WO2023162188A1 - Signal processing device, signal processing method, and radar device - Google Patents

Abstract

This signal processing device (13) comprises a beat signal acquisition unit (71) and is configured such that after radio waves are transmitted to an object under inspection, which moves relative to a radar platform, from each of a plurality of transmitting antennas (31-1) to (31-M) arranged in a row on the radar platform, the reflected waves of the radio waves from the object under inspection are received by each of a plurality of receiving antennas (41-1) to (41-N) arranged in a row on the radar platform at installation positions different from the installation positions of the plurality of transmitting antennas (31-1) to (31-M), and the beat signal acquisition unit (71) acquires a beat signal generated from the received signal of the reflected waves. Further, the signal processing device (13) further comprises: a signal conversion unit (72) that converts each beat signal acquired by the beat signal acquisition unit (71) into a signal in a four-dimensional wavenumber space and outputs each signal in the four-dimensional wavenumber space; a phase error elimination unit (73) that eliminates a phase error associated with a difference between the installation positions of the plurality of transmitting antennas (31-1) to (31-M) and the installation positions of the plurality of receiving antennas (41-1) to (41-N), which are included in each signal in the four-dimensional wavenumber space output from the signal conversion unit (72); and an image generation unit (74) that generates a three-dimensional radar image of the object under inspection from the signal in the four-dimensional wavenumber space after the phase error is eliminated by the phase error elimination unit (73).

Description

SIGNAL PROCESSING DEVICE, SIGNAL PROCESSING METHOD, AND RADAR DEVICE

The present disclosure relates to a signal processing device, a signal processing method, and a radar device.

For example, there is a radar device (hereinafter referred to as "conventional radar device") that is placed in a place where a security check is required and detects prohibited items possessed by a subject to be inspected.
Among conventional radar devices, for example, after transmitting radio waves in the millimeter wave band toward an object to be inspected, the reflected wave, which is the radio wave after being reflected by the object, is received, and based on the received signal of the reflected wave, the object There is a radar device that generates a three-dimensional radar image of (see, for example, Non-Patent Document 1).
The radar device disclosed in Non-Patent Document 1 includes a plurality of transmitting antennas and a plurality of receiving antennas. The radar apparatus employs a TDM (Time Division Multiplexing) method for switching, among a plurality of transmitting antennas, transmitting antennas for transmitting radio waves in a time division manner. Further, the radar device increases the resolution of the three-dimensional radar image by coherently adding received signals of reflected waves of radio waves transmitted from a plurality of transmitting antennas.

In the radar device disclosed in Non-Patent Document 1, if the object to be inspected moves while the transmitting antennas are switched, the relative azimuth direction between the respective transmitting antennas and the object to be inspected when receiving the reflected waves. Since the positions are different from each other, the received signals of the reflected waves cannot be coherently added. If the received signals of the reflected waves cannot be coherently added, blurring may occur in the three-dimensional radar image generated by the radar device. Therefore, the radar apparatus has a problem that an object that moves while the transmission antenna is being switched cannot be inspected.

The present disclosure has been made to solve the above problems, and provides a signal processing device and a signal processing method capable of generating a three-dimensional radar image of an inspection target while the inspection target is moving. with the aim of obtaining

In the signal processing device according to the present disclosure, after radio waves are transmitted from each of a plurality of transmitting antennas arranged in a row on the radar platform toward an inspection target that moves relatively to the radar platform, , The reflected waves of the radio waves from the test object are received by each of the plurality of receiving antennas arranged in a row at the installation position different from the installation position of the plurality of transmitting antennas, and the beat signal generated from the received signals of the reflected waves is obtained. It has a beat signal acquisition unit that The signal processing device also includes a signal conversion unit that converts each beat signal acquired by the beat signal acquisition unit into a signal in a four-dimensional wavenumber space and outputs each signal in the four-dimensional wavenumber space; a phase error elimination unit that eliminates phase errors associated with differences between the installation positions of the plurality of transmitting antennas and the installation positions of the plurality of receiving antennas, which are contained in the respective output signals in the four-dimensional wavenumber space; and an image generation unit for generating a three-dimensional radar image of the inspection target from each signal in the four-dimensional wavenumber space after the phase error is eliminated by the elimination unit.

According to the present disclosure, it is possible to generate a three-dimensional radar image of the inspection target while the inspection target is moving.

1 is a configuration diagram showing a radar device including a signal processing device 13 according to Embodiment 1; FIG. 1 is a configuration diagram showing a signal processing device 13 according to Embodiment 1; FIG. 2 is a hardware configuration diagram showing hardware of the signal processing device 13 according to Embodiment 1. FIG. 3 is a hardware configuration diagram of a computer when the signal processing device 13 is implemented by software, firmware, or the like; FIG. FIG. 4 is an explanatory diagram showing an example of a transmission signal after initial phase setting by a phase control section 22-m; 4 is an explanatory diagram showing the relationship between the installation positions of transmitting antennas 31-1 to 31-M, the installation positions of receiving antennas 41-1 to 41-N, and the positions of targets to be inspected. FIG. FIG. 4 is a schematic diagram showing the positional relationship between the horizontal directivity of an antenna and a target; FIG. 2 is a schematic diagram showing how transmission signals are separated in the wavenumber domain by the DDM-MIMO system; FIG. 4 is a schematic diagram showing a virtual two-dimensional antenna arrangement before transmission signal separation; FIG. 4 is a schematic diagram showing a virtual two-dimensional antenna arrangement after transmission signal separation; FIG. 4 is an explanatory diagram showing radio waves modulated by the TDM-MIMO system; FIG. 4 is a schematic diagram showing a virtual two-dimensional antenna arrangement generated by the TDM-MIMO scheme; 4 is a flowchart showing a signal processing method, which is a processing procedure of the signal processing device 13 according to Embodiment 1; 4 is a schematic diagram showing the positional relationship between transmitting antennas 31-1 to 31-4 and receiving antennas 41-1 to 41-16 and a target. FIG. 4 is an antenna layout diagram showing the layout of transmitting antennas 31-1 to 31-4 and receiving antennas 41-1 to 41-16. FIG. FIG. 4 is an explanatory diagram showing a reproduced image on the xy plane of a point target whose z-coordinate position is 0; 9 is a flowchart showing a signal processing method, which is a processing procedure of the signal processing device 13 according to Embodiment 2; 10 is a flowchart showing a signal processing method, which is a processing procedure of the signal processing device 13 according to Embodiment 3. FIG. 1 shows the relationship between the installation positions of transmitting antennas 31-1 to 31-M and receiving antennas 41-1 to 41-N mounted on each of a plurality of boards, and the position of a target to be inspected. It is an explanatory diagram. FIG. 4 is an explanatory diagram showing an example of a transmission signal after initial phase setting by a phase control section 22-m; 10 is a flowchart showing a signal processing method, which is a processing procedure of the signal processing device 13 according to Embodiment 4;

Hereinafter, in order to describe the present disclosure in more detail, embodiments for carrying out the present disclosure will be described according to the attached drawings.

Embodiment 1.
FIG. 1 is a configuration diagram showing a radar device including a signal processing device 13 according to Embodiment 1. As shown in FIG.
FIG. 2 is a configuration diagram showing the signal processing device 13 according to the first embodiment.
FIG. 3 is a hardware configuration diagram showing hardware of the signal processing device 13 according to the first embodiment.
The radar apparatus shown in FIG. ing.

The radar device shown in FIG. 1 will be described as a FMCW (Frequency Modulated Continuous Wave) radar device that continuously modulates the frequency of transmission radio waves. However, the radar device according to the first embodiment is not limited to the FMCW type radar device. An SFCW (Stepped Frequency Continuous Wave) type radar device may be used. In any of the FMCW system radar system, the radar system in which the transmitted radio wave is a pulse, and the SFCW system radar system, the received signal of the reflected wave can be reduced to the form of Equation (16) described later by preprocessing. can.

The radar signal processor 1 has a control section 11 , a data storage section 12 and a signal processing device 13 .
The control unit 11 outputs a VCO (Voltage Controlled Oscillator) control signal, a transmission control signal, and a phase control signal to the transmission signal generator 2, thereby controlling the operation timing of the transmission signal generator 2 and the like.
The control unit 11 outputs an A/D control signal to the A/D converter 6 to control the operation timing of the A/D converter 6 and the like.
The control unit 11 outputs a signal processing control signal to the signal processing device 13 to control operation timing and the like of the signal processing device 13 .

The data storage unit 12 includes, for example, RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Non-volatile or volatile such as only memory) semiconductor memory, magnetic disk, flexible disk, optical disk, compact disk, mini disk, or DVD (Digital Versatile Disc).
The data storage unit 12 stores digital data output from the A/D converter 6 .

The signal processing device 13 includes a beat signal acquisition section 71, a signal conversion section 72, a phase error elimination section 73, and an image generation section 74, as shown in FIG.
The signal processing device 13 reproduces a three-dimensional radar image of the inspection target based on the digital data stored in the data storage unit 12 . The inspected object is one that moves relative to the radar platform. The radar platform implements a transmitter 3 and a receiver 4 respectively.

The transmission signal generator 2 includes a VCO 21, phase controllers 22-1 to 22-M, and power amplifiers 23-1 to 23-M. M is an integer of 2 or more.
Based on the VCO control signal output from the control unit 11, the VCO 21 generates a transmission signal whose frequency changes over time.
The VCO 21 outputs transmission signals to the phase control units 22-1 to 22-M and a distribution circuit 52, which will be described later.

Phase control unit 22-m (m=1, . . . , M) sets the initial phase of the transmission signal generated by VCO 21 based on the phase control signal output from control unit 11, The subsequent transmission signal is output to the power amplifier 23-m.
The initial phases set by the phase controllers 22-1 to 22-M are different from each other.
The power amplifier 23-m (m=1, . It amplifies the signal and outputs the amplified transmission signal to the transmission antenna 31-m.

The transmitter 3 has M transmitting antennas 31-1 to 31-M.
Each of the transmitting antennas 31-1 to 31-M is arranged in a row in a direction orthogonal to the azimuth direction of the inspection target and the vertical direction of the antenna installation plane on the radar platform.
Here, it is assumed that the transmitting antennas 31-1 to 31-M are arranged in a straight line in orthogonal directions. However, "aligned in a line in an orthogonal direction" does not mean that each of the transmitting antennas 31-1 to 31-M is strictly aligned in a straight line, and is within a range that poses no practical problem. It is a concept that includes things that are lined up on a straight line inside.
The transmission antenna 31-m (m=1, . . . , M) transmits radio waves related to the amplified transmission signal output from the power amplifier 23-m toward the inspection object. The radio wave associated with the transmission signal is, for example, a millimeter waveband radio wave. Radio waves in the millimeter wave band have the property of penetrating the clothing of a person and the property of emitting a small amount of radiation to a person. By transmitting radio waves in the millimeter wave band from the radar device, it is possible to detect both metallic prohibited items and non-metallic prohibited items. However, radio waves transmitted by the radar device are not limited to radio waves in the millimeter wave band, and may be radio waves other than in the millimeter wave band. Contraband items include, for example, knives or firearms.

The receiver 4 has N receiving antennas 41-1 to 41-N. N is an integer of 2 or more.
Each of the receiving antennas 41-1 to 41-N is arranged in a line in a direction orthogonal to the azimuth direction of the inspection object and the vertical direction of the antenna installation plane on the radar platform.
Here, it is assumed that the receiving antennas 41-1 to 41-N are arranged in a straight line in the orthogonal direction. However, "aligned in a line in an orthogonal direction" does not mean that each of the receiving antennas 41-1 to 41-N is strictly aligned in a straight line. It is a concept that includes things that are lined up on a straight line inside.
The installation positions of the receiving antennas 41-1 to 41-N in the azimuth direction are different from the installation positions of the transmitting antennas 31-1 to 31-M in the azimuth direction.
The receiving antenna 41-n (n=1, . 51-n (referred to as "LNA").

The beat signal generator 5 includes LNAs 51-1 to 51-N, a distribution circuit 52, mixers 53-1 to 53-N and a filtering circuit .
The LNA 51-n (n=1, . . . , N) amplifies the received signal of the reflected wave output from the receiving antenna 41-n and outputs the amplified received signal to the mixer 53-n.
The distribution circuit 52 distributes the transmission signal generated by the VCO 21 to N and outputs each of the distributed transmission signals to the mixers 53-n.

The mixer 53-n (n=1, . . . , N) generates a beat signal by multiplying the received signal output from the LNA 51-n by the distributed transmission signal output from the distribution circuit 52. and outputs the beat signal to the filtering circuit 54 .
The filtering circuit 54 is implemented by, for example, a bandpass filter (hereinafter referred to as "BPF") and an amplifier.
The filtering circuit 54 filters the beat signal output from the mixer 53-n, and outputs the filtered beat signal to the A/D conversion circuit 61-n. By filtering the beat signal with the BPF, the low frequency component and high frequency component unnecessary for radar detection, which are included in the beat signal, are suppressed.

The A/D converter 6 includes N A/D conversion circuits 61-1 to 61-N.
A/D conversion circuits 61-n (n=1, . is A/D-converted, and digital data, which is a signal after A/D conversion, is output to the data storage unit 12 of the signal processing device 13 . The A/D conversion circuit 61-n A/D-converts the voltage value of the beat signal at a desired sampling frequency and a desired number of sampling points by controlling the operation timing by the A/D control signal.

The beat signal acquisition unit 71 is implemented by, for example, the beat signal acquisition circuit 81 shown in FIG.
The beat signal acquisition unit 71 acquires N pieces of digital data stored in the data storage unit 12 as N pieces of beat signals generated from the received signals of the reflected waves.
The beat signal acquisition unit 71 outputs N pieces of digital data to the signal conversion unit 72 .

The signal conversion unit 72 is implemented by, for example, the signal conversion circuit 82 shown in FIG.
The signal conversion unit 72 converts each beat signal acquired by the beat signal acquisition unit 71 into a signal in a four-dimensional wavenumber space.
That is, the signal conversion unit 72 converts each beat signal into a signal in a four-dimensional wavenumber space, the dimension of the wavenumber of the radio wave, the dimension of the spatial wavenumber in the azimuth direction, and the M transmitting antennas 31-1 to 31-M. , and the spatial wavenumber dimension in the direction in which the N receiving antennas 41-1 to 41-N are arranged.
The signal conversion section 72 outputs each signal in the four-dimensional wavenumber space to the phase error elimination section 73 .

The phase error elimination unit 73 is realized by, for example, the phase error elimination circuit 83 shown in FIG.
The phase error canceller 73 acquires each signal in the four-dimensional wavenumber space from the signal converter 72 .
The phase error canceling unit 73 detects the difference between the installation positions of the transmitting antennas 31-1 to 31-M and the installation positions of the receiving antennas 41-1 to 41-N, which are included in the respective four-dimensional wave number space signals. This phase error is eliminated.
The phase error elimination unit 73 outputs each signal in the four-dimensional wavenumber space after phase error elimination to the image generation unit 74 .

The image generation unit 74 is implemented by, for example, the image generation circuit 84 shown in FIG.
The image generation unit 74 acquires each signal in the four-dimensional wavenumber space after phase error elimination from the phase error elimination unit 73 .
The image generator 74 generates a three-dimensional radar image of the inspection target from each signal in the four-dimensional wavenumber space after the phase error is eliminated.

In FIG. 2, each of the beat signal acquisition unit 71, the signal conversion unit 72, the phase error elimination unit 73, and the image generation unit 74, which are components of the signal processing device 13, is realized by dedicated hardware as shown in FIG. It assumes what will be done. That is, it is assumed that the signal processing device 13 is implemented by a beat signal acquisition circuit 81, a signal conversion circuit 82, a phase error elimination circuit 83, and an image generation circuit 84. FIG.
Each of the beat signal acquisition circuit 81, the signal conversion circuit 82, the phase error elimination circuit 83, and the image generation circuit 84 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, or an Application Specific Integrated Integrated Circuit (ASIC). Circuit), FPGA (Field-Programmable Gate Array), or a combination thereof.

The constituent elements of the signal processing device 13 are not limited to those realized by dedicated hardware, and the signal processing device 13 may be realized by software, firmware, or a combination of software and firmware. good too.
Software or firmware is stored as a program in a computer's memory. A computer means hardware that executes a program, for example, a CPU (Central Processing Unit), a central processing unit, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a processor, or a DSP (Digital Signal Processor). do.

FIG. 4 is a hardware configuration diagram of a computer when the signal processing device 13 is implemented by software, firmware, or the like.
When the signal processing device 13 is realized by software, firmware, etc., a program for causing a computer to execute respective processing procedures in the beat signal acquisition unit 71, the signal conversion unit 72, the phase error elimination unit 73, and the image generation unit 74. is stored in memory 91 . Then, the processor 92 of the computer executes the program stored in the memory 91 .

3 shows an example in which each component of the signal processing device 13 is implemented by dedicated hardware, and FIG. 4 shows an example in which the signal processing device 13 is implemented by software, firmware, or the like. . However, this is only an example, and some components in the signal processing device 13 may be implemented by dedicated hardware, and the remaining components may be implemented by software, firmware, or the like.

Next, the operation of the radar device shown in FIG. 1 will be described.
Based on the VCO control signal output from the control section 11, the VCO 21 of the transmission signal generator 2 generates a transmission signal whose frequency changes over time. The transmission signal whose frequency changes over time may be an up-chirp signal whose frequency increases over time or a down-chirp signal whose frequency decreases over time. good too.
The VCO 21 outputs transmission signals to the phase controllers 22-1 to 22-M and the distribution circuit 52, respectively.

The phase controller 22-m (m=1, . . . , M) acquires a transmission signal from the VCO 21. FIG.
Based on the phase control signal output from the control section 11, the phase control section 22-m sets the initial phase of the transmission signal.
The initial phases set by the phase controllers 22-1 to 22-M are different from each other, as shown in FIG.
The phase controller 22-m outputs the transmission signal after initial phase setting to the power amplifier 23-m.

FIG. 5 is an explanatory diagram showing an example of a transmission signal after initial phase setting by the phase control section 22-m.
In FIG. 5, the horizontal axis indicates time, and the vertical axis indicates frequency.
In the example of FIG. 5, M=4. The initial phase rotation rate, which is the initial phase of the transmission signal by the phase control section 22-1, is 0 [rad], and the initial phase rotation rate of the transmission signal by the phase control section 22-2 is π/2 [rad]. be.
The initial phase rotation rate of the transmission signal by the phase control section 22-3 is π [rad], and the initial phase rotation rate of the transmission signal by the phase control section 22-4 is −π/2 [rad]. .
Since the initial phases set by the phase controllers 22-1 to 22-M are different from each other, the radar apparatus shown in FIG. be able to. The DDM-MIMO system is a system in which radio waves are simultaneously transmitted from M transmission antennas 31-1 to 31-M, and M transmission signals are separated in the Doppler frequency domain.

The power amplifier 23-m (m=1, . . . , M) acquires the transmission signal after the initial phase setting from the phase controller 22-m.
The power amplifier 23-m amplifies the transmission signal after the initial phase setting with the amplification factor indicated by the transmission control signal output from the control section 11. FIG.
The power amplifier 23-m outputs the amplified transmission signal to the transmission antenna 31-m.

As shown in FIG. 6, each of the transmitting antennas 31-1 to 31-M is arranged in a line in a direction orthogonal to the azimuth direction of the inspection target and the vertical direction of the antenna installation plane on the radar platform.
The transmission antenna 31-m (m=1, . . . , M) transmits radio waves related to the amplified transmission signal output from the power amplifier 23-m toward the inspection object.
FIG. 6 is an explanatory diagram showing the relationship between the installation positions of the transmitting antennas 31-1 to 31-M, the installation positions of the receiving antennas 41-1 to 41-N, and the positions of targets to be inspected. A target is a subject. Subjects include, for example, people or baggage.
In FIG. 6, the arrows indicate the direction of movement of the radar platform on which the transmitting antennas 31-1 to 31-M and receiving antennas 41-1 to 41-N are respectively installed. The radar platform moves horizontally relative to the target.
In the example of FIG. 6, the target is located at the origin O of the three-dimensional coordinate system, the radar platform is in uniform linear motion in the positive direction of the x-axis, and the target is in the negative direction of the x-axis. is in uniform linear motion.

Tx _m (m=1, . . . , M) indicates the transmitting antenna 31-m, and the coordinates of the installation position of Tx _m are (x′+Δx, y _T +y _m hat, z ₀ ). .
Rx _n (n=1, . . . , N) indicates the receiving antenna 41-n, and the coordinates of the installation position of Rx _n are (x', y _R +y _n ', z ₀ ).
In the text of the specification, the symbol "^" cannot be added above the letter "y" due to electronic filing, so it is written as y _m hat.

Each of the M transmitting antennas 31-1 to 31-M and the N receiving antennas 41-1 to 41-N constitutes a vertical linear array. The direction in which the transmitting antennas 31-1 to 31-M and the receiving antennas 41-1 to 41-N are arranged is parallel to the y-axis.
The transmitting antenna 31-m (m=1, . . . , M) and the receiving antenna 41-n (n=1, . . . , N) are separated by Δx in the direction parallel to the x-axis.
_yT is the center coordinate in the y-axis direction in the vertical linear array having M transmitting antennas 31-1 to 31-M. _yR is the center coordinate in the y-axis direction in the vertical linear array having N receiving antennas 41-1 to 41-N.
y _m hat is the y-axis direction offset distance from the center coordinate y _T in the y-axis direction to the position where the transmitting antenna 31-m is installed. y _n ' is the y-axis direction offset distance from the center coordinate y _R in the y-axis direction to the position where the receiving antenna 41-n is installed.
_z0 is the z-coordinate of the radar platform in a three-dimensional coordinate system.
x' is the x-coordinate of the receiving antenna 41-n as the radar platform moves horizontally relative to the target.
l(x', y _n ', y _m hat|x, y, z) is transmitted from the transmitting antenna 31-m and then received as a radio wave reflected at one point (x, y, z) on the target. It represents the radio wave round-trip distance until it returns to the antenna 41-n.

In the signal processing device 13 shown in FIG. 1, the transmission antenna 31-(m−1) and the transmission antenna 31-m (m=2, . M) is an integral multiple of the specific distance interval d _Tx (first length). Further, the interval between the receiving antenna 41-(n−1) and the receiving antenna 41-n (n=2, . . . , N) is an integral multiple of the specific distance interval d _Rx (second length). . However, not all the intervals between the transmitting antennas 31-(m−1) and the transmitting antennas 31-m (m=2, . . . , M) are equal. Moreover, not all the intervals between the receiving antennas 41-(n−1) and the receiving antennas 41-n (n=2, . . . , N) are equal.

The radio waves transmitted from each of the transmission antennas 31-1 to 31-M are reflected by the targets to be inspected.
Reflected radio waves, which are radio waves after being reflected by the target, are received by the receiving antennas 41-1 to 41-N, respectively.
The receiving antenna 41-n (n=1, . . . , N) outputs the received signal of the reflected wave to the LNA 51-n.

The LNA 51-n (n=1, . . . , N) acquires the received signal of the reflected wave from the receiving antenna 41-n and amplifies the received signal.
The LNA 51-n outputs the amplified received signal to the mixer 53-n.
The distribution circuit 52 acquires the transmission signal from the VCO 21 and distributes the transmission signal to N pieces.
The distribution circuit 52 outputs each distributed transmission signal to the mixer 53-n.

The mixer 53-n (n=1, . . . , N) acquires the reception signal from the LNA 51-n and acquires the distributed transmission signal from the distribution circuit 52. FIG.
The mixer 53 - n generates a beat signal by multiplying the received signal by the distributed transmission signal, and outputs the beat signal to the filtering circuit 54 .
The filtering circuit 54 acquires beat signals from each of the mixers 53-1 to 53-N.
The filtering circuit 54 performs filtering processing on each beat signal to suppress low frequency components and high frequency components that are included in each beat signal and are unnecessary for radar detection.
The filtering circuit 54 outputs each beat signal after filtering to the A/D conversion circuit 61-n.

The A/D conversion circuit 61-n (n=1, . . . , N) acquires each filtered beat signal from the filtering circuit .
The A/D conversion circuit 61-n A/D-converts the voltage value of each beat signal according to the A/D control signal output from the control section 11. FIG.
The A/D conversion circuit 61-n outputs digital data, which are respective signals after A/D conversion, to the data storage section 12 of the signal processing device 13. FIG.

The data storage unit 12 stores each digital data.
The signal processing device 13 reproduces a three-dimensional radar image of the inspection object based on each digital data stored in the data storage unit 12 .

Next, the principle of reproducing a three-dimensional radar image in the radar apparatus shown in FIG. 1 will be described.
The transmission signal s _TX (t) generated by the VCO 21 is subjected to FMCW modulation as shown in FIG. 5, and the transmission signal s _TX (t) is represented by Equation (1) below.

In equation (1), f ₀ is the sweep start frequency and μ is the modulation slope. t is time, and if the modulation time of the transmission signal s _TX (t) is T, then 0≦t≦T.

When the x-coordinate of the position of the receiving antenna 41-n (n=1, . . . , N) mounted on the radar platform is x′, the power amplifier 23-m (m=1, . M) to the transmitting antenna 31-m (m=1, _. . . , M) is given by the following equation (2). The transmission signal s _TXm (x', t) is a signal obtained by changing only the initial phase of the transmission signal s _TX (t).

In equation (2), ω _m is the initial phase rotation rate.

After being transmitted from the transmitting antenna 31-m, a reflected wave, which is a radio wave reflected at one point (x, y, z) on the target, is received by the receiving antenna 41-n. At this time, the received signal s _RXn,TXm (x', t) of the reflected wave output from the receiving antenna 41-n is represented by the following equation (3).

In equation (3), c is the speed of light.

In the mixer 53-n (n=1, . . . , N), when the reception signal s _RXn,TXm (x′, t) of the reflected wave and the transmission signal s _TXm (t) are mixed, Equation (4) ), a beat signal s _IFn,m (x′,t) is generated.

In equation (4), LPF[] represents low-pass filtering in filtering circuit 54, and j is the imaginary unit. s _TX+90deg (t) is a signal obtained by advancing the phase of the transmission signal s _TXm (t) generated by the VCO 21 by 90 degrees.
Although IQ detection is assumed here, a similar beat signal s _IFn,m (x', t) can be generated by Hilbert transform even in non-IQ detection.

When the beat signal s _IFn,m (x′, t) is fast Fourier transformed, a pseudo-time signal s _quasin,m (x′, t), such as a received signal of a pulse radar, represented by the following equation (5): τ) is obtained.

In Equation (5), the sinc function is defined as sinc(x)=(sin(πx))/πx. The range of pseudo-time τ is expressed as −F _s /2≦τ≦F _s /2, where F _s is the sampling frequency of s _RXn,TXm (x′, t).

There is an extra phase term exp(-j2π(l ² μ/2c ² )) related to range in the pseudo-time signal s _quasin,m (x′,t). Therefore, the pseudo-time signal s _quasin,m (x′, τ) is multiplied by exp(j2π(lμT/2c)) to cancel the extra phase term exp(−j2π(l ² μ/2c ² )). A phase-corrected pseudo-time signal s _{quasi-compn,m} (x′, τ) as shown in the following equation (6) is generated by performing the phase correction.

By performing an inverse fast Fourier transform on the phase-corrected pseudo-time signal s _{quasi-comp n,m} (x′, τ), the signal s _{n, transformed into the wavenumber domain as shown in the following equation (7): m} (x',k) is obtained. At this time, the range N of the frequency f is expressed as −N/2F _s ≦N≦N/2F _s as the number of samples of the received signals s _RXn,TXm (x′, t).

Up to this point, it is assumed that the inspection object is a point target, but in reality, the inspection object is a spatially spread target g(x, y, z). g(x, y, z) is a function representing the reflection intensity at coordinates (x, y, z).
In FIG. 6, when there is a target g (x, y, z) that spreads spatially, the received signal s _n,m (x′, k) of the reflected wave is expressed by the following equation (8): expressed.

In the DDM-MIMO system, since all the transmitting antennas 31-1 to 31-M transmit radio waves simultaneously, the reflected waves received by the receiving antennas 41-n (n=1, . . . , N) are This is a superposition of reflected waves related to radio waves from all the transmitting antennas 31-1 to 31-M. Therefore, the received signal s(x', y _n ', k) output from the receiving antenna 41-n is represented by the following equation (9).

Next, in order to separate a plurality of transmission signals superimposed on the reception signal s(x', y _n ', k), the reception signal s (x', y _n ', k) is subjected to fast Fourier processing in the x' direction. The transform produces a spectrum S(k _x , y _n ', k) as shown in Equation (10) below. In the example of FIG. 6, the x' direction is horizontal.

In equation (10), k _x is the wave number corresponding to x'. The spectrum S(k _x , y _n ', k) is the spectrum of the radio wave transmitted from the transmitting antenna 31-m in the received signal s(x', y _n ', k) output from the receiving antenna 41-n. It represents spectral components.

Assuming that the horizontal directivity 3 dB one-sided half-value width of each of the transmitting antenna 31-m and the receiving antenna 41-n is θ _{3 dB} (rad), the radar platform is positioned relative to the target from P1 in the positive x-axis direction. The positional relationship between the transmitted radio wave and the target while moving to P2 is depicted as in FIG.
FIG. 7 is a schematic diagram showing the positional relationship between the horizontal directivity of the antenna and the target.

As shown in FIG. 8, the spectrum support of the spectrum S (k _x , y _n ', k) of the radio wave transmitted from the transmitting antenna 31-m is [ω _m −2k _max sin θ _{3 dB} on the wave number k _x axis. , ω _m +2k _max sin θ _{3 dB} ].
FIG. 8 is a schematic diagram showing how transmission signals are separated in the wavenumber domain by the DDM-MIMO system.
In FIG. 8, the horizontal axis is the wave number k _x and the vertical axis is the wave number k. k _max is the maximum wavenumber of transmission radio waves, and k _min is the minimum wavenumber of transmission radio waves.
If the spectral support width from the transmitting antenna 31-m is sufficiently small, the transmitted signal can be completely transmitted on the wavenumber k _x- axis without overlapping the spectral support widths of adjacent transmitting antennas, as shown in FIG. can be separated into
In order to separate the transmission signals on the wavenumber k _x- axis, the inequality sign shown in the following equation (11) must hold for the M transmission antennas 31-1 to 31-M.

Assuming that the inequality sign shown in Equation (11) holds, the spectrum S (k _x , y _n ', k) of the radio wave transmitted from the transmitting antenna 31-m is cut out and subjected to an inverse fast Fourier transform. , as shown in the following equation (12), the received signal s(x′, y _n ', y _m hat, k ) is obtained.

Here, assume the respective virtual positions of the transmitting antenna 31-m and the receiving antenna 41-n after the transmission signals are separated. For example, it is assumed that M=4 and four transmitting antennas 31-1 to 31-4 transmit radio waves in the DDM-MIMO scheme shown in FIG.
FIG. 9 is a schematic diagram showing a virtual two-dimensional antenna arrangement before transmission signal separation. FIG. 9 shows an example in which the number of transmission cycles of radio waves in the four transmission antennas 31-1 to 31-4 is 8 cycles.
At this stage, multiple transmitted signals are not separated in the received signal. By performing the transmission signal separation processing, virtual positions of the transmission antenna 31-m and the reception antenna 41-n become as shown in FIG.
FIG. 10 is a schematic diagram showing a virtual two-dimensional antenna arrangement after transmission signal separation.
In addition to the virtual two-dimensional antenna arrangement after transmission signal separation, FIG. 10 also shows a virtual two-dimensional antenna arrangement before transmission signal separation. The virtual two-dimensional antenna arrangement before transmission signal separation is shown in lighter gray than the virtual two-dimensional antenna arrangement after transmission signal separation.
By performing the separation processing of the transmission signal, virtually two cycles of transmission and reception operations are performed. Also, within that one period, the radar platform is equivalent to being stationary relative to the target. This means that the transmitting antennas 31-1 to 31-4 and the receiving antennas 41-1 to 41-N after the transmission signal separation constitute vertical arrays different from each other, realizing high-speed image reproduction processing. it becomes possible to

The radar device disclosed in Non-Patent Document 1 employs the TDM-MIMO system. For example, it is assumed that M=4 and four transmitting antennas 31-1 to 31-4 transmit radio waves in the TDM-MIMO scheme as shown in FIG.
FIG. 11 is an explanatory diagram showing radio waves modulated by the TDM-MIMO system.
In the TDM-MIMO system, transmission signals are separated in the time direction. Therefore, the positional relationship between the transmitting antennas 31-1 to 31-4, the receiving antennas 41-1 to 41-N, and the target is as shown in FIG. Therefore, the receiving antennas 41-1 to 41-N form a vertical array, but the transmitting antennas 31-1 to 31-4 do not form a vertical array.
FIG. 12 is a schematic diagram showing a virtual two-dimensional antenna arrangement generated by the TDM-MIMO scheme.

Since the radar apparatus shown in FIG. 1 employs the DDM-MIMO system, the transmission antennas 31-1 to 31-4 and the reception antennas 41-1 to 41-N after transmission signal separation are different vertical arrays. constitutes Therefore, the radar device shown in FIG. 1 can implement high-speed image reproduction processing described below.
The radio wave round-trip distance l (x', _yn ', y _m hat|x, y, z) included in the received signal s (x', y _n ', y _m hat, k) of the reflected wave is given below. As shown in equation (13), it can be divided into an outward distance l _T (x', y hat|x, y, z) and a return distance l _R (x', y'|x, y, z) can be done.
Outbound distance l _T (x′, y hat|x, y, z) is the distance from the position of the transmitting antenna 31-m to the target position (x, y, z), and is given by the following equation (14): is represented as
The return distance l _R (x′, y′|x, y, z) is the distance from the target position (x, y, z) to the position of the receiving antenna 41-n, and is given by the following equation (15): is represented as

The received signal s (x', y _n ', y _m hat, k) of the reflected wave can be represented by s (x', y', y hat, k) as in the following equation (16) .

A three-dimensional spectrum S (k x , k y , y hat, k) obtained by two-dimensional Fourier transforming the signal s (x _′ , _y ′, y hat, k) in the x′ direction and the y′ direction is as follows. It is expressed as in Equation (17). In FIG. 6, the x' direction is the horizontal direction, and the y' direction is the vertical direction along which the receiving antennas 41-1 to 41-N are aligned. _kx is the wave number corresponding to x', and k _y is the wave number corresponding to y'.

The Fourier transform in the y′ direction is approximated by Equation (18) below by applying the stationary phase method.
Using the approximation formula shown in formula (18), the three-dimensional spectrum S(k _x , k _y , y hat, k) is approximated as in formula (19) below.

Fourier transforming the three-dimensional spectrum S (k _x , k _y , y hat, k) in the y hat direction yields a four-dimensional spectrum S (k _x , k y , _k) as shown in Equation (20) below. _ky hat, k) is obtained. In FIG. 6, the y-hat direction is the vertical direction in which the transmitting antennas 31-1 to 31-M are aligned. _ky hat is the wavenumber corresponding to y hat.

The Fourier transform in the y-hat direction is approximated by Equation (21) below by applying the stationary phase method.
Using the approximation formula shown in formula (21), the four-dimensional spectrum S(k _x , _ky , _ky hat, k) is approximated as in formula (22) below.

To analytically solve the four-dimensional spectrum S(k _x , k _y , k _y hat, k), it is necessary to obtain an analytical solution of the Fourier transform in the x′ direction. However, since the phase term of the Fourier transform contains the form of the sum of two square roots, it cannot be solved by the stationary phase method. Therefore, the approximate calculation shown below is performed.
First, a part of the phase term φ(x′) in the Fourier transform of the four-dimensional spectrum S(k _x , _ky , _ky hat, k) in the x′ direction is defined as shown in Equation (23) below.

Part of the phase term φ(x′) is split into two terms, the transmitter phase φ _T (x′) and the receiver phase φ _R (x′), as shown in equation (24) below. be able to.
The transmission-side phase φ _T (x′) is expressed as in Equation (25) below. The receiving-side phase φ _R (x′) is expressed as in Equation (26) below.

The transmission-side phase φ _T (x′) is approximated by Equation (27) below by applying Taylor expansion up to second-order terms.
The receiving-side phase φ _R (x′) is approximated by Equation (28) below by applying Taylor expansion up to the second-order term.

In equations (27) to (28), the variable k _Z hat is represented by equation (29) below, and the variable k _Z is represented by equation (30) below.
The variable k _T ' is represented by the following equation (31), and the variable k _R ' is represented by the following equation (32).

　　　　　　　　　　　　　

A part of the phase term φ(x′) is obtained by using the transmitting side phase φ _T (x′) shown in Equation (27) and the receiving side phase φ _R (x′) shown in Equation (28). It is approximated as shown in Equation (33) below.

Finally, by further approximating the sum of the fourth and fifth terms on the right side of Equation (33) with a first-order Taylor expansion, the approximate expression shown in Equation (34) below is derived.

From the above, the four-dimensional spectrum S(k _x , _ky , _ky hat, k) is analytically approximated by the following equation (35).

Equation (35) is obtained by Fourier transforming g(x, y, z) in the three-dimensional directions of x, y, and z, and then multiplying the first five complex constants on the right side of Equation (35) to obtain a four-dimensional spectrum It means that S(k _x , _ky , _ky hat, k) is obtained.
That is, by tracing the reverse, g ( _x , _y , _z ), which is the reflectance distribution of the target, can be obtained as the reproduced image of the target from the four-dimensional spectrum S (k x , ky, ky hat, k). means that
In short, for the four-dimensional spectrum S(k _x , _ky , _ky hat, k), after multiplying the complex conjugate of the first five complex constants on the right side of Equation (35), k _x , _ky + _ky This means that the target reproduced image g( _x , y, z) can be obtained by inverse Fourier transform in the three-dimensional direction of hat, k z +k _z hat. The process of multiplying the 4-dimensional spectrum S (k _x , _ky , _ky hat, k) by the complex conjugate of five complex constants is called "bulk compression process" or "Huygens-Frennel transform process". .
If this is expressed by a formula, it becomes like the following Formula (36). Equation (36) is a fast image reconstruction equation for bistatic antenna configurations.

When the signal processor 13 implements the processing shown in equation (36), there are some points to be noted. The input 4-dimensional spectrum S(k _x , _ky , _ky hat, k) is 4-dimensional, whereas the output g(x, y, z) is 3-dimensional. A point to note.
The signal processing device 13 performs variable transformation processing called Stolt transformation as transformation processing from four dimensions to three dimensions.
As the Stolt transformation, the signal processing device 13 transforms the variable set { _kx , _ky , _ky hat, k} from the variable set { _{k x} , ky, ky hat, _k } with k _{x and} ky fixed. _z + k _z hat}. A specific formulation showing the Stolt transform is Equation (37) shown below.

In Equation (37), IFFT[ ] represents the three-dimensional inverse Fourier transform with the variables shown in { }. Stolt { } represents the Stolt transform from {k _x , _ky , _ky hat, k} to {k _x , _ky , ky _hat , k _z +k _z hat}.

Next, the operation of the signal processing device 13 shown in FIG. 1 will be described.
FIG. 13 is a flowchart showing a signal processing method, which is a processing procedure of the signal processing device 13 according to the first embodiment.
The beat signal acquisition unit 71 acquires N pieces of digital data stored in the data storage unit 12 as N pieces of beat signals generated from the received signals of the reflected waves. The digital data is the received signal s(x', y', y, k) shown in Equation (16).
The beat signal acquisition unit 71 outputs the received signal s(x′, y′, y hat, k) to the signal conversion unit 72 .

The signal conversion unit 72 acquires the received signal s(x′, y′, y, k) from the beat signal acquisition unit 71 .
The signal transforming unit 72 fast Fourier transforms the received signal s(x', y', y, k) in the three-dimensional direction of x', y', y according to equations (17) to (20). (Step ST1 in FIG. 13). In FIG. 13, the fast Fourier transform is expressed like FFT. A four-dimensional spectrum S(k x , ky, ky hat, k) is obtained by fast Fourier transforming the received signal s( _x ′, y _′ , _y hat, k) in the three-dimensional direction.
The signal transforming section 72 outputs the four-dimensional spectrum S(k _x , _ky , _ky hat, k) to the phase error eliminating section 73 as a signal in the four-dimensional wavenumber space.

The phase error elimination unit 73 acquires the four-dimensional spectrum S(k _x , _ky , _ky hat, k) from the signal conversion unit 72 .
In order to eliminate the phase error contained in the four-dimensional spectrum S (k _x , _ky , _ky hat, k), the phase error elimination unit 73 performs the four-dimensional spectrum S (k _x , _ky , _ky hat , k) are subjected to bulk compression processing in which complex conjugates of five complex constants are multiplied (step ST2 in FIG. 13). The phase error is based on the difference between the installation positions of the transmitting antennas 31-1 to 31-M and the installation positions of the receiving antennas 41-1 to 41-N.
The phase error elimination unit 73 outputs the four-dimensional spectrum S (k _x , _ky , _ky hat, k) after the bulk compression processing to the image generation unit 74 .

The image generator 74 acquires the bulk-compressed four-dimensional spectrum S(k _x , _ky , _ky hat, k) from the phase error canceler 73 .
The image generator 74 converts the variable set {k _x , _ky , _ky hat, k} to the variable set {k _x , _ky , _ky hat, k _{z +} k _z hat} is performed (step ST3 in FIG. 13).
Next, the image generator 74 performs inverse fast Fourier transform on the four-dimensional spectrum after the Stolt transform in three-dimensional directions of _kx , _ky + _ky hat, and _kz + _kz hat (step ST4 in FIG. 13). In FIG. 13, the inverse fast Fourier transform is expressed as IFFT. A rough reconstructed image is obtained for each k _y by subjecting the four-dimensional spectrum after the Stolt transform to inverse fast Fourier transform in the three-dimensional direction.
Next, the image generator 74 performs phase correction by multiplying the rough reproduced image for each k _y by e ^jkyy as shown in equation (37) (step ST5 in FIG. 13).
Finally, the image generating unit 74 adds the rough reconstructed images for all _ky after phase correction (step ST6 in FIG. 13) to generate the target reconstructed image g(x, y, z).
By the way, since the processing for each k _y can be processed independently of each other, it is possible to perform parallel processing using a multi-core CPU or multi-core GPU.

An example of reproduction of the target reproduction image g(x, y, z) will be described below.
FIG. 14 is a schematic diagram showing the positional relationship between the transmitting antennas 31-1 to 31-4 and the receiving antennas 41-1 to 41-16 and the target. In the example of FIG. 14, M=4 and N=16.
FIG. 15 is an antenna layout diagram showing the layout of the transmitting antennas 31-1 to 31-4 and the receiving antennas 41-1 to 41-16.
The object to be inspected is a point target located at the origin O of the three-dimensional coordinates. The movement of the radar platform relative to the point target is uniform linear motion in the positive direction of the x-axis, as in FIG. The relative velocity is 0.25 m/s.
The distance between the antenna plane and the point target is |z ₀ |=1.5 m in the z-axis direction. The four transmitting antennas 31-1 to 31-4 form a vertical linear array, and the intervals d _TX between adjacent transmitting antennas are all integral multiples of 8.55 mm. Specifically, the distance d _TX between the transmitting antennas 31-1 and 31-2 is 8.55 mm, and the distance d _TX between the transmitting antennas 31-3 and 31-4 is 8.55 mm. is. Also, the distance d _TX between the transmitting antenna 31-2 and the transmitting antenna 31-3 is 68.4 (=8.55×8) mm.
The 16 receiving antennas 41-1 to 41-16 form a vertical linear array, and the distance d _RX between adjacent receiving antennas is all 5.7 mm.

The modulation method of the transmission radio wave is FMCW, and the frequency band is 77-81 GHz. The horizontal directivity width of each of the transmitting antennas 31-1 to 31-4 and the receiving antennas 41-1 to 41-16 is ±60 degrees, and each of the receiving antennas 41-1 to 41-16 is ±60 degrees. Radio waves from a wider angle range shall not be received.
The initial phase change pattern of each of the transmitting antennas 31-1 to 31-4 is the same as in FIG. 5, and one period is 0.5 ms. The number of cycles of the received signal used for image reproduction is 14000 cycles.
FIG. 16 is an explanatory diagram showing a reproduced image on the xy plane of a point target whose z-coordinate position is 0. FIG.
In FIG. 16, the point image is correctly reproduced at the coordinate origin, which is the position of the point target.

In the first embodiment described above, radio waves are transmitted from each of the plurality of transmitting antennas 31-1 to 31-M arranged in a row on the radar platform toward the inspection target that moves relative to the radar platform. After that, on the radar platform, a plurality of receiving antennas 41-1 to 41-N arranged in a row at installation positions different from the installation positions of the plurality of transmitting antennas 31-1 to 31-M receive radio waves from the inspection object, respectively. is received, and the signal processing device 13 is configured to include the beat signal acquisition unit 71 that acquires the beat signal generated from the received signal of the reflected wave. The signal processing device 13 also includes a signal conversion unit 72 that converts each beat signal acquired by the beat signal acquisition unit 71 into a signal in the four-dimensional wavenumber space and outputs the signal in the four-dimensional wavenumber space; The installation positions of the plurality of transmitting antennas 31-1 to 31-M and the installation positions of the plurality of receiving antennas 41-1 to 41-N included in the respective four-dimensional wavenumber space signals output from the conversion unit 72. Image generation for generating a three-dimensional radar image of the inspection object from the phase error elimination unit 73 that eliminates the phase error related to the difference between the a portion 74; Therefore, the signal processing device 13 can generate a three-dimensional radar image of the inspection target while the inspection target is moving. In other words, in the signal processing device 13 that acquires beat signals from a radar device having a plurality of transmitting antennas 31-1 to 31-M and a plurality of receiving antennas 41-1 to 41-N, the object to be inspected moves. A three-dimensional radar image of the inspection object can be generated in this state.

Embodiment 2.
The _{signal processing device} 13 according to Embodiment ₁ converts the variable set {k _{x , ky} , k _y hat, k _z + k _z hat}.
As the Stolt transformation, the signal _processing device 13 according to Embodiment 2 _converts the variable set {k _{x , ky} + _ky + _ky hat, k _z + k _z hat} is different from the signal processing device 13 according to the first embodiment.
A specific formulation representing the Stolt transform in the signal processing device 13 according to the second embodiment is Equation (38) shown below.

FIG. 17 is a flowchart showing a signal processing method, which is a processing procedure of the signal processing device 13 according to the second embodiment.
The configuration of the signal processing device 13 according to Embodiment 2 is the same as the configuration of the signal processing device 13 according to Embodiment 1, and the configuration diagram showing the signal processing device 13 according to Embodiment 2 is shown in FIG. be.

The signal conversion unit 72 acquires the received signal s(x′, y′, y, k) from the beat signal acquisition unit 71 .
The signal transforming unit 72 fast Fourier transforms the received signal s(x', y', y, k) in the three-dimensional direction of x', y', y according to equations (17) to (20). (Step ST1 in FIG. 17). A four-dimensional spectrum S(k x , ky, ky hat, k) is obtained by fast Fourier transforming the received signal s( _x ′, y _′ , _y hat, k) in the three-dimensional direction.
The signal transforming section 72 outputs the four-dimensional spectrum S(k _x , _ky , _ky hat, k) to the phase error eliminating section 73 as a signal in the four-dimensional wavenumber space.

The phase error elimination unit 73 acquires the four-dimensional spectrum S(k _x , _ky , _ky hat, k) from the signal conversion unit 72 .
In order to eliminate the phase error contained in the four-dimensional spectrum S (k _x , _ky , _ky hat, k), the phase error elimination unit 73 performs the four-dimensional spectrum S (k _x , _ky , _ky hat , k) are subjected to bulk compression processing in which complex conjugates of five complex constants are multiplied (step ST2 in FIG. 17).
The phase error elimination unit 73 outputs the four-dimensional spectrum S (k _x , _ky , _ky hat, k) after the bulk compression processing to the image generation unit 74 .

The image generator 74 acquires the bulk-compressed four-dimensional spectrum S(k _x , _ky , _ky hat, k) from the phase error canceler 73 .
The image generation unit 74 performs Stolt transformation from the variable set { _kx , _ky , _ky hat, k} to the variable set { _kx , _ky + _ky hat, _kz + _kz hat} by Equation (38). (step ST7 in FIG. 17).
Next, the image generating unit 74 performs an inverse fast Fourier transform on the four-dimensional spectrum after the Stolt transform in three-dimensional directions of _kx , _ky + _ky hat, and _kz + _kz hat (step ST8 in FIG. 17). A target reproduced image g(x, y, z) is generated by inverse fast Fourier transforming the four-dimensional spectrum after the Stolt transform in the three-dimensional direction.

Embodiment 3.
The _{signal processing device} 13 according to Embodiment ₁ converts the variable set {k _{x , ky} , k _y hat, k _z + k _z hat}.
The signal _processing device 13 according _to Embodiment 3 _converts the variable set _{{ k x ,} k _y , k _y hat, k _z + k _z hat} is different from the signal processing device 13 according to the first embodiment.
A specific formulation representing the Stolt transform in the signal processing device 13 according to Embodiment 3 is Equation (39) shown below.

FIG. 18 is a flow chart showing a signal processing method, which is a processing procedure of the signal processing device 13 according to the third embodiment.
The configuration of the signal processing device 13 according to Embodiment 3 is the same as the configuration of the signal processing device 13 according to Embodiment 1, and the configuration diagram showing the signal processing device 13 according to Embodiment 3 is shown in FIG. be.

The signal conversion unit 72 acquires the received signal s(x′, y′, y, k) from the beat signal acquisition unit 71 .
The signal transforming unit 72 fast Fourier transforms the received signal s(x', y', y, k) in the three-dimensional direction of x', y', y according to equations (17) to (20). (Step ST1 in FIG. 18). A four-dimensional spectrum S(k x , ky, ky hat, k) is obtained by fast Fourier transforming the received signal s( _x ′, y _′ , _y hat, k) in the three-dimensional direction.
The signal transforming section 72 outputs the four-dimensional spectrum S(k _x , _ky , _ky hat, k) to the phase error eliminating section 73 as a signal in the four-dimensional wavenumber space.

The phase error elimination unit 73 acquires the four-dimensional spectrum S(k _x , _ky , _ky hat, k) from the signal conversion unit 72 .
In order to eliminate the phase error contained in the four-dimensional spectrum S (k _x , _ky , _ky hat, k), the phase error elimination unit 73 performs the four-dimensional spectrum S (k _x , _ky , _ky hat , k) are subjected to bulk compression processing in which complex conjugates of five complex constants are multiplied (step ST2 in FIG. 18).
The phase error elimination unit 73 outputs the four-dimensional spectrum S (k _x , _ky , _ky hat, k) after the bulk compression processing to the image generation unit 74 .

The image generator 74 acquires the bulk-compressed four-dimensional spectrum S(k _x , _ky , _ky hat, k) from the phase error canceler 73 .
The image generator 74 converts the variable set {k _x , ky, _{ky hat} , k} to the variable set {k _x , _ky , _ky hat, _{k z} +k _z hat} is performed (step ST9 in FIG. 18).
Next, the image generation unit 74 performs an inverse fast Fourier transform on the four-dimensional spectrum after the Stolt transform in the three-dimensional directions of _kx , _ky , _kz + _kz (step ST10 in FIG. 18). A rough reconstructed image is obtained for each k _y hat by inverse fast Fourier transforming the four-dimensional spectrum after the Stolt transform in the three-dimensional direction.
Next, the image generation unit 74 performs phase correction by multiplying the rough reconstructed image for each k _y hat by e ^{jky hat y} as shown in equation (39) (step ST11).
Finally, the image generating unit 74 adds the rough reconstructed images for all _ky hats after phase correction (step ST12 in FIG. 18) to generate the target reconstructed image g(x, y, z). .

Embodiment 4.
In the radar devices according to the first to third embodiments, the radar platform has one board, and the transmitting antennas 31-1 to 31-M and the receiving antennas 41-1 to 41-N are mounted on the one board. It is
In the radar device according to the fourth embodiment, the radar platform has a plurality of boards, and the transmitting antennas 31-1 to 31-M and the receiving antennas 41-1 to 41-N are mounted on the respective boards. is different from the radar apparatus according to the first to third embodiments.
The configuration of the signal processing device 13 according to Embodiment 4 is the same as the configuration of the signal processing device 13 according to Embodiment 1, and the configuration diagram showing the signal processing device 13 according to Embodiment 4 is shown in FIG. be.

FIG. 19 shows the installation positions of the transmitting antennas 31-1 to 31-M, the installation positions of the receiving antennas 41-1 to 41-N, and the positions of the targets to be inspected, which are mounted on each of a plurality of boards. is an explanatory diagram showing the relationship between.
In the example of FIG. 19, the radar platform has three boards (1)-(3), on boards (1)-(3) respectively, transmitting antennas 31-1-31-M and receiving antennas 41- 1 through 41-N are implemented.
By mounting the transmitting antennas 31-1 to 31-M and the receiving antennas 41-1 to 41-N on the three substrates (1) to (3), respectively, the radar according to the first to third embodiments The virtual MIMO aperture length in the vertical direction is larger than that of the apparatus, and as a result, the vertical resolution of contraband detection is improved.

FIG. 20 is an explanatory diagram showing an example of a transmission signal after initial phase setting by the phase control section 22-m.
FIG. 20 shows an example in which four transmitting antennas 31-1 to 31-4 are mounted on each of three boards (1) to (3).
In FIG. 20, the horizontal axis indicates time and the vertical axis indicates frequency.
In the example of FIG. 20, the initial phase rotation rate, which is the initial phase of the transmission signal given to the transmission antenna 31-1 mounted on each of the substrates (1) to (4), is 0 [rad]. The initial phase rotation rate of the transmission signal given to 31-2 is π/2 [rad].
Further, the initial phase rotation rate of the transmission signal given to the transmission antenna 31-3 mounted on each of the substrates (1) to (4) is π [rad], and the rate of the transmission signal given to the transmission antenna 31-4 is π [rad]. The initial phase rotation rate is -π/2 [rad].
However, the transmission times of the transmission antennas 31-1-1 to 31-4 mounted on the board (1) and the transmission times of the transmission antennas 31-1-1 to 31-4 mounted on the board (2) , the transmission times of the transmission antennas 31-1-1 to 31-4 mounted on the board (3) and the transmission times of the transmission antennas 31-1-1 to 31-4 mounted on the board (4) are different from each other.

FIG. 21 is a flowchart showing a signal processing method, which is a processing procedure of the signal processing device 13 according to the fourth embodiment.
The image generator 74 generates a target reproduced image g(x, y, z) for each of the plurality of substrates (step ST21 in FIG. 21). In step ST21 of FIG. 21, it is described as image reproduction processing for each substrate.
The image generating unit 74 finally generates the target reproduced image g(x, y, z) by adding the plurality of target reproduced images g(x, y, z) (step ST22 in FIG. 21).

The radar devices according to Embodiments 1 to 4 can inspect, for example, a person riding an escalator or a moving walkway. That is, by installing the transmitting antennas 31-1 to 31-M and the receiving antennas 41-1 to 41-N on both sides of the escalator or moving walkway, it is possible to ride the escalator or moving walkway. It is possible to monitor whether a person is in possession of contraband.

The radar devices according to Embodiments 1 to 4 can inspect baggage placed on moving bodies such as belt conveyors at, for example, airports, railway stations, or ports. That is, by installing the transmitting antennas 31-1 to 31-M and the receiving antennas 41-1 to 41-N on both sides of the moving body, it is possible to prevent prohibited items from being carried in baggage placed on the moving body. You can monitor whether it is included or not.

The radar devices according to Embodiments 1 to 4 can inspect, for example, cars, bicycles, or people traveling on the road. That is, by installing the transmitting antennas 31-1 to 31-M and the receiving antennas 41-1 to 41-N on both sides of the road, it is possible to detect whether or not a vehicle or the like traveling on the road carries prohibited items. can be monitored.

It should be noted that the present disclosure allows free combination of each embodiment, modification of arbitrary constituent elements of each embodiment, or omission of arbitrary constituent elements in each embodiment.

The present disclosure is suitable for signal processing devices, signal processing methods, and radar devices.

1 radar signal processor, 2 transmission signal generator, 3 transmitter, 4 receiver, 5 beat signal generator, 6 A/D converter, 11 control section, 12 data storage section, 13 signal processing device, 21 VCO, 22-1 to 22-M phase control unit, 23-1 to 23-M power amplifier, 31-1 to 31-M transmitting antenna, 41-1 to 41-N receiving antenna, 51-1 to 51-N LNA, 52 distribution circuit, 53-1 to 53-N mixer, 54 filtering circuit, 61-1 to 61-N A/D conversion circuit, 71 beat signal acquisition unit, 72 signal conversion unit, 73 phase error elimination unit, 74 image generation Section, 81 beat signal acquisition circuit, 82 signal conversion circuit, 83 phase error elimination circuit, 84 image generation circuit, 91 memory, 92 processor.

Claims (8)

1. After radio waves are transmitted from each of a plurality of transmitting antennas arranged in a row on a radar platform toward an inspection target that moves relative to the radar platform, the plurality of transmitting antennas are transmitted onto the radar platform. A beat for obtaining a beat signal generated from a received signal of each reflected wave by receiving the reflected wave of the radio wave from the inspection object by each of a plurality of receiving antennas arranged in a row at an installation position different from the installation position. a signal acquisition unit;
   a signal conversion unit that converts each beat signal acquired by the beat signal acquisition unit into a signal in a four-dimensional wavenumber space and outputs each signal in the four-dimensional wavenumber space;
   A phase that eliminates a phase error associated with differences between the installation positions of the plurality of transmitting antennas and the installation positions of the plurality of receiving antennas, which are included in the respective signals in the four-dimensional wavenumber space output from the signal conversion unit. an error elimination unit;
   A signal processing apparatus comprising: an image generation unit that generates a three-dimensional radar image of the inspection object from each signal in the four-dimensional wavenumber space after the phase error is eliminated by the phase error elimination unit.
2. Each of the plurality of transmitting antennas and the plurality of receiving antennas are arranged in a row in a direction orthogonal to the azimuth direction of the inspection object and the vertical direction of the antenna installation surface on the radar platform, and 2. The signal processing apparatus according to claim 1, wherein the installation position of the transmission antenna in the azimuth direction is different from the installation position of the plurality of reception antennas in the azimuth direction.
3. The signal conversion unit is
   Each beat signal acquired by the beat signal acquisition unit is used as a signal in a four-dimensional wavenumber space, and the dimension of the wavenumber of the radio waves, the dimension of the spatial wavenumber in the azimuth direction, and the plurality of transmitting antennas are arranged. 3. The signal processing apparatus according to claim 2, wherein the signal is converted into a signal having a spatial wavenumber dimension in a direction and a spatial wavenumber dimension in the direction in which the plurality of receiving antennas are arranged.
4. The phase error elimination unit
   2. The signal processing apparatus according to claim 1, wherein the phase error contained in each of the four-dimensional wavenumber space signals output from the signal conversion unit is approximated by Taylor expansion.
5. After radio waves are transmitted from each of a plurality of transmitting antennas arranged in a row on a radar platform toward an inspection target that moves relative to the radar platform, the plurality of transmitting antennas are transmitted onto the radar platform. each of a plurality of receiving antennas arranged in a row at an installation position different from the installation position receives the reflected wave of the radio wave from the inspection object;
   A beat signal acquisition unit acquires a beat signal generated from the received signal of the reflected wave,
   A signal conversion unit converts each beat signal acquired by the beat signal acquisition unit into a signal in a four-dimensional wavenumber space, and outputs each signal in a four-dimensional wavenumber space;
   A phase error elimination unit relates to differences between the installation positions of the plurality of transmitting antennas and the installation positions of the plurality of receiving antennas, which are included in the respective signals in the four-dimensional wavenumber space output from the signal conversion unit. Eliminate phase error,
   The signal processing method, wherein an image generation unit generates a three-dimensional radar image of the inspection target from each signal in a four-dimensional wavenumber space after the phase error is eliminated by the phase error elimination unit.
6. a transmission signal generator that generates a plurality of transmission signals having different initial phase rotation rates;
   a plurality of transmitting antennas arranged in a row on a radar platform and transmitting radio waves associated with respective transmission signals toward an inspection target that moves relative to the radar platform;
   a plurality of receiving antennas arranged in a line on the radar platform at installation positions different from the installation positions of the plurality of transmitting antennas and receiving reflected waves of the radio waves from the inspection object;
   a beat signal generator that generates a beat signal from the received signal of the reflected wave received by each receiving antenna;
   a beat signal acquisition unit that acquires each beat signal generated by the beat signal generator;
   a signal conversion unit that converts each beat signal acquired by the beat signal acquisition unit into a signal in a four-dimensional wavenumber space and outputs each signal in the four-dimensional wavenumber space;
   A phase that eliminates a phase error associated with differences between the installation positions of the plurality of transmitting antennas and the installation positions of the plurality of receiving antennas, which are included in the respective signals in the four-dimensional wavenumber space output from the signal conversion unit. an error elimination unit;
   and an image generation unit that generates a three-dimensional radar image of the inspection object from each signal in the four-dimensional wavenumber space after the phase error is eliminated by the phase error elimination unit.
7. The plurality of transmitting antennas simultaneously transmit radio waves associated with respective transmission signals,
   7. The radar apparatus according to claim 6, wherein the signal conversion section separates a plurality of transmission signals superimposed on each beat signal in a wavenumber domain.
8. the spacing of each transmit antenna is an integer multiple of the first length;
   8. The radar apparatus according to claim 7, wherein the distance between each receiving antenna is an integral multiple of the second length.

Images