CN114494473A - Millimeter wave sparse array time domain type rapid image reconstruction method and system - Google Patents
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Abstract
The invention discloses a millimeter wave sparse array time domain type rapid image reconstruction method and a millimeter wave sparse array time domain type rapid image reconstruction system, which belong to the technical field of millimeter wave personal safety inspection and comprise the following steps: s1: receiving a sparse array echo signal; s2: dividing a subarray; s3: dividing an imaging area; s4: calculating the oblique moment; s5: reconstructing a four-subarray image; s6: turning and sequencing subgraphs; s7: and (5) image splicing. The method for synthesizing limited echo data, dividing limited imaging grid regions and sharing a group of matched filter coefficients and interpolation coefficients reduces the calculated amount of the traditional back projection reconstruction algorithm, is properly balanced in the aspects of imaging quality and calculation efficiency, effectively improves the calculation efficiency compared with the traditional back projection reconstruction algorithm, and is worthy of popularization and use.
Description
Technical Field
The invention relates to the technical field of millimeter wave personal safety inspection, in particular to a millimeter wave sparse array time domain type rapid image reconstruction method and system.
Background
With the commercialized application of millimeter wave human body security inspection imaging technology, mainstream security inspection imaging systems are divided into a one-dimensional dense array plane scanning system, a one-dimensional dense array cylindrical surface scanning system, a two-dimensional phased array imaging system, and a two-dimensional sparse array imaging system. The imaging system of one-dimensional dense array scanning needs the human body to stay still for 1-2 seconds in a fixed scene because the process of acquiring echo data is slow, so that the passing efficiency of passengers is limited, and the imaging system is only suitable for occasions with low passenger flow for security inspection. The two-dimensional phased array imaging system and the two-dimensional sparse array imaging system have obvious advantages in the speed of acquiring the echo data of the human body, and the backscattering echo data covering the human body area can be acquired only by tens of milliseconds, so that the method has the potential of rapid passing application of the human body. The two-dimensional sparse array imaging system has obvious advantage in the speed of acquiring echo data, so the bottleneck of the rapid human body passing application is the speed of image reconstruction.
Due to the sparse characteristic of spatial distribution, the sparse array configuration adopts a back projection reconstruction algorithm which is the best choice, and the basic principle of the back projection reconstruction algorithm is delay phase compensation and accumulation calculation, so that the calculation amount of the algorithm is large. In order to improve the computational efficiency of the back projection reconstruction algorithm, either the processing capability of a hardware signal processing platform is improved, or the computational efficiency of the back projection reconstruction algorithm is improved. The improvement of the processing capability of the hardware signal processing platform means that computing resources, control resources and storage resources need to be added, and along with the increase of the hardware cost, how to improve the existing processing capability and improve the computing efficiency of the back projection reconstruction algorithm on the premise of not increasing the hardware cost is an urgent problem to be solved. Therefore, a millimeter wave sparse array time domain type rapid image reconstruction method is provided.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: on the premise of not increasing hardware cost, the conventional processing capacity is improved, the calculation efficiency of a back projection reconstruction algorithm is improved, and a millimeter wave sparse array time domain type rapid image reconstruction method is provided.
The invention solves the technical problems through the following technical scheme, and the invention comprises the following steps:
s1: receiving sparse array echo signals
The two-dimensional sparse array arranged in space realizes antenna beam scanning in two dimensions in space by switching of an antenna array switch, an imaging target range is covered, a single transmitting antenna is utilized to transmit electromagnetic wave signals, all receiving antennas simultaneously receive backscattered electromagnetic waves, down-conversion is carried out on the backscattered electromagnetic waves to intermediate frequency signals, then digitization of analog signals is realized through a multi-channel digital acquisition module, the digitized signals are demodulated into digital I/Q signals through digital down-conversion, and the obtained target backscattered three-dimensional echo signals are s (x)Tx,yTx,xRx,yRx,k)，xTxFor the horizontal dimension of the transmit array, yTxFor the vertical dimension of the emitting array, xRxTo receive the array horizontal dimension, yRxFor the receive array vertical dimension, k 2 × pi × fre/c is the frequency scan dimension, where fre is the frequency of the transmit signal and fre e [ f ∈ [ f [ ]min,fmax]；
S2: subarray division
Dividing sixteen sub-arrays into groups, overlapping every four sub-arrays into a group, and obtaining an echo signal ssub4(xTx,yTx,xRx,yRx,k)；
S3: imaging region partitioning
Dividing an imaging area, and according to the idea of an equivalent array, obtaining the sampling position coordinates of the equivalent array elements by using a single-subarray transmitting array element and a four-subarray receiving array element as a group in a four-subarray unit, wherein the obtained area is divided into four imaging areas in the four-subarray unit;
s4: calculating skew moment
Calculating the slant range R of the back projection reconstruction algorithm under the single sub-array transmitting four sub-array receiving modesub_Tx、Rsub_RxAccording to array spatial distributionThe slant distances of other single sub-array transmitting four sub-array receiving modules in the four sub-arrays are consistent, and the calculated matched filter Href (x) of the back projection reconstruction algorithmsub_Tx，ysub_Tx，xsub_Rx，ysub_RxX, y, z) are consistent, the vertex of the emission single subarray is respectively taken as an origin according to the principle of a relative coordinate system, the grid coordinate values of the divided imaging sub-regions are consistent, and then the three-dimensional complex image sigma of the back projection reconstruction algorithm of the four imaging sub-regions is calculatedsub(x',y',z')；
S5: four subarray image reconstruction
According to the symmetry principle and the relative coordinate system principle, the three-dimensional images of the four imaging sub-areas are symmetrically turned and sequenced, and the overlapped areas are accumulated to obtain four sub-array module sub-images
S6: subgraph turning and sorting
Repeating the steps S3-S5 until the calculation of the sub-images of the imaging area of all the four sub-array modules is completed;
s7: image stitching
And splicing all the three-dimensional complex sub-images to obtain a final three-dimensional complex image, and then performing maximum projection of a distance dimension to obtain two-dimensional projection images of two azimuth dimensions.
Furthermore, in step S1, the two-dimensional sparse array is formed by sixteen square sub-arrays arranged at equal intervals, the frequency range of the signal transmitted by the imaging system is 30 to 40GHz, the number of the transmission array elements of each square sub-array is 46, and the interval is Δ xT0.0068m, the number of receiving array elements in the sub-array is 46, and the distance is delta yR＝0.0068m。
Furthermore, when the imaging system works, the transmitting array element is opened in a time-sharing mode under the trigger of a time sequence generator of the whole system, and the receiving array element is normally opened and simultaneously receives a target backscatter echo signal.
Further, in the step S2The position coordinate of the equivalent array element is xc＝(xTx+xRx)/2，yc＝(yTx+yRx)/2，zcAnd (0) dividing sub-areas imaged in the four sub-arrays according to the coverage area of the equivalent array element position coordinates.
Further, in the step S4, the calculated slant range expression of the single sub-array transmission four sub-array receiving mode is:
further, in the step S4, the matched filter calculation expression is:
Href(xsub_Tx,ysub_Tx,xsub_Rx,ysub_Rx,x',y',z')＝exp(jkmin(Rsub_Tx+Rsub_Rx))
wherein k ismin＝2×π×fmin/c，fminC is the velocity of the electromagnetic wave in vacuum, which is the minimum frequency of the transmitted signal.
Further, in step S4, the three-dimensional complex image of the imaging sub-region is obtained as follows:
wherein,
the invention also provides a millimeter wave sparse array time domain type rapid image reconstruction system, which adopts the reconstruction method to reconstruct the image and comprises the following steps:
an echo signal receiving module for transmitting electromagnetic wave signals through a single transmitting antenna, all receiving antennas simultaneously receiving back scattering electromagnetic waves, converting the signals into intermediate frequency signals through down conversion, then realizing analog signal digitization through a multi-channel digital acquisition module, and demodulating the digitized signals into digital down conversion signalsDigital I/Q signal, and obtaining target backscattering three-dimensional echo signal s (x)Tx,yTx,xRx,yRx,k)；
A sub-array division module for dividing sixteen sub-arrays into groups, wherein every four sub-arrays are overlapped into a group, and the obtained echo signal is ssub4(xTx,yTx,xRx,yRx,k)；
The imaging area division module is used for dividing an imaging area, obtaining the sampling position coordinates of the equivalent array elements by taking the single-subarray transmitting array elements and the four-subarray receiving array elements as a group in the four-subarray units according to the equivalent array idea, and dividing the obtained area into four imaging areas in total for the imaging area division in the four-subarray units;
an oblique moment calculation module for calculating the oblique distance R of the back projection reconstruction algorithm in the single sub-array transmitting four sub-array receiving modesub_Tx、Rsub_RxAnd calculating a back projection reconstruction algorithm three-dimensional complex image sigma of the four imaging sub-regionssub(x',y',z')；
The image reconstruction module is used for symmetrically overturning and sequencing the three-dimensional images of the four imaging sub-areas according to a symmetry principle and a relative coordinate system principle and accumulating the overlapped areas to obtain sub-images of the four sub-array module
The overturning and sequencing module is used for repeating the steps S3-S5 until the calculation of the sub-images of the imaging area of all the four sub-array modules is completed;
the image splicing module is used for splicing all the three-dimensional complex sub-images to obtain a final three-dimensional complex image, and then performing maximum projection of distance dimensions to obtain two-dimensional projection images of two azimuth dimensions;
the control processing module is used for sending instructions to each module to complete corresponding actions;
the echo signal receiving module, the subarray division module, the imaging region division module, the oblique moment calculation module, the image reconstruction module, the overturning and sequencing module and the image splicing module are all electrically connected with the central processing module.
Compared with the prior art, the invention has the following advantages: the millimeter wave sparse array time domain type rapid image reconstruction method is applied to the human body security inspection occasions with larger passenger flow and high traffic efficiency, a millimeter wave Ka waveband two-dimensional sparse array configuration is designed, a matrix arrangement mode of sixteen square subarrays is adopted, a time domain type rapid imaging method is designed aiming at the array configuration, the calculation efficiency is greatly improved compared with the well-known back projection reconstruction algorithm, the space distribution characteristic of the square matrix arrangement mode is mainly adopted, the echo data are reasonably divided by fully utilizing an equivalent array method, a symmetry principle and a relative coordinate system principle, when the slant distance from a transmitting-receiving antenna array element to an imaging area is calculated, only one time needs to be calculated, other module units can use the same group of slant distance data which correspond to the same group of matched filters and interpolation coefficients, on the one hand, the calculation efficiency of image reconstruction is improved, the matched filter coefficients and the interpolation coefficients can be stored in a coefficient file during real-time calculation, the matched filter coefficients and the interpolation coefficients are automatically loaded to a hardware signal processing platform when the whole system is started, and the coefficients can be called from an internal memory during image reconstruction; the algorithm provided by the invention has larger parallelism in the whole structure, the data among the whole four-subarray imaging module are not related, and the data are not interdependent, and meanwhile, in the four-subarray imaging module, a single subarray transmits four subarray receiving modes and has parallelism, so that the algorithm is particularly suitable for parallel processing by adopting the hardware structures of FPGA, DSP and GPU.
Drawings
FIG. 1 is a schematic flow chart of a millimeter wave sparse array time domain class fast image reconstruction method according to the present invention;
FIG. 2 is a schematic diagram of the distribution of millimeter wave two-dimensional sparse array elements in the embodiment of the present invention, where horizontal dotted lines represent transmit array elements, and vertical solid lines represent receive array elements;
fig. 3 is an internal division of an imaging area of a four-subarray module in an embodiment of the present invention, where fig. 3(a) shows an equivalent array coverage area of all receiving subarrays of a first transmitting subarray, a shaded area shows the equivalent array coverage area, fig. 3(b) shows an equivalent array coverage area of all receiving subarrays of a second transmitting subarray, a shaded area shows the equivalent array coverage area, fig. 3(c) shows an equivalent array coverage area of all receiving subarrays of a third transmitting subarray, a shaded area shows the equivalent array coverage area, fig. 3(d) shows an equivalent array coverage area of all receiving subarrays of a fourth transmitting subarray, a shaded area shows the equivalent array coverage area, fig. 3(e) shows a schematic diagram of a relative coordinate system when the first transmitting subarray operates, and other transmitting subarrays operate similarly;
fig. 4 is a schematic diagram of a module for dividing a sixteen sub-array into four sub-arrays in an embodiment of the present invention, and a shaded portion is a division of an imaging area when four receiving sub-arrays of a single transmitting sub-array work, where fig. 4(a) to fig. 4(f) are schematic diagrams of a division of an imaging area when starting from a first transmitting sub-array to a sixth transmitting sub-array and working sequentially according to a sequence order, and the working of the sixteenth transmitting sub-array is completed in an implementation process.
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.
The embodiment provides a technical scheme: the configuration of the millimeter wave two-dimensional sparse array in the embodiment is shown in fig. 2, a horizontal dotted line type represents a transmitting array element, a vertical solid line type represents a receiving array element, the whole two-dimensional array is composed of sixteen square sub-arrays, and the interval between the transmitting array elements is delta xT0.0068m, the receiving array element spacing is DeltayR0.0068m, the number of transmitting array elements is 736, the number of receiving array elements is 736, the number of transmitting array elements in a single sub-array is 46, and the number of receiving array elements is 46. The arrows shown in FIG. 2 point to the working sequence of the transmitting array, the transmitting array is switched from left to right in turn, and the array elements of the receiving arrayWhile backscatter echoes of the target are received. The echo signal demodulated by the millimeter wave digital intermediate frequency receiver is s (x)Tx,yTx,xRx,yRx,k)，xTxFor the horizontal dimension of the transmit array, yTxFor the vertical dimension of the emitting array, xRxTo receive the array horizontal dimension, yRxFor the receive array vertical dimension, k is the frequency scan dimension, k 2 × pi × fre/c is the frequency scan dimension, where fre is the frequency of the transmit signal, fre ∈ [ f [ ]min,fmax]，fminTo minimum frequency of the transmitted signal, fmaxIs the maximum frequency of the transmitted signal.
For the echo signal s (x)Tx,yTx,xRx,yRxK) dividing the sixteen sub-arrays into four sub-array groups according to the overlapping rule based on the symmetrical characteristic, and obtaining the signal ssub4(xTx,yTx,xRx,yRxK) for said four sub-array signal s, as shown in fig. 3sub(xTx,yTx,xRx,yRxAnd k) further performing subarray division into a pattern of sub-apertures of four receiving arrays of a single transmitting array, the obtained signals being
To pair
Performing equivalent phase center processing to obtain equivalent array coordinate xc＝(xTx+xRx)/2，yc＝(yTx+yRx)/2，z c0, wherein xc∈[x'min,x'max]，yc∈[y'min,y'max]From xcAnd ycAnd the range of the imaged area of the human body in the distance dimension z 'epsilon [ z'min,z'max]Determining the spatial coverage range Ω (x ', y ', z ') of the equivalent array, wherein the specific way to determine the spatial coverage range is calculated as: x'min＝0，x'max＝2×(NTsub/2)×ΔxT，y'min＝0，y'max＝2×(NRsub/2)×ΔyR，z'min＝0.2m，z'max＝0.6m。
According to the range of the equivalent array coverage area Ω (x ', y ', z '), as shown in fig. 3, the gray shaded area is gridded with the vertex of the transmitting array as the origin, and the coordinates of the grid are (x ', y ', z '), and the slant distances from the transmitting array elements and the receiving array elements to the equivalent array spatial coverage area Ω (x ', y ', z ') are calculated as
Calculating to obtain matched filter coefficient Href (x)sub_Tx,ysub_Tx,xsub_Rx,ysub_Rx,x',y',z')＝exp(jkmin(Rsub_Tx+Rsub_Rx) Wherein k) ismin＝2×π×fmin/c，fminFor the minimum frequency of the transmitted signal, c ≈ 3 × 108For the velocity of electromagnetic waves in vacuum, according to Rsub_Rc＝(Rsub_Tx+Rsub_Rx) /2 calculating distance compressed domain signal
The interpolation coefficient of the distance dimension is calculated,
is composed of
Inverse fast fourier transform in the frequency scan dimension k, lr Rsub_Rc/taor+1，
Is the space sampling interval after the frequency scanning dimension is subjected to IFFT up-sampling, Nf is the number of frequency dimension scanning points, Nf0For IFFT point number, B ═ fmax-fminIs the bandwidth of the transmitted signal.
For the obtained echo signal
Is the frequency scan dimension of as Nf0Fast Fourier inverse transformation of points to obtain distance compressed domain signals
Computing distance compressed domain signals
Interpolated sampling points of
The three-dimensional complex image of the imaging subarea obtained by calculation is as follows:
wherein:
according to the principle of symmetry and the principle of a relative coordinate system, three-dimensional sub-images sigma of four imaging sub-areassub(x ', y ', z ') turning and sequencing, turning the image formed by the relative coordinate system up and down, left and right to convert the relative coordinate system to the absolute coordinate system, splicing and sequencing the corresponding positions of the turned image in the whole imaging field of view, and accumulating the overlapped area to obtain the image in the four-subarray mode
And parallelly calculating images of other four subarray modules until all three-dimensional complex images sigma of imaging areas corresponding to the four subarray modulessub4(x ', y ', z ') calculation is completed.
All three-dimensional complex sub-images sigmasub4(x ', y', z ') are spliced to obtain a final three-dimensional complex image sigma (x', y ', z'), and an amplitude signal sigma is extractedamp(x ', y', z ') -abs (σ (x', y ', z')), maximum projection of the distance dimension is performedAnd calculating to obtain two-dimensional projection images sigma of two azimuth dimensionsamp(x ', y'). For two-dimensional amplitude image sigmaamp(x ', y') for target detection, identification or image processing, and then sending to the display terminal for image display.
To sum up, according to the millimeter wave sparse array time domain type fast image reconstruction method in the above embodiment, according to the equivalent array distribution and the antenna irradiation characteristics, a 4 × 4 sixteen sub-array is divided into a 2 × 2 four sub-array mode, the four sub-arrays are overlapped with each other, and the beam width of the receiving array antenna is limited due to the limitation of the antenna beam width, so that the received target effective echo is limited in a certain area on the spatial distribution. Therefore, when an imaging grid region is divided, echo data corresponding to a single subarray transmitting four subarray receiving mode only needs to be divided into space regions distributed by equivalent arrays; when four subarray subgraphs are calculated, a relative coordinate system is set, and according to the symmetry characteristic of subarray spatial distribution, the receiving and transmitting slant distances of different single subarray transmitting and four subarray receiving modes are repeated, so that the whole algorithm only needs to calculate the slant distances of single subarray transmitting and four subarray receiving, matched filter coefficients and interpolation coefficients in the corresponding back projection algorithm are the same set of coefficients, and meanwhile, the subgraphs of all four subarray modules can be calculated in parallel. Therefore, the calculation amount of the traditional back projection reconstruction algorithm is reduced by synthesizing limited echo data, dividing limited imaging grid regions and sharing a group of matched filter coefficients and interpolation coefficients, the imaging quality and the calculation efficiency are properly balanced, the calculation efficiency is effectively improved compared with that of the traditional back projection reconstruction algorithm, and the method is worthy of popularization and use.
Although embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are exemplary and not to be construed as limiting the present invention, and that changes, 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.
Claims (8)
1. A millimeter wave sparse array time domain type fast image reconstruction method is characterized by comprising the following steps:
s1: receiving sparse array echo signals
The two-dimensional sparse array arranged in space realizes antenna beam scanning in two dimensions in space by switching of an antenna array switch, an imaging target range is covered, a single transmitting antenna is utilized to transmit electromagnetic wave signals, all receiving antennas simultaneously receive backscattered electromagnetic waves, down-conversion is carried out on the backscattered electromagnetic waves to intermediate frequency signals, then digitization of analog signals is realized through a multi-channel digital acquisition module, the digitized signals are demodulated into digital I/Q signals through digital down-conversion, and the obtained target backscattered three-dimensional echo signals are s (x)Tx，yTx，xRx，yRx，k)，xTxFor the horizontal dimension of the transmit array, yTxTo transmit the vertical dimension of the array, xRxTo receive the array horizontal dimension, yRxFor the receive array vertical dimension, k 2 × pi × fre/c is the frequency scan dimension, where fre is the frequency of the transmit signal and fre e [ f ∈ [ f [ ]min，fmax]；
S2: subarray division
Dividing sixteen sub-arrays into groups, overlapping every four sub-arrays into a group, and obtaining an echo signal ssub4(xTx，yTx，xRx，yRx，k)；
S3: imaging region partitioning
Dividing an imaging area, and according to the idea of an equivalent array, obtaining the sampling position coordinates of the equivalent array elements by using a single-subarray transmitting array element and a four-subarray receiving array element as a group in a four-subarray unit, wherein the obtained area is divided into four imaging areas in the four-subarray unit;
s4: calculating skew moment
Calculating the slant range R of the back projection reconstruction algorithm under the single sub-array transmitting four sub-array receiving modesub_Tx、Rsub_RxAccording to the symmetry of the spatial distribution of the arrayIn principle, the slant distances of other single sub-array transmitting four sub-array receiving modules in the four sub-arrays are all consistent, and the calculated matched filter Href (x) of the back projection reconstruction algorithmsub_Tx，ysub_Tx，xsub_Rx，ysub_RxX, y, z) are consistent, the vertex of the emission single subarray is respectively taken as an origin according to the principle of a relative coordinate system, the grid coordinate values of the divided imaging sub-regions are consistent, and then the three-dimensional complex image sigma of the back projection reconstruction algorithm of the four imaging sub-regions is calculatedsub(x′，y′，z′)；
S5: four subarray image reconstruction
According to the symmetry principle and the relative coordinate system principle, the three-dimensional images of the four imaging sub-areas are symmetrically turned and sequenced, and the overlapped areas are accumulated to obtain four sub-array module sub-images
S6: subgraph flipping and ranking
Repeating the steps S3-S5 until the calculation of the sub-images of the imaging area of all the four sub-array modules is completed;
s7: image stitching
And splicing all the three-dimensional complex sub-images to obtain a final three-dimensional complex image, and then performing maximum projection of a distance dimension to obtain two-dimensional projection images of two azimuth dimensions.
2. The millimeter wave sparse array time domain type fast image reconstruction method according to claim 1, characterized in that: in the step S1, the two-dimensional sparse array is formed by sixteen square sub-arrays arranged at equal intervals, and the frequency range of the signal transmitted by the imaging system is 30 to 40 GHz.
3. The millimeter wave sparse array time domain type fast image reconstruction method according to claim 2, characterized in that: when the imaging system works, under the trigger of a time sequence generator of the whole system, the transmitting array element is opened in a time-sharing mode, and the receiving array element is normally opened and simultaneously receives a target backscatter echo signal.
4. The millimeter wave sparse array time domain type fast image reconstruction method according to claim 2, characterized in that: in step S2, the position coordinates of the equivalent array element are xc＝(xTx+xRx)/2，yc＝(yTx+yRx)/2，zcAnd (0) dividing sub-areas imaged in the four sub-arrays according to the coverage area of the equivalent array element position coordinates.
5. The millimeter wave sparse array time domain type fast image reconstruction method according to claim 4, characterized in that: in step S4, the calculated slant range expression of the single sub-array transmission four sub-array reception mode is:
6. the millimeter wave sparse array time domain type fast image reconstruction method according to claim 5, characterized in that: in step S4, the matched filter calculation expression is:
Href(xsub_Tx,ysub_Tx,xsub_Rx,ysub_Rx,x',y',z')＝exp(jkmin(Rsub_Tx+Rsub_Rx))
wherein k ismin＝2×π×fmin/c，fminC is the velocity of the electromagnetic wave in vacuum, which is the minimum frequency of the transmitted signal.
7. The millimeter wave sparse array time domain type fast image reconstruction method according to claim 6, characterized in that: in step S4, the obtained three-dimensional complex image of the imaging sub-region is:
wherein,
8. a millimeter wave sparse array time domain type fast image reconstruction system is characterized in that the reconstruction method according to any one of claims 1 to 7 is adopted to reconstruct an image, and the millimeter wave sparse array time domain type fast image reconstruction system comprises the following steps:
the echo signal receiving module is used for transmitting electromagnetic wave signals through a single transmitting antenna, all receiving antennas simultaneously receive backscattering electromagnetic waves, the backscattering electromagnetic waves are converted into intermediate frequency signals through down conversion, then analog signal digitization is realized through the multi-channel digital acquisition module, the digitized signals are demodulated into digital I/Q signals through digital down conversion, and the obtained target backscattering three-dimensional echo signals are s (x)Tx,yTx,xRx,yRx,k)；
A sub-array division module for dividing sixteen sub-arrays into groups, wherein every four sub-arrays are overlapped into a group, and the obtained echo signal is ssub4(xTx,yTx,xRx,yRx,k)；
The imaging area division module is used for dividing an imaging area, and obtaining the sampling position coordinates of the equivalent array elements by using a single-subarray transmitting array element and a four-subarray receiving array element as a group in a four-subarray unit according to the idea of an equivalent array, wherein the obtained area is the imaging area division in the four-subarray unit and is divided into four imaging areas;
an oblique moment calculation module for calculating the oblique distance R of the back projection reconstruction algorithm in the single sub-array transmitting four sub-array receiving modesub_Tx、Rsub_RxAnd calculating a back projection reconstruction algorithm three-dimensional complex image sigma of the four imaging sub-regionssub(x',y',z')；
The image reconstruction module is used for symmetrically overturning and sequencing the three-dimensional images of the four imaging sub-regions according to the symmetry principle and the relative coordinate system principle and accumulating the overlapped regions to obtain sub-images of the four sub-array module
The overturning and sequencing module is used for repeating the steps S3-S5 until the calculation of the sub-images of the imaging area of all the four sub-array modules is completed;
the image splicing module is used for splicing all the three-dimensional complex sub-images to obtain a final three-dimensional complex image, and then performing maximum projection of distance dimensions to obtain two-dimensional projection images of two azimuth dimensions;
the control processing module is used for sending instructions to each module to complete corresponding actions;
the echo signal receiving module, the subarray division module, the imaging region division module, the oblique moment calculation module, the image reconstruction module, the overturning and sequencing module and the image splicing module are all electrically connected with the central processing module.
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