Millimeter wave synthetic aperture radar imaging device and method based on arc antenna array

Abstract

The present invention proposes a millimeter wave synthetic aperture radar imaging device based on an arc antenna array, comprising a control and processing terminal, a mechanical rotating mechanism and a SISO linear array, wherein the SISO linear array comprises a plurality of transceiver array elements, the plurality of transceiver array elements are arranged in an arc shape, and the distance between two adjacent transceiver array elements is the same, the SISO linear array is arranged on the mechanical rotating mechanism, the control and processing terminal is respectively connected to the mechanical rotating mechanism and the SISO linear array signal, and the control and processing terminal is loaded with a SAR imaging algorithm of an echo signal. The device breaks through the limitations of traditional SISO-SAR by introducing a one-dimensional arc SISO linear array and combining it with a mechanical rotating structure, increases the viewing angle, and realizes all-round imaging of the environment.

Description

Technical Field

[0001] The present invention relates to the field of radar imaging technology, and in particular to a millimeter wave synthetic aperture radar imaging device and method based on an arc antenna array. Background Art

[0002] Synthetic Aperture Radar (SAR) is an imaging radar technology that forms a large array aperture through mechanical scanning of the transceiver antenna. It has the characteristics of all-day, all-weather and high resolution. Active millimeter-wave near-field array radar imaging technology is an important application form of SAR imaging. This technology is widely used in near-field civilian fields such as security inspection, medical diagnosis and non-destructive testing.

[0003] Single-Input Single-Output Synthetic Aperture Radar (SISO-SAR) is the earliest and most mature SAR array imaging technology, first proposed by the Pacific Northwest National Laboratory in the United States in 2001. This system uses a one-dimensional real aperture SISO array, combined with a one-dimensional mechanical scanning to synthesize a two-dimensional aperture, and obtains range resolution by emitting broadband millimeter-wave signals into the scene, and forms lateral resolution through a two-dimensional aperture, thereby achieving three-dimensional reconstruction of the target.

[0004] Most of the existing cylindrical and planar SISO-SARs currently use one-dimensional linear SISO arrays, which effectively reduce the number of required array elements and reduce hardware costs compared to two-dimensional SISO real aperture arrays. However, due to its linear array structure, its imaging field of view is limited and it cannot take into account both forward and side imaging at the same time. This limitation makes it impossible to perform all-round imaging in indoor environments or other scenarios.

[0005] Therefore, there is an urgent need for an imaging device with a larger viewing angle, higher imaging efficiency and lower hardware cost. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention proposes a millimeter-wave synthetic aperture radar imaging device and method based on an arc antenna array, which not only has high imaging efficiency and low hardware cost, but also can achieve omnidirectional imaging in indoor environments or other scenarios.

[0007] In order to solve the above technical problems, the technical solution of the present invention is:

[0008] A millimeter wave synthetic aperture radar imaging device based on an arc antenna array comprises a control and processing terminal, a mechanical rotating mechanism and a SISO linear array, wherein the SISO linear array comprises a plurality of transceiver array elements, the plurality of transceiver array elements are arranged in an arc shape, and the distance between two adjacent transceiver array elements is the same, the SISO linear array is arranged on the mechanical rotating mechanism, the control and processing terminal is respectively connected to the mechanical rotating mechanism and the SISO linear array signal, and the control and processing terminal is loaded with a SAR imaging algorithm of an echo signal.

[0009] Preferably, the transceiver array element includes a transmitting array element and a receiving array element, the control and processing terminal outputs a control signal to control the transmitting array element to transmit a millimeter wave signal, the receiving array element receives the echo signal of the millimeter wave signal and transmits it to the control and processing terminal, and the control and processing terminal performs imaging processing on the echo signal through a SAR imaging algorithm.

[0010] Preferably, the mechanical rotating mechanism comprises a rotating disk and a driving mechanism, the control and processing terminal outputs a control signal to the driving mechanism to drive the rotating disk to rotate, and the SISO linear array is arranged on the rotating disk.

[0011] Preferably, the center of the SISO linear array is on the axis of the rotating disk, and the lowest transceiver array element is located on the surface of the rotating disk.

[0012] Preferably, the radius of the SISO linear array is 0.3 m.

[0013] Preferably, the SAR imaging algorithm adopts a back-projection algorithm.

[0014] The present invention provides a millimeter wave synthetic aperture radar imaging method based on an arc antenna array, comprising the following steps:

[0015] Step 1: Establish a spatial rectangular coordinate system, wherein the origin of the coordinate system coincides with the center of the arc-shaped SISO linear array;

[0016] Step 2: Rotate the SISO linear array to form a spherical crown SISO array, and determine the coordinates of the array elements according to the spatial rectangular coordinate system;

[0017] Step 3: Determine and eliminate redundant array element coordinates according to the optimization method;

[0018] Step 4: Sample according to the coordinates of the selected array elements and infer the echo signal model:

[0019] s(k,θ,φ)=∫∫∫σ(x',y',z')·exp(-2jkR R )dx'dy'dz'

[0020] Where j represents the imaginary unit, s(·) represents the echo signal, k = 2π / λ is the spatial wave number, σ(·) represents the target function, R R is the distance from the target to the receiving array element, x', y', z' respectively represent the azimuth, height and range coordinate position of the target point to be reconstructed;

[0021] Step 5: Based on the echo signal model, the sampled echo data is used as input to reconstruct the image through the SAR imaging algorithm.

[0022] Preferably, the coordinate calculation method of the array element formed by the rotation is:

[0023] (R 0 cosφ i cosθ j ,R 0 cosφ i sinθ j ,R 0 sinφ i )

[0024]

[0025] Among them, R 0 is the radius of the SISO linear array, φ c The central angle of the circle is N pairs of transmitting and receiving elements are distributed on the linear array, and the frequency range is f min ~f max , the number of frequency sampling N f The azimuth scanning span is 360° and the number of samples is M.

[0026] According to the coordinates of the array element, the distance R from the target to the array element is obtained. R :

[0027]

[0028] Preferably, in step 3, the method for screening array elements is:

[0029] First, the largest azimuth scanning interval in the array element in the transceiver array is taken as the optimal distance:

[0030]

[0031] Thus, each pitch angle φ under the uniform ideal array arrangement is obtained ideal,i Corresponding array element number:

[0032]

[0033] Based on this, the ideal sampling point distribution can be deduced as:

[0034] (R 0 cosφ ideal,i cosθ ideal,j ,R 0 cosφ ideal,i sinθ ideal,j ,R 0 sinφ ideal,i )

[0035]

[0036] For each array element under the ideal arrangement, find the actual array element closest to it and mark it as a valid array element:

[0037] (R 0 cosφ useful,i cosθ useful,j ,R 0 cosφ useful,i sinθ useful,j ,R 0 sinφ useful,i )

[0038]

[0039] Finally, the echo data of the unmarked redundant array elements are discarded to obtain the echo data under the approximately uniform array arrangement.

[0040] Preferably, the sampling frequency of the array element echo data is: frequency range [f min ,f max ]=[30,36]GHz.

[0041] The present invention has the following characteristics and beneficial effects:

[0042] 1. The present invention utilizes a one-dimensional arc-shaped SISO linear array in combination with a mechanical rotating structure and a polar coordinate modeling method to break through the limitations of traditional SISO-SAR, increase the viewing angle, and simultaneously take into account forward and side imaging to achieve all-round imaging of the environment.

[0043] 2. The present invention proposes a method for discarding redundant array element echo data. By calculating the ideal array arrangement, finding the actual array element closest to the element under the ideal arrangement and marking it as a valid element, and then discarding the unmarked redundant array element echo data, approximately uniform array echo data is obtained, which effectively suppresses the artifacts caused by the uneven array arrangement and greatly improves the imaging quality.

[0044] 3. Using the above structure and method, the millimeter-wave synthetic aperture radar imaging device based on the arc antenna array can achieve full coverage, high frame rate, and high-quality scanning imaging of the detection target area. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0046] Figure 1 A schematic diagram of the structure of a millimeter wave synthetic aperture radar imaging device based on an arc antenna array provided by the present invention;

[0047] Figure 2 A schematic diagram of the flow of a millimeter wave synthetic aperture radar imaging method based on an arc antenna array provided by the present invention;

[0048] Figure 3 This is a schematic diagram of the simulation results of traditional planar SISO-SAR imaging;

[0049] Figure 4 Schematic diagram of the imaging simulation results of millimeter wave synthetic aperture radar based on curved antenna array on bare BPA;

[0050] Figure 5 Schematic diagram of the imaging simulation results of the millimeter-wave synthetic aperture radar based on the arc antenna array in this embodiment under the optimization method of discarding redundant sampling point data.

[0051] Figure numerals: 1-control and processing terminal, 2-mechanical rotating mechanism, 3-SISO linear array, 301-transceiver array element, 4-target. DETAILED DESCRIPTION

[0052] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0053] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0054] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0055] Example 1

[0056] This embodiment provides a millimeter wave synthetic aperture radar imaging device based on an arc antenna array, such as Figure 1 As shown, it includes a control and processing terminal 1, a mechanical rotating mechanism 2 and a SISO linear array 3, wherein the SISO linear array 3 includes a plurality of transceiver array elements 301, wherein the plurality of transceiver array elements 301 are arranged in an arc shape, and the distance between two adjacent transceiver array elements is the same, and the SISO linear array 3 is arranged on the mechanical rotating mechanism 2. Specifically, the center of the SISO linear array is on the rotating axis of the rotating disk, and the lowest transceiver array element is located on the surface of the rotating disk.

[0057] Furthermore, the transceiver array element includes a transmitting array element and a receiving array element. The control and processing terminal 1 is respectively connected to the mechanical rotating mechanism 2 and the SISO linear array 3 by signals, and the control and processing terminal 1 is loaded with a SAR imaging algorithm of the echo signal.

[0058] In the above technical solution, if Figure 2As shown, the control and processing terminal 1 is connected to the mechanical rotating structure 2. In this embodiment, the mechanical rotating structure 2 is driven to rotate at a speed of 360° / 2s, and the arc-shaped SISO linear array 3 fixed thereon is driven to rotate to form a spherical crown SISO array. At the same time, the control and processing terminal 1 controls the transmitting array elements in the arc-shaped SISO linear array 3 to transmit linear frequency modulated millimeter wave signals to scan the target 4 in the target area, and then the receiving array elements in the arc-shaped SISO linear array 3 collect the scattered echo signals on the surface of the target 4, and return them to the control and processing terminal for imaging processing, and finally obtain the image of the target. Finally, the imaging processing performed by the control and processing terminal refers to imaging processing performed through a SAR imaging algorithm. In this embodiment, the SAR imaging algorithm adopts the existing back-projection algorithm.

[0059] It should be noted that the control and processing terminal 1 includes a microcontroller and a terminal server loaded with a SAR imaging algorithm. The microcontroller and the SAR imaging algorithm are both conventional technical means, so they are not described in detail in this embodiment.

[0060] Furthermore, in this embodiment, the beam angle of the millimeter wave signal emitted by the transmitting array element is 60°, and the radiation direction is perpendicular to the tangent direction of the arc at this point. Considering the influence of the beam angle, the radius of the linear array is set to R 0 =0.3m, the central angle is set to φ c = 60°, with N = 31 pairs of transmitting and receiving array elements distributed on it, and the frequency range [f min ,f max ]=[30,36]GHz, the number of frequency sampling points is N f =101, the azimuth scanning span is 360°, and the sampling number is M=180, thus achieving all-round imaging with an azimuth span of 0-360° and an elevation span of 0-90°.

[0061] In this embodiment, by introducing a one-dimensional arc-shaped SISO linear array and combining it with a mechanical rotating structure, the limitations of the traditional SISO-SAR are overcome, the viewing angle is increased, and all-round imaging of the environment is achieved.

[0062] Example 2

[0063] This embodiment provides a millimeter wave synthetic aperture radar imaging method based on an arc antenna array, comprising the following steps:

[0064] Step 1: Establish a spatial rectangular coordinate system, the origin of which coincides with the center of the arc-shaped SISO line array, and define: the positive direction of the horizontal axis x is to the right, the positive direction of the vertical axis z is vertically upward, and the positive direction of the lateral axis y is backward.

[0065] Step 2: The SISO linear array is rotated to form a spherical crown SISO array, and the coordinates of the array elements in the spherical crown SISO array are determined according to the spatial rectangular coordinate system.

[0066] Specifically, the coordinates of the array elements formed by the rotation are:

[0067] (R 0 cosφ i cosθ j ,R 0 cosφ i sinθ j ,R 0 sinφ i )

[0068]

[0069] Among them, R 0 is the radius of the SISO linear array, φ c The central angle of the circle is N pairs of transmitting and receiving elements in the linear array, and the frequency range is f min ~f max , the number of frequency sampling N f The azimuth scanning span is 360° and the number of samples is M.

[0070] In this embodiment, the beam angle of the millimeter wave signal emitted by the array element is 60°, and the radiation direction is perpendicular to the tangent direction of the arc at this point. Considering the influence of the beam angle, the radius of the linear array is set to R 0 =0.3m, the central angle is set to φ c = 60°, with N = 31 pairs of transmitting and receiving array elements distributed on it, and the frequency range [f min ,f max ]=[30,36]GHz, the number of frequency sampling points is N f =101, the azimuth scanning span is 360°, and the number of samples is M=180, which realizes omnidirectional imaging with a 0-360° azimuth span and a 0-90° elevation span. Therefore, the coordinates of the array element are:

[0071] (R 0 cosφ i cosθ j ,R 0 cosφ i sinθ j ,R 0 sinφ i )

[0072]

[0073] Step 3: Determine and eliminate redundant array element coordinates according to the optimization method.

[0074] Specifically, since BPA uses range pulse compression and projects it onto a spatial grid for energy coherent accumulation imaging, and the spherical crown array formed by the rotation of the imaging device of the present invention is arranged non-uniformly, the noise in the dense array element area is amplified to form artifacts. Therefore, the present invention proposes a method for discarding redundant array element echo data to enhance the imaging effect.

[0075] Considering that at the same pitch angle φ, the distribution density of array elements will increase with the increase of pitch angle φ, some element echo data can be evenly discarded according to the size of the pitch angle φ, in order to make the average distance between elements at different pitch angles φ tend to be equal, so as to achieve an approximately uniform arrangement of the array and improve the imaging quality. First, the largest azimuth scanning interval in the element of the transceiver array is taken as the optimal distance.

[0076]

[0077] Then we can get the uniform ideal array arrangement for each pitch angle φ ideal,i Corresponding array element number

[0078]

[0079] Based on this, the ideal sampling point distribution can be deduced as

[0080] (R 0 cosφ ideal,i cosθ ideal,j ,R 0 cosφ ideal,i sinθ ideal,j ,R 0 sinφ ideal,i )

[0081]

[0082] For each array element under the ideal arrangement, find the actual array element closest to it and mark it as the effective array element

[0083] (R 0 cosφ useful,i cosθ useful,j ,R 0 cosφ useful,i sinθ useful,j ,R 0 sinφ useful,i )

[0084]

[0085] Based on this, the echo data of the unmarked redundant array elements are discarded, and the echo data under the approximately uniform array arrangement can be obtained.

[0086] In the above steps, according to the above optimization method for discarding redundant array element echo data, the ideal array arrangement is calculated, and the effective elements are marked, and then the unmarked redundant array element echo data is discarded, so as to obtain approximately uniform array echo data, and combined with the existing interpolation backprojection algorithm, imaging can be completed.

[0087] Step 4: Sample according to the coordinates of the selected array elements and infer the echo signal model:

[0088] s(k,θ,φ)=∫∫∫σ(x',y',z')·exp(-2jkR R )dx'dy'dz'

[0089] Where j represents the imaginary unit, s(·) represents the echo signal, k = 2π / λ is the spatial wave number, σ(·) represents the target function, R R is the distance from the target to the receiving array element, x', y', z' respectively represent the azimuth, height and range coordinate position of the target point to be reconstructed;

[0090] Among them, R R is the distance from the target to the array element, which is defined as:

[0091]

[0092] Step 5: Based on the echo signal model, the sampled echo data is used as input to reconstruct the image through the SAR imaging algorithm.

[0093] In this embodiment, a planar SISO-SAR device with a similar footprint is selected for comparison with the embodiment, and its parameters are that the linear array is placed along the x-axis, the length is 0.3m, 67 pairs of transmitting and receiving array elements are distributed thereon, the frequency range and the number of frequency sampling points are consistent with the embodiment, and mechanical scanning is performed along the y-axis, and the number of samplings is 67. Two devices are used to simultaneously image a 11×11 planar dot array target of 0.5×0.5m in size placed 0.5m away from the antenna.

[0094] See also Figure 5 The imaging result of the method for discarding redundant array element echo data provided by the present invention is as follows: Figure 4The imaging results of the bare back-projection imaging algorithm are shown in Figure 2. Both of them are simulated on the embodiments. The bare back-projection algorithm does not work well due to the non-uniform array arrangement of the system, and large-area artifacts appear. The back-projection algorithm that discards the redundant array element echo data performs better. The comparison shows that the method of discarding redundant array element echo data proposed in the present invention can effectively improve the imaging performance of the back-projection algorithm applied to non-uniform arrays.

[0095] Figure 5 For example, imaging results are shown in Figure 2. Figure 3 The planar SISO-SAR imaging result shows that the planar SISO-SAR can only image some point targets, while the embodiment can successfully image all the set point targets. By comparison, the millimeter-wave synthetic aperture radar imaging device based on the arc antenna array effectively solves the problem of insufficient viewing angle of the traditional SISO-SAR, can take into account both forward and side imaging, and realize all-round imaging of the environment, which is of great significance to improving the imaging performance of the array SAR, such as the viewing angle.

[0096] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments including components are made without departing from the principles and spirit of the present invention, and still fall within the scope of protection of the present invention.

Claims

1. An imaging method for a millimeter wave synthetic aperture radar imaging device based on an arc antenna array, the imaging device comprising a control and processing terminal (1), a mechanical rotating mechanism (2) and a SISO linear array (3), the SISO linear array (3) comprising a plurality of transceiver array elements (301), the plurality of transceiver array elements (301) being arranged in an arc shape, and the distance between two adjacent transceiver array elements (301) being the same, the SISO linear array (3) being arranged on the mechanical rotating mechanism (2), the control and processing terminal (1) being respectively connected to the mechanical rotating mechanism (2) and the SISO linear array (3) by signal, the control and processing terminal (1) being loaded with a SAR imaging algorithm of an echo signal, characterized in that: The steps include: Step 1: Establish a spatial rectangular coordinate system, with the origin of the coordinate system coinciding with the center of the arc-shaped SISO linear array; Step 2, rotating the SISO linear array to form a spherical crown SISO array, and determining the coordinates of the array elements in the spherical crown SISO array according to the spatial rectangular coordinate system; Step 3: Determine and eliminate redundant array element coordinates through optimization; The screening method of the array elements is: First, the optimal distance is the largest azimuth scanning interval of the array elements in the transceiver array: Where R0 is the radius of the SISO linear array, N refers to the N pairs of transmitting and receiving array elements distributed on the linear array, Thus, the number of array elements corresponding to each pitch angle φ under a uniform ideal array arrangement is obtained: Based on this, the ideal sampling point distribution can be deduced as: Among them, φ c is the size of its central angle; For each array element under the ideal arrangement, find the actual array element closest to it and mark it as a valid array element: Finally, the echo data of the redundant array elements that are not marked are discarded, and the echo data under the approximately uniform array arrangement can be obtained; Step 4: Sampling is performed according to the coordinates of the array elements after screening to obtain the echo signal model: s(k,θ,φ)=∫∫∫σ(x',y',z')·exp(-2jkR R )dx'dy'dz' Where j represents the imaginary unit, s(·) represents the echo signal, k = 2π / λ is the spatial wave number, σ(·) represents the target function, R R is the distance from the target to the receiving array element, x', y', z' respectively represent the azimuth, height and range coordinate position of the target point to be reconstructed; Step 5: Based on the echo signal model, the sampled echo data is used as input to reconstruct the image through the SAR imaging algorithm.

2. The millimeter wave synthetic aperture radar imaging method based on an arc antenna array according to claim 1, characterized in that: The transceiver array element comprises a transmitting array element and a receiving array element. The control and processing terminal (1) outputs a control signal to control the transmitting array element to transmit a millimeter wave signal. The receiving array element receives an echo signal of the millimeter wave signal and transmits it to the control and processing terminal (1). The control and processing terminal (1) performs imaging processing on the echo signal using a SAR imaging algorithm.

3. The millimeter wave synthetic aperture radar imaging method based on an arc antenna array according to claim 1, characterized in that: The mechanical rotating mechanism (2) comprises a rotating disk and a driving mechanism, the control and processing terminal (1) outputs a control signal to the driving mechanism to drive the rotating disk to rotate, and the SISO linear array (3) is arranged on the rotating disk.

4. The millimeter wave synthetic aperture radar imaging method based on an arc antenna array according to claim 3, characterized in that: The center of the SISO linear array (3) is on the rotating axis of the rotating disk, and the lowest transceiver array element (301) is located on the surface of the rotating disk.

5. The millimeter wave synthetic aperture radar imaging method based on arc antenna array according to claim 3 is characterized in that: The radius of the SISO linear array (3) is 0.3 m.

6. The millimeter wave synthetic aperture radar imaging method based on an arc antenna array according to claim 1, characterized in that: The SAR imaging algorithm adopts a back-projection algorithm.

7. The millimeter wave synthetic aperture radar imaging method based on arc antenna array according to claim 1, characterized in that: The coordinate expression of the array element is as follows: (R0 cosφ i cosθ j ,R0 cosφ i sinθ j ,R0 sinφ i ) in, Where R0 is the radius of the SISO linear array, φ c The central angle of the circle is N pairs of transmitting and receiving elements are distributed on the linear array, and the frequency range is f min ~f max , the number of frequency sampling N f The azimuth scanning span is 360° and the number of samples is M.

8. The millimeter wave synthetic aperture radar imaging method based on arc antenna array according to claim 7, characterized in that: In step 2, the distance R from the target to the array element is obtained according to the coordinates of the array element. R :

9. The millimeter wave synthetic aperture radar imaging method based on arc antenna array according to claim 8, characterized in that: The sampling frequency of the array element echo data is: frequency range [f min ,f max ]=[30,36]GHz.

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