CN113933834B - Cylindrical scanning microwave imaging method - Google Patents
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Abstract
The invention relates to the technical fields of optical imaging, microwave imaging, radar detection, sonar, ultrasonic imaging, target detection based on sound, light, electricity and other media, imaging identification and wireless communication, in particular to a cylindrical scanning microwave imaging method and application thereof in the fields. The method can firstly use the passive imaging technology to realize the ultra-fast scanning of the target, when the suspected object is found, the active imaging technology can be used to observe the details of the object in detail, and the two imaging methods can share one set of signal processing system, thereby greatly reducing the hardware cost, improving the imaging speed, and providing great convenience for practical application. In addition, the method has the advantages of good compatibility, small operand, good imaging effect, wide application range and the like.
Description
Technical Field
The invention relates to the technical fields of optical imaging, microwave imaging, radar detection, sonar, ultrasonic imaging, target detection based on sound, light, electricity and other media, imaging identification and wireless communication, in particular to a cylindrical scanning microwave imaging method and application thereof in the fields.
Background
The digital holographic imaging technology evolved from the laser holographic imaging technology has high imaging resolution, is one of the first-choice technologies of millimeter wave active imaging at present, and related products are popularized and applied in different fields at home and abroad.
However, the conventional digital holographic imaging technology still has many defects and shortcomings, mainly including:
1) large operation amount, high cost and low imaging speed
In the existing digital holographic imaging technology, two operations of Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) are required to be performed in sequence during imaging, the operation amount is extremely large, the configuration requirements on hardware environment and computing resources are high, the hardware price and the operation cost are high, and in addition, the two operations of FFT and IFFT are required to be performed in sequence, so the imaging speed is low.
2) Can only be used for near-field imaging, and cannot be used for long-distance imaging
In the existing digital holographic imaging technology, when the target distance is long, the phase compensation can be ignored, which is equivalent to performing "FFT-IFFT" operation, and imaging distortion and even imaging failure can be caused.
In addition, as a new expansion of the holographic imaging technology, the cylindrical scanning imaging has the three-dimensional imaging capability, can quickly realize the circumferential scanning and the omnibearing imaging of the target, and has wider application range compared with a planar linear scanning system. However, although the conventional holographic imaging technology can also realize cylindrical scanning imaging, the imaging method is often very complex, the hardware cost is high, the imaging speed is low, different technologies are required for passive imaging and active imaging, and the mutual compatibility is poor, so that the difficulty is increased for practical use, the conventional method is mostly not suitable for large-angle imaging application scenes, the imaging effect is poor when a target deviates from the normal direction of an array by a large angle, and the resolution is low at the moment and a satisfactory imaging effect cannot be obtained, so that the development of the cylindrical scanning imaging method which has good compatibility, an excellent imaging effect, a wider application range and a higher imaging speed has a great application value.
Disclosure of Invention
In order to overcome the defects and shortcomings of the traditional digital holographic active imaging technology, particularly the cylindrical scanning imaging technology, the invention provides a set of solutions.
As shown in fig. 1, a linear array is adopted to scan circumferentially around a target P, the echo distribution on the swept cylindrical array surface is recorded in sequence, and the data is imaged, so that the target can be imaged in an all-round manner.
And establishing a coordinate system of the imaging system, wherein P is the target, Q is the image of the target, the synthesized local antenna array surface is positioned on a plane with z being equal to 0, and the mark X represents a transmitting and receiving antenna unit.
Let the radius of the scanning cylinder be p,
representing the angle of the array elements from the center of the array in a cylindrical coordinate system. The coordinates of the array unit are expressed by (x, y, z), and the coordinates of the array unit exist as the following calculation formula as the scanning position changes:
the signal passes through a single pass R 1 、R 2 The propagation phase shift introduced during propagation is:
among the variables useful for imaging focus are:
wherein: phi is a 1 Is the propagation phase shift, phi, of the scattering source P to the array elements 2 For the propagation phase shift of the array element to the image point Q,
is the wave number, U is the object distance, V is the image distance, (ζ, ξ) are the scattering source coordinates, (x, y, z) are the array element coordinates, and (δ, σ) are the image point coordinates.
With cylindrical scanning, the synthesized antenna array is equivalent to a lens with a focal length F, and the effective phase shift of the lens unit is:
wherein: phi is a unit of L F is the focal length for the lens phase shift of the array element.
In passive imaging, the antenna unit does not emit detection signals and is only used for receiving scattering signals of a targetAfter receiving the target scattering signal, the line is scattered for the second time in the form of spherical wave and passes through different transmission paths R 1 、R 2 And the field intensity reaching the image plane after phase shifting of the lens unit is as follows:
in holographic imaging, a signal is transmitted from an antenna unit, is reflected to a target and then is received by the antenna unit, and the distance traveled by the signal is R 1 Corresponding to a phase delay of 2 phi 1 . In the imaging process, it is necessary to shift the phase of the lens unit, R 2 The propagation phase shift is processed in two passes: the receiving and transmitting antenna units sequentially transmit detection signals, and the signals reflected by the target P are subjected to secondary scattering in the form of spherical waves after reaching the receiving and transmitting antenna units and then pass through different transmission paths R 1 、R 2 The field strength at the image plane after the two-way phase shift is:
comparing the imaging formulas under the two conditions, and unifying the two formulas by introducing an auxiliary selection parameter η as follows:
Where η ═ 1 is suitable for passive imaging and η ═ 2 is suitable for active holographic imaging.
In actual imaging, only the following processing needs to be performed:
the target signal received by the antenna unit is E, and A is an amplitude weighting coefficient. Substitution of phi L And phi 2 After the expression goes onSimplifying to obtain:
wherein,
when the imaging condition is satisfied
In time, the above equation can be simplified as:
using the relationship:
after integral transformation:
discretizing the above formula:
where the notation exp denotes an exponential function with the euler constant e as base. Order to
y n ＝y 0 +nΔ y The formula is simplified and arranged as follows:
wherein,
the right coefficient of the above formula satisfies
The spatial fluctuation characteristic of an image field is reflected, and the influence on imaging is basically avoided and can be ignored. Considering no influence of the coefficient, the summation operation can be rapidly solved by using two-dimensional IFFT, and then the image field calculation formula is:
without taking into account the operation cores
The calculation formula can be further simplified:
herein, IFFT denotes a two-dimensional or three-dimensional IFFT operation. Omega corresponding to IFFT calculation result δ 、ω σ The value range is as follows: omega δ ∈[0,2π]、ω σ ∈[0,2π]After fftshift operation, the value of ω is calculated δ 、ω σ The value range is transformed into: omega δ ∈[-π,π]、ω σ ∈[-π,π]The image at this time is the image which is in accordance with the actual distribution, and has a good linear mapping relation with the source field.
Combined with array antenna theory, there is omega δ ＝ηkΔ x sinθ δ 、ω σ ＝ηkΔ y sinθ σ 。
Because the repetition period of the discrete FFT is 2 pi, if no image aliasing occurs, the method should be applied
|ω|≤π；
Let the cell pitch be Δ, so that there is:
typically, the effective range of θ is [ - π/2, π/2], and the conditions that ensure that the above equation is always true are:
the non-aliasing condition of the cylindrical scanning semi-airspace image is as follows:
correcting the scanning angular coordinate of the image point by adopting an array antenna theory:
our research shows that the phase matching formula
Further improvement can be achieved, and the imaging performance under the condition of a large angle can be improved by replacing the object distance parameter U with the target slope distance R:
on the basis of the above knowledge, the invention provides a cylindrical scanning microwave imaging method, which is based on a lens imaging principle, combines an electromagnetic field theory, and obtains image field distribution corresponding to a target by weighting the amplitude and phase of a unit signal according to a target signal received by an antenna array and adopting an efficient parallel algorithm, wherein the specific algorithm is as follows:
wherein: j is an imaginary unit, e is an Euler constant,
in order to be the image field distribution,
for the target signal received by the array unit, A mn Is a weighting coefficient for the array element amplitude,
is a weighted value of the amplitude of the cylindrical sweep,
in order to focus the phase weighting coefficients,
is a compensation coefficient of the phase of the cylindrical scanning, 
For scanning the phase weighting coefficients, M is the number of array elements in the x-direction, and N is the number of array elements in the y-direction, (x) m ，y n ) Is the coordinate of the array unit, (delta, sigma) is the coordinate of the image point, V is the image distance, i.e. the distance between the image plane and the array plane, eta is the object selectivity parameter, different values are selected according to the characteristics of the imaging system, m and n are the serial numbers of the array unit in the x direction and the y direction respectively,
is the wavenumber, λ is the wavelength, and the symbol Σ represents the summation operation.
Further, the method of the present invention is applicable to different imaging systems by selecting different values of parameter η, specifically:
when the eta is 1, the method is suitable for a passive imaging system and a semi-active imaging system;
when η is 2, it is suitable for active holographic imaging system.
Further, the method of the invention comprises the following steps:
the method comprises the following steps: carrying out amplitude weighting on the array unit signals to reduce side lobe levels;
step two: carrying out focusing phase weighting on the array unit signals to realize imaging focusing;
step three: performing cylindrical scanning amplitude compensation and phase compensation on the array unit signals to improve imaging performance;
step four: carrying out beam scanning phase weighting on the array unit signals to adjust the central visual angle direction of the imaging system;
Step five: performing rapid imaging processing on the array unit signals by adopting an efficient parallel algorithm;
step six: and resolving the image field coordinates, and performing coordinate inversion on the image field to obtain the position of the real target.
Further, the amplitude weighting method in step one of the method of the present invention includes, but is not limited to, uniform distribution, cosine weighting, hamming window, Taylor distribution, chebyshev distribution, and hybrid weighting method.
Further, in step two of the method of the present invention, the focusing phase weighting is performed on the array unit signals to realize the imaging focusing, wherein:
the autofocus phase weighted focus phase calculation is given by:
wherein R is the target slant distance, namely the distance from the target to the center of the array;
the zoom or fixed focus phase weighted focus phase calculation formula is:
wherein F is the focal length, V is the image distance, i.e. the distance from the image plane to the plane of the receiving array, and F < U, F < V.
Further, in step three of the method of the present invention, cylindrical scanning amplitude compensation and phase compensation are performed on the array unit signals to improve the imaging performance, wherein:
the calculation formula of the cylindrical scanning amplitude compensation is as follows:
wherein,
representing the angle of the array unit from the center of the array in a polar coordinate system, requires 
When the range of the intercepted synthetic array is small, namely the equivalent array aperture is small, the method directly selects
To simplify the operation process.
Further, in step three of the method of the present invention, cylindrical scanning amplitude compensation and phase compensation are performed on the array unit signals to improve the imaging performance, wherein:
the calculation formula of the cylindrical scanning phase compensation is as follows:
wherein p is the radius of the scanning cylinder,
representing the angle of the array elements from the center of the array in a polar coordinate system.
Preferably, in the uniform-speed cylindrical scanning imaging system, the calculation formula of the cylindrical scanning phase compensation can be improved as follows:
where Ω is the angular frequency of the cylindrical scan, t mn The scanning time is counted as zero time by the time when the scanning reaches the center of the array surface.
Furthermore, in the fourth step of the method of the present invention, the scanning phase weighting adjusts the central view direction of the imaging system, and the phase calculation formula of the scanning phase weighting is as follows:
wherein:
the phase difference between the adjacent cells of the array in the x direction and the y direction respectively has the following calculation formula:
wherein:
angle of scanning step, Δ, for cylindrical scanning y Array cell pitch in the y-direction, θ ζ 、θ ξ The x and y scanning angle coordinates when the central visual angle direction points to the source coordinates (zeta, xi) are respectively calculated as follows:
Wherein: u is the object distance, i.e., the distance from the plane of the target to the plane of the array.
Furthermore, in the fifth step of the method, the high-efficiency parallel algorithm is adopted to carry out rapid imaging processing on the array unit signals; the efficient parallel algorithm comprises two-dimensional or three-dimensional FFT, IFFT, non-uniform FFT and sparse FFT, and the calculation formula is as follows:
wherein: symbol
Represents an efficient parallel algorithm function and is,
for the target signal received by the array unit, A is the amplitude weighting coefficient of the array unit, A C For cylinder scanning amplitude weighting values, phi F For focusing the phase weighting coefficients, [ phi ] C For cylindrical scanning phase compensation coefficient, phi S Weighting coefficients for the scanning phases;
omega corresponding to image field calculation result δ 、ω σ The value range is as follows: omega δ ∈[0,2π]、ω σ ∈[0,2π]After fftshift operation, the value of ω is calculated δ 、ω σ The value range is transformed into: omega δ ∈[-π,π]、ω σ ∈[-π,π]The image at this time is an image conforming to the actual distribution:
further, the method comprises the following steps: carrying out coordinate calculation on an image field obtained by the efficient parallel algorithm, and carrying out coordinate inversion on the image field to obtain the position of a real target; wherein:
for the efficient parallel algorithm of the IFFT class, the calculation formula of the angular coordinate of the image field scanning is as follows:
for the FFT-like efficient parallel algorithm, the calculation formula of the image field scanning angle coordinate is as follows:
The rectangular coordinate calculation formula of the image is as follows:
δ＝V tanθ δ ，
σ＝V tanθ σ ；
the coordinate inversion calculation formula of the real target is as follows:
wherein:
angle of scanning step, Δ, for cylindrical scanning y The array unit spacing in the y direction (zeta ) is the source coordinate, rho is the radius of the scanning cylinder, and U is the object distance, i.e. the plane of the target to theDistance of the array plane.
Further, the method of the present invention sets the scanning steps of the receiving and transmitting antenna to satisfy:
to avoid imaging aliasing; wherein:
angle of scanning step, Δ, for cylindrical scanning y And p is the radius of the scanning cylinder.
In addition, the method is also suitable for an imaging system with an antenna fixed and a target rotating, and comprises an ISAR imaging system and a turntable imaging system; when the method is used in the imaging system, the angular frequency of the cylindrical scan is replaced by the angular frequency of rotation of the target or the turntable, and the radius of the cylindrical scan is replaced by the distance from the antenna to the center of rotation.
Meanwhile, the invention also relates to the application of the method in the fields of optical imaging, microwave imaging, radar detection, sonar, ultrasonic imaging, sound, light and electric target detection, imaging identification and wireless communication.
In conclusion, the cylindrical scanning microwave imaging method has the following advantages:
1) Creates a rapid imaging method suitable for cylindrical scanning
The invention realizes low-cost and quick cylindrical scanning imaging, the calculation amount of the imaging system is far lower than that of an active holographic imaging system, hardware resources can be greatly saved, and the imaging speed is improved.
2) Creates a unified imaging method compatible with passive imaging and active imaging
The method can firstly use the passive imaging technology to realize the ultra-fast scanning of the target, when the suspected object is found, the active imaging technology can be used to observe the details of the object in detail, and the two imaging methods can share one set of signal processing system, thereby greatly reducing the hardware cost, improving the scanning speed, and providing great convenience for practical application.
3) Further improves the imaging effect
In the phase compensation method, the target slant distance R is used for replacing the object distance parameter U, and compared with the object distance parameter U, the parameter R is easier to obtain and has better imaging effect.
4) Can be suitable for remote imaging and has wider application range
In the invention, when the remote imaging is carried out, the phase compensation can be ignored, and the IFFT operation is equivalently carried out, so that the imaging of the remote target can be realized.
In addition, the method has good application prospect, can be widely applied to the technical field of target detection and wireless communication taking sound, light, electricity and the like as media, and when the detection media are electromagnetic waves, the technology is suitable for microwave imaging, radar detection, wireless communication, synthetic aperture radar and inverse synthetic aperture radar; when the detection medium is sound wave or ultrasonic wave, the technology is suitable for sonar, ultrasonic imaging and synthetic aperture sonar; when the detection medium is light, the technology is suitable for optical imaging and synthetic aperture optical imaging.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments of the present invention will be briefly described below, and it is obvious that the following drawings are only some embodiments described in the present invention, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without inventive labor.
Fig. 1 is a schematic diagram of an imaging system coordinate system of the imaging method of the present invention.
Fig. 2 is an algorithmic block diagram of the imaging method of the present invention.
Fig. 3 is a diagram of the imaging result of case 1 of passive imaging by using the imaging method of the present invention.
Fig. 4 is a diagram of the imaging result of case 2 of active holographic imaging by using the imaging method of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail and completely with reference to the following embodiments and accompanying drawings. It is to be understood that the embodiments described are merely illustrative of some, but not all, of the present invention and that the invention may be embodied or carried out in various other specific forms, and that various modifications and changes in the details of the specification may be made without departing from the spirit of the invention.
Also, it should be understood that the scope of the invention is not limited to the particular embodiments described below; it is also to be understood that the terminology used in the examples is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention.
Example 1: a cylindrical scanning microwave imaging method (refer to the attached figures 1-2) is based on a lens imaging principle, combines an electromagnetic field theory, and obtains image field distribution corresponding to a target by weighting the amplitude and the phase of a unit signal according to a target signal received by an antenna array and adopting an efficient parallel algorithm, wherein the specific algorithm is as follows:
Wherein: j is an imaginary unit, e is an Euler constant,
in order to be the image field distribution,
for the target signal received by the array unit, A mn Is a weighting coefficient for the array element amplitude,
is a weighted value of the amplitude of the cylindrical sweep,
in order to focus the phase weighting coefficients,
is a compensation coefficient of the phase of the cylindrical scanning,
for scanning the phase weighting coefficients, M is the number of array elements in the x-direction, and N is the number of array elements in the y-direction, (x) m ，y n ) Is the coordinate of the array unit, (delta, sigma) is the coordinate of the image point, V is the image distance, i.e. the distance between the image plane and the array plane, eta is the object selectivity parameter, different values are selected according to the characteristics of the imaging system, m and n are the serial numbers of the array unit in the x direction and the y direction respectively,
in wavenumber, λ is the wavelength, and the symbol Σ represents the summation operation.
Further, the method can be applied to different imaging systems by selecting different parameter η values: when the eta is 1, the method is suitable for a passive imaging system and a semi-active imaging system; when η is 2, it is suitable for active holographic imaging system.
Specifically, the present imaging method includes the steps of:
the method comprises the following steps: carrying out amplitude weighting on the array unit signals to reduce side lobe levels;
methods of amplitude weighting include, but are not limited to, uniform distribution, cosine weighting, hamming window, Taylor distribution, chebyshev distribution, and hybrid weighting methods.
Step two: carrying out focusing phase weighting on the array unit signals to realize imaging focusing;
wherein: the autofocus phase weighted focus phase calculation formula is:
wherein R is the target slant distance, namely the distance from the target to the center of the array;
the zoom or fixed focus phase weighted focus phase calculation formula is:
wherein F is the focal length, V is the image distance, i.e. the distance from the image plane to the plane of the receiving array, and F < U, F < V.
Step three: performing cylindrical scanning amplitude compensation and phase compensation on the array unit signals to improve imaging performance;
the calculation formula of the cylindrical scanning amplitude compensation is as follows:
wherein,
representing the angle of the array unit from the center of the array in a polar coordinate system, requires
When the intercepted synthetic array range is small, namely the equivalent array aperture is small, the direct selection is carried out
To simplify the operation process.
The calculation formula of the cylindrical scanning phase compensation is as follows:
wherein p is the radius of the scanning cylinder,
representing the angle of the array elements from the center of the array in a polar coordinate system.
In addition, in the uniform-speed cylindrical scanning imaging system, the calculation formula of the cylindrical scanning phase compensation can be improved as follows:
where Ω is the angular frequency of the cylindrical scan, t mn The scanning time is counted as zero time by the time when the scanning reaches the center of the array surface.
Step four: carrying out beam scanning phase weighting on the array unit signals to adjust the central visual angle direction of the imaging system;
the phase calculation formula of the scanning phase weighting is as follows:
wherein:
the phase difference between the adjacent cells of the array in the x direction and the y direction respectively has the following calculation formula:
wherein:
angle of scanning step, Δ, for cylindrical scanning y Array cell pitch in the y-direction, θ ζ 、θ ξ The x and y scanning angle coordinates when the central visual angle direction points to the source coordinates (zeta, xi) are respectively calculated as follows:
wherein: u is the object distance, i.e., the distance from the plane of the target to the plane of the array.
Step five: performing rapid imaging processing on the array unit signals by adopting an efficient parallel algorithm;
the efficient parallel algorithm comprises two-dimensional or three-dimensional FFT, IFFT, non-uniform FFT and sparse FFT, and the calculation formula is as follows:
wherein: symbol
Represents an efficient parallel algorithm function and is,
for the target signal received by the array unit, A is the amplitude weighting coefficient of the array unit, A C For cylinder scanning amplitude weighting values, phi F For focusing the phase weighting coefficients, [ phi ] C For cylindrical scanning phase compensation coefficient, phi S Weighting coefficients for the scanning phases;
Omega corresponding to image field calculation result δ 、ω σ The value range is as follows: omega δ ∈[0，2π]、ω σ ∈[0，2π]After fftshift operation, the value of ω is calculated δ 、ω σ The value range is transformed into: omega δ ∈[-π，π]、ω σ ∈[-π，π]The image at this time is an image conforming to the actual distribution:
step six: and resolving the image field coordinates, and performing coordinate inversion on the image field to obtain the position of the real target.
Wherein: for the efficient parallel algorithm of the IFFT class, the calculation formula of the angular coordinate of the image field scanning is as follows:
for the FFT-like efficient parallel algorithm, the calculation formula of the image field scanning angle coordinate is as follows:
the rectangular coordinate calculation formula of the image is as follows:
δ＝V tanθ δ ，
σ＝V tanθ σ ；
the coordinate inversion calculation formula of the real target is as follows:
wherein:
angle of scanning step, Δ, for cylindrical scanning y The array element spacing in the y direction, (ζ, ξ) are the source coordinates, ρ is the radius of the scanning cylinder, and U is the object distance, i.e., the distance from the plane of the target to the array plane.
In addition, the scanning steps of the transmitting and receiving antenna are set to satisfy the following conditions:
to avoid imaging aliasing; wherein:
angle of scanning step, Δ, for cylindrical scanning y And p is the radius of the scanning cylinder.
Moreover, the imaging method is also suitable for an imaging system with a fixed antenna and a rotating target, and comprises an ISAR imaging system and a turntable imaging system; when the method is used in the imaging system, the angular frequency of the cylindrical scan is replaced by the angular frequency of rotation of the target or the turntable, and the radius of the cylindrical scan is replaced by the distance from the antenna to the center of rotation.
Example 2: effect verification test of the present imaging method (method of example 1) for Passive imaging
The test conditions are as follows: the working frequency is 30GHz, the spacing between the antenna units is kept to be lambda/4 during scanning, the array scale is 66 x 66, one target is located in the normal direction of the array, the other two targets are respectively deviated from the normal direction by a certain angle, the scanning cylinder takes the target as the center, the radius is 1m, and the imaging result is shown in figure 3.
Example 3: effect verification test of the present imaging method (method of example 1) for active holographic imaging
The test conditions are as follows: the working frequency is 30GHz, the antenna unit spacing is lambda/4, the array scale is 66, one target is located in the normal direction of the array, the other target deviates from the normal direction by 30 degrees, the other two targets respectively deviate from the normal direction by certain angles, the scanning cylinder takes the target as the center, the radius is 1m, and the imaging result is shown in figure 4.
The embodiments of the present invention are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The above description is only an example of the present invention, and is not intended to limit the present invention. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, replacement, or the like that comes within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (13)
1. A cylindrical scanning microwave imaging method is characterized in that the method is based on a lens imaging principle, combines an electromagnetic field theory, and obtains image field distribution corresponding to a target by adopting an efficient parallel algorithm through amplitude and phase weighting of unit signals according to target signals received by an antenna array, wherein the specific algorithm is as follows:
wherein: j is an imaginary unit, e is an Euler constant,
in order to be the image field distribution,
for the target signal received by the array unit, A mn Is a weighting coefficient for the array element amplitude,
is a weighted value of the amplitude of the cylindrical sweep,
in order to focus the phase weighting coefficients,
is a compensation coefficient of the phase of the cylindrical scanning,
for scanning the phase weighting coefficients, M is the number of array elements in the x-direction, and N isNumber of array elements in y-direction, (x) m ，y n ) Is the coordinate of the array unit, (delta, sigma) is the coordinate of the image point, V is the image distance, i.e. the distance between the image plane and the array plane, eta is the object selectivity parameter, different values are selected according to the characteristics of the imaging system, m and n are the serial numbers of the array unit in the x direction and the y direction respectively,
in wavenumber, λ is the wavelength, and the symbol Σ represents the summation operation.
2. The method according to claim 1, characterized in that it is applicable to different imaging systems by selecting different values of parameter η, in particular:
When the eta is 1, the method is suitable for a passive imaging system and a semi-active imaging system;
when eta is 2, the method is suitable for the active holographic imaging system.
3. Method according to claim 1, characterized in that it comprises the following steps:
the method comprises the following steps: carrying out amplitude weighting on the array unit signals to reduce side lobe levels;
step two: carrying out focusing phase weighting on the array unit signals to realize imaging focusing;
step three: performing cylindrical scanning amplitude compensation and phase compensation on the array unit signals to improve imaging performance;
step four: carrying out beam scanning phase weighting on the array unit signals to adjust the central visual angle direction of the imaging system;
step five: performing rapid imaging processing on the array unit signals by adopting an efficient parallel algorithm;
step six: and resolving the image field coordinates, and performing coordinate inversion on the image field to obtain the position of the real target.
4. The method of claim 3, wherein the amplitude weighting method in step one comprises uniform distribution, cosine weighting, Hamming window, Taylor distribution, Chebyshev distribution and hybrid weighting method.
5. The method of claim 3, wherein the focusing phase weighting is performed on the array element signals in step two to realize imaging focusing, wherein:
The autofocus phase weighted focus phase calculation is given by:
wherein, R is the slant distance of the target, namely the distance from the target to the center of the array;
the zoom or fixed focus phase weighted focus phase calculation formula is:
wherein F is the focal length, V is the image distance, i.e. the distance from the image plane to the plane of the receiving array, and F < U, F < V.
6. The method of claim 3, wherein the cylindrical scanning amplitude compensation and phase compensation are performed on the array element signals in step three to improve the imaging performance, wherein:
the calculation formula of the cylindrical scanning amplitude compensation is as follows:
wherein,
representing the angle of the array unit from the center of the array in a polar coordinate system, requires
When the intercepted synthetic array range is small, namely the equivalent array aperture is small, the direct selection is carried out
To simplify the operation process.
7. The method of claim 3, wherein the cylindrical scanning amplitude compensation and phase compensation are performed on the array element signals in step three to improve the imaging performance, wherein:
the calculation formula of the cylindrical scanning phase compensation is as follows:
wherein p is the radius of the scanning cylinder,
representing the angle of the array elements from the center of the array in a polar coordinate system.
8. The method of claim 3, wherein in step four, the scan phase weighting adjusts the central view angle direction of the imaging system, and the phase of the scan phase weighting is calculated as:
wherein:
the phase difference between the adjacent cells of the array in the x direction and the y direction respectively has the following calculation formula:
wherein:
angle of scanning step, Δ, for cylindrical scanning y Array cell pitch in the y-direction, θ ζ 、θ ξ The x and y scanning angle coordinates when the central visual angle direction points to the source coordinates (zeta, xi) are respectively calculated as follows:
wherein: u is the object distance, i.e., the distance from the plane of the target to the plane of the array.
9. The method according to claim 3, wherein in step five, the array unit signals are subjected to fast imaging processing by using an efficient parallel algorithm; the efficient parallel algorithm comprises two-dimensional or three-dimensional FFT, IFFT, non-uniform FFT and sparse FFT, and the calculation formula is as follows:
wherein: symbol
Represents an efficient parallel algorithm function and is,
for the target signal received by the array unit, A is the amplitude weighting coefficient of the array unit, A C For cylinder scanning amplitude weighting values, phi F For focusing the phase weighting coefficients, [ phi ] C For cylindrical scanning phase compensation coefficient, phi S Weighting coefficients for the scan phases;
omega corresponding to image field calculation result δ 、ω σ The value range is as follows: omega δ ∈[0，2π]、ω σ ∈[0，2π]After fftshift operation, the value of ω is calculated δ 、ω σ The value range is transformed into: omega δ ∈[-π，π]、ω σ ∈[-π，π]The image at this time is an image conforming to the actual distribution:
10. the method of claim 3, wherein step six comprises: carrying out coordinate calculation on an image field obtained by the efficient parallel algorithm, and carrying out coordinate inversion on the image field to obtain the position of a real target; wherein:
for the efficient parallel algorithm of the IFFT class, the calculation formula of the angular coordinate of the image field scanning is as follows:
for the FFT-like efficient parallel algorithm, the calculation formula of the image field scanning angle coordinate is as follows:
the rectangular coordinate calculation formula of the image is as follows:
δ＝V tanθ δ ，
σ＝V tanθ σ ；
the coordinate inversion calculation formula of the real target is as follows:
wherein:
angle of scanning step, Δ, for cylindrical scanning y The array element spacing in the y direction, (ζ, ξ) are the source coordinates, ρ is the radius of the scanning cylinder, and U is the object distance, i.e., the distance from the plane of the target to the array plane.
11. A method according to claim 3, characterized in that the scanning steps for setting the transceiving antennas are such that:
to avoid imaging aliasing;
wherein:
angle of scanning step, Δ, for cylindrical scanning y And p is the radius of the scanning cylinder.
12. The method according to any of claims 1-11, wherein the method is further applicable to antenna-stationary, target-rotating imaging systems, including ISAR imaging systems and gantry imaging systems.
13. Use of the method according to any one of claims 1 to 11 in the fields of optical imaging, microwave imaging, radar detection, sonar, ultrasound imaging, and acoustic, optical, electrical object detection, image recognition, wireless communication.
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