CN116047509A - Millimeter wave MIMO array scanning and imaging method for uniformly sampling equivalent half wavelength - Google Patents
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Abstract
The invention discloses a millimeter wave MIMO array scanning and imaging method capable of uniformly sampling equivalent half wavelength, and belongs to the technical field of millimeter wave imaging. Different from the mode of fixing the paired receiving and transmitting units of the traditional active millimeter wave scanning imaging system, the invention skillfully designs the MIMO linear array arrangement mode by utilizing the equivalent phase center approximation principle, flexibly configures the pairing condition of receiving and transmitting antennas at each moment, realizes the uniform equivalent sampling of half wavelength interval, greatly reduces the antenna units required by half wavelength full array sampling under the condition of ensuring that the uniform equivalent sampling position of half wavelength is not lost and is not repeated, and reduces the hardware cost. Aiming at the designed MIMO linear array arrangement mode, the invention provides a corresponding high-efficiency and high-resolution rapid three-dimensional imaging method.
Description
Technical Field
The invention belongs to the technical field of millimeter wave imaging, and relates to a special MIMO array scanning and a three-dimensional imaging method thereof.
Background
Millimeter waves have strong penetrability, can penetrate common clothes, textiles, packaging paper and the like, have high resolution, good directivity and strong anti-interference capability, and do not have ionizing radiation harm to detected targets, especially human bodies, so the millimeter waves are widely regarded as key technologies in the fields of security inspection, nondestructive inspection and the like of new-generation personnel, and are primary choices for replacing the existing low-efficiency metal detection and combining manual search. In recent years, along with the continuous growth of millimeter wave imaging technology research teams, a great deal of scientific research results emerge. The most successful commercial application direction of the millimeter wave imaging technology at present is a security gate facing to human body security inspection application, such as Provision series products of L3 company in the United states, thousands of millimeter wave human body security inspection products have been sold worldwide, and R & S company in Germany and some millimeter wave human body security inspection products in China are becoming mature and form part of sales. The existing active millimeter wave human body security gate generally adopts a holographic imaging system, the phase of the reflected millimeter wave signal is directly measured through heterodyne mixing, and then the human body surface image is obtained based on inversion of phase information. The technology adopts synthetic aperture imaging, has high resolution, can reach half wavelength magnitude, reflects reflection information of the body surface of the human body, can clearly see the surface details of articles carried by the human body, and has high differentiation of different types of articles.
Although millimeter wave imaging technology is rapidly developed, numerous scientific research institutions and related enterprises at home and abroad have achieved remarkable results, the existing millimeter wave security inspection imaging technology is still far immature, and the research and development of the millimeter wave imaging technology with low cost, high reliability and high resolution still face great challenges. For example, in the imaging system of planar scanning, in order to ensure high resolution of imaging, the sampling interval must reach half a wavelength or less, and thus a large number of transceiver antenna units are required. In the most extreme case of pure electric scanning without mechanical scanning, a two-dimensional full array would be able to achieve real-time gaze scanning, with the scanning speed reaching the fastest, but the cost of the transceiver units in this case and the complexity of the switching network controlling the operation of the array would also be extremely great.
In order to balance the complexity and the scanning efficiency of the security imaging system, the most widely applied technical scheme at present is to realize two-dimensional plane scanning by utilizing a linear array electric scanning and machine scanning mode. However, with the commercialization and popularization of millimeter wave security inspection systems, the cost of the transceiver unit required for a linear full array with a half wavelength scanning interval is quite huge, so it is of great interest to study how to further reduce the hardware cost. The linear multiple-input multiple-output (MIMO) sparse array technology can just solve the problem, the number of the antennas is reduced by sparse array, the antennas with larger calibers are allowed to be used for more convenient installation, fewer mutual interference is generated between the receiving and transmitting antennas, the isolation is larger, and the array performance is improved.
Aiming at the sparse array technology, a plurality of scholars at home and abroad also put forward different solutions. As proposed by David m.green et al in pacific laboratories, north america, a linear sparse array solution (Proceedings ofSPIE,90780i, 2014) that can be summarized as sparse in the manner of n1:n2:nc, where the linear sparse array consists of Nc repeating units, with N1 transmit antennas and N2 receive antennas evenly distributed within each unit, and where N1 and N2 are required to be mutually homogeneous. When the array is in operation, each transmitting antenna is paired with 2N2 receiving antennas adjacent to the left and right sides respectively to sequentially operate (only one pair of receiving antennas operate at the same time) so as to obtain 2N2 equivalent sampling positions, so that the whole array theoretically obtains 2N1N2Nc sampling points, but the transmitting antennas at the two ends of the array cannot obtain the pairing of the 2N2 receiving antennas at the left and right sides, sampling leakage points can occur at the two ends of the array due to the fact that each transmitting antenna is paired with the 2N2 receiving antennas adjacent to the left and right sides, the distance span of the receiving antennas is large, and the introduced equivalent phase center approximation error is too large. The patent CN106707275B further optimizes the array arrangement mode for this problem, and the array arrangement mode is sparse according to the mode of N1 to N2 to Nc, but the transmitting antennas in each unit are not uniformly arranged in the whole unit, but are aligned to one side of the receiving antennas at 1 time wavelength interval, so that the problem of sampling omission in the scheme of green is avoided, but the transmitting antennas are all gathered at one end, so that the distance between the transmitting antennas and the receiving antennas is increased, and a larger phase error is introduced. The invention comprehensively considers the relation between the array sparsity and the equivalent phase center error, and provides a novel MIMO sparse array arrangement mode, namely, the array is ensured to be sampled at equal intervals according to half wavelength, the problems of sampling leakage and repeated sampling are avoided, the maximum distance of a receiving and transmitting antenna is moderate, the corresponding equivalent phase center error is smaller, accurate calibration can be carried out in the imaging algorithm process, and finally, the more ideal imaging effect is obtained.
Disclosure of Invention
The present invention is directed to solving the above problems of the prior art. A millimeter wave MIMO array scanning and imaging method with equivalent half-wavelength uniform sampling is provided. The technical scheme of the invention is as follows:
a millimeter wave MIMO array scanning and imaging method with equivalent half-wavelength uniform sampling comprises the following steps:
step 101, designing an arrangement mode of a millimeter wave MIMO array with equivalent half-wavelength uniform sampling; the millimeter wave MIMO array with the equivalent half wavelength being uniformly sampled consists of Nc MIMO units, wherein each MIMO unit comprises N transmitting antennas and M receiving antennas; the MIMO unit realizes the equal and uniform sampling of half-wavelength interval in the array direction by configuring the working state of the receiving and transmitting antenna at each moment, and realizes the equal and uniform sampling of half-wavelength interval in the area with the scanning length L in the array direction;
102, designing an imaging method corresponding to MIMO array scanning; the method comprises the steps of performing millimeter wave image three-dimensional reconstruction of a target by utilizing a received target area echo signal;
further, the step 101 designs an arrangement mode of the millimeter wave MIMO array with equivalent half-wavelength uniform sampling, and specifically includes:
each MIMO unit forming the MIMO scanning array comprises N transmitting antennas and M receiving antennas, wherein the M receiving antennas are uniformly distributed, and the interval is 1 time of wavelength lambda; the N transmitting antennas are also uniformly distributed, and the interval is M times of wavelength (M lambda);
the transmitting antennas in each MIMO unit sequentially work according to the sequence numbers, all M receiving antennas simultaneously receive echo signals when each transmitting antenna works, the MIMO unit can obtain NM equivalent sampling points, and the scanning length of the covered array direction is (NM-1) lambda/2;
two adjacent MIMO units are rotationally symmetrical at 180 degrees, and the interval between the nearest receiving and transmitting antennas in the two adjacent MIMO units is half-wavelength (lambda/2); and (3) obtaining NcNM equivalent sampling points in total by the MIMO scanning array formed by Nc MIMO units, wherein the scanning length of the covered array direction is L= (NcNM-1) lambda/2.
Further, the N transmitting antennas and the M receiving antennas in each MIMO unit may be arranged in a centered alignment or arranged in a non-centered alignment according to actual conditions, i.e. left aligned or right aligned or not aligned; the transceiver antennas can be arranged in two rows, and the distance h between the two rows is determined according to practical situations, or the transceiver antennas can be arranged on the same straight line, namely, h=0.
Further, the millimeter wave MIMO array scanning and imaging method with uniformly sampling equivalent half wavelength is characterized in that the functions of receiving and transmitting antennas in the array can be interchanged, namely each MIMO unit comprises N receiving antennas and M transmitting antennas, wherein the M transmitting antennas are uniformly distributed, and the interval is 1 time of wavelength lambda; the N receiving-transmitting antennas are also uniformly distributed, and the interval is M times of wavelength (M lambda); the transmitting antennas in each MIMO unit sequentially work according to sequence numbers, all N receiving antennas simultaneously receive echo signals when each transmitting antenna works, the MIMO unit also obtains NM equivalent sampling points, and the scanning length of the covered array direction is (NM-1) lambda/2; the method for forming the MIMO array by the MIMO units is the same, and the obtained equivalent sampling points are the same.
Further, the step 102 designs the imaging method corresponding to the MIMO array scanning, which specifically includes:
(1) Millimeter wave MIMO array scanning with equivalent half-wavelength uniform sampling to obtain echo data s (r) with size of NcNMXH XF r K), wherein F is the sampling point number of the broadband frequency sweeping process at each sampling position, H is the number of times of movement in the vertical direction, r r The position of the receiving antenna is represented, k is the wave number;
(2) Calculating the equivalent phase center approximation error e of the MIMO array -jkΔR Where ΔR is the phase error factor generated by the phase center equivalence;
(3) Compensating the echo signal by using the phase center approximation error to obtain a compensated echo signal s c (r r ,k)；
(4) Compensated echo signal s c (r r K) performing azimuthal two-dimensional Fourier transform to obtainTo S (k) x ,k y ,k)；
(5) For S (k) x ,k y K) resampling to obtain a sample in (k) x ,k y ,k z ) Data with evenly distributed domains;
(6) And obtaining a three-dimensional reconstruction result of the target by utilizing three-dimensional inverse Fourier transform.
Further, the position of the target to be measured in step 102 is r o ＝(x o ,y o ,z o ) The target is characterized by the reflectivity of each pixel point, i.e. sigma (r o ) The method comprises the steps of carrying out a first treatment on the surface of the The positions of the receiving and transmitting antennas on the scanning plane are respectively defined by r t ＝(x t ,y t,z) and rr ＝(x r ,y r z) represents; the echo signal received by each receive antenna is represented as:
where k=2pi f/c is wave number, f is frequency, c is speed of light, R to and Ror Transmitting antennas to respectively
The target and the distance of the target to the receiving antenna, namely:
further, the step (2) calculates a phase center approximation error e of the MIMO array -jkΔR The method specifically comprises the following steps:
phase error factor generated by phase center equivalence
Wherein the distance from the equivalent phase center of the R receiving and transmitting antenna to the target center, d l Indicating that the first channel transceiver antenna is in the array direction, i.e. x directionIs a distance difference of (2); when the target is reconstructed by utilizing the echo obtained by MIMO array scanning, the receiving and transmitting antenna separation mode is approximated to be a single-station mode at the equivalent phase center position, and the phase center approximation error to be compensated is obtained by delta R and is e -jkΔR 。
Further, the step (3) compensates the echo signal by using the phase center approximation error to obtain a compensated echo signal s c (r r The method specifically comprises the following steps:
further, the echo signal s compensated in the step (4) c (r r K) performing azimuth two-dimensional Fourier transform to obtain S (k) x ,K y The method specifically comprises the following steps:
S(k x ,k y ,k)＝∫∫s(r r ,k)exp(-jk x x-jk y y)dxdy
wherein ,kx ,k y ,k z Representing the components of the spatial wavenumber in three coordinate directions, respectively.
Further, the step (5) is performed on the S (k x ,k y K) resampling to obtain a sample in (k) x ,k y ,k z ) The data of the domain uniform distribution specifically comprises:
further, the step (6) obtains a three-dimensional reconstruction result of the target by using three-dimensional inverse fourier transform, and specifically includes:
wherein ,
representing the inverseThree-dimensional fourier transformation.
The invention has the advantages and beneficial effects as follows:
the invention firstly provides a millimeter wave MIMO (multiple input multiple output) linear array arrangement mode which has universality and adjustable parameters and can realize half-wavelength uniform and equivalent sampling, and then provides a corresponding three-dimensional rapid reconstruction method based on a MIMO array scanning mode. The invention has the advantages of realizing high-efficiency and high-resolution imaging on the premise of greatly reducing hardware cost, and can be effectively applied to the fields of personnel security inspection, nondestructive detection, radar SAR detection imaging and the like.
The millimeter wave MIMO linear array arrangement mode with uniform and equivalent half-wavelength sampling provided by the invention has universality, the number of receiving and transmitting antennas of the MIMO array, the array length and other parameters are adjustable, the equivalent half-wavelength sampling is realized by utilizing the effective multiplexing of the receiving and transmitting antennas by utilizing the arrangement mode, and the leakage sampling and repeated sampling of any equivalent sampling point are avoided, but the number of receiving and transmitting antennas required by full-array half-wavelength sampling is greatly reduced. The three-dimensional rapid reconstruction method based on the phase error accuracy of the equivalent phase center near principle is provided by the MIMO array-based scanning mode, and high-efficiency and high-resolution imaging is realized on the premise of greatly reducing hardware cost. The method can be widely applied to the fields of personnel security inspection, nondestructive detection, radar SAR detection imaging and the like.
Step 101 designs an arrangement manner of the millimeter wave MIMO array with equivalent half-wavelength uniform sampling, namely, the specific arrangement manner of the MIMO array described in claims 2 and 3 is not easily conceivable: the number of the receiving antennas in the MIMO unit is arbitrarily adjustable, on the premise that the receiving antennas are uniformly spaced by one time of wavelength, the number of the receiving antennas determines the interval between the transmitting antennas, and then the number of the transmitting antennas can be better set (the same situation that the functions of the receiving antennas are interchanged is the same), so that the arrangement mode is very ingenious and is not easy to think; in addition, when the array is formed by the MIMO units, 180-degree rotation symmetry and the like of two adjacent units are also very ingenious. As the MIMO array parameters are adjustable, the arrangement mode of the MIMO array is equivalent to that of a type of MIMO array, and half-wavelength uniform equivalent sampling can be realized. And a corresponding high-efficiency high-resolution three-dimensional reconstruction method is provided for the MIMO sparse arrangement mode, so that the method has strong universality.
Drawings
Fig. 1 is a schematic diagram of a MIMO unit according to a preferred embodiment of the present invention, which provides a preferred embodiment of the present invention.
Fig. 2 is a schematic diagram of a MIMO array according to a preferred embodiment of the present invention.
Fig. 3 is a schematic diagram of a MIMO array with (3, 4) values according to a preferred embodiment of the present invention.
Fig. 4 is a schematic diagram of a (2, 5) MIMO array with (N, M) values according to a preferred embodiment of the present invention.
Fig. 5 is a schematic diagram of phase error analysis for the first channel according to a preferred embodiment of the present invention.
FIG. 6 is a graph of reconstructed image versus real image for a target in accordance with a preferred embodiment of the present invention.
FIG. 7 is a graph showing the image reconstructed for the second object versus the real image according to the preferred embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and specifically described below with reference to the drawings in the embodiments of the present invention. The described embodiments are only a few embodiments of the present invention.
The technical scheme for solving the technical problems is as follows:
according to the millimeter wave MIMO array scanning and imaging method for uniformly sampling equivalent half wavelength, high-efficiency and high-resolution imaging is achieved on the premise that hardware cost is greatly reduced.
Referring to fig. 1, a MIMO unit constituting a MIMO scanning array includes N transmitting antennas and M receiving antennas, wherein the M receiving antennas are uniformly arranged, and are represented by square blocks with an interval of 1 time wavelength (λ); the N transmitting antennas are also uniformly distributed and are represented by triangular blocks, and the interval is M times of wavelength (Mlambda); n transmitting antennas and M receiving antennas in each MIMO unit can be arranged in a centered manner or in a non-centered manner (such as left alignment or right alignment or non-alignment) according to actual conditions; the receiving and transmitting antennas can be distributed in two rows (the distance h between the two rows is determined according to the actual situation), and can also be distributed on the same straight line (i.e. h=0); the transmitting antennas in each MIMO unit sequentially work according to sequence numbers, all M receiving antennas simultaneously receive echo signals when each transmitting antenna works, the MIMO unit can obtain NM equivalent sampling points, the scanning length of the covered array direction is (NM-1) lambda/2, the center of connection of the receiving and transmitting antennas is the position of the equivalent phase center sampling point, and the interval between two adjacent points is lambda/2.
Referring to fig. 2, the millimeter wave MIMO array with equivalent half-wavelength uniform sampling is composed of Nc MIMO units, two adjacent MIMO units are rotationally symmetrical at 180 ° with each other, and the interval between the nearest receiving and transmitting antennas in the two adjacent MIMO units is λ/2; the working modes of the receiving and transmitting antennas of each MIMO unit are the same, and the MIMO scanning array formed by Nc MIMO units is totally provided with NcNM equivalent sampling points, and the scanning length of the array direction which can be covered is L= (NcNM-1) lambda/2.
The arrangement mode of the millimeter wave MIMO array with the equivalent half-wavelength uniformly sampled comprises a plurality of variable parameters, such as the number Nc of MIMO units, the number N of transmitting antennas in each MIMO unit, the number M of receiving antennas, the wavelength lambda, the row spacing h of receiving and transmitting antennas and the like. For better understanding, FIG. 3 shows an array layout diagram for (N, M) values of (3, 4). FIG. 4 shows an array layout for (N, M) values of (2, 5). In practical application, the value of (N, M) can be freely defined according to the situation.
The method comprises the steps that a target scene is scanned by using an MIMO array, half-wavelength interval equivalent uniform sampling is realized by controlling the working state of a receiving and transmitting antenna in an array at each moment in an area with a scanning length L in the array direction, the MIMO array is uniformly moved at half-wavelength intervals after the electronic scanning in the array direction is completed each time in the vertical array direction, the number of times H of movement in the vertical direction is determined by the actual scanning scene size, and NcNM multiplied by H sampling positions on a two-dimensional scanning plane can be obtained in the mode; the sampling point number of the broadband sweep process at each sampling position is F, and the size of the complete echo data s for completing one target sweep is NcNM multiplied by H multiplied by F.
In addition to the design of the arrangement mode of the millimeter wave MIMO array comprising equivalent half-wavelength uniform sampling, the invention also comprises an imaging method corresponding to MIMO array scanning.
The specific imaging steps are as follows:
(1) Millimeter wave MIMO array scanning with equivalent half-wavelength uniform sampling to obtain a millimeter wave MIMO array with a size of
Echo data s (r) of ncnm×h×f r ,k)；
(2) Calculating the phase center approximation error e of the MIMO array -jkΔR ；
Referring to fig. 5, because of the phase error factor generated by the phase center equivalent
wherein dl The distance difference of the first channel transmitting/receiving antenna in the array direction (x direction) is shown. When the MIMO array scanning is utilized to obtain the reconstruction of the echo to the target, the receiving and transmitting antenna separation mode is approximated to be a single-station mode at the equivalent phase center position, and the phase center approximation error to be compensated is obtained by delta R and is e -jkΔR 。
(3) Compensating the echo signal by using the phase center approximation error to obtain a compensated echo signal s c (r r ,k)；
(4) For the compensated echo signal s c (r r K) performing azimuth two-dimensional Fourier transform to obtain S (k) x ,k y ,k)；
s(k x ,k y ,k)＝∫∫s(r r ,k)exp(-jk x x-jk y y)dxdy
(5) For S (k) x ,k y K) resampling to obtain a sample in (k) x ,k y ,k z ) Data with evenly distributed domains;
(6) And obtaining a three-dimensional reconstruction result of the target by utilizing three-dimensional inverse Fourier transform.
The invention will be further illustrated by the following two specific examples, with the understanding that the present invention is clear.
Embodiment one:
referring to fig. 4, the MIMO array layout is performed, n=3, m=4, nc=10, the equivalent sampling point number ncnm=120, the total number of transmit-receive antennas is (n+m) nc=70, the total number of transmit-receive antennas required for the corresponding half-wavelength full array is 240, and the total number of transmit-receive antennas required in this embodiment is 7/24 of the corresponding full array. The row spacing h=10mm of the receiving and transmitting antenna, the frequency range of the millimeter wave broadband linear frequency modulation signal is 60-64GHz, the frequency dimension sampling point number F=64, the half wavelength lambda/2=2.5mm is obtained by taking the initial frequency of 60GHz as an example, the equivalent sampling length (NM-1) lambda/2=27.5mm of the MIMO unit, and the scanning coverage length (NcNM-1) lambda/2=297.5mm of the MIMO array. Scanning an object 0.35m in front of it, the imaging size being 0.3m×0.3m, the vertical array direction is repeatedly shifted by half a wavelength for the number of times h=120.
Embodiment two:
referring to fig. 5, a MIMO array layout is performed, n=2, m=5, nc=12, the equivalent sampling point number ncnm=120, the total number of transmit-receive antennas is (n+m) nc=84, the total number of transmit-receive antennas required for the corresponding half-wavelength full array is 240, and the total number of transmit-receive antennas required in this embodiment is 7/20 of the total number of transmit-receive antennas required for the corresponding full array. The row spacing h=10mm of the receiving and transmitting antenna, the frequency range of the millimeter wave broadband linear frequency modulation signal is 60-64GHz, the frequency dimension sampling point number F=64, the half wavelength lambda/2=2.5mm is obtained by taking the initial frequency of 60GHz as an example, the equivalent sampling length (NM-1) lambda/2=22.5mm of the MIMO unit, and the scanning coverage length (NcNM-1) lambda/2=297.5mm of the MIMO array. Scanning an object 0.35m in front of it, the imaging size being 0.3m×0.3m, the vertical array direction is repeatedly shifted by half a wavelength for the number of times h=120.
The two embodiments are the same in working mode, and the scanning of the tested object is completed by the electric scanning in the array direction and the mechanical scanning in the vertical array direction uniformly at half-wavelength intervals. In the scanning process using the MIMO array, the transmitting antenna transmits a wideband chirp signal, and the echo signal scattered by the object to be measured is received by the receiving antenna to obtain echo data s (r r K) is ncnm×h×f=120×120×64. Finally, the echo data is processed and imaged by using the imaging method of the embodiment.
Two different targets were tested in both examples, one target was a resolution plate engraved with metallic stripes of different widths with a copper-clad plate, as shown in fig. 6 (a), each stripe had a length of 30mm, 4 groups of stripes in the vertical direction, 5 groups of stripes in the horizontal direction, 5 groups of stripes in the diagonal direction, 3 stripes were included in each group (the widest 10mm group included only two stripes), the stripe intervals in the groups of 5 stripes in the horizontal direction were 3mm,4mm,5mm,7mm,10mm in order from small to large, and the stripe intervals in the groups of 4 stripes in the vertical direction were 3mm,4mm,5mm,7mm in order from small to large; the stripe interval in the 5 groups of stripes in the diagonal direction is 3mm,4mm,5mm and 7mm from small to large in sequence; the second object is a paper box with scissors and fruit knives inside, as shown in fig. 7 (a), the photo is taken after the box is opened, and the box is in a closed state during testing.
The sampled echo data is processed and imaged by utilizing the six steps of the imaging method of the embodiment. Specifically, the imaging results for the resolution plate target and the scissors and fruit knives within the carton are shown in fig. 6 (b) and 7 (b), respectively. It can be seen from fig. 6 (b) that the narrowest 3mm stripe of the system is also clearly distinguishable; the scissors and fruit knives in fig. 7 (b) are clearly visible. The ideal results of the two actually measured targets also illustrate the effectiveness and practicality of millimeter wave MIMO array scanning and imaging methods thereof for equivalent half-wavelength uniform sampling in the two embodiments described above.
In summary, the millimeter wave MIMO array scanning and imaging method for uniformly sampling equivalent half wavelength provided by the invention provides a generalized MIMO array arrangement mode and an efficient three-dimensional imaging method. The effective multiplexing of the receiving and transmitting antennas is utilized to realize equivalent half-wavelength sampling, the number of the receiving and transmitting antennas required by full-array half-wavelength sampling is greatly reduced, and the leakage sampling and repeated sampling of any equivalent sampling point do not exist. Millimeter wave scanning is carried out on a detected target in an array direction electric scanning and vertical array direction mechanical scanning mode, millimeter wave echoes scattered by the target are sequentially processed through 6 steps of an imaging method, and finally a high-efficiency and high-resolution three-dimensional millimeter wave image is obtained. The method can be widely applied to the fields of personnel security inspection, nondestructive detection, radar SAR detection imaging and the like.
The system, apparatus, module or unit set forth in the above embodiments may be implemented in particular by a computer chip or entity, or by a product having a certain function.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article or apparatus that comprises the element.
The above examples should be understood as illustrative only and not limiting the scope of the invention. Various changes and modifications to the present invention may be made by one skilled in the art after reading the teachings herein, and such equivalent changes and modifications are intended to fall within the scope of the invention as defined in the appended claims.
Claims (10)
1. The millimeter wave MIMO array scanning and imaging method with equivalent half-wavelength uniform sampling is characterized by comprising the following steps:
step 101, designing an arrangement mode of a millimeter wave MIMO array with equivalent half-wavelength uniform sampling; the millimeter wave MIMO array with the equivalent half wavelength being uniformly sampled consists of Nc MIMO units, wherein each MIMO unit comprises N transmitting antennas and M receiving antennas; the MIMO unit realizes the equal and uniform sampling of half-wavelength interval in the array direction by configuring the working state of the receiving and transmitting antenna at each moment, and realizes the equal and uniform sampling of half-wavelength interval in the area with the scanning length L in the array direction;
102, designing an imaging method corresponding to MIMO array scanning; and performing millimeter wave image three-dimensional reconstruction of the target by using the received echo signals of the target area.
2. The method for scanning and imaging an equivalent half-wavelength uniformly sampled millimeter wave MIMO array according to claim 1, wherein the step 101 designs an arrangement mode of the equivalent half-wavelength uniformly sampled millimeter wave MIMO array, and specifically includes:
each MIMO unit forming the MIMO scanning array comprises N transmitting antennas and M receiving antennas, wherein the M receiving antennas are uniformly distributed, and the interval is 1 time of wavelength lambda; the N transmitting antennas are also uniformly distributed, and the interval is M times of wavelength (M lambda);
the transmitting antennas in each MIMO unit sequentially work according to the sequence numbers, all M receiving antennas simultaneously receive echo signals when each transmitting antenna works, the MIMO unit can obtain NM equivalent sampling points, and the scanning length of the covered array direction is (NM-1) lambda/2;
two adjacent MIMO units are rotationally symmetrical at 180 degrees, and the interval between the nearest receiving and transmitting antennas in the two adjacent MIMO units is half-wavelength (lambda/2); and (3) obtaining NcNM equivalent sampling points in total by the MIMO scanning array formed by Nc MIMO units, wherein the scanning length of the covered array direction is L= (NcNM-1) lambda/2.
3. The millimeter wave MIMO array scanning and imaging method for uniformly sampling equivalent half wavelength according to claim 2, wherein N transmitting antennas and M receiving antennas in each MIMO unit can be arranged in a centered alignment or in a non-centered arrangement according to actual conditions, namely left alignment or right alignment or non-alignment; the receiving and transmitting antennas can be distributed in two rows, and the distance h between the two rows is determined according to actual conditions, or the receiving and transmitting antennas can be distributed on the same straight line, namely h=0;
the functions of the receiving and transmitting antennas in the array can be interchanged, namely each MIMO unit comprises N receiving antennas and M transmitting antennas, wherein the M transmitting antennas are uniformly distributed and the interval is 1 time of wavelength lambda; the N receiving-transmitting antennas are also uniformly distributed, and the interval is M times of wavelength (M lambda); the transmitting antennas in each MIMO unit sequentially work according to sequence numbers, all N receiving antennas simultaneously receive echo signals when each transmitting antenna works, the MIMO unit also obtains NM equivalent sampling points, and the scanning length of the covered array direction is (NM-1) lambda/2; the method for forming the MIMO array by the MIMO units is the same, and the obtained equivalent sampling points are the same.
4. A millimeter wave MIMO array scanning and imaging method for uniformly sampling an equivalent half wavelength according to claim 2 or 3, wherein said step 102 is a step of designing an imaging method corresponding to the MIMO array scanning, and specifically comprises:
(1) Millimeter wave MIMO array scanning with equivalent half-wavelength uniform sampling to obtain echo data s (r) with size of NcNMXH XF r K), wherein F is the sampling point number of the broadband frequency sweeping process at each sampling position, H is the number of times of movement in the vertical direction, r r The position of the receiving antenna is represented, k is the wave number;
(2) Calculating the equivalent phase center approximation error e of the MIMO array -jkΔR Where ΔR is the phase error factor generated by the phase center equivalence;
(3) Compensating the echo signal by using the phase center approximation error to obtain a compensated echo signal s c (r r ,k)；
(4) Compensated echo signal s c (r r K) performing azimuth two-dimensional Fourier transform to obtain S (k) x ,k y ,k)；
(5) For S (k) x ,k y K) resampling to obtain a sample in (k) x ,k y ,k z ) Data with evenly distributed domains;
(6) And obtaining a three-dimensional reconstruction result of the target by utilizing three-dimensional inverse Fourier transform.
5. The method for uniformly sampling millimeter wave MIMO array scanning and imaging according to claim 4, wherein r is used for the position of the target to be measured in step 102 o ＝(x o ,y o ,z o ) The target is characterized by the reflectivity of each pixel point, i.e. sigma (r o ) The method comprises the steps of carrying out a first treatment on the surface of the The positions of the receiving and transmitting antennas on the scanning plane are respectively defined by r t ＝(x t ,y t,z) and rr ＝(x r ,y r z) represents; the echo signal received by each receive antenna is represented as:
where k=2pi f/c is wave number, f is frequency, c is speed of light, R to and Ror The distances of the transmitting antenna to the target and the target to the receiving antenna, respectively, are:
6. the method for scanning and imaging an equivalent half-wavelength uniformly sampled millimeter wave MIMO array according to claim 5, wherein said step (2) calculates the phase center approximation error e of the MIMO array -jkΔR The method specifically comprises the following steps:
phase error factor generated by phase center equivalence
Wherein the distance from the equivalent phase center of the R receiving and transmitting antenna to the target center, d l The distance difference of the first channel transceiver antenna in the array direction, namely the x direction is shown; when the target is reconstructed by utilizing the echo obtained by MIMO array scanning, the receiving and transmitting antenna separation mode is approximated to be a single-station mode at the equivalent phase center position, and the phase center approximation error to be compensated is obtained by delta R and is e -jkΔR 。
7. The method for scanning and imaging an equivalent half-wavelength uniformly sampled millimeter wave MIMO array according to claim 6, wherein said step (3) compensates the echo signal by using the phase center approximation error to obtain a compensated echo signal s c (r r The method specifically comprises the following steps:
8. the method for scanning and imaging an equivalent half-wavelength uniformly sampled millimeter wave MIMO array according to claim 7, wherein said step (4) compensates the echo signal s c (r r K) performing azimuth two-dimensional Fourier transform to obtain S (k) x ,k y The method specifically comprises the following steps:
S(k x ,k y ,k)＝∫∫s(r r ,k)exp(-jk x x-jk y y)dxdy
wherein ,kx ,k y ,k z Representing the components of the spatial wavenumber in three coordinate directions, respectively.
9. The method for scanning and imaging an equivalent half-wavelength uniformly sampled millimeter wave MIMO array according to claim 8, wherein said step (5) comprises the steps of x ,k y K) resampling to obtain a sample in (k) x ,k y ,k z ) The data of the domain uniform distribution specifically comprises:
10. the millimeter wave MIMO array scanning and imaging method for uniformly sampling equivalent half wavelength according to claim 9, wherein the step (6) obtains a three-dimensional reconstruction result of the target by using three-dimensional inverse fourier transform, and specifically comprises:
wherein ,
representing an inverse three-dimensional fourier transform. />
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