CN112965061A - Imaging system and imaging method based on cylindrical surface MIMO area array - Google Patents

Imaging system and imaging method based on cylindrical surface MIMO area array Download PDF

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CN112965061A
CN112965061A CN202011602665.1A CN202011602665A CN112965061A CN 112965061 A CN112965061 A CN 112965061A CN 202011602665 A CN202011602665 A CN 202011602665A CN 112965061 A CN112965061 A CN 112965061A
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mimo
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CN112965061B (en
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李世勇
王硕光
邢光楠
赵国强
孙厚军
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Beijing Institute of Technology BIT
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/887—Radar or analogous systems specially adapted for specific applications for detection of concealed objects, e.g. contraband or weapons
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    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
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Abstract

The imaging system comprises a plurality of arc MIMO linear arrays and a plurality of bus MIMO linear arrays, wherein the plurality of arc MIMO linear arrays and the plurality of bus MIMO linear arrays are expanded into a two-dimensional cylindrical MIMO planar array; the transmitting antennas are distributed in the arc MIMO linear array direction at equal angular intervals of full sampling/under sampling, and distributed in the bus MIMO linear array direction at equal angular intervals of under sampling/full sampling; the receiving antennas are distributed in the arc MIMO linear array direction at equal angular intervals of under-sampling/full-sampling, and distributed in the bus MIMO linear array direction at equal intervals of full-sampling/under-sampling. The system provides a corresponding imaging algorithm, can realize more uniform coverage of antenna beams on a target area of a detected human body while the detected human body is not damaged, obtains higher imaging resolution, reduces manufacturing cost, is easy to arrange, has strong applicability to application environment, and realizes rapid human body security inspection in the environments of airports, subways, railway stations and the like.

Description

Imaging system and imaging method based on cylindrical surface MIMO area array
Technical Field
The invention belongs to the technical field of security inspection, and particularly relates to an imaging system and an imaging method based on a cylindrical surface MIMO area array.
Background
Public safety issues have attracted considerable attention in the international society in recent years due to the occurrence of violent criminal events and terrorist events. At present, places with dense personnel, such as subways, squares, airports and the like, are the main places where attack events occur. Therefore, the security inspection and safety problems in public places also bring great attention to all the social circles, and higher requirements are also put forward on the characteristics of the security inspection system, such as accuracy, instantaneity, intellectualization and the like.
Human body security inspection always faces some technical difficulties: and traditional safety detection equipment such as a metal detector and an X-ray imaging device. The metal detector can detect metal contraband carried by a human body, but can not detect non-metal contraband objects such as ceramic knives and powder bombs, and can not distinguish the types of the contraband objects and realize accurate positioning; although the X-ray imaging device can carry out high-resolution imaging on the human body carrying hidden objects, the X-ray has ionization property and is not suitable for human body security check imaging.
The millimeter wave is used for security inspection imaging, is a novel security inspection technology appearing in recent years, has the advantages of high safety, good reliability, difference in electromagnetic scattering characteristics of different materials and the like, and becomes the mainstream development direction of the current human body security inspection technology.
Disclosure of Invention
In view of this, the present disclosure provides an imaging system and an imaging method based on a cylindrical MIMO area array, which can cover a target area of a detected human body more uniformly without damaging the detected human body, improve security inspection resolution, reduce manufacturing cost, are easy to arrange, have strong applicability to application environments, and implement rapid human body security inspection in environments such as airports, subways, train stations, and the like.
According to an aspect of the present invention, an imaging system based on a cylindrical MIMO area array is provided, the system comprising: the MIMO linear array comprises a plurality of arc MIMO linear arrays and a plurality of bus MIMO linear arrays, wherein the arc MIMO linear arrays and the bus MIMO linear arrays are expanded into a two-dimensional cylindrical surface MIMO area array; the arc MIMO linear array and the bus MIMO linear array comprise a transmitting antenna and a receiving antenna;
the transmitting antennas are distributed in the arc MIMO linear array direction at equal angular intervals of full sampling/under sampling, and distributed in the bus MIMO linear array direction at equal angular intervals of under sampling/full sampling;
the receiving antennas are distributed in the arc MIMO linear array direction at equal angular intervals of under-sampling/full-sampling, and distributed in the bus MIMO linear array direction at equal angular intervals of full-sampling/under-sampling.
In a possible implementation manner, when the transmitting antennas are distributed in the arc MIMO linear array direction at equal angular intervals in a full-sampling manner, the transmitting antennas are distributed in the bus MIMO linear array direction at equal angular intervals in an under-sampling manner; receiving antenna is in pitch arc MIMO linear array direction is angular interval distribution such as undersampling when generating line MIMO linear array direction is angular interval distribution such as full sampling, include:
the transmitting antennas are distributed between two adjacent receiving antennas at equal angle intervals along the arc direction of the arc MIMO linear array.
The receiving antennas are distributed at equal intervals between two adjacent transmitting antennas along the bus direction of the bus MIMO linear array.
In a possible implementation manner, when the transmitting antennas are distributed in the arc MIMO linear array direction at equal angular intervals under sampling, the transmitting antennas are distributed in the bus MIMO linear array direction at equal angular intervals under full sampling; receiving antenna is in pitch arc MIMO linear array direction is angle interval distribution such as full sampling when generating line MIMO linear array direction is angular interval distribution such as undersampling, include:
the receiving antennas are distributed between two adjacent transmitting antennas at equal angle intervals along the arc direction of the arc MIMO linear array.
The transmitting antennas are distributed at equal intervals between two adjacent receiving antennas along the bus direction of the bus MIMO linear array.
In one possible implementation, the transmitting antenna transmits the signal in a time-sharing manner;
when each transmitting antenna transmits a radio frequency signal, all receiving antennas simultaneously receive reflected echo signals.
In one possible implementation, the echo signal is a five-dimensional vector s (k, θ)T,θR,zT,zR) Where k is the dimension of the transmitted and received wave number, thetaTFor transmitting antenna position in arc direction, thetaRIs the position of the receiving antenna in the direction of the arc, zTFor transmitting antenna position in height direction, zRIs the receiving antenna position in the elevation direction.
According to another aspect of the present disclosure, an imaging method based on an arc MIMO area array is provided, where the method employs the above-mentioned imaging system, and the method includes:
the echo signal s (k, theta)T,θR,zT,zR) At thetaTDirection, thetaRFourier transform is respectively carried out in the direction and the z direction to obtain
Figure BDA0002869258370000031
And to
Figure BDA0002869258370000032
Performing matched filtering, wherein xiT、ξR、
Figure BDA0002869258370000033
And
Figure BDA0002869258370000034
are each thetaTDirection, thetaRFourier transform results of direction and z direction;
performing inverse Fourier transform on the matched and filtered signals in the angular frequency direction, and performing dimensionality raising and decoupling on the dimension k of the receiving and transmitting wave number to obtain
Figure BDA0002869258370000035
Wherein the content of the first and second substances,
Figure BDA0002869258370000036
and
Figure BDA0002869258370000037
respectively is the wave number dimensions of the transmitting antenna direction and the receiving antenna direction of the receiving and transmitting beam dimension k under the cylindrical coordinates;
to pair
Figure BDA0002869258370000038
Two-dimensional interpolation is carried out twice to obtain
Figure BDA0002869258370000039
Reducing the dimension according to the dimension k of the receiving and transmitting wave number to obtain G (k)x,ky,kz) Wherein k isx、kyAnd kzThe components of the receiving and transmitting wave number dimension k in the x direction, the y direction and the z direction under a rectangular coordinate system are respectively;
g (k) isx,ky,kz) And performing three-dimensional inverse Fourier transform to obtain an imaging result g (x, y, z) based on the cylindrical MIMO area array.
In one possible implementation, the pair
Figure BDA00028692583700000310
Two-dimensional interpolation is carried out twice to obtain
Figure BDA00028692583700000311
The method comprises the following steps:
circulation of
Figure BDA00028692583700000312
θR、
Figure BDA00028692583700000313
And
Figure BDA00028692583700000314
variables, to which each cycle is coupledThe above-mentioned
Figure BDA00028692583700000315
And thetaTPerforming two-dimensional interpolation to obtain
Figure BDA00028692583700000316
Cycling said kxT、kyT、
Figure BDA00028692583700000317
And
Figure BDA00028692583700000318
variable, for said k in each cycleRAnd thetaRPerforming two-dimensional interpolation to obtain
Figure BDA00028692583700000319
Wherein the content of the first and second substances,
Figure BDA00028692583700000320
and
Figure BDA00028692583700000321
the wave number dimension in the direction of the transmitting antenna is respectively projected in the x direction and the y direction under a rectangular coordinate system;
Figure BDA00028692583700000322
and
Figure BDA00028692583700000323
the wave number dimension in the direction of the receiving antenna is the projection in the x direction and the y direction respectively under a rectangular coordinate system.
The imaging system and the imaging method based on the cylindrical MIMO area array work in a time-sharing mode through the transmitting channel of each transmitting antenna of the cylindrical MIMO area array, when the transmitting channel of each transmitting antenna works, the receiving channels of all the receiving antennas work simultaneously, data acquisition of a target imaging area is completed, the detected human body can be prevented from being damaged, compared with a planar array, the imaging system can uniformly cover the target area of the detected human body, a good three-dimensional imaging effect can be quickly obtained, the imaging system is suitable for millimeter wave human body security inspection imaging, higher security inspection resolution is obtained, the manufacturing cost is reduced, the arrangement is easy, the applicability of an application environment is high, and quick human body security inspection is realized.
Other features and aspects of the present disclosure will become apparent from the following detailed description of exemplary embodiments, which proceeds with reference to the accompanying drawings.
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The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments, features, and aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure.
Fig. 1 shows a schematic structural diagram of an imaging system based on a cylindrical MIMO area array according to an embodiment of the present disclosure;
FIG. 2 shows a flow chart of a cylindrical MIMO area array based imaging method according to an embodiment of the present disclosure;
FIG. 3 is a schematic diagram illustrating the ascending and descending dimensions of the transmit-receive wavenumber dimension k according to an embodiment of the present disclosure;
figure 4a illustrates a two-dimensional imaging result of an azimuth-elevation direction of a cylindrical MIMO area array based imaging system according to an embodiment of the present disclosure;
figure 4b illustrates the results of two-dimensional imaging in azimuth-distance directions for a cylindrical MIMO area array based imaging system according to an embodiment of the present disclosure;
figure 4c illustrates a height-distance two-dimensional imaging result of a cylindrical MIMO area array based imaging system according to an embodiment of the present disclosure;
figure 4d shows a cross-sectional pictorial illustration of the imaging result azimuth of a cylindrical MIMO area array based imaging system, in accordance with an embodiment of the present disclosure;
figure 4e shows a cross-sectional view diagram view of an imaging result range direction for a cylindrical MIMO area array based imaging system, in accordance with an embodiment of the present disclosure;
figure 4f shows a diagrammatic representation of a cross-sectional view in elevation of the imaging results of a cylindrical MIMO area array based imaging system in accordance with an embodiment of the present disclosure;
Detailed Description
Various exemplary embodiments, features and aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers can indicate functionally identical or similar elements. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a better understanding of the present disclosure. It will be understood by those skilled in the art that the present disclosure may be practiced without some of these specific details. In some instances, methods, means, elements and circuits that are well known to those skilled in the art have not been described in detail so as not to obscure the present disclosure.
The invention provides an imaging system and an imaging method based on a cylindrical surface MIMO (Multiple-Input Multiple-output) area array, aiming at the requirements of low cost and high quality imaging in millimeter wave security inspection. Compared with a plane aperture, the cylindrical aperture of the cylindrical MIMO area array can enable the beam of the receiving and transmitting antenna unit to face the target imaging position, and the target area is covered more uniformly. The cylindrical MIMO area array has a larger aperture, so that high resolution can be guaranteed, the number of the receiving and transmitting antenna units is reduced, and the manufacturing cost of the cylindrical MIMO area array is reduced. In order to realize rapid imaging, the invention adopts a rapid three-dimensional near-field imaging algorithm based on a cylindrical MIMO area array based on the traditional wk algorithm, has high resolution in a high distance direction, an azimuth direction and a height direction, and has the advantages of low time complexity, low cost and rapid security imaging.
Fig. 1 shows a schematic structural diagram of an imaging system based on a cylindrical MIMO area array according to an embodiment of the present disclosure.
As shown in fig. 1, the system may include: the MIMO antenna array comprises a plurality of arc MIMO linear arrays (horizontal MIMO linear arrays in fig. 1) and a plurality of bus MIMO linear arrays (vertical MIMO linear arrays in fig. 1), wherein the arc MIMO linear arrays and the bus MIMO linear arrays respectively comprise transmitting antennas (black solid circles in fig. 1) and receiving antennas (white solid circles in fig. 1), and the plurality of arc MIMO linear arrays and the plurality of bus MIMO linear arrays are expanded to form a two-dimensional cylindrical MIMO area array.
The transmitting antennas are distributed at equal angular intervals in the direction of the arc MIMO linear array, namely under-sampling (the distance between the transmitting antennas is larger and does not accord with the Nyquist sampling condition), and are distributed at equal intervals in the direction of the bus MIMO linear array, namely full-sampling (the distance between the transmitting antennas is smaller and accords with the Nyquist sampling condition); the receiving antennas are distributed at equal angular intervals in the direction of the arc MIMO linear array in a full sampling mode (the distance between the receiving antennas is small and the nyquist sampling condition is met), and distributed at equal intervals in the direction of the bus MIMO linear array in an undersampling mode (the distance between the receiving antennas is large and the nyquist sampling condition is not met).
The receiving antennas are distributed at equal angle intervals along the arc direction of the arc MIMO linear array between two adjacent transmitting antennas, and the transmitting antennas are distributed at equal intervals along the bus direction of the bus MIMO linear array between two adjacent receiving antennas, wherein the receiving antennas can be overlapped with the transmitting antennas, can be set according to specific requirements, and are not limited one by one. As shown in fig. 1, since the spacing of the receiving antennas in the direction of the arc MIMO line array is smaller and the spacing of the transmitting antennas in the direction of the bus MIMO line array is smaller, the receiving antennas are not shown in the direction of the arc MIMO line array in fig. 1, and the transmitting antennas are not shown in the direction of the bus MIMO line array in fig. 1. The intersection point position of the arc MIMO linear array and the linear MIMO linear array is an antenna for transmitting and receiving.
Of course, the transmitting antennas can also be distributed in the arc MIMO linear array direction at equal angular intervals in a full sampling mode, and in the bus MIMO linear array direction at equal angular intervals in an under sampling mode; the receiving antennas can be distributed in the arc MIMO linear array direction at equal angular intervals in an undersampling mode, and are distributed in the bus MIMO linear array direction at equal angular intervals in a full-sampling mode. The transmitting antennas are distributed at equal angle intervals between two adjacent receiving antennas along the arc direction of the arc MIMO linear array; the receiving antennas are distributed at equal intervals between two adjacent transmitting antennas along the bus direction of the bus MIMO linear array, and certainly, the receiving antennas can also be overlapped with the transmitting antennas and can be set according to specific requirements, and the receiving antennas are not limited one by one here. In practical applications, the angles of the transmitting antenna and the receiving antenna may be set according to specific requirements, and are not limited herein.
In one example, the transmit antennas transmit the radio frequency signals in a time sharing manner; when each transmitting antenna transmits a radio frequency signal, all receiving antennas simultaneously receive reflected echo signals.
As shown in fig. 1, when the imaging system works, the transmitting channels of the transmitting antennas work in sequence in a time-sharing manner, and when the transmitting channel of each transmitting antenna works, the receiving channels of all the receiving antennas work simultaneously until all the transmitting channels of the transmitting antennas are traversed. The receiving antenna of the cylindrical MIMO area array can simultaneously receive echo signals reflected by a detected target, baseband complex signals of the echo signals are obtained after the echo signals are processed by the signal processing system, and imaging is carried out by utilizing the near field imaging algorithm. Wherein the echo signal is a four-dimensional vector s (k, theta)T,θR,zT,zR) Where k is the transmit-receive wavenumber dimension, θTFor transmitting antenna position in arc direction, thetaRIs the position of the receiving antenna in the direction of the arc, zTFor transmitting antenna position in height direction, zRIs the receiving antenna position in the elevation direction. Therefore, the beam direction of the transmitting and receiving antenna is enabled to face the target imaging area in a cylindrical MIMO area array mode, and the problem that the imaging image quality is deteriorated due to the fact that the gain of the transmitting and receiving antenna in the non-line-of-sight direction is reduced under the plane aperture is solved.
The imaging system based on the cylindrical surface MIMO area array comprises a plurality of arc MIMO linear arrays and a plurality of bus MIMO linear arrays, wherein the arc MIMO linear arrays and the bus MIMO linear arrays are expanded into a two-dimensional cylindrical surface MIMO area array; the arc MIMO linear array and the bus MIMO linear array comprise a transmitting antenna and a receiving antenna; the transmitting antennas are distributed in the arc MIMO linear array direction at equal angular intervals of full sampling/under sampling, and distributed in the bus MIMO linear array direction at equal angular intervals of under sampling/full sampling; the receiving antennas are distributed in the arc MIMO linear array direction at equal angular intervals of undersampling/full sampling, and distributed in the bus MIMO linear array direction at equal angular intervals of full sampling/undersampling. The system can uniformly cover the target area of the detected human body while not damaging the detected human body, improves the security inspection resolution, reduces the manufacturing cost, is easy to arrange, has strong applicability to the application environment, and realizes rapid human body security inspection in the environments of airports, subways, railway stations and the like.
The imaging system of the cylindrical MIMO area array can realize data acquisition of a target area of a detected human body by traversing all transmitting channels of transmitting antennas, and acquire three-dimensional imaging data of the target area. When the three-dimensional imaging data of the detected target area is processed, the processing can be carried out according to the cylindrical aperture MIMO, so that the three-dimensional resolution of an imaging system of a cylindrical MIMO area array can be determined after the imaging system is set.
A three-dimensional resolution determination process for processing three-dimensional imaging data of a target region to be inspected in accordance with a cylindrical MIMO array will be described as an example. Wherein the three-dimensional resolution of the imaging system includes an azimuth resolution, an elevation resolution, and a range resolution.
The azimuthal resolution is determined by the range of spatial frequencies, i.e.
Figure BDA0002869258370000081
The transmit-receive dimension k can be split into the dimensions of the transmit antennas and the dimensions of the receive antennas in each direction, i.e. the transmit and receive dimensions k are
Figure BDA0002869258370000082
Then
Figure BDA0002869258370000083
Let Θ be assumedHIs the maximum opening angle, k, corresponding to the arc MIMO linear array aperturecRepresenting the wave number corresponding to the center frequency of the transmitted signal, then
Figure BDA0002869258370000084
The three-dimensional resolution of the imaging system is the same as the resolution of a full-array single-station scene, i.e. the result is
Figure BDA0002869258370000085
If theta is supposed to bezThe maximum field angle corresponding to the height direction array aperture of the arc MIMO linear array is represented, the height direction array is a full array single station scene, and the height direction resolution is as follows:
Figure BDA0002869258370000086
if B denotes the imaging system bandwidth, C is the beam, and the range-wise resolution is determined by the imaging system bandwidth, then the range-wise resolution is:
Figure BDA0002869258370000087
through the above calculation, in a near-field security inspection imaging scene, a large array face aperture of the cylindrical MIMO area array (that is, a large length direction and a large height direction of the arc MIMO linear array) can be ensured, so that a horizontal dimension (azimuth direction) and a vertical dimension (height direction) of three-dimensional imaging of the imaging system based on the arc MIMO area array can reach a high resolution, and a high distance dimension (distance direction) resolution is realized, thereby realizing three-dimensional high-resolution imaging of a certain target area of a detected human body. The high-resolution and high-speed security inspection imaging is realized by a high-speed imaging algorithm based on the transmitting-receiving dimensions (wave numbers) of the transmitting-receiving antenna.
The following description will be given by taking as an example a determination process according to a three-dimensional imaging algorithm for a target region to be detected based on an arc MIMO area array.
Fig. 2 shows a flowchart of an imaging method based on an arc MIMO area array according to another embodiment of the present disclosure. As shown in fig. 2, the method may include:
step S1: the echo signal s (k, theta)T,θR,zT,zR) At thetaTDirection, thetaRFourier transform is respectively carried out in the direction and the z direction to obtain
Figure BDA0002869258370000088
And to
Figure BDA0002869258370000089
Performing matched filtering, wherein xiT、ξR、
Figure BDA0002869258370000091
And
Figure BDA0002869258370000092
are each thetaTDirection, thetaRThe fourier transform results of the directions and z-direction.
As shown in fig. 1, in the standard cylindrical coordinate system, the reflection coefficient at a certain point in the imaging target area is g (x, y, z), and the transmitting antenna position of the cylindrical MIMO area array can be represented as (R, θ)T,zT) The position of the receiving antenna at a certain position can be expressed as (R, theta)R,zR) Then the echo signal s (k, theta) of a certain frequency signal transmitted by a transmitting antenna at a certain positionT,θR,zT,zR) Can be expressed as: s (k, θ)T,θR,zT,zR)＝∫∫∫g(x,y,z)exp(-jkRT)exp(-jkRR) dxdydz, where k is the transmit-receive dimension (wave number), RTAnd RRRespectively representing the distances from the measured target point to the transmitting antenna and the receiving antenna.
If the radius of the cylinder formed by the arc MIMO linear array is R0Then R is in rectangular coordinate systemTAnd RRRespectively as follows:
Figure BDA0002869258370000093
Figure BDA0002869258370000094
in order to ensure that the water-soluble organic acid,
Figure BDA0002869258370000095
Figure BDA0002869258370000096
then the following results are obtained:
Figure BDA0002869258370000097
then, the echo signal s (k, θ)T,θR,zT,zR) Fourier transform in the z direction yields:
Figure BDA0002869258370000098
phi in the general formulaTPhi and phiRIs expressed with respect to thetaTAnd thetaRIs expressed as:
Figure BDA0002869258370000099
whereinTAndRrespectively represent the pair thetaTAnd thetaRIs performed.
The echo signal s (k, theta) of a certain frequency signal transmitted by a transmitting antenna at a certain position can be obtained through the processT,θR,zT,zR) At zT，zRFourier transform results in the direction, and then separately combining the signals
Figure BDA00028692583700000910
At thetaTDirection and thetaRThe direction is subjected to Fourier transform, and the convolution property (multiplication of time domain convolution and corresponding frequency domain) is utilized to obtain
Figure BDA0002869258370000101
Wherein ξT,ξRDenotes thetaTAnd thetaRThe angular frequency of the fourier transform of (a),
Figure BDA0002869258370000102
presentation pair
Figure BDA0002869258370000103
Is subjected to thetaTDirection and direction thetaRAs a result of the fourier transform of (a),
Figure BDA0002869258370000104
is representative of xiT/ξRFirst class of Hankel functions of order, when xi < kρR0Time, first class of hank function
Figure BDA0002869258370000105
Can be expressed as:
Figure BDA0002869258370000106
thus, an echo signal s (k, θ) can be obtainedT,θR,zT,zR) At thetaTDirection, thetaRDirection zTAnd zRResults of the respective Fourier transforms of the directions
Figure BDA0002869258370000107
According to the above formula pair
Figure BDA0002869258370000108
Performing matched filtering (removing)
Figure BDA0002869258370000109
And
Figure BDA00028692583700001010
) Can obtain
Figure BDA00028692583700001011
Step S2: performing inverse Fourier transform on the matched and filtered signal in the angular frequency direction, and performing transmission and receptionThe wave number dimension k is subjected to dimension raising and decoupling to obtain
Figure BDA00028692583700001012
Wherein the content of the first and second substances,
Figure BDA00028692583700001013
and
Figure BDA00028692583700001014
the wave number dimensions of the transmitting antenna direction and the receiving antenna direction of the transmitting and receiving wave number dimension k under the cylindrical coordinates are respectively. Wherein the angular direction may include θTAnd thetaRTwo directions.
Fig. 3 shows a schematic diagram of ascending and descending dimensions for a transceiving dimension k according to another embodiment of the present disclosure.
As shown in FIG. 3, the sampled data is upscaled, i.e., one-dimensional data G (k)1),G(k2),…,G(kn) And reconstructing, and sequentially arranging the data on the reverse diagonal lines of the data after the dimension is increased. After the dimension increasing operation is completed, k is carried outT/kRAnd
Figure BDA00028692583700001015
is decoupled. Decomposing data coupled in transmit and receive dimensions into (k)T,θT) And (k)R,θR) Corresponding data, i.e. splitting the transmitting-receiving dimension k (wave number k) into the wave number dimension k of the transmitting direction in a rectangular coordinate systemTAnd wave number dimension k of the receive directionRThen using the dispersion relation
Figure BDA00028692583700001016
And
Figure BDA00028692583700001017
dimension k of the transmitting antenna directionTAnd the dimension k of the receive antenna directionRWave number dimension k converted into emission direction in cylindrical coordinate systemρTAnd wave number dimension k of the receive directionρRThereby, pair
Figure BDA00028692583700001018
Performing matched filtering, increasing the dimension of the receiving-transmitting dimension k, and decoupling to obtain
Figure BDA0002869258370000111
Step S3: to pair
Figure BDA0002869258370000112
Two-dimensional interpolation is carried out twice to obtain
Figure BDA0002869258370000113
Reducing the dimension according to the dimension k of the receiving and transmitting wave number to obtain G (k)x,ky,kz) Wherein k isx、kyAnd kzThe components of the transmitting-receiving wave number dimension k in the x, y and z directions under a rectangular coordinate system are respectively.
In one example, pair
Figure BDA0002869258370000114
Two-dimensional interpolation is carried out twice to obtain
Figure BDA0002869258370000115
The method can comprise the following steps: circulation of
Figure BDA0002869258370000116
θR、
Figure BDA0002869258370000117
And
Figure BDA0002869258370000118
variables, for said in each cycle
Figure BDA0002869258370000119
And thetaTPerforming two-dimensional interpolation to obtain
Figure BDA00028692583700001110
Cycling said kxT、kyT、
Figure BDA00028692583700001111
And
Figure BDA00028692583700001112
variable, for said k in each cycleRAnd thetaRPerforming two-dimensional interpolation to obtain
Figure BDA00028692583700001113
Wherein the content of the first and second substances,
Figure BDA00028692583700001114
and
Figure BDA00028692583700001115
the wave number dimension in the direction of the transmitting antenna is respectively projected in the x direction and the y direction under a rectangular coordinate system;
Figure BDA00028692583700001116
and
Figure BDA00028692583700001117
the wave number dimension in the direction of the receiving antenna is the projection in the x direction and the y direction respectively under a rectangular coordinate system.
Then, will
Figure BDA00028692583700001118
Performing dimension reduction on the dimension k of the transmitting and receiving wave number to obtain G (k)x,ky,kz). Wherein the dimension reduction process is opposite to the dimension increasing process, and the dimension reduction process and the dimension increasing process are opposite to each other
Figure BDA00028692583700001119
And
Figure BDA00028692583700001120
the grid data is subjected to inverse diagonal addition or averaging to obtain the data after dimensionality reduction, as shown in fig. 3, the values of the inverse diagonal are added or averaged in a rectangular coordinate system to obtain the emission horizontal dimensionality
Figure BDA00028692583700001121
And receive horizontal dimension
Figure BDA00028692583700001122
The value in the x direction on the anticline diagonal is kx. Similarly, pairs can be calculated
Figure BDA00028692583700001123
Figure BDA00028692583700001124
Result of performing dimension reduction G (k)x,ky,kz)。
Step S4: g (k) isx,ky,kz) And performing three-dimensional inverse Fourier transform to obtain an imaging result g (x, y, z) based on the cylindrical MIMO area array.
4a, 4b, and 4c illustrate two-dimensional imaging results of an azimuth-elevation direction, an azimuth-distance direction, and an elevation-distance direction, respectively, of a cylindrical MIMO area array based imaging system according to an embodiment of the present disclosure; fig. 4d, 4e, and 4f show cross-sectional view illustrations of azimuth, distance, and elevation directions, respectively, of imaging results of a cylindrical MIMO area array-based imaging system according to an embodiment of the present disclosure.
For example, an arc-shaped MIMO linear array (including 5 transmitting antenna array elements and 41 receiving antenna array elements, and the chord length corresponding to the arc is 0.4m) of 41 × 5 is adopted in the arc dimension, and an arc-shaped MIMO array (41 transmitting antenna array elements, a transmitting antenna array element interval of 0.01m, 5 receiving antenna array elements, and a receiving antenna array element interval of 0.1m) of 41 × 5 is also adopted in the vertical direction (bus direction) so as to ensure that the distance intervals of the transmitting antenna elements are the same and the distance intervals of the receiving antenna elements are also the same. The radius of the arc MIMO linear array is 1.5m, the radio frequency used for simulation is 31-39 GHz, the aperture of the cylindrical surface in the vertical direction is 0.4m, and the corresponding opening angle of the arc MIMO linear array in the azimuth direction is the same as the opening angle of the corresponding imaging center of the vertical bus.
As shown in fig. 1, all the transmit-receive antenna element beams of the imaging system are directed toward the person or object to be detected, and when the person to be detected is detected to be within the detectable range, the imaging system based on the cylindrical MIMO area array starts to operate. All the transmitting channels work in a time-sharing mode, all the receiving channels work simultaneously, and after the acquisition of the echo data of the detected human body or the target is finished, the detected human body is rapidly imaged by using an imaging method based on a cylindrical MIMO area array, so that a three-dimensional imaging result of a target area of the detected human body is obtained, as shown in FIGS. 4a, 4b, 4c, 4d, 4e and 4 f.
In addition, as shown in fig. 4d, 4e, and 4f, the solid line represents a cross-sectional view of a target three-dimensional imaging result of the imaging method based on the arc MIMO area array, and the broken line represents a cross-sectional view of a target three-dimensional imaging result based on the standard BP algorithm. As can be seen from fig. 4d, 4e, and 4f, the imaging result of the imaging method based on the arc MIMO area array is very close to the target three-dimensional imaging result based on the BP algorithm, which shows that the imaging method based on the arc MIMO area array of the present invention has a good imaging effect, and can meet the requirements of high image quality and fast imaging.
The cylindrical surface MIMO area array imaging system combines the rapid imaging algorithm (method) disclosed by the invention, so that the security inspection system realizes rapid high-resolution imaging, has the advantages of high imaging speed and high resolution, is easy to arrange and low in cost, and can be widely applied to human body security inspection in the environments of airports, high-flux subways, railway stations and the like.
Having described embodiments of the present disclosure, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen in order to best explain the principles of the embodiments, the practical application, or improvements made to the technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims (7)

1. An imaging system based on a cylindrical MIMO area array, the system comprising: the MIMO linear array comprises a plurality of arc MIMO linear arrays and a plurality of bus MIMO linear arrays, wherein the arc MIMO linear arrays and the bus MIMO linear arrays are expanded into a two-dimensional cylindrical surface MIMO area array; the arc MIMO linear array and the bus MIMO linear array comprise a transmitting antenna and a receiving antenna;
the transmitting antennas are distributed in the arc MIMO linear array direction at equal angular intervals of full sampling/under sampling, and distributed in the bus MIMO linear array direction at equal angular intervals of under sampling/full sampling;
the receiving antennas are distributed in the arc MIMO linear array direction at equal angular intervals of under-sampling/full-sampling, and distributed in the bus MIMO linear array direction at equal angular intervals of full-sampling/under-sampling.
2. The imaging system of claim 1, wherein when the transmit antennas are equally angularly spaced apart in the direction of the curved MIMO linear array at full sampling, they are equally spaced apart in the direction of the bus MIMO linear array at under sampling; receiving antenna is in pitch arc MIMO linear array direction is angular interval distribution such as undersampling when generating line MIMO linear array direction is angular interval distribution such as full sampling, include:
the transmitting antennas are distributed between two adjacent receiving antennas at equal angle intervals along the arc direction of the arc MIMO linear array;
the receiving antennas are distributed at equal intervals between two adjacent transmitting antennas along the bus direction of the bus MIMO linear array.
3. The imaging system of claim 1, wherein when the transmit antennas are under-sampled at equal angular intervals in the direction of the curved MIMO linear arrays, they are fully sampled at equal angular intervals in the direction of the bus MIMO linear arrays; receiving antenna is in pitch arc MIMO linear array direction is angle interval distribution such as full sampling when generating line MIMO linear array direction is angular interval distribution such as undersampling, include:
the receiving antennas are distributed between two adjacent transmitting antennas at equal angle intervals along the arc direction of the arc MIMO linear array;
the transmitting antennas are distributed at equal intervals between two adjacent receiving antennas along the bus direction of the bus MIMO linear array.
4. The imaging system of claim 1, wherein the transmit antenna time-divisionally transmits radio frequency signals;
when each transmitting antenna transmits a radio frequency signal, all receiving antennas simultaneously receive reflected echo signals.
5. The imaging system of claim 4, wherein the echo signal is a five-dimensional vector s (k, θ)T,θR,zT,zR) Where k is the dimension of the transmitted and received wave number, thetaTFor transmitting antenna position in arc direction, thetaRIs the position of the receiving antenna in the direction of the arc, zTFor transmitting antenna position in height direction, zRIs the receiving antenna position in the elevation direction.
6. An imaging method based on a cylindrical MIMO area array, which is characterized by adopting the imaging system of claims 1-5, and the method comprises the following steps:
the echo signal s (k, theta)T,θR,zT,zR) At thetaTDirection, thetaRFourier transform is respectively carried out in the direction and the z direction to obtain
Figure RE-FDA0003060329610000021
And to
Figure RE-FDA0003060329610000022
Performing matched filtering, wherein xiT、ξR、
Figure RE-FDA0003060329610000023
And
Figure RE-FDA0003060329610000024
are each thetaTDirection, thetaRFourier transform results of direction and z direction;
performing inverse Fourier transform on the matched and filtered signals in the angular frequency direction, and performing dimensionality raising and decoupling on the dimension k of the receiving and transmitting wave number to obtain
Figure RE-FDA0003060329610000025
Wherein the content of the first and second substances,
Figure RE-FDA0003060329610000026
and
Figure RE-FDA0003060329610000027
respectively is the wave number dimension of the transmitting antenna direction and the receiving antenna direction under the cylindrical surface coordinate of the transmitting and receiving wave number dimension k;
to pair
Figure RE-FDA0003060329610000028
Two-dimensional interpolation is carried out twice to obtain
Figure RE-FDA0003060329610000029
Reducing the dimension according to the dimension k of the receiving and transmitting wave number to obtain G (k)x,ky,kz) Wherein k isx、kyAnd kzThe components of the receiving and transmitting wave number dimension k in the x direction, the y direction and the z direction under a rectangular coordinate system are respectively;
g (k) isx,ky,kz) And performing three-dimensional inverse Fourier transform to obtain an imaging result g (x, y, z) based on the cylindrical MIMO area array.
7. The imaging method of claim 6, wherein the pair
Figure RE-FDA00030603296100000210
Two-dimensional interpolation is carried out twice to obtain
Figure RE-FDA00030603296100000211
The method comprises the following steps:
circulation of
Figure RE-FDA00030603296100000212
θR、
Figure RE-FDA00030603296100000213
And
Figure RE-FDA00030603296100000214
variables, for said in each cycle
Figure RE-FDA00030603296100000215
And thetaTPerforming two-dimensional interpolation to obtain
Figure RE-FDA00030603296100000216
Cycling said kxT、kyT、
Figure RE-FDA00030603296100000217
And
Figure RE-FDA00030603296100000218
variable, for said k in each cycleRAnd thetaRPerforming two-dimensional interpolation to obtain
Figure RE-FDA0003060329610000031
Wherein the content of the first and second substances,
Figure RE-FDA0003060329610000032
and
Figure RE-FDA0003060329610000033
the wave number dimension in the direction of the transmitting antenna is respectively projected in the x direction and the y direction under a rectangular coordinate system;
Figure RE-FDA0003060329610000034
and
Figure RE-FDA0003060329610000035
the wave number dimension in the direction of the receiving antenna is the projection in the x direction and the y direction respectively under a rectangular coordinate system.
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