of a beam forming direction, a null forming direction, and the null width of the null beam changes. Each weight includes M weight elements.

The DBF unit <NUM> acquires M signals after the pulse compression from the pulse compressing units <NUM>-<NUM> to <NUM>-M.

The DBF unit <NUM> forms the null beam having the null in the arrival direction of the reflected wave, by performing digital beam forming on the M signals after the pulse compression output from the pulse compressing units <NUM>-<NUM> to <NUM>-M.

After forming the null beams, when the DBF unit <NUM> acquires a null beam forming command from the angle width estimating unit <NUM>, the DBF unit <NUM> performs the digital beam forming on the M signals after the pulse compression, thereby forming the null beam having the null with the null width wider than that of the null of the previously formed null beam.

That is, when acquiring the M signals after the pulse compression from the pulse compressing units <NUM>-<NUM> to <NUM>-M, the DBF unit <NUM> acquires one weight from the table 8a.

The DBF unit <NUM> multiplies the signals after the pulse compression by the respective weight elements included in the acquired weight, and calculates the sum of a plurality of signals after the weight element multiplication, thereby forming the null beam having the null in the arrival direction of the reflected wave. The DBF unit <NUM> outputs the null beam to the angle width estimating unit <NUM>.

After forming the null beam, when the DBF unit <NUM> acquires the null beam forming command from the angle width estimating unit <NUM>, the DBF unit <NUM> acquires one weight different from the already acquired weight from the table 8a.

The DBF unit <NUM> multiplies the signals after the pulse compression by the respective weight elements included in the acquired weight, and calculates the sum of a plurality of signals after the weight element multiplication, thereby forming the null beam having the null with the null width wider than that of the null of the previously formed null beam. The DBF unit <NUM> outputs the null beam to the angle width estimating unit <NUM>.

In the target angle measurement device illustrated in <FIG>, the beam forming unit <NUM> is provided with the pulse compressing units <NUM>-<NUM> to <NUM>-M. However, the beam forming unit <NUM> is not required to be provided with the pulse compressing units <NUM>-<NUM> to <NUM>-M.

The angle width estimating unit <NUM> is implemented by an angle width estimating circuit <NUM> illustrated in <FIG>, for example.

The angle width estimating unit <NUM> compares powers of the plurality of null beams formed by the beam forming unit <NUM> with each other, and estimates the null width indicating the angle width of the reflected wave on the basis of a comparison result of the powers.

That is, when acquiring one null beam from the DBF unit <NUM>, the angle width estimating unit <NUM> repeatedly outputs the null beam forming command to the DBF unit <NUM>, thereby acquiring a plurality of null beams from the DBF unit <NUM>.

The angle width estimating unit <NUM> monitors a change in power of the null beam output from the DBF unit <NUM>, and searches for, as the null width indicating the angle width, the null width of the null beam when the power stops decreasing from a state in which the power decreases.

The angle width estimating unit <NUM> outputs the angle width indicated by the estimated null width to the target angle measuring unit <NUM>.

The target angle measuring unit <NUM> is implemented by a target angle measuring circuit <NUM> illustrated in <FIG>, for example.

The target angle measuring unit <NUM> measures an angle of the target using the angle width output from the angle width estimating unit <NUM>.

In <FIG>, it is supposed that each of the coherent integrating units <NUM>-<NUM> to <NUM>-M, the pulse compressing units <NUM>-<NUM> to <NUM>-M, the DBF unit <NUM>, and the angle width estimating unit <NUM>, which are components of the angle width estimation device <NUM>, is implemented by dedicated hardware as illustrated in <FIG>. That is, it is supposed that the angle width estimation device <NUM> is implemented by the coherent integrating circuit <NUM>, the pulse compressing circuit <NUM>, the DBF circuit <NUM>, and the angle width estimating circuit <NUM>.

Each of the coherent integrating circuit <NUM>, the pulse compressing circuit <NUM>, the DBF circuit <NUM>, and the angle width estimating circuit <NUM> corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel-programmed processor, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof.

The components of the angle width estimation device <NUM> are not limited to those implemented by the dedicated hardware, and the angle width estimation device <NUM> may also be implemented by software, firmware, or a combination of the software and firmware.

The software or firmware is stored, as a program, in a memory of a computer. The computer is intended to mean hardware that executes the program, and corresponds to, for example, a central processing unit (CPU), a central processing device, a processing device, an arithmetic device, a microprocessor, a microcomputer, a processor, or a digital signal processor (DSP).

<FIG> is a hardware configuration diagram of the computer when the angle width estimation device <NUM> is implemented by the software, firmware or the like.

When the angle width estimation device <NUM> is implemented by the software, firmware or the like, a program for causing the computer to execute each processing procedure in the coherent integrating units <NUM>-<NUM> to <NUM>-M, the pulse compressing units <NUM>-<NUM> to <NUM>-M, the DBF unit <NUM>, and the angle width estimating unit <NUM> is stored in a memory <NUM>. Then, a processor <NUM> of the computer executes the program stored in the memory <NUM>.

<FIG> illustrates an example in which each of the components of the angle width estimation device <NUM> is implemented by the dedicated hardware, and <FIG> illustrates an example in which the angle width estimation device <NUM> is implemented by the software, firmware or the like. However, these are merely examples, and some components in the angle width estimation device <NUM> may be implemented by the dedicated hardware, and the remaining components may be implemented by the software, firmware or the like.

Next, an operation of the target angle measurement device illustrated in <FIG> is described.

The reception antenna element <NUM>-m (m = <NUM>,. , M) receives the reflected wave from the target to be observed, and outputs the reception signal rm of the reflected wave to the A/D converter <NUM>-m.

When receiving the reception signal rm from the reception antenna element <NUM>-m, the A/D converter <NUM>-m converts the reception signal rm from the analog signal to the digital signal and outputs the digital signal to the angle width estimation device <NUM>.

The angle width estimation device <NUM> estimates the angle width of the reflected wave by performing signal processing on the digital signal output from the A/D converter <NUM>-m.

Hereinafter, the signal processing by the angle width estimation device <NUM> is specifically described.

<FIG> is a flowchart illustrating an angle width estimation method being the processing procedure of the angle width estimation device <NUM> according to the first embodiment.

When only one reflected wave having no angle width is incident on the reception antenna element <NUM>-m (m = <NUM>,. , M), a reception array signal rARE(t) at time t in the reception array antenna with the number of channels M is expressed by the following Expression (<NUM>).

In Expression (<NUM>), a(θ,ϕ) represents a steering vector when an elevation angle is θ and an azimuth angle is ϕ. Herein, s(t) represents a signal complex amplitude at time t, and n(t) represents a thermal noise vector at time t.

When each of the elevation angle θ and the azimuth angle ϕ is expressed by a coordinate system illustrated in <FIG>, the steering vector a(θ,ϕ) is expressed by the following Expression (<NUM>).

<FIG> is an explanatory diagram illustrating each of the elevation angle θ and the azimuth angle ϕ in the steering vector a(θ,ϕ).

In the coordinate system illustrated in <FIG>, the elevation angle θ is an angle formed by the steering vector a(θ,ϕ) with respect to an x-y plane, and when the steering vector a(θ,ϕ) is a direction parallel to the x-y plane, θ = <NUM> [deg. ] is satisfied.

The azimuth angle ϕ is an angle formed by the steering vector a(θ,ϕ) with respect to a direction parallel to a y-axis on the x-y plane, and when the steering vector a(θ,ϕ) is in the direction parallel to the y-axis, ϕ = <NUM> [deg. ] is satisfied. <MAT> <MAT> <MAT>.

In Expressions (<NUM>) to (<NUM>), λ represents a wavelength, R represents an element coordinate matrix in the reception antenna elements <NUM>-<NUM> to <NUM>-M, xm represents an x coordinate of a position at which an m-th reception antenna element <NUM>-m is installed, and ym represents a y coordinate of the position at which the m-th reception antenna element <NUM>-m is installed. L(θ,ϕ) represents a line-of-sight direction vector when the elevation angle is θ and the azimuth angle is ϕ.

Hereinafter, for the sake of simplicity, it is described using a steering vector a(u,v) in which u = cosθsinϕ and v = sinθ.

A weight w for forming the null beam having the null with respect to u,v is acquired by the following Expression (<NUM>) on the basis of a directionally constrained minimization of power (DCMP) method when beam forming directions ud and vd are determined.

In Expression (<NUM>), α represents any normalization coefficient, and Rxx-<NUM> represents an inverse matrix of a correlation matrix Rxx of the reflected wave having the angle width.

Hereinafter, directions in which the null is formed are expressed as uc and vc.

The null width of the null beam in which the null forming directions are uc and vc is defined by the correlation matrix Rxx of the reflected wave having the angle width.

<FIG> is an explanatory diagram illustrating the null width in the beam forming direction ud in the null beam.

In the example in <FIG>, the beam forming direction ud in a u-axis direction coincides with the null forming direction uc in the u-axis direction. Around the null forming direction uc, the width in the u-axis direction of the null beam in which a gain of the null beam is equal to or smaller than a threshold Th coincides with the null width in the u-axis direction of the null beam. As the threshold Th, for example, a gain lower, by a signal to noise ratio (SNR), than a gain Gr of the beam having no null in the beam forming direction ud is used, as expressed by the following Expression (<NUM>). The SNR is calculated from receiver noise power and reception signal power in the receiver included in the reflected wave receiving unit <NUM>.

The null width in a v-axis direction in the null beam is handled similarly to the null width in the u-axis direction in the null beam.

That is, the beam forming direction vd in the v-axis direction coincides with the null forming direction vc in the v-axis direction. Around the null forming direction vc, the width in the v-axis direction of the null beam in which a gain of the null beam is equal to or smaller than a threshold Th coincides with the null width in the v-axis direction of the null beam.

<FIG> is an explanatory diagram illustrating a relationship between the null width of the null beam and the target.

<FIG> illustrates an example in which the null widths in the u-axis direction and the v-axis direction of the null beam are wider than the widths in the u-axis direction and the v-axis direction of the target, so that the gains in the null forming directions uc and vc of the null beam are equal to or smaller than the threshold Th.

The correlation matrix Rxx of the reflected wave having the angle width is expressed by the following Expression (<NUM>).

In Expression (<NUM>), Pd represents power of the reflected wave received by the reception antenna element <NUM>-m. Herein, Δumax represents a constant indicating a maximum angle of the null beam in the u-axis direction, and Δumin represents a constant indicating a minimum angle of the null beam in the u-axis direction. Furthermore, Δvmax represents a constant indicating a maximum angle of the null beam in the v-axis direction, and Δvmin represents a constant indicating a minimum angle of the null beam in the v-axis direction.

Herein, ρ(u,v) represents a spatial distribution of desired wave power, β represents pseudo noise, and I represents a unit matrix.

By substituting the inverse matrix of the correlation matrix Rxx expressed by Expression (<NUM>) into Expression (<NUM>), a weight w(θBeam,ϕBeam,θNULL,ϕNULL) capable of forming the null beam having the null in the null forming directions uc and vc can be calculated. Herein, θBeam represents a center direction of the beam forming direction ud, and ϕBeam represents a center direction of the beam forming direction vd. Furthermore, θNULL represents the null forming direction uc, and ϕNULL represents the null forming direction vc.

The null width can be changed by changing each value of Δumax, Δumin, Δvmax, and Δvmin.

Hereinafter, it is supposed that the null is formed in an angular range of uc ± Δu/<NUM>, and the null is formed in an angular range of vc ± Δv/<NUM>, where Δu = Δumax - Δumin, and Δv = Δvmax - Δvmin.

When receiving the digital signal from the A/D converter <NUM>-m, the coherent integrating unit <NUM>-m (m = <NUM>,. , M) performs coherent integration on the digital signal by performing, for example, FFT on the digital signal in the time direction (step ST1 in <FIG>).

The coherent integrating unit <NUM>-m outputs the signal after the coherent integration to the pulse compressing unit <NUM>-m.

When receiving the signal after the coherent integration from the coherent integrating unit <NUM>-m, the pulse compressing unit <NUM>-m performs pulse compression on the signal after the coherent integration in order to suppress an unnecessary wave received by the reception antenna element <NUM>-m (step ST2 in <FIG>).

The pulse compressing unit <NUM>-m outputs a signal rAPC,m(t) after the pulse compression to the DBF unit <NUM>.

The table 8a of the DBF unit <NUM> stores the weight w(θBeam,ϕBeam,θNULL,ϕNULL) calculated by substituting the inverse matrix of the correlation matrix Rxx in Expression (<NUM>) into Expression (<NUM>).

That is, the table 8a stores a plurality of weights w(θBeam,ϕBeam,θNULL,ϕNULL) in which at least one of the null width uc ± Δu/<NUM> in the u-axis direction and the null width vc ± Δv/<NUM> in the v-axis direction is different for each of the null forming directions uc and vc.

Each of the DBF unit <NUM> and the angle width estimating unit <NUM> repeatedly performs the following processing a plurality of times. The following processing can be repeated a plurality of times as long as one reception array signal rARE(t) is acquired.

Here, for convenience of description, an example of changing the null width uc ± Δu/<NUM> in the u-axis direction is described supposing that the null width vc ± Δv/<NUM> in the v-axis direction is constant. It is supposed that the null width in the v-axis direction is sufficiently wider than the width in the v-axis direction of the target. Further, it is supposed that the null forming directions uc and vc are constant.

The DBF unit <NUM> acquires a weight w<NUM>(θBeam,ϕBeam,θNULL,ϕNULL) for forming the null with the null width of <NUM> in the u-axis direction or the null with a narrow null width in the u-axis direction from the table 8a. The null with the narrow null width is the null with the null width close to <NUM>.

The DBF unit <NUM> multiplies the signal rAPC,m(t) after the pulse compression output from the pulse compressing unit <NUM>-m, by a weight element w<NUM>,m corresponding to the m-th pulse compressing unit <NUM>-m out of M weight elements w<NUM>,<NUM> to w<NUM>,M included in the weight w<NUM>(θBeam,ϕBeam,θNULL,ϕNULL).

The DBF unit <NUM> forms a null beam BNULL,<NUM> by calculating the sum ΣrAPC,m(t) × w<NUM>,m of the M multiplication results (step ST3 in <FIG>).

The DBF unit <NUM> outputs the null beam BNULL,<NUM> to the angle width estimating unit <NUM>.

When acquiring the null beam BNULL,<NUM> from the DBF unit <NUM>, the angle width estimating unit <NUM> calculates power P<NUM>(θBeam,ϕBeam,θNULL,ϕNULL) of the null beam BNULL,<NUM>, as expressed by the following Expression (<NUM>) (step ST4 in <FIG>).

The angle width estimating unit <NUM> stores the power P<NUM>(θBeam,ϕBeam,θNULL,ϕNULL) of the null beam BNULL,<NUM> in an internal memory.

When acquiring the null beam forming command from the angle width estimating unit <NUM>, the DBF unit <NUM> acquires a weight wj(θBeam,ϕBeam,θNULL,ϕNULL) for forming the null with a wider null width in the u-axis direction than that in (j-<NUM>)-th processing from the table 8a.

The DBF unit <NUM> multiplies the signal rAPC,m(t) after the pulse compression output from the pulse compressing unit <NUM>-m, by a weight element wj,m corresponding to the m-th pulse compressing unit <NUM>-m out of the M weight elements wj,<NUM> to wj,M included in the weight wj(θBeam,ϕBeam,θNULL,ϕNULL).

The DBF unit <NUM> forms a null beam BNULL,j by calculating the sum ΣrAPC,m(t) × wj,m of M multiplication results (step ST3 in <FIG>).

The DBF unit <NUM> outputs the null beam BNULL,j to the angle width estimating unit <NUM>.

When acquiring the null beam BNULL,j from the DBF unit <NUM>, the angle width estimating unit <NUM> calculates power Pj(θBeam,ϕBeam,θNULL,ϕNULL) of the null beam BNULL,j, as expressed by the following Expression (<NUM>) (step ST4 in <FIG>).

The angle width estimating unit <NUM> stores the power Pj(θBeam,ϕBeam,θNULL,ϕNULL) of the null beam BNULL,j in the internal memory.

Each of the DBF unit <NUM> and the angle width estimating unit <NUM> repeatedly performs the j-th processing until the power Pj(θBeam,ϕBeam,θNULL,ϕNULL) of the null beam BNULL,j stops decreasing even when the null width in the u-axis direction is widened.

<FIG> is an explanatory diagram illustrating a relationship between the null width of the null beam and the power of the null beam.

As the null width is narrower, the radio waves reflected by the target increase, so that the power of the null beam increases. In contrast, when the null width becomes wider, the radio waves reflected by the target decrease, so that the power of the null beam decreases. Note that, for example, when the null width of the null beam is wider than the width of the target as illustrated in <FIG>, even when the null width becomes further wider, the radio wave reflected by the target does not change, so that the power of the null beam does not decrease. That is, the power of the null beam is not smaller than known receiver noise power.

In the example in <FIG>, the processing is performed four times, and the power Pj(θBeam,ϕBeam,θNULL,ϕNULL) stops decreasing in the third processing.

Therefore, in the example in <FIG>, the null width in the third processing indicates the angle width of the reflected wave.

The angle width estimating unit <NUM> compares J pieces of power P<NUM>(θBeam,ϕBeam,θNULL,ϕNULL) to PJ(θBeam,ϕBeam,θNULL,ϕNULL) stored in the internal memory with one another.

The angle width estimating unit <NUM> searches for a null width Be in the u-axis direction when the power Pj(θBeam,ϕBeam,θNULL,ϕNULL) stops decreasing from a state in which the power Pj(θBeam,ϕBeam,θNULL,ϕNULL) decreases, on the basis of a comparison result of the powers (step ST5 in <FIG>).

Heretofore, the DBF unit <NUM> changes the null width uc ± Δu/<NUM> in the u-axis direction supposing that the null width vc ± Δv/<NUM> in the v-axis direction is constant.

Next, the DBF unit <NUM> changes the null width vc ± Δv/<NUM> in the v-axis direction supposing that the null width uc ± Δu/<NUM> in the u-axis direction is constant. It is supposed that the null width in the u-axis direction is sufficiently wider than the width in the u-axis direction of the target. Further, it is supposed that the null forming directions uc and vc are constant.

Each of the DBF unit <NUM> and the angle width estimating unit <NUM> searches for a null width Bϕ in the v-axis direction by a method similar to that of the processing of searching for the null width Be in the u-axis direction while changing the null width vc ± Δv/<NUM> in the v-axis direction.

The angle width estimating unit <NUM> outputs, as an angle width Ae in the u-axis direction of the reflected wave, the searched null width Be in the u-axis direction to the target angle measuring unit <NUM>, and outputs, as an angle width Aϕ in the v-axis direction of the reflected wave, the searched null width Bϕ in the v-axis direction to the target angle measuring unit <NUM>.

The target angle measuring unit <NUM> measures the angle of the target using the angle widths Aθ and Aϕ output from the angle width estimating unit <NUM>.

The target angle measuring unit <NUM> outputs an angle measurement value of the target to an external display or the like.

Because angle measurement processing of the target by the target angle measuring unit <NUM> is a known technology, the detailed description thereof is omitted. Hereinafter, an example of the angle measurement processing of the target is briefly described.

The target angle measuring unit <NUM> acquires a weight wj(θBeam,ϕBeam,θNULL,ϕNULL) corresponding to both the angle width Aθ in the u-axis direction and the angle width Aϕ in the v-axis direction from the table 8a of the DBF unit <NUM>.

The target angle measuring unit <NUM> acquires θBeam which is a parameter of the acquired weight wj(θBeam,ϕBeam,θNULL,ϕNULL).

The target angle measuring unit <NUM> also acquires ϕBeam which is a parameter of the acquired weight wj(θBeam,ϕBeam,θNULL,ϕNULL).

In the center direction θBeam in the beam forming direction ud, the angle measurement value in the u-axis direction of the target is θBeam, and in the center direction ϕBeam in the beam forming direction vd, the angle measurement value in the v-axis direction of the target is ϕBeam.

However, since the reflected wave has the angle width Ae in the u-axis direction, the angle measurement value in the u-axis direction of the target is not θBeam except for the center direction θBeam in the beam forming direction ud. Therefore, the target angle measuring unit <NUM> provides a latitude in the angle measurement value in the u-axis direction of the target, depending on the angle width Ae in the u-axis direction of the reflected wave. That is, the target angle measuring unit <NUM> calculates θBeam ± Aθ/<NUM> as the angle measurement value in the u-axis direction of the target.

Since the reflected wave has the angle width Aϕ in the v-axis direction, the angle measurement value in the v-axis direction of the target is not ϕBeam except for the center direction ϕBeam in the beam forming direction va. Therefore, the target angle measuring unit <NUM> provides a latitude in the angle measurement value in the v-axis direction of the target, depending on the angle width Aϕ in the v-axis direction of the reflected wave. That is, the target angle measuring unit <NUM> calculates ϕBeam ± Aϕ/<NUM> as the angle measurement value in the v-axis direction of the target.

In the first embodiment described above, the angle width estimation device <NUM> is configured in such a way as to include: the beam forming unit <NUM> to acquire one reception array signal of the reflected wave from the target to be observed, and form, from the one reception array signal, a plurality of null beams having nulls in the arrival direction of the reflected wave, and having null widths which are widths of the nulls and different from each other; and the angle width estimating unit <NUM> to compare powers of the plurality of null beams formed by the beam forming unit <NUM> with each other, and estimate the null width indicating the angle width of the reflected wave on the basis of the comparison result of the powers. Therefore, the angle width estimation device <NUM> can estimate the angle width of the reflected wave from the target from the one reception array signal.

In the angle width estimation device <NUM> illustrated in <FIG>, the DBF unit <NUM> forms the null beam BNULL,j (j = <NUM>,. , J), using the weight wj(θBeam,ϕBeam,θNULL,ϕNULL) calculated by substituting the inverse matrix of the correlation matrix Rxx in Expression (<NUM>) into Expression (<NUM>). However, this is merely an example, and the DBF unit <NUM> may form the null beam BNULL,j (j = <NUM>,. , J), by using the weight wj(θBeam,ϕBeam,θNULL,ϕNULL) calculated by substituting an inverse matrix of a correlation matrix Rxx expressed by the following Expression (<NUM>) into Expression (<NUM>) in place of the correlation matrix Rxx expressed by Expression (<NUM>).

The correlation matrix Rxx expressed by Expression (<NUM>) is calculated, by acquiring an Hadamard product of a correlation matrix Rxx' of the reflected wave having no angle width expressed by the following Expression (<NUM>) and a covariance matrix taper (CMT) matrix T. The correlation matrix Rxx expressed by Expression (<NUM>) is the correlation matrix Rxx of the reflected wave having the angle width, and is acquired without numerical integration. <MAT> <MAT> In Expression (<NUM>), ⊙ represents an Hadamard product.

An m,n element [T]m,n of the CMT matrix T is expressed by the following Expression (<NUM>).

In Expression (<NUM>), Δxm,n = xm- xn and Δym,n = ym- yn are satisfied.

In the angle width estimation device <NUM> illustrated in <FIG>, the DBF unit <NUM> forms null beams BNULL,j (j = <NUM>,. , J) in order from a null beam with a narrow null width. Then, the angle width estimating unit <NUM> monitors a change in power of the null beam BNULL,j output from the beam forming unit <NUM>, and searches for, as the null width indicating the angle width, the null width of the null beam when the power stops decreasing from the state in which the power decreases. However, this is merely an example, and the DBF unit <NUM> forms the null beams BNULL,j (j = <NUM>,. , J) in order from a null beam with a wider null width. Then, the angle width estimating unit <NUM> may monitor a change in power of the null beam BNULL,j output from the DBF unit <NUM>, and search for, as the null width indicating the angle width, the null width of the null beam immediately before the power starts increasing from a state in which there is no change in the power. In this case also, in the example in <FIG>, the null width in the third processing indicates the angle width of the reflected wave.

In a second embodiment, an angle width estimation device <NUM> in which a DBF unit <NUM> of a beam forming unit <NUM> forms a beam at an end of a null beam BNULL,j (j = <NUM>,. , J) is described.

<FIG> is a configuration diagram illustrating a target angle measurement device including the angle width estimation device <NUM> according to the second embodiment. In <FIG>, the same reference sign as that in <FIG> represents the same or corresponding portion, so that the description thereof is omitted.

<FIG> is a hardware configuration diagram illustrating hardware of a digital signal processing unit in the target angle measurement device illustrated in <FIG>. In <FIG>, the same reference sign as that in <FIG> represents the same or corresponding portion, so that the description thereof is omitted.

The beam forming unit <NUM> is provided with coherent integrating units <NUM>-<NUM> to <NUM>-M, pulse compressing units <NUM>-<NUM> to <NUM>-M, and the DBF unit <NUM>.

The beam forming unit <NUM> forms, from one reception array signal rARE output from a reflected wave receiving unit <NUM>, a plurality of null beams having nulls in an arrival direction of a reflected wave, and having null widths different from each other, as is the case of the beam forming unit <NUM> illustrated in <FIG>.

The beam forming unit <NUM> forms a beam at an end of each null beam.

The DBF unit <NUM> is provided with a table 12a.

The table 12a stores a plurality of weights regarding the null beam formed by the DBF unit <NUM> as is the case of the table 8a illustrated in <FIG>. Note that, a weight w stored in the table 12a is different from the weight w stored in the table 8a, and is the weight capable of forming a beam at an end in a u-axis direction of the null beam BNULL,j (j = <NUM>,. , J) and forming a beam at an end in a v-axis direction of the null beam BNULL,j.

The DBF unit <NUM> forms the null beam BNULL,j having the beam at the end, by performing digital beam forming on a plurality of signals after pulse compression output from the pulse compressing units <NUM>-<NUM> to <NUM>-M.

In <FIG>, it is supposed that each of the coherent integrating units <NUM>-<NUM> to <NUM>-M, the pulse compressing units <NUM>-<NUM> to <NUM>-M, the DBF unit <NUM>, and the angle width estimating unit <NUM>, which are components of the angle width estimation device <NUM>, is implemented by dedicated hardware as illustrated in <FIG>. That is, it is supposed that the angle width estimation device <NUM> is implemented by a coherent integrating circuit <NUM>, a pulse compressing circuit <NUM>, the DBF circuit <NUM>, and an angle width estimating circuit <NUM>.

Each of the coherent integrating circuit <NUM>, the pulse compressing circuit <NUM>, the DBF circuit <NUM>, and the angle width estimating circuit <NUM> corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel-programmed processor, an ASIC, a FPGA, or a combination thereof.

When the angle width estimation device <NUM> is implemented by the software, firmware or the like, a program for causing a computer to execute each processing procedure in the coherent integrating units <NUM>-<NUM> to <NUM>-M, the pulse compressing units <NUM>-<NUM> to <NUM>-M, the DBF unit <NUM>, and the angle width estimating unit <NUM> is stored in a memory <NUM> illustrated in <FIG>. Then, a processor <NUM> illustrated in <FIG> executes the program stored in the memory <NUM>.

Next, an operation of the target angle measurement device illustrated in <FIG> is described. Note that, since components other than the DBF unit <NUM> are similar to those of the target angle measurement device illustrated in <FIG>, only an operation of the DBF unit <NUM> is herein described.

In the target angle measurement device illustrated in <FIG>, the DBF unit <NUM> forms the null beam BNULL,j (j = <NUM>,. , J) having the null in the arrival direction of the reflected wave. However, there is no guarantee that the null width of the null beam BNULL,j formed by the DBF unit <NUM> coincides with the angle width of the reflected wave. Therefore, there is a possibility that the null beam BNULL,j having the null with the null width wider than the angle width of the reflected wave is formed by first processing by the DBF unit <NUM>. In this case, even when the DBF unit <NUM> forms the null beam BNULL,j having the null with a wider null width in j-th processing than that in (j-<NUM>)-th processing, null widths Bθ and Bϕ cannot be searched for in some cases.

In the target angle measurement device illustrated in <FIG>, in order to prevent the null width of the null beam BNULL,j from being widened more than necessary, the DBF unit <NUM> forms the beam BNULL,j having the beam at the end.

The DBF unit <NUM> acquires a weight w calculated by the following Expression (<NUM>) from the table 12a and forms the null beam BNULL,j using the weight w. <MAT> <MAT> <MAT>.

In Expressions (<NUM>) to (<NUM>), C represents a constraint matrix, and H represents a constraint response value for the constraint matrix C.

<FIG> is an explanatory diagram illustrating a null beam formed by the DBF unit <NUM>.

In the example in <FIG>, the null beam BNULL,j is formed in null forming directions uc and vc. A hatched region is a null region, the null width in the u-axis direction is (uc + Δu/<NUM>) - (uc - Δu/<NUM>), and the null width in the v-axis direction is (vc + Δv/<NUM>) - (vc - Δv/<NUM>).

In the example in <FIG>, beams are formed at ends in the u-axis direction of the null beam BNULL,j, and beams are formed at ends in the v-axis direction of the null beam BNULL,j.

That is, the beams a longitudinal direction each of which is a direction parallel to the v-axis are formed at uc ± Δu/<NUM>, and the beams a longitudinal direction each of which are a direction parallel to the u-axis is formed at vc ± Δv/<NUM>.

Since the DBF unit <NUM> is constrained to form the beam at the end, the null width of the null beam BNULL,j formed by the DBF unit <NUM> is likely to be narrower than the null width of the null beam BNULL,j formed by the DBF unit <NUM> illustrated in <FIG>.

Therefore, the target angle measurement device illustrated in <FIG> is more likely to be able to search for the null widths Bθ and Bϕ than the target angle measurement device illustrated in <FIG>.

In a third embodiment, an angle width estimation device <NUM> in which a DBF unit <NUM> of a beam forming unit <NUM> rotates a forming direction of a null beam BNULL,j (j = <NUM>,. , J) is described.

<FIG> is a configuration diagram illustrating a target angle measurement device including the angle width estimation device <NUM> according to the third embodiment. In <FIG>, the same reference sign as that in <FIG> and <FIG> represents the same or corresponding part, so that the description thereof is omitted.

<FIG> is a hardware configuration diagram illustrating hardware of a digital signal processing unit in the target angle measurement device illustrated in <FIG>. In <FIG>, the same reference sign as that in <FIG> and <FIG> represents the same or corresponding part, so that the description thereof is omitted.

The beam forming unit <NUM> rotates the forming direction of each null beam.

The DBF unit <NUM> is provided with a table 12a as is the case of the DBF unit <NUM> illustrated in <FIG>.

In the target angle measurement device illustrated in <FIG>, the DBF unit <NUM> is provided with the table 12a. However, this is merely an example, and the DBF unit <NUM> may be provided with the table 8a as is the case with the DBF unit <NUM> illustrated in <FIG>.

The DBF unit <NUM> forms the null beam BNULL,j (j = <NUM>,. , J) by performing digital beam forming on a plurality of signals after pulse compression output from the pulse compressing units <NUM>-<NUM> to <NUM>-M, as is the case with the DBF unit <NUM> illustrated in <FIG> or the DBF unit <NUM> illustrated in <FIG>.

Unlike the DBF unit <NUM> and the like illustrated in <FIG>, the DBF unit <NUM> rotates the forming direction of the null beam BNULL,j.

Next, an operation of the target angle measurement device illustrated in <FIG> is described. Note that, since components other than the DBF unit <NUM> are similar to those of the target angle measurement device illustrated in each of <FIG> and <FIG>, only an operation of the DBF unit <NUM> is herein described.

The DBF unit <NUM> forms the null beam BNULL,j by a method similar to that of the DBF unit <NUM> illustrated in <FIG> or the DBF unit <NUM> illustrated in <FIG>.

As expressed by the following Expression (<NUM>), the DBF unit <NUM> rotates the forming direction of the null beam BNULL,j, by multiplying an element coordinate matrix R expressed by Expression (<NUM>) by a rotation matrix Rrot(θrot) corresponding to a rotation angle θrot expressed by Expression (<NUM>). The DBF unit <NUM> can rotate the forming direction of the null beam BNULL,j by a desired angle by appropriately adjusting the rotation angle θrot. <MAT> <MAT>.

In Expression (<NUM>), Rr represents the element coordinate matrix after coordinate rotation.

<FIG> is an explanatory diagram illustrating the rotation of the forming direction of the null beam.

In <FIG>, a hatched region is a null region.

In an example in <FIG>, beams are formed at ends in a u-axis direction of the null beam, and beams are formed at ends in a v-axis direction of the null beam. However, this is merely an example, and the null beam may also be that without the beams formed at the ends in the u-axis direction of the null beam and without the beams formed at the ends in the v-axis direction of the null beam.

The DBF unit <NUM> can control null forming directions uc and vc, by calculating a CMT matrix T expressed by the following Expression (<NUM>) using the element coordinate matrix Rr after coordinate rotation.

The DBF unit <NUM> can also control a null expanding direction, by calculating the CMT matrix T expressed by the following Expression (<NUM>) using the element coordinate matrix Rr after coordinate rotation.

In Expression (<NUM>), Δxrm,n = xrm - xm and Δyrm,n = yrm - ym are satisfied.

In the third embodiment described above, the angle width estimation device <NUM> illustrated in <FIG> is configured in such a manner that the beam forming unit <NUM> rotates the forming direction of the null beam. Therefore, as is the case of the angle width estimation device <NUM> illustrated in <FIG>, the angle width estimation device <NUM> illustrated in <FIG> can estimate the angle width of the reflected wave from the target from one reception array signal, and can form the null beam suitable for a shape of the target, a posture of the target or the like.

Note that, in the present disclosure, the embodiments can be freely combined, any component of each embodiment can be modified, or any component can be omitted in each embodiment.

The present disclosure is suitable for an angle width estimation device, an angle width estimation method, and a target angle measurement device.

Claim 1:
An angle width estimation device (<NUM>) comprising:
a beam forming unit (<NUM>, <NUM>, <NUM>) configured to acquire one reception array signal of a reflected wave from a target to be observed, and form, from the one reception array signal, a plurality of null beams by applying null beam forming to the reception array signal, each null beam having a null width which is width of the null in an arrival direction of the reflected wave, the null widths of the plurality of null beams being different from each other; and
an angle width estimating unit (<NUM>) configured to compare powers of the plurality of null beams formed by the beam forming unit (<NUM>, <NUM>, <NUM>) with each other, and to estimate a null width indicating an angle width of the reflected wave by determining, on a basis of a comparison result of the powers, one of the null widths of the plurality of null beams.