Three-dimensional imaging method and system of millimeter wave MIMO radar

Abstract

The embodiment of the invention discloses a three-dimensional imaging method and system of a millimeter wave MIMO radar. The method comprises the following steps: acquiring echo data of a to-be-measured target by using a millimeter wave MIMO radar; carrying out IFFT (Inverse Fast Fourier Transform) processing about time angular frequency on the echo data to obtain a one-dimensional range profile image; determining the position range of the to-be-measured target according to the one-dimensional range profile image; performing phase compensation of distance layering on the echo data according to the position range and the distance resolution of the millimeter wave MIMO radar; performing slicing processing and wavenumber domain imaging on the phase compensation result in the distance direction within the position range of the to-be-measured target to obtain a two-dimensional image at the distance direction slicing position; and traversing the two-dimensional images at the distance direction slices to synthesize a three-dimensional image.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of image imaging. More particularly, it relates to a three-dimensional imaging method and system of millimeter wave MIMO radar. BACKGROUND

[0002] Active millimeter wave imaging technology can easily penetrate clothing and other coverings to image hidden objects and provide high-resolution images needed to reliably detect hidden threats. Security inspection equipment based on active millimeter wave imaging technology can detect hidden threats of metal and non-metal objects, and it is non-ionizing radiation, has small transmission power, and is harmless to the human body; compared with traditional manual search security inspection methods, it has the advantages of high efficiency and non-contact. Many countries have deployed active millimeter wave imaging systems for personnel security checks. Millimeter wave imaging has been widely used for personnel security checks in airports, security checkpoints and other related public or military areas.

[0003] The imaging of the plane scanning system millimeter wave security inspection equipment adopts the synthetic aperture radar (SAR) imaging technology under the system of combining multiple-input multiple-output (MIMO) array with one-dimensional mechanical scanning. Compared with the single-transmit single-receive radar array, the MIMO radar needs fewer actual antennas at the same angle resolution (azimuth resolution) through virtual array technology, which can reduce the hardware cost of the equipment. How to compensate the MIMO radar to obtain the same imaging effect as the single-transmit single-receive radar in terms of resolution, so as to ensure real-time high-quality imaging is the key technology of such system. SUMMARY

[0004] The present application aims to provide a three-dimensional imaging method and system of millimeter wave MIMO radar to solve at least one of the problems in the prior art.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] The present application provides a three-dimensional imaging method of millimeter wave MIMO radar in the first aspect, which comprises:

[0007] Collecting echo data of the target to be measured by using the millimeter wave MIMO radar;

[0008] Performing IFFT processing on the echo data with respect to time angle frequency to obtain a one-dimensional range image;

[0009] Determining the position range of the target to be measured according to the one-dimensional range image;

[0010] phase compensation according to the range of the position and the range resolution of the millimeter wave MIMO radar on the echo data;

[0011] slicing and wave number domain imaging on the result of the phase compensation in the range of the position of the target to be measured to obtain a two-dimensional image at the distance slice;

[0012] synthesizing a three-dimensional image by traversing the two-dimensional image at the distance slice.

[0013] Optionally, the echo data of the target to be measured collected by the millimeter wave MIMO radar comprises:

[0014] The echo data of any point of the target to be measured collected by the millimeter wave MIMO radar is:

[0015]

[0016] wherein x is the first coordinate component of any point; y is the second coordinate component of any point; z is the third coordinate component of any point; f(x, y, z) is the reflection characteristic function; j is the imaginary unit; k=ω / c is the wave number, ω is the time angular frequency, and c is the electromagnetic wave propagation speed; x T is the first coordinate component of the transmitting element position in the millimeter wave MIMO radar antenna plane; y T is the second coordinate component of the transmitting element position in the millimeter wave MIMO radar antenna plane; x R is the first coordinate component of the receiving element position in the millimeter wave MIMO radar antenna plane; y R is the second coordinate component of the receiving element position in the millimeter wave MIMO radar antenna plane, and z1 is the third coordinate component of the transmitting element position in the millimeter wave MIMO radar antenna plane or the third coordinate component of the receiving element position in the millimeter wave MIMO radar antenna plane.

[0017] Optionally, the determination of the range of the position of the target to be measured according to the one-dimensional range image comprises:

[0018] determining the range of the position of the target to be measured according to the target position with a signal-to-noise ratio higher than a preset signal-to-noise ratio of background noise in the one-dimensional range image.

[0019] Optionally, the preset signal-to-noise ratio of the background noise is greater than or equal to 35 dB.

[0020] Optionally, the phase compensation according to the range of the position and the range resolution of the millimeter wave MIMO radar on the echo data comprises:

[0021] The echo data is phase compensated from multi-station to equivalent single station, and the compensated echo data equivalent to phase center is:

[0022]

[0023] wherein, R u (x T ,y T ,x R ,y R ,ω) is the echo data of the reference point in the millimeter wave MIMO radar mode; R0(n x ,n y ,ω) is the echo data of the equivalent single station phase center to the reference point; n x is the first coordinate component of the equivalent phase center; n y is the second coordinate component of the equivalent phase center.

[0024] Optionally, the calculation formula of the echo data of the reference point in the millimeter wave MIMO radar mode is:

[0025]

[0026] wherein, is the position of the transmitting unit; is the position of the receiving unit; is the position of the reference point, including a plurality of reference points located at different levels || is the modulus of the vector.

[0027] Optionally, the calculation formula of the echo data of the equivalent single station phase center to the reference point is:

[0028]

[0029] wherein, is the position of the phase center.

[0030] Optionally, the calculation formula of the two-dimensional image at the distance slice of the phase compensation result in the position range of the target to be measured is:

[0031]

[0032] wherein, f′(x,y,z m ) is the two-dimensional image at the distance slice z m ∈{z1,z2,…,z M}, z m is the mth distance slice, z M is the total number of distance slices; FT 2Dis a two-dimensional Fourier transform; is a two-dimensional inverse Fourier transform; k0=ω0 / c, ω0is the angular frequency of the stepped frequency signal; 0x is the first coordinate component of the wave number corresponding to the angular frequency; is the second coordinate component of the wave number corresponding to the angular frequency.

[0033] Optionally, the calculation formula for traversing the two-dimensional image at the distance direction slice to synthesize a three-dimensional image is:

[0034] f(x,y,z)=comp(f′(x,y,z m ),z m )

[0035] In the formula, comp() represents the composition about the distance direction slice z m traversing composition; m=1,2,…,M.

[0036] The second aspect of the present application provides a three-dimensional imaging system of a millimeter wave MIMO radar, which comprises:

[0037] The millimeter wave MIMO radar is used for collecting echo data of a target to be measured;

[0038] The first processing unit is used for performing IFFT processing on the echo data about time angular frequency to obtain a one-dimensional range image;

[0039] The second processing unit is used for determining a position range of the target to be measured according to the one-dimensional range image;

[0040] The third processing unit is used for performing distance layering phase compensation on the echo data according to the position range and the distance resolution of the millimeter wave MIMO radar;

[0041] The fourth processing unit is used for performing slice processing and wave number domain imaging on the result of the phase compensation in the distance direction within the position range of the target to be measured to obtain a two-dimensional image at the distance direction slice;

[0042] The fifth processing unit is used for traversing the two-dimensional image at the distance direction slice to synthesize a three-dimensional image.

[0043] The present application has the following beneficial effects:

[0044] The technical scheme of the present application adopts the distance layering phase compensation method, realizes accurate compensation in the imaging range, solves the image blurring problem caused by the large distance range of the target to be measured, and obtains a high-quality three-dimensional imaging result; the accurate distance slice traversal range in imaging is determined, which is smaller than the distance range of the imaging area, thereby reducing the calculation amount of imaging and improving the imaging efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0045] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0046] Figure 1 A flow chart of a three-dimensional imaging method of a millimeter wave MIMO radar according to an embodiment of the present application is shown.

[0047] Figure 2 A planar scanning imaging schematic diagram of a three-dimensional imaging system of a millimeter wave MIMO radar according to an embodiment of the present application is shown.

[0048] Figure 3 A range layering and slice traversal range schematic diagram of a three-dimensional imaging method of a millimeter wave MIMO radar according to an embodiment of the present application is shown.

[0049] Figure 4 A flow chart of a three-dimensional imaging method of a millimeter wave MIMO radar according to another embodiment of the present application is shown. DETAILED DESCRIPTION

[0050] In order to more clearly illustrate the present application, the present application will be further described below with reference to the embodiments and the accompanying drawings. Like components are denoted by the same reference signs in the drawings. Those skilled in the art should understand that the specific description below is illustrative rather than limiting, and should not limit the protection scope of the present application.

[0051] The imaging of a planar scanning system millimeter wave security inspection device adopts a synthetic aperture (SAR) imaging technology under a combination system of a multiple-input multiple-output (MIMO) array and one-dimensional mechanical scanning. Compared with a single-transmit single-receive radar array, the MIMO radar needs less actual antenna quantity at the same angle resolution (azimuth resolution) through virtual array technology, and can reduce the hardware cost of the device. How to compensate the MIMO radar to obtain the same imaging effect as the single-transmit single-receive radar at the same resolution, so as to ensure real-time high-quality imaging is a key technology of such a system.

[0052] Therefore, as Figure 1As shown, one embodiment of the application provides a three-dimensional imaging method of a millimeter wave MIMO radar, which comprises: collecting echo data of a target to be measured by the millimeter wave MIMO radar; performing IFFT processing on the echo data with respect to time angle frequency to obtain a one-dimensional range image; determining a position range of the target to be measured according to the one-dimensional range image; performing phase compensation of distance layering on the echo data according to the position range and a distance resolution of the millimeter wave MIMO radar; performing slice processing and wave number domain imaging on a result of the phase compensation in a distance direction within the position range of the target to be measured to obtain a two-dimensional image at a distance slice; and traversing the two-dimensional image at the distance slice to synthesize a three-dimensional image.

[0053] In one specific example, the method comprises:

[0054] Step one: positioning the target to be measured in a distance range, considering that the target to be measured presents a certain range along the distance direction, performing IFFT processing on ω dimension of the original echo s(x T ,y T ,x R ,y R ,ω) to obtain a one-dimensional range image, and determining a real distance position range of the target according to a position of the target to be measured which is obviously higher than background noise (for example, taking 35 dB signal-to-noise ratio as a threshold) in the one-dimensional range image.

[0055] Step two: performing phase compensation of distance layering according to the real distance position range obtained in step one and a distance resolution of the millimeter wave MIMO radar imaging.

[0056] Further, the distance resolution is δ z =c / 2B, B is a signal bandwidth, and c is an electromagnetic wave propagation speed.

[0057] Step three: determining a distance slice traversal range according to the real distance position range obtained in step one, and the distance slice traversal range obtained at this time is a real distance range of the target, which is usually smaller than a distance range of an imaging region.

[0058] The embodiment firstly performs distance positioning on the to-be-measured target in the imaging process, determines the specific position of the to-be-measured target in the imaging scene, then divides the distance range according to the position, and in the MIMO imaging process, adopts the distance layering phase compensation method to realize accurate compensation in the imaging range, solves the image blurring problem caused by the large range of the to-be-measured target in the distance direction, and obtains high-quality three-dimensional imaging results. Meanwhile, compared with imaging the entire distance imaging range in the traditional algorithm, the distance positioning on the to-be-measured target can reduce the calculation amount of imaging and improve the imaging efficiency. The distance layering compensation optimization three-dimensional imaging method based on target positioning of the near-distance millimeter wave MIMO radar disclosed in the embodiment meets the high requirements of the near-distance millimeter wave MIMO radar security inspection equipment on imaging quality and efficiency.

[0059] In a possible implementation manner, the collecting, by the millimeter wave MIMO radar, of echo data of the to-be-measured target includes: collecting, by the millimeter wave MIMO radar, echo data of any point of the to-be-measured target as follows:

[0060]

[0061] In the formula, x is the first coordinate component of any point; y is the second coordinate component of any point; z is the third coordinate component of any point; f(x, y, z) is a reflection characteristic function; j is an imaginary unit; k=ω / c is a wave number, ω is a time angular frequency, and c is an electromagnetic wave propagation speed; x T is the first coordinate component of the position of a transmitting array element in the plane of the millimeter wave MIMO radar; y T is the second coordinate component of the position of the transmitting array element in the plane of the millimeter wave MIMO radar; x R is the first coordinate component of the position of a receiving array element in the plane of the millimeter wave MIMO radar; y R is the second coordinate component of the position of the receiving array element in the plane of the millimeter wave MIMO radar, and z1 is the third coordinate component of the position of the transmitting array element in the plane of the millimeter wave MIMO radar or the third coordinate component of the position of the receiving array element in the plane of the millimeter wave MIMO radar.

[0062] In a specific example, a schematic diagram of a near-distance millimeter wave MIMO radar plane scanning three-dimensional imaging measurement system is as shown in Figure 2 and Figure 3 . The horizontally placed near-distance millimeter wave MIMO radar array is driven by a mechanical structure to scan along the vertical direction, to realize plane synthetic aperture. The to-be-measured target is placed in front of the near-distance millimeter wave MIMO radar array. The near-distance millimeter wave MIMO radar array obtains a high-resolution three-dimensional image of the to-be-measured target by transmitting a wideband stepped frequency signal and simultaneously performing synthetic aperture scanning in the horizontal direction and the vertical direction.

[0063] In a specific example, define s(x) T ,y T ,x R ,y R (x, ω) represents the echo data of a broadband signal sampled in a two-dimensional plane at each frequency point, where (x, ω) represents the echo data of the signal sampled in the two-dimensional plane at each frequency point. T ,y T Z1) represents the position of the transmitting element in the antenna plane, (x R ,y R Z1) represents the position of the receiving array element, ω represents the time angular frequency, and the distance from the scanning aperture plane to the center of the imaging region of the target is z = Z1, (x T ,y T (,Z1) and (x R ,y R The spatial coordinates of the equivalent phase center formed by Z1) are (n x ,n y ,Z1), fill in the missing phase center points in the plane with zeros. The coordinates of any point on the target in the imaging area are (x,y,z), and the reflection characteristics are f(x,y,z). If the target remains stationary during the scanning measurement, the echo signal of point (x,y,z) is given by formula (1):

[0064]

[0065] In the formula, , respectively, are the distances from the transmitting and receiving array elements to point (x,y,z); k=ω / c is the wave number, c is the electromagnetic wave propagation speed, and the amplitude attenuation with distance is ignored.

[0066] In one possible implementation, determining the location range of the target under test based on the one-dimensional distance image includes: determining the location range of the target under test based on the target position in the one-dimensional distance image where the signal-to-noise ratio is higher than the background noise by a preset signal-to-noise ratio.

[0067] In one possible implementation, the preset signal-to-noise ratio of the background noise is greater than or equal to 35dB.

[0068] In one possible implementation, the phase compensation for range-layered echo data based on the location range and the range resolution of the millimeter-wave MIMO radar includes: performing multi-station to equivalent single-station phase compensation on the echo data to obtain the compensated echo data equivalent to the phase center as follows:

[0069]

[0070] In the formula, R u (x T ,yT R R R0(n x ,n y R1(n x is the first coordinate component of the equivalent phase center; y is the second coordinate component of the equivalent phase center.

[0071] In a possible implementation, the formula for calculating the echo data of the reference point in the millimeter wave MIMO radar mode is:

[0072]

[0073] wherein, is the position of the transmitting unit; is the position of the receiving unit; is the position of the reference point, includes multiple reference points at different levels || is the modulus of the vector.

[0074] In a possible implementation, the formula for calculating the echo data of the reference point in the millimeter wave MIMO radar mode is:

[0075]

[0076] wherein, is the position of the phase center.

[0077] In a specific example, since the rigid method adopts a near-distance millimeter wave MIMO radar array system with transceiver separation, the phase calibration of the echo data from multiple stations to the equivalent single station is required. Generally, the center of the imaging area is taken as the reference point for calibration, and the echo data of the calibrated phase center is equivalent to formula (2):

[0078]

[0079] Further, R u (x T ,y T (x R ,y R ,ω) is the echo data of the reference point in the MIMO mode, which is formula (3):

[0080]

[0081] Further, R0(n x ,n y ​​where is the echo data of the equivalent single station phase center to the reference point is formula (4) :

[0082]

[0083] where, is the position of the transmitting unit, is the position of the receiving unit, is the position of the reference point, is the position of the phase center; that is, is not a fixed reference point, but a plurality of reference points at different levels

[0084] Further, after compensation by formula (2), the echo signal of point (x, y, z) can be approximated as the echo of the single-transmitting single-receiving system, which is formula (5) :

[0085]

[0086] Further, the exponential term represents the near-spherical wave from point (n x ,n y (z1) and can be decomposed into the accumulation of infinite plane waves as formula (6) :

[0087]

[0088] where, is the wave number corresponding to n x ; is the wave number corresponding to n y ; and The change range is (-2k, 2k).

[0089] Further, according to formula (5) and formula (6), the calibrated data can be written as formula (7) :

[0090]

[0091] where,

[0092] Further, two-dimensional Fourier transform is performed on both sides of formula (7), and the difference between the phase center coordinates and the target coordinates is ignored, and formula (8) is obtained:

[0093]

[0094] In a possible implementation, the calculation formula of the two-dimensional image at the distance slice obtained by slicing the result of the phase compensation in the distance direction of the position range of the to-be-measured target and wave number domain imaging is:

[0095]

[0096] In the formula, f′(x,y,z) m ) is the distance slice z m ∈{z1,z2,…,z M The two-dimensional image at}, z m For the m-th distance slice, z M Total number of distance-oriented slices; FT 2D It is a two-dimensional Fourier transform; This is a two-dimensional inverse Fourier transform; k0 = ω0 / c, where ω0 is the angular frequency of the step frequency signal; k 0x The first coordinate component of the wavenumber corresponding to the angular frequency; This is the second coordinate component of the wavenumber corresponding to the angular frequency.

[0097] In a specific example, three-dimensional imaging is achieved by using range slicing, two-dimensional IFFT, and coherent superposition of each frequency point. This facilitates parallel computation of the imaging algorithm and improves imaging efficiency. The implementation method includes formula (9):

[0098]

[0099] Furthermore, its implementation method includes formula (10):

[0100]

[0101] In the formula, f′(x,y,z) m ) represents slicing the distance range {z1, z2, ..., z} within the imaging region. M After processing, the distance slice z m ∈{z1,z2,…,z M The two-dimensional image result at} is k0=ω0 / c.

[0102] Furthermore, by analyzing the distance slices {z1, z2, ..., z} within the imaging region... M By traversing the area, the three-dimensional imaging result of the imaging region can be obtained; this implementation method is very suitable for parallel algorithms to achieve real-time performance.

[0103] In one possible implementation, the formula for synthesizing a three-dimensional image by traversing the two-dimensional images at the distance slices is:

[0104] f(x,y,z)=comp(f′(x,y,z m ),z m )

[0105] In the formula, comp() represents the distance z at the slice.m Iterative synthesis; m = 1, 2, …, M.

[0106] In one specific example, the formula for the range- dependent slice-wise synthesis is (11):

[0107] f(x, y, z) = comp(f'(x, y, z m ), z m )

[0108] where comp(f, z m ) denotes the z m iterative synthesis.

[0109] In one specific example, as shown in Figure 4 , the flow of the near-range millimeter-wave MIMO radar optimized 3D imaging method is:

[0110] Step 1.1: The MIMO radar transceiver acquires the sampling data s(x T , y T , x R , y R , ω);

[0111] Step 1.2: IFFT with respect to ω, obtain the one-dimensional range image ss(x T , y T , x R , y R , t), t is time;

[0112] Step 1.3: Determine the real distance position range of the target according to the target position which is obviously higher than the background noise (such as taking 35 dB signal-to-noise ratio as the threshold) in the range image;

[0113] Step 1.4: MIMO range layer phase compensation calibration;

[0114]

[0115] where,

[0116]

[0117] Step 1.5: Wave number domain imaging to obtain a two-dimensional image;

[0118]

[0119] Step 1.6: Range-dependent slice-wise synthesis in the target range;

[0120] f(x, y, z) = comp(f'(x, y, z m ), z m), m = 1, 2,..., M

[0121] where comp(f, z m ) denotes the complex value of the signal at frequency f and location z m iteratively.

[0122] Step 1.7: Obtain the three-dimensional imaging result.

[0123] Another embodiment of the present application provides a three-dimensional imaging system of a millimeter wave MIMO radar, comprising: a millimeter wave MIMO radar, configured to collect echo data of a target to be measured; a first processing unit, configured to perform IFFT processing on the echo data with respect to time angle frequency to obtain a one-dimensional range image; a second processing unit, configured to determine a position range of the target to be measured according to the one-dimensional range image; a third processing unit, configured to perform distance-layered phase compensation on the echo data according to the position range and a range resolution of the millimeter wave MIMO radar; a fourth processing unit, configured to perform slicing processing and wave number domain imaging on a result of the phase compensation in a range direction of the position range of the target to be measured to obtain a two-dimensional image at a distance direction slice; and a fifth processing unit, configured to synthesize a three-dimensional image by traversing the two-dimensional image at the distance direction slice.

[0124] In the imaging process, the present embodiment first performs distance positioning on the target to be measured to determine the specific position of the target to be measured in the imaging scene, and then divides a distance range according to the position. In the MIMO imaging process, a distance-layered phase compensation method is adopted to realize accurate compensation in the imaging range, thereby solving the image blurring problem caused by a large range of the target to be measured in the range direction and obtaining a high-quality three-dimensional imaging result. Meanwhile, compared with the imaging of the entire range imaging range in the traditional algorithm, the distance positioning of the target to be measured can reduce the calculation amount of imaging and improve the imaging efficiency. The distance-layered compensation optimization three-dimensional imaging method based on target positioning of the near-range millimeter wave MIMO radar disclosed in the present embodiment meets the high requirements of the imaging quality and efficiency of the near-range millimeter wave MIMO radar security inspection equipment.

[0125] In the description of the present application, it needs to be explained that the terms "upper", "lower" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise expressly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication between two elements inside. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0126] It also needs to be explained that in the description of the present application, the relationship terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device. Without more limitation, the element defined by the sentence "including a…" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0127] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not a limitation on the embodiments of the present application. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made, and it is impossible to enumerate all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A method of three-dimensional imaging of a millimeter wave MIMO radar, characterized by, The method comprises: acquiring echo data of a target to be measured by a millimeter wave MIMO radar; performing IFFT processing on the echo data with respect to time angle frequency to obtain a one-dimensional range image; determining a position range of the target to be measured according to the one-dimensional range image; performing phase compensation on the echo data in a distance layer according to the position range and a distance resolution of the millimeter wave MIMO radar; performing slice processing and wave number domain imaging on a result of the phase compensation in a distance direction within the position range of the target to be measured to obtain a two-dimensional image at a distance direction slice; synthesizing a three-dimensional image by traversing the two-dimensional image at the distance direction slice.

2. The three-dimensional imaging method according to claim 1, wherein the acquiring echo data of a target to be measured by a millimeter wave MIMO radar comprises: acquiring echo data of any point of a target to be measured by a millimeter wave MIMO radar as: where x is the first coordinate component of an arbitrary point; y is the second coordinate component of an arbitrary point; z is the third coordinate component of an arbitrary point; f(x, y, z) is the reflection characteristic function; j is the imaginary unit; k = ω / c is the wave number, ω is the time angular frequency, and c is the electromagnetic wave propagation speed; x T is the first coordinate component of the position of a transmitting array element in the plane of the millimeter wave MIMO radar antenna; y T is the second coordinate component of the position of a transmitting array element in the plane of the millimeter wave MIMO radar antenna; x R is the first coordinate component of the position of a receiving array element in the plane of the millimeter wave MIMO radar antenna; y R is the second coordinate component of the position of a receiving array element in the plane of the millimeter wave MIMO radar antenna, and z1 is the third coordinate component of the position of a transmitting array element in the plane of the millimeter wave MIMO radar antenna or the third coordinate component of the position of a receiving array element in the plane of the millimeter wave MIMO radar antenna.

3. The three-dimensional imaging method according to claim 2, wherein the determining a position range of the target to be measured according to the one-dimensional range image comprises: determining a position range of the target to be measured according to a target position in the one-dimensional range image whose signal-to-noise ratio is higher than a preset signal-to-noise ratio of background noise.

4. The three-dimensional imaging method according to claim 3, wherein a value range of the preset signal-to-noise ratio of the background noise is greater than or equal to 35 dB.

5. The three-dimensional imaging method according to claim 4, wherein the performing phase compensation on the echo data in a distance layer according to the position range and a distance resolution of the millimeter wave MIMO radar comprises: performing phase compensation on the echo data from multiple stations to an equivalent single station to obtain echo data equivalent to a phase center after compensation as: wherein R u (x T ,y T ,x R ,y R ,ω) is the echo data of the reference point in the millimeter wave MIMO radar mode; R0(n x ,n y ,ω) is the echo data of the equivalent single station phase center to the reference point; n x is the first coordinate component of the equivalent phase center; n y is the second coordinate component of the equivalent phase center.

6. The three-dimensional imaging method according to claim 5, wherein a calculation formula of echo data of a reference point in the millimeter wave MIMO radar mode is: wherein is a transmitting unit position; is a receiving unit position; is a reference point position, comprises a plurality of reference points located at different levels || is a modulus of a vector.

7. The three-dimensional imaging method according to claim 5, wherein a calculation formula of echo data of the equivalent single station phase center to the reference point is: In the formulae, is the phase center position.

8. The three-dimensional imaging method according to claim 5, wherein a calculation formula of the performing slice processing and wave number domain imaging on a result of the phase compensation in a distance direction within the position range of the target to be measured to obtain a two-dimensional image at a distance direction slice is: where f'(x, y, z) is the two-dimensional image at the distance direction slice z m ) is the two-dimensional image at the distance direction slice z m ∈{z1,z2,…,z M}, z m is the mth distance direction slice, and z M is the total number of distance direction slices; FT 2D is the two-dimensional Fourier transform; is the two-dimensional inverse Fourier transform; k0=ω0 / c, ω0is the step frequency signal angular frequency; k 0x is the first coordinate component of the angular frequency corresponding wave number; k 0y is the second coordinate component of the angular frequency corresponding wave number.

9. The three-dimensional imaging method according to claim 8, wherein a calculation formula of the synthesizing a three-dimensional image by traversing the two-dimensional image at the distance direction slice is: f(x,y,z) = comp(f'(x,y,z m ),z m ) where comp() denotes the distance to the slice at z m traversing the composition; m = 1, 2,..., M.

10. A three-dimensional imaging system for a millimeter wave MIMO radar, characterized by The system comprises: a millimeter wave MIMO radar configured to acquire echo data of a target to be measured; a first processing unit configured to perform IFFT processing on the echo data with respect to time angle frequency to obtain a one-dimensional range image; a second processing unit configured to determine a position range of the target to be measured according to the one-dimensional range image; a third processing unit configured to perform phase compensation on the echo data in a distance layer according to the position range and a distance resolution of the millimeter wave MIMO radar; and a fourth processing unit configured to perform slice processing and wave number domain imaging on a result of the phase compensation in a distance direction within the position range of the target to be measured to obtain a two-dimensional image at a distance direction slice. a fourth processing unit configured to slice the result of the phase compensation in the distance direction within the position range of the target to be detected and perform wave number domain imaging to obtain a two-dimensional image at a distance slice; a fifth processing unit configured to traverse the two-dimensional images at the distance slices to synthesize a three-dimensional image.

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