阅读说明：本技术 一种稀疏阵列稀疏频点平面扫描体制快速成像方法 (Rapid imaging method of sparse array sparse frequency point planar scanning system ) 是由 孟祥新 高炳西 李霆 安德越 于 2020-12-24 设计创作，主要内容包括：本发明公开了一种稀疏阵列稀疏频点平面扫描体制快速成像方法,属于毫米波人身安全检查应用技术领域,包括以下步骤：S1：采集回波信号；S2：频率维度稀疏重建；S3：数据重排；S4：相位补偿；S5：计算距离分布函数；S6：后向投影算法重建。本发明通过获得目标距离分布函数,只需要重建目标的二维图像,相比于传统的三维重建算法,计算流程较为简单,计算效率较高；采用一维稀疏阵列构型,接收阵元相比于密集阵列的接收阵元数目相一致,但是发射阵元是稀疏的,因此阵元总数目能够得到大幅降低,相应的硬件成本也能够得到降低。同时在信号模式上采用的是稀疏信号体制,使得阵列维度扫描的速度得以提升。(The invention discloses a sparse array sparse frequency point planar scanning system rapid imaging method, which belongs to the technical field of millimeter wave personal safety inspection application and comprises the following steps: s1: collecting echo signals; s2: sparse reconstruction of frequency dimension; s3: rearranging data; s4: phase compensation; s5: calculating a distance distribution function; s6: and (4) reconstructing by using a back projection algorithm. According to the method, only a two-dimensional image of the target needs to be reconstructed by obtaining the target distance distribution function, and compared with a traditional three-dimensional reconstruction algorithm, the method is simple in calculation process and high in calculation efficiency; by adopting a one-dimensional sparse array configuration, the number of receiving array elements is consistent compared with that of receiving array elements of a dense array, but the transmitting array elements are sparse, so that the total number of the array elements can be greatly reduced, and the corresponding hardware cost can also be reduced. Meanwhile, a sparse signal system is adopted in a signal mode, so that the array dimension scanning speed is improved.)

1. A sparse array sparse frequency point planar scanning system rapid imaging method is characterized by comprising the following steps:

s1: collecting echo signals

The imaging system generates a sparse frequency signal according to a preset sparse frequency point, the sparse frequency signal is transmitted through a transmitting antenna, and a sparse echo signal demodulated by a millimeter wave intermediate frequency receiver is s (x)_Tx,x_Rx,y,k_sparse)，x_TxFor the horizontal dimension of the transmit array, x_RxFor the receive array horizontal dimension, y is the mechanical scan dimension, and k is the frequency scan dimension;

s2: frequency dimension sparse reconstruction

For echo signal s (x)_Tx,x_Rx,y,k_sparse) Performing sparse recovery reconstruction on the frequency scanning dimension to obtain a recovery signal s (x)_Tx,x_Rx,y,k)；

S3: data rearrangement

For the recovered signal s (x)_Tx,x_RxY, k) performing equivalent phase center processing to obtain a sparse array equivalent echo signal s (x, y, k);

s4: phase compensation

Performing phase compensation and correction on the equivalent echo signal s (x, y, k), and compensating a phase error caused by processing of an equivalent phase center;

s5: calculating a distance distribution function

Calculating a distance distribution function z (x, y) of s (x, y, k) by adopting a distance position distribution calculation method;

s6: backprojection algorithm reconstruction

And according to the calculated distance distribution function z (x, y), calculating to obtain a two-dimensional complex image of the target by adopting a back projection reconstruction algorithm.

2. The method for rapidly imaging the sparse array sparse frequency point planar scanning system according to claim 1, wherein the method comprises the following steps: in the step S1, the signal system transmitted by the imaging system is a step-frequency continuous wave signal, the frequency range of the signal is 70 to 80GHz, the number of the transmitting array elements is M, and the array element interval is Δ x_T(ii) a The number of receiving array elements is N, and the array element interval is Deltax_RWhile the imaging system is in operationThe transmitting channel is opened in time-sharing mode, and the receiving channels receive in a segmented and simultaneous mode.

3. The method for rapidly imaging the sparse array sparse frequency point planar scanning system according to claim 2, wherein the method comprises the following steps: in the step S2, a recovery signal S (x) is obtained_Tx,x_RxThe specific process of y, k) is as follows:

s21: first pair s (x)_Tx,x_Rx,y,k_sparse) Zero filling processing is carried out on the sparse position of the k-dimension frequency points;

s22: obtaining a frequency spectrum signal s by adopting a non-uniform Fourier transform algorithm_f(x_Tx,x_Rx,y,k)＝FFT_non-uniform[s(x_Tx,x_Rx,y,k_sparse)]；

S23: finally, the obtained frequency spectrum signal s is subjected to_f(x_Tx，x_RxY, k) is subjected to inverse Fourier transform to obtain a uniform frequency point signal s (x)_Tx，x_Rx，y，k)。

4. The method for rapid imaging of sparse array sparse frequency point planar scanning system according to claim 3, wherein the method comprises the following steps: in step S3, the specific process of the equivalent phase center processing is as follows:

s31: the position coordinates of the transmitting and receiving antenna are calculated as follows to obtain the coordinates of the equivalent array element position, and the calculation formula is as follows:

x＝(x_Tx+x_Rx)/2，y＝(y_Tx+y_Rx)/2；

s32: and rearranging the echo data according to the array dimension equivalent position to obtain a sparse array equivalent echo signal s (x, y, k).

Further, in step S4, the phase compensation signal is:

where k 2 pi f/c is the spatial frequency wavenumber,in order to transmit the coordinates of the array,in order to receive the array coordinates,as reference point target coordinates, z_refIs a reference point distance coordinate.

5. The method for rapid imaging of sparse array sparse frequency point planar scanning system according to claim 4, wherein the method comprises the following steps: in step S5, the distance position distribution calculation method is to calculate different frequency points as follows:

s51: multiplying all frequency point data by complex conjugate of first frequency point data to obtain signal ofWhere superscript denotes conjugation;

s52: for signal S_inter(x,y,k₁,k_n) Calculating an initial phase value S_phase(x,y,k₁,k_n)＝angle(S_inter(x,y,k₁,k_n) Angle () represents the phase of the complex signal;

s53: for the initial phase value S_phase(x,y,k₁,k_n) Performing unwrapping operation on the frequency dimension k to obtain an unwrapped phase signal S_unwrapphase(x,y,k₁,k_n)＝unwrap(S_phase(x,y,k₁,k_n) Unwrap () represents an unwrapping operation;

s54: according to the unwinding signal S_unwrapphase(x,y,k₁,k_n) Calculating the delay time DeltT from the target to the antenna aperture_n＝S_unwrapphase(x,y,k₁,k_n)/(-2*pi*f_n)；

S55: finally obtaining the position of the target in the distance dimensionLabeled z (x, y) ═ 2 × DeltT_max*c。

6. The method for rapid imaging of sparse array sparse frequency point planar scanning system according to claim 5, wherein the method comprises the following steps: in step S6, calculating a target two-dimensional image σ (x, y) by using a back projection algorithm according to the obtained target distance position distribution function z (x, y); after recovering the signal s (x)_Tx,x_RxThe k dimension of y, k) is subjected to inverse Fourier transform to obtain s (x)_Tx,x_RxY, z), dividing two-dimensional grid coordinates (x, y, z (x, y)), where x is the coordinate of the equivalent echo signal array dimension and y is the coordinate of the mechanical scan dimension, and calculating as followsWherein M is [1, M ]]For the index of the transmitting array element, M is the number of the transmitting array element, N belongs to [1, N ∈]For the index of the receiving array element, N is the number of the receiving array element, and Q belongs to [1, Q ∈]An index that is a mechanical scan dimension;is the signal s (x)_Tx,x_RxY, z) of the same order,for a rounding-down operation, wherein B＝f_max-f_minB is the bandwidth of the transmitted signal, f_maxFor the maximum frequency value of the transmitted signal, f_minIs the minimum frequency value of the transmitted signal.

7. The method for rapid imaging of sparse array sparse frequency point planar scanning system according to claim 6, wherein the method comprises the following steps: after the two-dimensional complex images are obtained, the two-dimensional complex images are subjected to target detection, identification or image processing and then sent to a display end for image display.

Technical Field

The invention relates to the technical field of millimeter wave personal safety inspection application with small passenger flow and high precision, in particular to a rapid imaging method of a sparse array sparse frequency point planar scanning system.

Background

The millimeter wave array type holographic imaging technology has been widely applied to the field of personal safety inspection, in recent years, a millimeter wave array plane scanning type holographic imaging system has been applied to millimeter wave human body security inspection instruments, and part of manufacturers have already realized commercial application, thus really realizing industrialization of the millimeter wave technology.

At present, a one-dimensional dense array is adopted by a human body security check instrument of a plane scanning system, a classic back projection algorithm, a wave number domain algorithm or a phase shift migration algorithm is adopted by a traditional one-dimensional millimeter wave dense array type holographic imaging algorithm, a reconstructed image is a three-dimensional image, the three-dimensional image is converted into a two-dimensional image through projection when being displayed, most millimeter wave security check manufacturers directly adopt the two-dimensional image for target detection and subsequent processing, most pixel values in the calculated three-dimensional image are invalid, and corresponding hardware resources contributing to invalid pixels are also redundant. When the three-dimensional reconstruction algorithm is adopted to reconstruct the image, the requirements on the storage resources and the calculation resources of signal processing hardware are higher, and the calculation efficiency is lower. The above problems need to be solved, and therefore, a method for rapidly imaging a sparse array sparse frequency point planar scanning system is provided.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: how to solve the problem that the existing imaging method has higher calculation resource requirement, and the calculation efficiency is lower, etc., a sparse array sparse frequency point planar scanning system rapid imaging method is provided, by obtaining a target distance distribution function, only a two-dimensional image of a target needs to be reconstructed, compared with the traditional three-dimensional reconstruction algorithm, the calculation process is simpler, the calculation efficiency is higher, a one-dimensional sparse array configuration is adopted, the number of receiving array elements is consistent compared with that of receiving array elements of a dense array, but the transmitting array elements are sparse, therefore, the total number of array elements can be greatly reduced, the corresponding hardware cost can also be reduced, meanwhile, a sparse signal system is adopted on a signal mode, and the array dimension scanning speed is improved.

The invention solves the technical problems through the following technical scheme, and the invention comprises the following steps:

(1) the imaging system generates a sparse frequency signal according to a preset sparse frequency point, the sparse frequency signal is transmitted through a transmitting antenna, and a sparse echo signal demodulated by a millimeter wave intermediate frequency receiver is s (x)_Tx,x_Rx,y,k_sparse)，x_TxFor the horizontal dimension of the transmit array, x_RxTo receive the array horizontal dimension, y is the mechanical scan dimension and k is the frequency scan dimension.

(2) For the echo signal s (x)_Tx,x_Rx,y,k_sparse) Performing sparse recovery reconstruction on the frequency scanning dimension to obtain a recovery signal s (x)_Tx,x_Rx,y,k)。

(3) For the recovered signal s (x)_Tx,x_RxX of y, k)_TxDimension and x_RxAnd carrying out equivalent phase center processing on the dimension to obtain an echo signal s (x, y, k) of an equivalent array.

(4) The equivalent array echo signal s (x, y, k) is phase corrected by the following operation s_corr(x,y,k)＝s(x,y,k)*H₁(x, y, k) wherein H₁(x, y, k) is a phase compensation signal.

(5) For the corrected echo signal s_corrAnd (x, y, k) carrying out interference processing on different frequency points and calculating a distance distribution function of the target.

(6) And calculating a target two-dimensional image sigma (x, y) by adopting a back projection algorithm according to the obtained target distance distribution function z (x, y), and dividing the two-dimensional imaging grid coordinates into (x, y, z (x, y)), wherein (x, y) corresponds to the position of the equivalent echo array element and the position of the mechanical scanning dimension, and the distance dimension value is set as the solved distance distribution function z (x, y). Since the divided imaging grid coordinates are two-dimensional, the reconstructed image is also two-dimensional.

(7) Further, the two-dimensional complex image sigma (x, y) is subjected to target detection, identification or image processing, and then is sent to a display end for image display.

In the step (1), the space coverage range of the horizontal dimension of the one-dimensional sparse array is 0.99m, and the interval of the transmitting array elements is delta x_T0.99m, the receiving array element spacing is Deltax_R＝0003m, the transmission array element figure is 2, and the receiving array element figure is 330, at system work, opens single transmission array element, and all receiving array element segmentation are opened and are received simultaneously, and the segmentation figure is 10 for N, includes 33 passageways in every section, and the acquisition integrated circuit board is gathered 33 receiving channel simultaneously, and after data acquisition in one section array element finishes, next section receiving array element passageway is opened and is gathered. When the array dimension data is acquired, the one-dimensional sparse array integrally moves up and down, so that the coverage range of the mechanical scanning dimension is 2m, and finally the echo data of the target is obtained.

In the step (2), the sparse reconstruction method is to firstly perform the reconstruction on s (x)_Tx,x_Rx,y,k_sparse) The k-dimension sparse position zero filling processing is carried out, and then a known non-uniform Fourier transform algorithm is adopted to obtain a frequency spectrum signal s_f(x_Tx,x_Rx,y,k)＝FFT_non-uniform[s(x_Tx,x_Rx,y,k_sparse)]Finally, for the obtained spectrum signal s_f(x_Tx,x_RxY, k) is subjected to inverse Fourier transform to obtain a uniform frequency point signal s (x)_Tx,x_Rx,y,k)。

In the step (3), the specific processing method is to calculate the array element coordinates after the equivalent processing, where x is (x ═ x)_Tx+x_Rx)/2，y＝(y_Tx+y_Rx) And/2, directly equating the coordinate y to the central position of the transmitting-receiving array element in the y direction, equating the x-dimension array element interval to be 0.0015m, and recovering the signal s (x) when the two-dimension coordinates are equivalent_Tx,x_RxY, k) are rearranged according to the equivalent coordinate x.

In the step (4), the expression of the phase compensation signal isWhere k 2 pi f/c is the spatial frequency wavenumber,in order to transmit the coordinates of the array,in order to receive the array coordinates,target coordinates of (0,0, z) as reference points_ref)，z_refIs the distance coordinate of the reference point, in particular the center distance of the imaging target, and c is the speed of the electromagnetic wave in free space.

In the step (5), the specific processing method is to calculate different frequency points as follows:

1)

2) calculating an initial phase S_phase(x,y,k₁,k_n)＝angle(S_inter(x,y,k₁,k_n))；

3) De-winding the frequency dimension k to obtain a de-wound signal S_unwrapphase(x,y,k₁,k_n)＝unwrap(S_phase(x,y,k₁,k_n))；

4) Calculating the delay time DeltT from the target to the antenna aperture_n＝S_unwrapphase(x,y,k₁,k_n)/(-2*pi*f_n)；

5) The distance position where the target can be finally obtained is z (x, y) ═ 2 DeltT_max*c。

In the step (6), the signal s (x) is recovered_Tx,x_RxThe k dimension of y, k) is subjected to inverse Fourier transform to obtain s (x)_Tx,x_RxY, z), dividing two-dimensional grid coordinates (x, y, z (x, y)), where x is the coordinate of the equivalent echo signal array dimension and y is the coordinate of the mechanical scan dimension, and calculating as followsWherein M is [1, M ]]The index M of the transmitting array element is 2, N belongs to [1, N ∈]For the index of the receiving array element, N is 330, Q is equal to [1, Q ∈]Is an index of the mechanical scan dimension and,is the signal s (x)_Tx,x_RxY, z) of the same order,for a rounding-down operation, wherein B＝f_max-f_min，f_maxFor the maximum frequency value of the transmitted signal, f_minIs the minimum frequency value of the transmitted signal.

Compared with the prior art, the invention has the following advantages: the sparse array sparse frequency point planar scanning system rapid imaging method is applied to occasions with small passenger flow and fine security check, a one-dimensional sparse array sparse frequency point scanning and mechanical scanning mode is adopted, the whole aperture covers the field range of a human body, and due to the fact that the sparse system is adopted for transmitting signals, the scanning time of array dimensions is saved, and the time for obtaining target echoes is reduced. In the signal processing imaging algorithm, only the position coordinates of the distance dimension of the human body are calculated, and then the back projection reconstruction algorithm is adopted, the reconstructed image is a two-dimensional image.

Drawings

FIG. 1 is a flow chart of a sparse array sparse frequency point planar scanning system fast imaging method in an embodiment of the present invention;

FIG. 2 is a schematic distribution diagram of one-dimensional sparse array elements in an embodiment of the present invention;

FIG. 3 is a scanning schematic of an imaging system in an embodiment of the invention.

Detailed Description

The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.

As shown in fig. 1, the present embodiment provides a technical solution: a sparse array sparse frequency point planar scanning system rapid imaging method comprises the following specific processes:

the millimeter wave one-dimensional sparse array configuration is shown in fig. 2, the gray solid array elements are transmitting array elements, the white hollow array elements are receiving array elements, the spatial coverage range of the horizontal dimension of the one-dimensional sparse array is 0.99m, and the interval of the transmitting array elements is deltax_T0.99m, the receiving array element spacing is Deltax_RWhen the imaging system works, a single transmitting array element channel is opened, the transmitted signals are sparse signals, all receiving array element channels are opened in a segmented mode and received simultaneously, the segmented number is N10, each segment comprises 33 channels, the acquisition board card acquires 33 receiving channels simultaneously, and after data acquisition in one array element is finished, the next receiving array element channel is opened and acquired. When all receiving channels finish collecting, the next transmitting channel is started until all array dimension data are collected, and the one-dimensional sparse array integrally moves from top to bottom or from bottom to top while the array dimension data are collected, so that the aperture covers the whole human body, and finally echo data of the whole human body are obtained. The sparse echo signal after the demodulation of the millimeter wave intermediate frequency receiver is s (x)_Tx,x_Rx,y,k_sparse)，x_TxFor the horizontal dimension of the transmit array, x_RxTo receive the array horizontal dimension, y is the mechanical scan dimension and k is the frequency scan dimension. (k)_sparseRefers to the corresponding wave number, k, of the sparse frequency points_sparse＝2*pi*f_sparse/c；f_sparseFor sparse frequency points)

For sparse echo signal s (x)_Tx,x_Rx,y,k_sparse) The zero filling processing is carried out on the sparse position of the k-dimensional frequency points, and then a known non-uniform Fourier transform algorithm is adopted to obtain a frequency spectrum signal s_f(x_Tx,x_Rx,y,k)＝FFT_non-uniform[s(x_Tx,x_Rx,y,k_sparse)]For the resulting spectral signal s_f(x_Tx,x_RxY, k) is subjected to inverse Fourier transform to obtain a recovery signal s (x) of a uniform frequency point_Tx,x_Rx,y,k)。

For the recovered signal s (x)_Tx,x_RxX of y, k)_TxDimension and x_RxAnd carrying out equivalent phase center processing on the dimension to obtain an echo signal s (x, y, k) of an equivalent array. The equivalent array echo signal s (x, y, k) is phase corrected by the following operation s_corr(x,y,k)＝s(x,y,k)*H₁(x, y, k) wherein H₁(x, y, k) are phase compensation signals,where k 2 pi f/c is the spatial frequency wavenumber,in order to transmit the coordinates of the array,to receive the array coordinates.As equivalent echo position coordinates, x_c＝(x_Tx+x_Rx)/2，y_c＝(y_Tx+y_Rx)/2。Target coordinates of (0,0, z) as reference points_ref)，z_refThe distance coordinates of the reference point are the center distance of the human body target in the distance dimension in practical application.

For the corrected echo signal s_corrInterference processing is carried out on different frequency points of (x, y, k) and distance dimension coordinates are obtained to obtain a distance distribution function of the target, and the specific processing method comprises the following steps:

1) multiplying all frequency point data by the complex conjugate of the first frequency point data to obtain a signalWhere superscript denotes conjugation;

2) to the signal S_inter(x,y,k₁,k_n) Calculating an initial phase value S_phase(x,y,k₁,k_n)＝angle(S_inter(x,y,k₁,k_n) Angle () represents the phase of the complex signal;

3) to the initial phase value S_phase(x,y,k₁,k_n) Performing unwrapping operation on the frequency dimension k to obtain an unwrapped phase signal S_unwrapphase(x,y,k₁,k_n)＝unwrap(S_phase(x,y,k₁,k_n) Unwrap () represents an unwrapping operation;

4) based on the unwinding signal S_unwrapphase(x,y,k₁,k_n) Calculating the delay time DeltT from the target to the antenna aperture_n＝S_unwrapphase(x,y,k₁,k_n)/(-2*pi*f_n)；

5) And finally obtaining the position coordinate of the target in the distance dimension as z (x, y) ═ 2 DeltT_max*c。

And calculating a target two-dimensional image sigma (x, y) by adopting a back projection algorithm according to the obtained target distance position distribution function z (x, y). After recovering the signal s (x)_Tx,x_RxThe k dimension of y, k) is subjected to inverse Fourier transform to obtain s (x)_Tx,x_RxY, z), dividing two-dimensional grid coordinates (x, y, z (x, y)), where x is the coordinate of the equivalent echo signal array dimension and y is the coordinate of the mechanical scan dimension, and calculating as followsWherein M is [1, M ]]For the index of the transmitting array element, M is 2, N belongs to [1, N ∈]For the index of the receiving array element, N is 330, Q is equal to [1, Q ∈]For the index of the mechanical scan dimension, Q is 1000.Is the signal s (x)_Tx，x_RxY, z) of the same order,is a rounding-down operation; wherein B＝f_max-f_min，f_maxFor the maximum frequency value of the transmitted signal, f_minIs the minimum frequency value of the transmitted signal.

6) And further carrying out target detection, identification or image processing on the two-dimensional complex image sigma (x, y), and then sending to a display end for image display.

To sum up, in the rapid imaging method of the sparse array sparse frequency point planar scanning system of the embodiment, the imaging system adopts a design method of array element sparsity and frequency point sparsity, so that the acquisition speed of echo signals is improved, the duration of a human body in a static state is greatly shortened, and rapid passing of people streams is facilitated; according to the method, the distribution of the target in the distance direction is obtained through estimation of the target distance function, then two-dimensional image reconstruction is carried out on the target through a backward projection algorithm, the distance image is calculated only according to the frequency dimension of echo data, so that the target distance function can be calculated in a sparse array dimension and a mechanical scanning dimension in a large parallelism mode, the algorithm only reconstructs two-dimensional images, and the consumed storage resources and calculation resources of signal processing hardware are reduced, so that the image reconstruction speed can be increased, the signal processing hardware cost can be reduced, and the method is worthy of popularization and application.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.