CN111158056B - Security inspection device and method based on sparse array - Google Patents

Security inspection device and method based on sparse array Download PDF

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CN111158056B
CN111158056B CN201911371001.6A CN201911371001A CN111158056B CN 111158056 B CN111158056 B CN 111158056B CN 201911371001 A CN201911371001 A CN 201911371001A CN 111158056 B CN111158056 B CN 111158056B
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sparse
receiving
frequency
transmitting
processor
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CN111158056A (en
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任百玲
孙兆阳
许戎戎
朱明�
张焱
刘强
周利苹
高亚天
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Beijing Research Institute of Telemetry
Aerospace Long March Launch Vehicle Technology Co Ltd
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Aerospace Long March Launch Vehicle Technology Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/12—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with electromagnetic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/887—Radar or analogous systems specially adapted for specific applications for detection of concealed objects, e.g. contraband or weapons
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/28—Details of pulse systems
    • G01S7/282—Transmitters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/28—Details of pulse systems
    • G01S7/285—Receivers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section

Abstract

A security inspection device and method based on sparse arrays comprises a servo system, an antenna arm, a switch and a processor. In the process of controlling the rotation of the antenna arm, the servo system continuously feeds back real-time angle information in the rotation process of the antenna arm to the processor through the switch, the processor monitors the angle information transmitted by the servo system in real time and calculates angle information increment, and the processor gives control signals of a group of sparse transmitting antenna arrays and sparse receiving antenna arrays when the angle is increased by delta theta, so that the electrical scanning of the sparse transmitting antenna arrays and the sparse receiving antenna arrays is completed. And according to the imaging result of the processor, after detection is carried out through a deep learning algorithm, whether the detected person carries dangerous goods or not is determined.

Description

Security inspection device and method based on sparse array
Technical Field
The invention relates to a security inspection device and method based on a sparse array, and relates to the field of millimeter wave security inspection imaging.
Background
In recent years, terrorist attacks at home and abroad frequently occur, the types of dangerous goods are more and more, and the traditional security inspection means can not meet the requirements of the current security inspection market. The traditional metal detector can only detect metal contraband and has no effect on plastic bombs and ceramic cutters; although the X-ray security inspection equipment can detect all prohibited articles, it poses certain threat to human health and is not an optimal security inspection means. The existing millimeter wave three-dimensional imaging technology is an effective method for replacing the traditional security inspection means. A cylindrical scanning three-dimensional imaging system of L3, a QPS three-dimensional imaging system of RS, and a reflector array imaging system of Smith are the main millimeter wave three-dimensional imaging systems on the market. The millimeter wave security inspection equipment on the market at present has the defects of more receiving and transmitting units and long imaging time. The invention provides a rapid security inspection device and method based on a sparse array. The invention adopts the sparse array technology and the mixed domain imaging algorithm based on the molecular array Fourier transform, solves the problem of sparse array imaging processing, improves the imaging precision of the azimuth dimension, supports parallel computation, can process while scanning, reasonably utilizes the scanning time to complete imaging, and greatly reduces the operation time of the algorithm.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the defects of the prior art are overcome, and the security inspection device and method based on the sparse array are provided.
The technical solution of the invention is as follows:
a sparse array based security inspection apparatus comprising: the system comprises a servo system, two antenna arms, a switch and a processor; the antenna arm comprises a radio frequency transceiving front end, a sparse transmitting antenna array and a sparse receiving antenna array;
in the process of controlling the rotation of the antenna arm, the servo system continuously feeds back real-time angle information in the rotation process of the antenna arm to the processor through the switch, the processor monitors the angle information transmitted by the servo system in real time and calculates angle information increment, and the processor gives control signals of a group of sparse transmitting antenna arrays and sparse receiving antenna arrays when the angle is increased by delta theta, so as to complete the electric scanning of the sparse transmitting antenna arrays and the sparse receiving antenna arrays;
when transmitting signals, under the control of a processor, sequentially opening 1 to N transmitting units of the sparse transmitting antenna array, ensuring that only one unit works at each time, and completing the signal transmission of M stepped frequency points within the starting time of each unit;
When receiving signals, under the control of the processor, each sparse transmitting antenna unit works, and simultaneously, the N1 sparse receiving antenna units closest to the sparse transmitting antenna units are opened.
Further, wherein the angle increment is 0.3 < delta theta < 0.8 degrees, delta theta is preferably 0.4 degrees; n is less than or equal to 100, preferably 48; 48M is less than or equal to 256, preferably 64; n1 is preferably 8.
Furthermore, the radio frequency transceiving front end comprises a frequency source module, a transmitting module and a receiving module; the radio frequency link specifically comprises: a direct digital frequency synthesizer DDS in a control processor generates 64 frequency point step frequency signals, the 64 frequency point step frequency signals are transmitted to a frequency source module through a radio frequency cable, the step frequency signals are subjected to frequency multiplication in the frequency source module through a phase-locked loop, the step frequency signals after frequency multiplication are divided into two paths, one path of power is divided into two paths of power and respectively transmitted to two receiving modules in a radio frequency transceiving front end as a receiving local oscillator, the other path of power is transmitted to a transmitting module in the radio frequency transceiving front end, and the two paths of power are mixed with intermediate frequency signals in the control processor and then transmitted to a sparse transmitting antenna array through the radio frequency cable as transmitting signals;
when an antenna arm controlled by a servo system rotates by an angle delta theta every time, transmitting units of 1 to N sparse transmitting antenna arrays are sequentially opened under the control of a processor, after each unit finishes the signal transmission of M1 periodic M stepping frequency points, the unit is switched to the next unit, only one unit works at each time, after the sparse transmitting antenna arrays radiate signals to the space, the transmitting signals are interacted with a target and then received by a sparse receiving antenna array.
Further, the receiving link specifically includes: after receiving an echo signal interacted with a target, a receiving unit of the sparse receiving antenna array sends the echo signal to a receiving module at the front end of radio frequency transceiving through a radio frequency cable, and the echo signal is mixed with a receiving local oscillator signal in the receiving module to obtain an intermediate frequency echo signal, and the intermediate frequency echo signal is transmitted to a processor; after the antenna arm rotates by the next fixed angle delta theta, repeating the process again to complete the acquisition of the echo data of the angle until the acquisition of the echo signals under all angles with the delta theta as the angle interval from 0 degree to 120 degrees is completed, and transmitting all the echo signals to the processor; after the echo signals are subjected to digital sampling and digital down-conversion processing in the processor, imaging processing is completed in the processor by using a mixed domain imaging algorithm, and the positions of forbidden articles are further detected.
Further, the imaging processing is completed by using a mixed domain imaging algorithm, which specifically includes:
(1) dividing echo data into 8 groups by an 8-time extraction method;
(2) respectively carrying out non-uniform Fourier transform on 8 groups of echo data in the elevation direction;
(3) performing matched filtering on the echo data subjected to non-uniform Fourier transform;
(4) Performing distance interpolation on the matched and filtered data;
(5) performing two-dimensional inverse Fourier transform on the echo signals subjected to the distance direction interpolation in the elevation direction and the distance direction;
(6) and finally, carrying out summation processing on the 8 groups of echo data after the two-dimensional Fourier change to obtain a group of summed echo data, and finally obtaining a three-dimensional imaging result by the summed echo data in the elevation direction through a BP imaging algorithm.
Further, the position of the antenna array is (rsin θ, y, rcos θ), and the position of the target is (x)i,yi,zi) Then the form of the target echo signal s is:
Figure BDA0002339646570000031
wherein r is the scanning radius of the antenna array, k is the wave number,
Figure BDA0002339646570000032
f is the operating frequency of the system and c is the speed of light；
The result S after non-uniform fourier transform is represented as follows:
Figure BDA0002339646570000033
wherein k isyThe wave number in the y direction.
Further, the matched filter term is
Figure BDA0002339646570000034
Echo signal S after matched filtering processing1As shown in the following formula:
Figure BDA0002339646570000041
echo signal S1In (1)
Figure BDA0002339646570000042
Echo S interpolated to 2k2As shown in the following formula:
Figure BDA0002339646570000043
will echo S2Performing two-dimensional inverse Fourier transform to obtain an imaging result s' of the YZ slice:
Figure BDA0002339646570000044
wherein k iscFor the center wave number, δ () is the impulse response function.
Further, 8 groups of imaging results s' obtained by calculation are subjected to summation operation, and the summation result is s ″:
Figure BDA0002339646570000045
And (3) processing the result s 'by one-dimensional BP to obtain a final three-dimensional imaging result s':
s″′＝δ(z-zi)δ(x-xi)δ(y-yi)。
further, the number of the sparse transmitting antenna elements and the sparse receiving antenna elements is preferably 48, the beam width of the antenna elements is 50 to 90 degrees, preferably 60 degrees, and the minimum distance is the central wavelength λ of the system operation0；
The 48 sparse transmitting antenna units are controlled by three-level switches, the first-level switch is a single-pole four-throw switch, one pin of the single-pole four-throw switch is suspended, the second-level switch is three single-pole four-throw switches, and the third-level switch is 12 single-pole four-throw switches; when an antenna arm controlled by a servo system rotates by an angle delta theta every time, transmitting units of 1 to N sparse transmitting antenna arrays are sequentially opened under the control of a processor, and after each unit finishes the signal transmission of M1 periodic M stepped frequency points, the unit is switched to the next unit, and only one unit works each time.
Echo signals of 48 sparse receiving antenna units are received by two receiving modules in a multiplexing mode, the 48 sparse receiving antenna units are divided into two groups, and each group comprises 24 sparse receiving antenna units; each group of sparse receiving antenna units is controlled by a three-level switch, the first-level switch is a single-pole four-throw switch, one pin of the single-pole four-throw switch is suspended, the second-level switches are three single-pole two-throw switches, and the third-level switches are 12 single-pole four-throw switches; when the antenna arm controlled by the servo system rotates by an angle delta theta every time, 1 to N groups of sparse transmitting antenna units are sequentially opened under the control of the processor, and when each sparse transmitting antenna unit works, N1 sparse receiving antenna units closest to the sparse transmitting antenna unit are opened in a time-sharing manner.
Furthermore, when the 1 st sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 2 periods is completed, and 1 to 4 sparse receiving antenna units participate in receiving; when the 2 nd sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 3 periods is completed, and 1 to 5 sparse receiving antenna units participate in receiving; when the 3 rd sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 3 periods is completed, and 1 to 6 sparse receiving antenna units participate in receiving; when the 4 th sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 1 to 7 sparse receiving antenna units participate in receiving; when the 5 th sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 1 to 8 sparse receiving antenna units participate in receiving; when the 6 th sparse transmitting antenna unit works, 2 to 9 sparse receiving antenna units participate in receiving; … …, repeating the above steps, when the 44 th sparse transmitting antenna unit works, completing signal transmission of 4 periods of M stepped frequency points, and 40 to 47 sparse receiving antenna units participating in receiving; when the 45 th sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 41 to 48 sparse receiving antenna units participate in receiving; when the 46 th sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 42 to 48 sparse receiving antenna units participate in receiving; when the 47 th sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 3 periods is completed, and 43 to 48 sparse receiving antenna units participate in receiving; when the 48 th sparse transmitting antenna unit works, the signal transmission of M stepped frequency points in 3 periods is completed, and 44 to 48 sparse receiving antenna units participate in receiving.
Further, the invention also provides a security inspection method realized according to the security inspection device of the sparse array, which comprises the following steps:
firstly, powering on a sparse array security inspection device to complete system self-inspection; the system self-checking comprises the steps of detecting the position of the antenna array, and controlling the servo to rotate the antenna to the initial position if the antenna array is not at the initial position;
secondly, placing a standard calibration piece, sending a scanning instruction to the servo by the processor, and controlling the servo to drive the antenna arm to rotate for a circle; the standard calibration piece is a plate, a cylinder or a calibration line; the rotation of one circle refers to any angle between 110 degrees and 140 degrees, and preferably 120 degrees;
thirdly, triggering a group of radio frequency signals to transmit and receive when the servo rotates for a fixed angle delta theta; after a processor receives code wheel angle information in a servo system and calculates angle increment, if the angle is increased by delta theta, the processor transmits an intermediate frequency signal, the processor sends a step frequency signal with the frequency range of 75MHz-93.75MHz and the frequency point number of 64 to a frequency source module in a radio frequency transceiving front end, and a phase-locked loop module in the radio frequency transceiving front end frequency source module generates the step frequency signal of 1.5GHz-1.875GHz after frequency multiplication is carried out by 20 times; after 16 times of frequency multiplication processing is carried out on the 1.5GHz-1.875GHz stepped frequency signal in a frequency source, power is divided into two paths, one path of signal is transmitted to a local oscillation signal input end of a transmitting module to be used as a transmitting local oscillation, frequency mixing processing is carried out on the signal and an intermediate frequency signal in the transmitting module, and then the signal is transmitted to a transmitting unit of the sparse antenna array through a radio frequency line; the other path of the local oscillation signals is divided into two paths, then the two paths of local oscillation signals are respectively used as two paths of receiving local oscillation signals, and the two paths of local oscillation signals are respectively transmitted to the local oscillation input ends of the two receiving modules through the radio frequency cable; when the rotation angle of the antenna arm increases by delta theta, the emission of 48 emission units of the sparse array is completed, namely after the first unit completes the emission of M1 periodic 64 frequency points, the switch is switched to the next emission unit to complete the emission of the next emission unit; switching in sequence until the 48 th antenna unit is transmitted;
The process of receiving signals is that the receiving antenna array finishes the receiving of 1 to 48 groups of receiving antenna units in sequence, the reflected echoes of the calibration material received by each group of receiving antenna units are transmitted to the radio frequency input ends of two receiving modules through a radio frequency cable, the two receiving modules are subjected to frequency mixing in sequence, and intermediate frequency signals after the frequency mixing are transmitted to a processor; after the antenna array rotates for a fixed angle delta theta, sequentially triggering the 48 transmitting and receiving antenna units again to complete the reception of the echo signals near the angle, and transmitting the echo signals to the processor; when the servo mechanism rotates by the next fixed angle delta theta, repeating the process again to complete the reception of the echo data near the angle until the reception of echo signals under all angles with the delta theta as the angle interval from 0 degree to 120 degrees is completed, and transmitting all echo signals to the processor;
fourthly, after the received intermediate frequency signal is subjected to digital sampling in a processor, imaging processing is completed by adopting a mixed domain imaging algorithm;
and fifthly, according to the imaging processing result, completing image recognition processing through a deep learning algorithm to obtain an image recognition result, thereby completing the detection of forbidden articles.
Compared with the prior art, the invention has the beneficial effects that:
(1) by adopting a sparse array arrangement scheme, the number of transmitting units and receiving units in the transmitting-receiving antenna array is reduced, the antenna array cost is reduced, the scanning speed is improved, and the popularization of the security inspection device in departments such as airports, railway stations, prisons, courts and the like in a large range is facilitated.
(2) The mode that the motor directly drives the antenna arm to rotate is adopted, the response speed and the motor efficiency are improved, and the scanning time of the security inspection device is shortened.
(3) And a signal form of linear frequency modulation step frequency is adopted, and the signal linearity is not required to be corrected.
(4) And a signal generation mode of adding a low-frequency DDS and a phase-locked loop is adopted, so that the hardware cost is reduced compared with a high-frequency DDS.
(5) A mixed domain imaging algorithm based on molecular array Fourier transform is adopted. The problem of sparse array imaging processing is solved, the imaging precision of the azimuth dimension is improved, and in addition, the imaging algorithm supports parallel computing, so that the imaging time can be greatly reduced.
(6) The method adopts a large database and a deep learning method, and improves the accuracy of detection.
Drawings
FIG. 1 is a schematic diagram of a sparse array three-dimensional security inspection device
FIG. 2 is an enlarged view of a sparse array periodic structure
FIG. 3 sparse array layout
FIG. 4 is a schematic block diagram of a receive antenna switch array
FIG. 5 is a flow chart of a mixed domain imaging algorithm based on molecular array Fourier transform
FIG. 6 two-dimensional wavenumber domain imaging algorithm flow chart
FIG. 7 is a connection diagram of each part of the sparse array security inspection system
FIG. 8 is a flowchart of a sparse array security inspection method
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings.
As shown in fig. 1 and 7, the invention provides a sparse array three-dimensional security inspection device, which mainly utilizes a sparse antenna array in combination with rotational scanning to realize security inspection of a human body. Fig. 1 is a schematic diagram of the sparse array three-dimensional security inspection device. The sparse array three-dimensional security inspection device mainly comprises: the system comprises a servo system, two antenna arms (wherein the antenna arm A comprises a radio frequency transceiving front end A, a sparse transmitting antenna array A and a sparse receiving antenna array A, and the antenna arm B comprises a radio frequency transceiving front end B, a sparse transmitting antenna array B and a sparse receiving antenna array B), a switch, a direct current power supply A, a direct current power supply B, a processor, a display and a manual processing seat.
The radio frequency transceiving front end comprises a frequency source module, a transmitting module and a receiving module.
Since the work flow of the antenna arm a is the same as that of the antenna arm B, the present invention takes the work flow of the antenna arm a as an example for detailed description.
In the process of controlling the rotation of the antenna arm by the servo system, an encoder in the servo system continuously feeds back real-time angle information in the rotation process of the antenna arm to the processor. The processor monitors angle information transmitted by an encoder in the servo system in real time, angle information increment is calculated, when the angle is increased by delta theta, the processor gives a group of control signals of the sparse transmitting antenna array and the sparse receiving antenna array, electric scanning of the sparse transmitting antenna array and the sparse receiving antenna array is completed, wherein delta theta is more than or equal to 0.3 and less than or equal to 0.8 degrees, and delta theta is preferably 0.4 degree. When the antenna arm controlled by the servo system rotates by an angle delta theta, the processor provides a group of control signals of the sparse transmitting antenna array and the sparse receiving antenna array.
When transmitting signals, under the control of a processor, the transmitting units of 1 to N sparse transmitting antenna arrays are sequentially opened, only one unit works at each time, and the signal transmission of M stepped frequency points is completed within the time of opening each unit. N is 100 or less, preferably 48. 48M 256, preferably 64.
When receiving signals, under the control of the processor, 1 to N groups of receiving antenna units are sequentially opened, and when each transmitting antenna unit works, N1 receiving antenna units, preferably N1 receiving antenna units, closest to the transmitting antenna unit are opened. Since the antenna array is not infinitely long, the number of receive antenna elements is less than N1 in the beginning and end portions of the array.
And a transmitting link: the processor sends the intermediate frequency signal to the radio frequency transceiving front end, and the intermediate frequency signal and the transmitting local oscillator signal are mixed into a transmitting signal at a transmitting module of the radio frequency transceiving front end. The intermediate frequency signal is a single frequency signal of 15MHz, and the transmission local oscillator signal is generated by a frequency source module in the radio frequency transceiving front end. The processor controls a direct Digital frequency synthesizer DDS (direct Digital synthesizer) in the processor to generate 64 frequency point step frequency signals with the frequency range of 75MHz-93.75MHz while transmitting intermediate frequency signals, the step frequency signals are transmitted to a frequency source module at the front end of the radio frequency transceiver through a radio frequency cable, the step frequency signals are subjected to 20 times frequency multiplication in the frequency source module at the front end of the radio frequency transceiver through a phase-locked loop, the frequency range of the frequency-multiplied signals is 1.5GHz-1.875GHz, and the frequency range of the step frequency signals is changed into 24GHz-30GHz after 16 times frequency multiplication. Dividing the stepped frequency signal after frequency multiplication into two paths, wherein one path of stepped frequency signal is transmitted to a transmitting module in the radio frequency transceiving front end to be used as a transmitting local oscillator, and the other path of stepped frequency signal is divided into two paths of stepped frequency signal and then transmitted to a receiving module 1 and a receiving module 2 in the radio frequency transceiving front end through a radio frequency cable to be used as receiving local oscillators. In a transmitting module at the front end of the radio frequency transceiving, the signals obtained after mixing the intermediate frequency signals and the transmitting local oscillator signals are step frequency signals of 24.015GHz-30.015GHz, and the step frequency signals obtained after mixing are transmitted to the sparse transmitting antenna array through a radio frequency cable.
When an antenna arm controlled by a servo system rotates by an angle delta theta every time, under the control of a processor, sequentially opening 1 to N transmitting units of the sparse transmitting antenna array, after each unit finishes the signal transmission of M1 periodic M stepping frequency points, switching to the next unit, and ensuring that only one unit works every time, wherein M is more than or equal to 21Less than or equal to 4. The transmitting antenna unit radiates the signal to the space. After the transmitted signal interacts with the target, the transmitted signal is received by the sparse receiving array.
And a receiving link: under the control of a processor, 1 to N groups of receiving antenna units are sequentially opened, when each transmitting unit works, N1 receiving antenna units nearest to the transmitting unit are opened in a time-sharing mode, in most cases, 2 receiving antenna units are opened simultaneously, and because an antenna array is not infinitely long, the number of the receiving antenna units is less than N1 in the initial and end parts of the array, and only 1 receiving antenna unit can be opened in each part.
After receiving an echo signal interacted with a target, a receiving unit of the sparse receiving antenna array sends the echo signal to a receiving module at the front end of a radio frequency transceiver through a radio frequency cable, the echo signal is mixed with a received local oscillator signal in the receiving module to obtain an intermediate frequency echo signal, and the intermediate frequency echo signal is transmitted to a processor. And after the antenna arm A rotates by the next fixed angle delta theta, repeating the process again to finish the acquisition of the echo data of the angle until the acquisition of the echo signals under all angles at the angle interval of delta theta from 0 degree to 120 degrees is finished, and transmitting all the echo signals to the processor.
After echo signals are subjected to digital sampling and digital down-conversion processing in a processor, imaging processing is completed in an imaging software module in the processor by a mixed domain imaging algorithm based on molecular array Fourier transform, picture information is transmitted to a detection software module in the processor, and the detection software module marks the positions of forbidden articles through a deep learning algorithm. And finally, the processor sends the detection result to a display and a manual seat processing unit. And displaying the artificial intelligent detection result and the final detection result fed back by the artificial processing seat in the display, and finishing the final judgment of the detection result by professional security personnel at the artificial processing seat to confirm whether the detected person carries prohibited articles. The manual treatment seats can be one or more, and each manual treatment seat is provided with a computer.
Sparse antenna array
The sparse antenna array comprises a sparse transmitting antenna array A, a sparse receiving antenna array A, a sparse transmitting antenna array B and a sparse receiving antenna array B. The sparse transmit antenna array a and the sparse transmit antenna array B are of identical design. The sparse transmit antenna array a and the sparse transmit antenna array B are also of identical design. And are therefore described herein in a unified manner.
In order to reduce the number of sparse antenna units, the scheme provided by the invention adopts a sparse antenna array 2, and the sparse antenna array is obtained by optimizing algorithms such as a simulated annealing algorithm or a genetic algorithm. The sparse antenna array adopts a periodic array mode, the arrangement mode of antenna array units in each period is shown in figure 2, and the array mode of the whole antenna array is shown in figure 3. After sparse arrangement, the number of the needed sparse transmitting antenna units and the number of the needed sparse receiving antenna units are reduced to be within 100, preferably 48 from 200 to 400. The beamwidth of the antenna element is 50 to 90 degrees, preferably 60 degrees. The minimum spacing of the antenna elements is the central wavelength λ of system operation0。
The 48 sparse transmitting antenna unit switch arrays are controlled by three-stage switches, the first-stage switch is a single-pole four-throw (SP4F) switch, one pin of the first-stage switch is suspended, the second-stage switch is three single-pole four-throw (SP4F) switches, and the third-stage switch is 12 single-pole four-throw (SP4F) switches. When an antenna arm controlled by a servo system rotates by an angle delta theta every time, transmitting units of 1 to N sparse transmitting antenna arrays are sequentially opened under the control of a processor, and after each unit finishes the signal transmission of M1 periodic M stepped frequency points, the unit is switched to the next unit, and only one unit works each time.
The echo signals of the 48 sparse receiving antenna units are received by multiplexing two receiving modules, as shown in fig. 4. The 48 sparse receive antenna elements are thus divided into two groups of 24 receive elements each. Each group of receiving antenna unit switch arrays are controlled by three-stage switches, the first-stage switch is a single-pole four-throw (SP4F) switch, one pin of the single-pole four-throw (SP4F) switch is suspended, the second-stage switch is three single-pole two-throw (SP2F) switches, and the third-stage switch is 12 single-pole four-throw (SP4F) switches. When the antenna arm controlled by the servo system rotates by an angle delta theta, 1 to N groups of transmitting antenna units are sequentially opened under the control of the processor, and when each transmitting unit works, N1 receiving antenna units N1 nearest to the transmitting unit are opened in a time-sharing mode, and preferably 8 receiving antenna units N1 are opened. In most cases, 2 receiving antenna units are opened simultaneously, and since the antenna array is not infinitely long, the number of receiving antenna units is less than N1 in the beginning and end parts of the array, and only 1 receiving antenna unit can be opened in each part.
Taking 48 receiving antenna units as an example, when the 1 st transmitting antenna unit works, the signal transmission of M stepped frequency points in 2 periods is completed, and 1 to 4 receiving units participate in receiving; when the 2 nd transmitting antenna unit works, signal transmission of M stepped frequency points in 3 periods is completed, and 1 to 5 receiving units participate in receiving; when the 3 rd transmitting antenna unit works, signal transmission of M stepped frequency points in 3 periods is completed, and 1 to 6 receiving units participate in receiving; when the 4 th transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 1 to 7 receiving units participate in receiving; when the 5 th transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 1 to 8 receiving units participate in receiving; when the 6 th transmitting antenna unit works, 2 to 9 receiving units participate in receiving; … …, respectively; when the 44 th transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 40 to 47 receiving units participate in receiving; when the 45 th transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 41 to 48 receiving units participate in receiving; when the 46 th transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 42 to 48 receiving units participate in receiving; when the 47 th transmitting antenna unit works, signal transmission of M stepped frequency points in 3 periods is completed, and 43 to 48 receiving units participate in receiving; when the 48 th transmitting antenna unit works, the signal transmission of M stepped frequency points in 3 periods is completed, and 44 to 48 receiving units participate in receiving. As can be seen from the above analysis, only when the first 1 st to 4 th transmitting antenna elements and the last 46 th to 48 th transmitting antenna elements are operated, there are cases where the number of receiving antenna elements in a group is less than N1, and the number of simultaneously operated receiving antenna elements is 1. When the other 41 transmitting antenna units except the 7 transmitting units work, the N1 receiving antenna units nearest to the transmitting unit are opened in time division, and 2 antenna units are opened at the same time each time. It is particularly emphasized that transmission and reception are performed synchronously.
Servo system
The servo system adopts a form of a direct drive motor, and the direct drive motor has quick relative reaction and high efficiency. The servo system 1 comprises an alternating current servo motor, a servo driver, a power adapter, a photoelectric switch, a coder, an information interaction module, a signal acquisition module, a self-checking correction control module and a scanning curve control module of a servo mechanism. And the main shaft of the alternating current servo motor is directly connected with the antenna array disc support to drive the antenna array disc support of the sparse array imaging system to complete circular scanning movement. The power adapter is connected with the servo driver and provides power for the servo motor. The processor transmits a scanning instruction to the information interaction module through a network cable, the information interaction module transmits scanning starting information to the servo driver, and the servo driver drives the servo mechanism to drive the sparse antenna array to rotate so as to complete angle scanning from 0 degree to 120 degrees. The signal interaction module is also responsible for transmitting the angle information measured by the encoder to the processor, and when the angle accumulation exceeds delta theta, one transmission and one reception are triggered. And a signal acquisition module in the servo system is responsible for acquiring signals of the photoelectric switch so as to determine the zero position of the system. The self-checking correction control module receives a self-checking instruction of a servo system in the processor, searches for a servo initial position and feeds back a servo current state. The scanning curve control module of the servo mechanism is mainly responsible for controlling the antenna arm to complete scanning movement according to the speed curve shown in fig. 5 after receiving the scanning instruction in the information interaction module.
Radio frequency transceiving front end
The radio frequency transceiving front end of the system is mainly responsible for transmitting and receiving system radio frequency signals. The radio frequency transceiving front end comprises: the device comprises a frequency source module, a transmitting module and 2 receiving modules.
The frequency source module is mainly responsible for receiving the intermediate frequency signal of the local oscillator signal transmitted by the processor, the intermediate frequency signal of the local oscillator signal is a step frequency signal, the number of points of the step frequency is M, the range of the step frequency signal is 75MHz-93.75MHz, wherein M is more than or equal to 48 and less than or equal to 256, and 64 are preferred. In the frequency source module, the phase-locked loop carries out frequency multiplication on the step frequency signal by 20 times, and the frequency range of the frequency-multiplied signal is 1.5GHz-1.875 GHz. And carrying out 16 times of frequency multiplication on the step frequency signal, wherein the step frequency signal after frequency multiplication is 24GHz-30 GHz. Dividing the stepped frequency signal after frequency multiplication into two paths, wherein one path is transmitted to a transmitting module through a radio frequency line to be used as a transmitting local oscillator, and the other path is transmitted to a receiving module to be used as a receiving local oscillator.
And the transmitting module for transmitting the local oscillation signal in the radio frequency transceiving front end mixes the local oscillation signal with an intermediate frequency transmitting signal, the intermediate frequency transmitting signal is a single-frequency-point continuous wave signal of 15MHz, and the frequency range of the stepped frequency signal after mixing is 24.015GHz-30.015 GHz. And transmitting the mixed signal to a sparse transmitting antenna array.
The received local oscillator signal is divided into two paths, which are respectively used as a received local oscillator 1 and a received local oscillator 2. As shown in fig. 4, the receiving local oscillator 1 is transmitted to the receiving module 1 at the front end of the radio frequency transceiver, and is mixed with the radio frequency echo signal returned by the sparse receiving antenna array in the receiving module 1, and the mixed intermediate frequency signal is transmitted to the processor through the radio frequency cable. The receiving local oscillator 2 is transmitted to a receiving module 2 at the front end of the radio frequency transceiving, the receiving module 2 mixes the frequency with the radio frequency echo signal returned by the sparse receiving antenna array, and the mixed intermediate frequency signal is transmitted to the processor through the radio frequency cable.
Processor
The functions of the processor include: generating an intermediate frequency transmitting signal which is a single-frequency continuous wave signal of 15 MHz; generating an intermediate frequency source signal in a radio frequency transceiving front end, generating 64 frequency point stepping frequency signals with the frequency range of 75MHz-93.75MHz as intermediate frequency transmitting signals by a direct Digital frequency synthesizer DDS (direct Digital synthesizer) in a processor; receiving the intermediate frequency echo signal, performing analog-to-digital conversion on the intermediate frequency echo signal, converting the digital intermediate frequency signal to a baseband after digital down-conversion, then performing imaging processing on the baseband signal in an imaging module, and then sending an imaging result to a detection software module for detection processing. And sending a control signal to the whole machine: the method comprises the steps of sending a control instruction to a servo, receiving accumulated angle information of a code disc, and triggering a transmitting signal and a receiving signal.
The imaging algorithm in the processor adopts a mixed domain imaging algorithm based on molecular array Fourier transform. The imaging algorithm can adopt a parallel computing implementation mode, can carry out computation while scanning, and reduces the actual imaging time of the algorithm
The derivation process of the transmit-receive mixed domain imaging algorithm is as follows:
assume that the position of the antenna array is (rsin θ, y, rcos θ) and the position of the target is (x)i,yi,zi) Then the form of the target echo signal s is:
Figure BDA0002339646570000141
where r is the scanning radius of the antenna array, k is the wave number,
Figure BDA0002339646570000142
f is the operating frequency of the system and c is the speed of light. Because the antenna array units are arranged in a non-uniform and sparse manner, a fast fourier transform method cannot be directly used, and the invention adopts a non-uniform fourier transform method to perform non-uniform fourier transform on the formula (1), and the result S after fourier transform is obtained is as follows:
Figure BDA0002339646570000143
multiplying equation (2) by a matched filter term of
Figure BDA0002339646570000144
Obtaining echo signal S after matched filtering processing1As shown in the following formula:
Figure BDA0002339646570000145
wherein k isyThe wave number in the y direction.
Will be described in the formula (3)
Figure BDA0002339646570000146
Echo S interpolated to 2k2As shown in the following formula:
Figure BDA0002339646570000147
performing two-dimensional inverse Fourier transform on the formula (4) to obtain an imaging result s' of the YZ slice:
Figure BDA0002339646570000148
Wherein k iscδ () is the impulse response function for the center wave number.
And after eight-time extraction, dividing echo data into 8 groups, wherein each group can be calculated by the imaging algorithm, and summing the calculated results to obtain a result s'.
Figure BDA0002339646570000151
The imaging result s' "is obtained by one-dimensional BP for equation (6):
s″′＝δ(z-zi)δ(x-xi)δ(y-yi)
the imaging algorithm flow chart is shown in fig. 5 and fig. 6. The method comprises the steps of firstly dividing echo data into 8 groups by an 8-time extraction method, then respectively carrying out non-uniform Fourier transform on the 8 groups of echo data in the elevation direction, then carrying out matched filtering on the echo data after the non-uniform Fourier transform, then carrying out range direction interpolation on the data after the matched filtering, then carrying out two-dimensional inverse Fourier transform on echo signals after the range direction interpolation in the elevation direction and the range direction to obtain 8 groups of echo data after two-dimensional Fourier transform, then carrying out summation processing to obtain a group of summed echo data, and finally obtaining a three-dimensional imaging result by the summed echo data in the elevation direction through a BP imaging algorithm.
The detection algorithm in the processor is to adopt a known deep learning algorithm to finish the classification and the identification of the target on the basis of a large database.
Manual seat processing
The function of manual seat processing is to manually mark the position of dangerous goods in the image in the imaging result or check the detection result of machine learning, delete the false alarm in the detection result and increase the position of missed detection. And making a final judgment whether the person to be detected carries the dangerous goods. The manual processing seat can be one or more.
Display device
The display has the main function of displaying the detection results transmitted by the processor, including the machine learning detection results and the manual seat feedback detection results.
Switch
The functions of the switch include: transmitting the scanning command and the correction command of the processor to the servo system to change the state of the servo system
Feeding back the state information to the processor; sending the imaging result and the detection result in the processor to a computer for manually processing seats for use by security personnel; and sending the final result processed by the security check personnel at the processing seat back to the processor.
The security inspection method of the sparse array scanning security inspection apparatus is described below, as shown in fig. 8.
Firstly, a sparse array scanning security inspection device is powered on to complete system self-inspection. The system self-test comprises the steps of detecting the position of the antenna array, and controlling the servo to rotate the antenna to the initial position if the antenna array is not at the initial position.
And secondly, placing a standard calibration piece inside the cylinder, sending a scanning instruction to the servo by the processor, and controlling the servo drive antenna arm to rotate for a circle. The standard calibration piece may be a plate, a cylinder or a calibration line. One rotation referred to herein means any angle of rotation from 110 degrees to 140 degrees, preferably 120 degrees.
And thirdly, triggering a group of radio frequency signals to transmit and receive every time the servo rotates for a fixed angle delta theta. The processor is used for transmitting intermediate frequency signals after receiving code disc angle information in the servo system and calculating angle increment, the processor is used for transmitting intermediate frequency signals when the angle is increased by delta theta, the processor is used for transmitting step frequency signals with the frequency range of 75MHz-93.75MHz and the frequency point number of 64 to a frequency source module in the radio frequency transceiving front end, and the step frequency signals with the frequency range of 1.5GHz-1.875GHz are generated after 20-time frequency multiplication is carried out on the step frequency signals by a phase-locked loop module in the radio frequency transceiving front end frequency source module. After 16 times of frequency multiplication processing is performed on the 1.5GHz-1.875GHz stepped frequency signal in a frequency source, the power is divided into two paths, one path of signal is transmitted to the local oscillator signal input end of the transmitting module to be used as a transmitting local oscillator, the signal is subjected to frequency mixing processing with an intermediate frequency signal in the transmitting module, then the signal is transmitted to the transmitting unit of the sparse antenna array through a radio frequency line, and the other path of signal is divided into two paths of signal to be respectively used as a receiving local oscillator signal 1 and a receiving local oscillator signal 2 and respectively transmitted to the local oscillator input ends of the receiving module 1 and the receiving module 2 through radio frequency cables. And finishing the transmission of the sparse array of 48 transmitting units every time the rotation angle of the antenna arm is increased by delta theta. That is, after the first unit completes the M1 periodic transmissions of 64 frequency points, the switch is switched to the next transmission unit to complete the transmission of the next transmission unit. And switching is performed in sequence until the 48 th antenna unit is completely transmitted. The process of receiving signals is that the receiving antenna array sequentially finishes the receiving of 1 to 48 groups of receiving antenna units, the reflected echoes of the calibration objects received by each group of receiving antenna units are transmitted to the radio frequency input ends of 2 receiving modules through radio frequency cables, the 2 receiving modules are sequentially subjected to frequency mixing processing, and intermediate frequency signals after the frequency mixing processing are transmitted to a processor. After the antenna array rotates by a fixed angle delta theta, the 48 transmitting and receiving antenna units are sequentially triggered again, the reception of the echo signals near the angle is completed, and the echo signals are transmitted to the processor. And after the servo mechanism rotates by the next fixed angle delta theta, repeating the process again to complete the reception of the echo data near the angle until the reception of the echo signals under all angles with the angle interval delta theta from 0 degree to 120 degrees is completed, and transmitting all the echo signals to the processor.
And fourthly, after the received intermediate frequency signals are subjected to digital sampling in the processor, transmitting the intermediate frequency signals to an imaging processing software module, and finishing imaging processing by adopting a mixed domain imaging algorithm based on molecular array Fourier transform. And transmitting the imaging processing result to a detection software module.
And fifthly, completing image recognition processing by the detection software module through a known deep learning algorithm, and transmitting the image recognition result to the manual image judging seat through the switch. And (5) carrying out final security check result confirmation at the manual image judging seat to confirm whether the detected person carries forbidden articles.

Claims (5)

1. A security inspection device based on a sparse array is characterized by comprising: the system comprises a servo system, two antenna arms, a switch and a processor; the antenna arm comprises a radio frequency transceiving front end, a sparse transmitting antenna array and a sparse receiving antenna array;
in the process that the servo system controls the rotation of the antenna arm, the servo system continuously feeds back real-time angle information in the rotation process of the antenna arm to the processor through the switch, the processor monitors the angle information transmitted by the servo system in real time and calculates angle information increment, and the processor gives control signals of a group of sparse transmitting antenna arrays and sparse receiving antenna arrays every time the angle is increased by delta theta, so that the electrical scanning of the sparse transmitting antenna arrays and the sparse receiving antenna arrays is completed;
When transmitting signals, under the control of a processor, sequentially opening 1 to N transmitting antenna units of the sparse transmitting antenna array, ensuring that only one unit works each time, and completing the signal transmission of M stepped frequency points within the time of opening each unit;
when receiving signals, under the control of a processor, when each sparse transmitting antenna unit works, opening N1 sparse receiving antenna units closest to the sparse transmitting antenna units;
the receiving link is specifically: after receiving an echo signal interacted with a target, a receiving antenna unit of the sparse receiving antenna array sends the echo signal to a receiving module at the front end of a radio frequency transceiver through a radio frequency cable, the echo signal is mixed with a receiving local oscillator signal in the receiving module to obtain an intermediate frequency echo signal, and the intermediate frequency echo signal is transmitted to a processor; after the antenna arm rotates by the next fixed angle delta theta, repeating the process again to complete the acquisition of the echo data of the angle until the acquisition of the echo signals under all angles with the delta theta as the angle interval from 0 degree to 120 degrees is completed, and transmitting all the echo signals to the processor; after the echo signal is subjected to digital sampling and digital down-conversion processing in the processor, imaging processing is completed in the processor by using a mixed domain imaging algorithm, and the position of forbidden articles is further detected;
The method for completing the imaging processing by using the mixed domain imaging algorithm specifically comprises the following steps of:
(1) dividing echo data into 8 groups by an 8-time extraction method;
(2) respectively carrying out non-uniform Fourier transform on 8 groups of echo data in the elevation direction;
(3) performing matched filtering on the echo data subjected to the non-uniform Fourier transform;
(4) performing distance interpolation on the matched and filtered data;
(5) performing two-dimensional inverse Fourier transform on the echo signals subjected to the distance direction interpolation in the elevation direction and the distance direction;
(6) obtaining 8 groups of echo data after two-dimensional inverse Fourier transform, then performing summation processing to obtain a group of summed echo data, and finally obtaining a three-dimensional imaging result by the summed echo data in the elevation direction through a BP imaging algorithm;
the position of the antenna array is (rsin theta, y, rcos theta) and the position of the target is (x)i,yi,zi) Then the form of the target echo signal s is:
Figure FDA0003548197850000021
wherein r is the scanning radius of the antenna array, k is the wave number,
Figure FDA0003548197850000022
f is the working frequency of the system, and c is the speed of light;
the result S after non-uniform fourier transform is represented as follows:
Figure FDA0003548197850000023
wherein k isyWave number in y direction;
matched filter term of
Figure FDA0003548197850000024
Echo signal S after matched filtering processing1As shown in the following formula:
Figure FDA0003548197850000025
echo signal S1In (1)
Figure FDA0003548197850000026
Echo S interpolated to 2k 2As shown in the following formula:
Figure FDA0003548197850000027
will echo S2Performing two-dimensional inverse Fourier transform to obtain an imaging result s' of the YZ slice:
Figure FDA0003548197850000028
wherein k iscFor the center wave number, δ () is the impulse response function;
and (3) performing summation operation on the imaging results s 'obtained by 8 groups of calculation, wherein the summed result is s':
Figure FDA0003548197850000029
and (3) processing the result s 'by one-dimensional BP to obtain a final three-dimensional imaging result s':
s″′＝δ(Z-zi)δ(X-xi)δ(Y-yi)；
the number of the sparse transmitting antenna units and the sparse receiving antenna units is 48, the beam widths of the transmitting antenna units and the receiving antenna units are 50-90 degrees, and the minimum distance is the central wavelength lambda of the system work0；
The 48 sparse transmitting antenna units are controlled by three-level switches, the first-level switch is a single-pole four-throw switch, one pin of the single-pole four-throw switch is suspended, the second-level switch is three single-pole four-throw switches, and the third-level switch is 12 single-pole four-throw switches; when an antenna arm controlled by a servo system rotates by an angle delta theta every time, under the control of a processor, sequentially opening 1 to N transmitting antenna units of the sparse transmitting antenna array, and after each unit finishes M1 periodic M stepped frequency point signal transmission, switching to the next unit, and ensuring that only one unit works each time;
echo signals of 48 sparse receiving antenna units are received by two receiving modules in a multiplexing mode, the 48 sparse receiving antenna units are divided into two groups, and each group comprises 24 sparse receiving antenna units; each group of sparse receiving antenna units is controlled by a three-level switch, the first-level switch is a single-pole four-throw switch, one pin of the single-pole four-throw switch is suspended, the second-level switches are three single-pole two-throw switches, and the third-level switches are 12 single-pole four-throw switches; when an antenna arm controlled by a servo system rotates by an angle delta theta, 1 to N groups of sparse transmitting antenna units are sequentially opened under the control of a processor, and when each sparse transmitting antenna unit works, N1 sparse receiving antenna units closest to the sparse transmitting antenna unit are opened in a time-sharing manner;
When the 1 st sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 2 periods is completed, and 1 to 4 sparse receiving antenna units participate in receiving; when the 2 nd sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 3 periods is completed, and 1 to 5 sparse receiving antenna units participate in receiving; when the 3 rd sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 3 periods is completed, and 1 to 6 sparse receiving antenna units participate in receiving; when the 4 th sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 1 to 7 sparse receiving antenna units participate in receiving; when the 5 th sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 1 to 8 sparse receiving antenna units participate in receiving; when the 6 th sparse transmitting antenna unit works, 2 to 9 sparse receiving antenna units participate in receiving; … …, repeating the above steps, when the 44 th sparse transmitting antenna unit works, completing signal transmission of 4 periods of M stepped frequency points, and 40 to 47 sparse receiving antenna units participating in receiving; when the 45 th sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 41 to 48 sparse receiving antenna units participate in receiving; when the 46 th sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 4 periods is completed, and 42 to 48 sparse receiving antenna units participate in receiving; when the 47 th sparse transmitting antenna unit works, signal transmission of M stepped frequency points in 3 periods is completed, and 43 to 48 sparse receiving antenna units participate in receiving; when the 48 th sparse transmitting antenna unit works, the signal transmission of M stepped frequency points in 3 periods is completed, and 44 to 48 sparse receiving antenna units participate in receiving.
2. The sparse array based security inspection device of claim 1, wherein: wherein the angle increment is more than or equal to 0.3 and less than or equal to 0.8 degrees; m is 64.
3. The sparse array based security inspection device of claim 1, wherein: the radio frequency transceiving front end comprises a frequency source module, a transmitting module and a receiving module; the radio frequency link specifically comprises: a direct digital frequency synthesizer DDS in a control processor generates 64 frequency point step frequency signals, the 64 frequency point step frequency signals are transmitted to a frequency source module through a radio frequency cable, frequency multiplication is carried out on the step frequency signals in the frequency source module through a phase-locked loop, the step frequency signals after frequency multiplication are divided into two paths, one path of power is divided into two paths of power and transmitted to two receiving modules in a radio frequency transceiving front end respectively to serve as a receiving local oscillator, the other path of power is transmitted to a transmitting module in the radio frequency transceiving front end, the other path of power is mixed with intermediate frequency signals in the control processor and then transmitted to a sparse transmitting antenna array through the radio frequency cable to serve as transmitting signals.
4. The sparse array based security inspection device of claim 1, wherein: the beamwidths of the transmit and receive antenna elements are preferably 60 degrees each.
5. A security inspection method implemented by the security inspection device of the sparse array according to any one of claims 1 to 4, characterized by the following steps:
Firstly, electrifying a sparse array security inspection device to complete system self-inspection; the system self-checking comprises the steps of detecting the positions of the transmitting and receiving antenna arrays, and controlling the servo system to rotate the antennas to the initial positions if the transmitting and receiving antenna arrays are not at the initial positions;
secondly, placing a standard calibration piece, sending a scanning instruction to a servo system by a processor, and controlling the servo system to drive an antenna arm to rotate for a circle; the standard calibration piece is a plate, a cylinder or a calibration line; the rotation of one circle is 120 degrees;
thirdly, triggering a group of radio frequency signals to transmit and receive when the servo system rotates for a fixed angle delta theta; after a processor receives code wheel angle information in a servo system and calculates angle increment, if the angle is increased by delta theta, the processor transmits an intermediate frequency signal, the processor sends a step frequency signal with the frequency range of 75MHz-93.75MHz and the frequency point number of 64 to a frequency source module in a radio frequency transceiving front end, and a phase-locked loop in the radio frequency transceiving front end frequency source module performs frequency multiplication by 20 times to generate the step frequency signal of 1.5GHz-1.875 GHz; after 16 times of frequency multiplication processing is carried out on the 1.5GHz-1.875GHz stepped frequency signal in the frequency source module, the power is divided into two paths, one path of signal is transmitted to the local oscillator signal input end of the transmitting module to be used as a transmitting local oscillator, frequency mixing processing is carried out on the signal and an intermediate frequency signal in the transmitting module, and then the signal is transmitted to a transmitting antenna unit of the sparse transmitting antenna array through a radio frequency cable; the other path of the local oscillation signals is divided into two paths, then the two paths of local oscillation signals are respectively used as two paths of receiving local oscillation signals, and the two paths of local oscillation signals are respectively transmitted to the local oscillation input ends of the two receiving modules through the radio frequency cable; when the rotation angle of the antenna arm increases delta theta, the emission of 48 sparse array transmitting antenna units is completed, namely after the first unit completes the emission of M1 periodic 64 frequency points, the switch is switched to the next transmitting antenna unit to complete the emission of the next transmitting antenna unit; switching in sequence until the 48 th antenna unit is transmitted;
The process of receiving signals is that the receiving antenna array sequentially completes the receiving of 1 to 48 groups of receiving antenna units, the reflected echoes of the calibration piece received by each group of receiving antenna units are transmitted to the radio frequency input ends of two receiving modules through a radio frequency cable, the two receiving modules are sequentially subjected to frequency mixing processing, and intermediate frequency signals after the frequency mixing processing are transmitted to a processor; after the transmitting and receiving antenna array rotates for a fixed angle delta theta, sequentially triggering the 48 transmitting and receiving antenna units again to complete the reception of the echo signals near the angle, and transmitting the echo signals to the processor; after the servo system rotates by the next fixed angle delta theta, repeating the process again to complete the reception of the echo data near the angle until the reception of echo signals under all angles with the angle interval delta theta from 0 degree to 120 degrees is completed, and transmitting all the echo signals to the processor;
fourthly, after the received intermediate frequency signal is digitally sampled in a processor, imaging processing is completed by adopting a mixed domain imaging algorithm;
and fifthly, according to the imaging processing result, completing image recognition processing through a deep learning algorithm to obtain an image recognition result, thereby completing the detection of the contraband.
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