CN112558065B - Three-dimensional imaging method based on reconfigurable electromagnetic surface array - Google Patents

Three-dimensional imaging method based on reconfigurable electromagnetic surface array Download PDF

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CN112558065B
CN112558065B CN202011070343.7A CN202011070343A CN112558065B CN 112558065 B CN112558065 B CN 112558065B CN 202011070343 A CN202011070343 A CN 202011070343A CN 112558065 B CN112558065 B CN 112558065B
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electromagnetic surface
transmitting
subarray
reconfigurable electromagnetic
receiving
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CN112558065A (en
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李世勇
赵国强
王硕光
敬汉丹
孙厚军
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Beijing Institute of Technology BIT
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    • 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
    • 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
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V8/00—Prospecting or detecting by optical means
    • G01V8/005—Prospecting or detecting by optical means operating with millimetre waves, e.g. measuring the black losey radiation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V8/00—Prospecting or detecting by optical means
    • G01V8/10—Detecting, e.g. by using light barriers
    • G01V8/20—Detecting, e.g. by using light barriers using multiple transmitters or receivers

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Abstract

The three-dimensional imaging method of the reconfigurable electromagnetic surface array comprises the steps that the reconfigurable electromagnetic surface array is constructed according to a target area, N transmitting sub-arrays and N receiving sub-arrays are corresponding and orthogonal, array elements of the adjacent sub-arrays are partially overlapped, and N is a positive integer; the multichannel transmitting digital beam and the corresponding multichannel receiving digital beam are orthogonal into a multichannel digital synthesis beam of a transmitting and receiving subarray, and are focused to the corresponding position of a target area to be a transmitting and receiving subarray scanning beam; compensating the phases of overlapped array elements of the transmitting subarray and the receiving subarray to focus the multi-channel digital synthesis beam to different positions of a target area; and dividing the target area into a plurality of parallel sections, and scanning by combining the transmitting-receiving subarray scanning beam and the multi-channel digital synthesis beam on each parallel section to obtain three-dimensional imaging of the target area. The space scanning times can be reduced by several orders of magnitude, the advantages of a sparse array and real beam imaging are integrated, the passing-through type rapid security inspection when the flow of people is large can be realized, and the human body is rapidly scanned and imaged.

Description

Three-dimensional imaging method based on reconfigurable electromagnetic surface array
Technical Field
The invention belongs to the technical field of security inspection, and particularly relates to a three-dimensional imaging method based on a reconfigurable electromagnetic surface array.
Background
Public safety issues are a focus of widespread concern in international society. The airport, subway, station, square and other places with dense personnel are the main places where the attack incident occurs, and then higher requirements are provided for the accuracy, real-time performance, intelligence and environmental applicability of the security inspection system.
The millimeter wave security inspection imaging technology is a novel security inspection technology in recent years, has the advantages of high safety, good penetrability, difference in electromagnetic scattering characteristics of different materials and the like, and has become the mainstream development direction of human body security inspection technology.
Millimeter wave security inspection imaging is mainly divided into an active mode and a passive mode. The dependence of an active imaging mode on the environment is low, the obtained information quantity is rich, the signal-to-noise ratio and the contrast of the image are high, and the target three-dimensional imaging can be realized by a millimeter wave single-channel two-dimensional mechanical scanning imaging system mainly developed by the American JPL laboratory; a ProVision millimeter wave human body imaging security inspection system which is developed by the company L3 and combines electric scanning and mechanical scanning; QPS millimeter wave imaging system based on MIMO area array of Germany Rohde & Schwarz company, Eqo imaging system based on two-dimensional reflective array of Brith Detection company of UK. In English, American and other countries, the terahertz frequency band human body security inspection imaging technology is developed, and passive systems are mostly adopted.
Reconfigurable digital electromagnetic surfaces have attracted extensive attention and research. Semiconductor electronic devices or Micro Electro Mechanical Systems (MEMS) are integrated in the design of the reconfigurable digital electromagnetic surface unit, so that the array radiation and phase modulation devices are combined into a whole, the reconfigurable antenna has the advantages of the traditional reflector antenna and the phased array antenna, is light and thin, is easy to conform, is easy to form a large opening surface, is easy to develop towards high frequency, and can realize batch production with high precision and low cost by adopting a mature semiconductor process in a millimeter wave frequency band.
The reconfigurable electromagnetic surface utilizes the voltage-controlled diode to control the reflection unit, beam space scanning can be realized without a plurality of radio frequency channels, the reconfigurable electromagnetic surface voltage-controlled diode can replace the traditional antenna array element to be used for subarray design of a receiving and transmitting array, three-dimensional high-resolution imaging can be completed by combining digital beam scanning on the basis of wide beam scanning of the subarray on the electromagnetic surface, and the beam scanning efficiency is improved.
Digital Beamforming (DBF) technology is widely used in ultrasound, radar signal processing and electronic countermeasure systems, and performs weighted summation on signals received by an array antenna from different spatial directions to form a Digital beam with a specific direction, wherein a weighted and summed weight vector determines beam direction and null and side lobe levels, thereby realizing beam scanning, target tracking, null of spatial interference signals and the like. In such applications, the signal model is usually based on far-field plane waves, and in near-field millimeter wave human body security imaging, electromagnetic waves transmitted and received by the antenna are in the form of spherical waves, so that the far-field DBF algorithm cannot be directly applied.
In the field of near-field ultrasonic fast imaging, beam imaging algorithms mainly exist, such as a near-field dynamic focusing beam forming algorithm based on FFT, a Chirp-z transformation algorithm, a non-uniform fast Fourier transform (NUFFT) based beam forming algorithm and the like.
However, the existing millimeter wave imaging technology is difficult to meet the requirement of rapid passing-through human body security inspection in a dense region in terms of processing algorithm and system cost. Therefore, a new imaging system and method are needed to meet the requirement of fast passing human body security inspection in a dense personnel area.
Disclosure of Invention
In view of the above, the present disclosure provides a three-dimensional imaging method based on a reconfigurable electromagnetic surface array, which can reduce the number of spatial scanning times by several orders, integrate the advantages of a sparse array and a real beam imaging, and can realize a pass-through type rapid security inspection when the flow of people is large, so as to perform rapid scanning imaging on a human body.
According to an aspect of the invention, a three-dimensional imaging method based on a reconfigurable electromagnetic surface array is provided, the method comprising:
the reconfigurable electromagnetic surface array is constructed according to a three-dimensional imaging target area, and comprises N reconfigurable electromagnetic surface transmitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays, wherein the N reconfigurable electromagnetic surface transmitting sub-arrays and the N reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence and are orthogonal in space, part of array elements of the adjacent reconfigurable electromagnetic surface transmitting sub-arrays or the adjacent reconfigurable electromagnetic surface receiving sub-arrays are overlapped, and N is a positive integer;
aiming at that a multichannel transmitting digital beam of each reconfigurable electromagnetic surface transmitting subarray and a multichannel receiving digital beam of a reconfigurable electromagnetic surface receiving subarray corresponding to the multichannel transmitting digital beam are orthogonal in space and synthesized into a multichannel digital synthesis beam of a transmitting and receiving subarray, and focusing the multichannel digital synthesis beam to a corresponding position of a three-dimensional imaging target area is a transmitting and receiving subarray scanning beam;
performing phase compensation on overlapped array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, adjusting the phase of a multi-channel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray and the phase of a multi-channel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray, and focusing the multi-channel digital synthesis beams of different transmitting and receiving subarrays to different positions of a three-dimensional imaging target area to obtain a plurality of transmitting and receiving subarray scanning beams;
and dividing the three-dimensional imaging target area into a plurality of parallel sections, and combining wide beam scanning of the scanning beams of the transmitting and receiving subarrays and narrow beam scanning of the multichannel digital synthesis beams in the main lobe of the transmitting and receiving subarrays on each parallel section to obtain three-dimensional imaging of the three-dimensional imaging target area.
In one possible implementation manner, the reconfigurable electromagnetic surface emitting subarray comprises an emitting feed source, a diode phase control array and an antenna unit;
the reconfigurable electromagnetic surface receiving subarray comprises a receiving feed source, a diode phase control array and an antenna unit.
In one possible implementation, the adjusting the phase of the multi-channel transmit digital beam of the reconfigurable electromagnetic surface transmit sub-array and the phase of the multi-channel receive digital beam of the reconfigurable electromagnetic surface receive sub-array includes:
and adjusting the on-off state of the diode phase control array of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, adjusting the phases of the antenna units of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, and adjusting the phase of the multichannel transmitting digital beam and the phase of the multichannel receiving digital beam according to the phases of the antenna units of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray to form a transmitting-receiving subarray scanning beam.
In a possible implementation manner, the multichannel transmitting signals are subjected to digital beam synthesis according to the adjustment of the phase of the transmitting feed source signal, and the multichannel transmitting signals are subjected to digital beam synthesis according to the adjustment of the phase of the transmitting feed source signal, so that multichannel digital synthesis beams which are orthogonal in space are a transmitting-receiving subarray.
In one possible implementation manner, performing phase compensation on the overlapped array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray includes:
and according to the phase distribution of the array element overlapping parts of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, carrying out phase compensation on the array element overlapping parts of the reconfigurable electromagnetic surface transmitting subarray or the reconfigurable electromagnetic surface receiving subarray by using a phase matching adjustment method of an average phase.
In a possible implementation mode, a non-uniform fast Fourier transform algorithm is used for obtaining a multichannel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray and a multichannel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray corresponding to the multichannel transmitting digital beam, and the multichannel transmitting digital beam and the multichannel receiving digital beam are orthogonal in space to form a multichannel digital synthesis beam of the transmitting subarray.
In one possible implementation, the total array of reconfigurable electro-magnetic surfaces is cross-shaped, T-shaped, or T-shaped.
The reconfigurable electromagnetic surface array is constructed according to a three-dimensional imaging target area, the reconfigurable electromagnetic surface array comprises N reconfigurable electromagnetic surface transmitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays, the N reconfigurable electromagnetic surface transmitting sub-arrays and the N reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence and are orthogonal in space, part of array elements of the adjacent reconfigurable electromagnetic surface transmitting sub-arrays or the adjacent reconfigurable electromagnetic surface receiving sub-arrays are overlapped, and N is a positive integer; aiming at a multichannel transmitting digital beam of each reconfigurable electromagnetic surface transmitting subarray and a multichannel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray corresponding to the multichannel transmitting digital beam, the multichannel transmitting digital beam is orthogonal in space to form a multichannel digital synthesis beam of a transmitting subarray, and the multichannel digital synthesis beam is focused to a corresponding position of a three-dimensional imaging target area to form a transmitting subarray scanning beam; performing phase compensation on overlapped array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, adjusting the phase of a multi-channel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray and the phase of a multi-channel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray, and focusing the multi-channel digital synthesis beams of different transmitting and receiving subarrays to different positions of a three-dimensional imaging target area to obtain a plurality of transmitting and receiving subarray scanning beams; and dividing the three-dimensional imaging target area into a plurality of parallel sections, and combining wide beam scanning of the scanning beams of the transmitting and receiving subarrays and narrow beam scanning of the multichannel digital synthesis beams in the main lobe of the transmitting and receiving subarrays on each parallel section to obtain three-dimensional imaging of the three-dimensional imaging target area. The space scanning times can be reduced by several orders of magnitude, the advantages of a sparse array and real beam imaging are integrated, the passing-through type rapid security inspection when the flow of people is large can be realized, and the human body is rapidly scanned and imaged.
Other features and aspects of the present disclosure will become apparent from the following detailed description of exemplary embodiments, which proceeds with reference to the accompanying drawings.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments, features, and aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure.
FIG. 1 shows a flow diagram of a method for three-dimensional imaging based on an array of reconfigurable electromagnetic surfaces according to an embodiment of the present disclosure;
2a, 2b respectively show a reconfigurable electromagnetic surface array security inspection schematic according to an embodiment of the present disclosure;
FIG. 3 illustrates a cross-shaped reconfigurable electromagnetic surface array topology according to an embodiment of the present disclosure;
4a-4d show a sub-array overlay multiplexing schematic of a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure;
FIG. 5 illustrates a reconfigurable electromagnetic surface array scanning schematic in accordance with an embodiment of the present disclosure;
figure 6a shows a composite beamforming schematic diagram without multiplexing of reconfigurable electromagnetic surface transmit and receive sub-arrays according to an embodiment of the present disclosure;
FIG. 6b is a schematic diagram showing the result of complex beam scanning for multiplexing reconfigurable electromagnetic surface transmit and receive sub-arrays according to an embodiment of the present disclosure;
FIG. 6c is a schematic diagram showing the result of complex beam scanning without multiplexing of the reconfigurable electromagnetic surface transmit subarrays and the receive subarrays according to an embodiment of the present disclosure;
figure 6d shows a composite beam scanning beam contrast before and after multiplexing of a reconfigurable electromagnetic surface transmit subarray and a receive subarray according to an embodiment of the present disclosure;
FIG. 7 shows a reconfigurable electromagnetic surface transmit subarray and receive subarray multiplexing phase matching schematic according to an embodiment of the present disclosure;
FIG. 8a shows a schematic cross-section of a reconfigurable electromagnetic surface emitting subarray and a receive subarray multiplexing in accordance with an embodiment of the present disclosure;
FIG. 8b shows a non-multiplexed azimuth view cross-section of a reconfigurable electromagnetic surface transmit sub-array and a receive sub-array according to an embodiment of the present disclosure;
FIG. 9 shows a schematic diagram of a near field digital synthesized beam of a reconfigurable electromagnetic surface array in accordance with an embodiment of the present disclosure;
FIG. 10 shows a near field focused dynamic depth of field schematic of a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure;
figure 11 shows a diagram of near field focusing dynamic depth of field simulation results for a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure.
Detailed Description
Various exemplary embodiments, features and aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers can indicate functionally identical or similar elements. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a better understanding of the present disclosure. It will be understood by those skilled in the art that the present disclosure may be practiced without some of these specific details. In some instances, methods, means, elements and circuits that are well known to those skilled in the art have not been described in detail so as not to obscure the present disclosure.
FIG. 1 shows a flow chart of a method for three-dimensional imaging based on a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure. As shown in fig. 1, the method may include:
step S11: the reconfigurable electromagnetic surface array is constructed according to a three-dimensional imaging target area and comprises N reconfigurable electromagnetic surface transmitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays, wherein the N reconfigurable electromagnetic surface transmitting sub-arrays and the N reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence and are orthogonal in space, part of array elements of the adjacent reconfigurable electromagnetic surface transmitting sub-arrays or the adjacent reconfigurable electromagnetic surface receiving sub-arrays are overlapped, and N is a positive integer.
The reconfigurable electromagnetic surface transmitting array and the reconfigurable electromagnetic surface receiving array are orthogonal in space, namely the N reconfigurable electromagnetic surface transmitting arrays and the N reconfigurable electromagnetic surface receiving arrays are also orthogonal in space, and the multichannel transmitting digital beams of the reconfigurable electromagnetic surface transmitting sub-array and the multichannel receiving digital beams of the reconfigurable electromagnetic surface receiving sub-array corresponding to the multichannel transmitting digital beams are also orthogonal in space.
Fig. 2a and 2b respectively show a reconfigurable electromagnetic surface array security inspection schematic diagram according to an embodiment of the present disclosure. FIG. 3 shows a cross-shaped reconfigurable electromagnetic surface array topology according to an embodiment of the present disclosure.
As shown in fig. 2a and 2b, the scale of the human body imaging area is 0.4m (distance direction), 0.8m (azimuth direction) and 2.0m (height direction), and a reconfigurable electromagnetic surface array (such as the cross reconfigurable electromagnetic surface array in fig. 2) is constructed according to the scale of the three-dimensional human body imaging area. In fig. 2a and 2b, different cross-shaped reconfigurable electromagnetic surface arrays are respectively responsible for imaging corresponding human target areas. The reconfigurable electromagnetic surface transmitting sub-array comprises a plurality of reconfigurable electromagnetic surface transmitting sub-arrays, a plurality of reconfigurable electromagnetic surface receiving sub-arrays and a plurality of reconfigurable electromagnetic surface transmitting sub-arrays, wherein the transverse square blocks represent the reconfigurable electromagnetic surface transmitting sub-arrays, the vertical square blocks represent the reconfigurable electromagnetic surface receiving sub-arrays, and the reconfigurable electromagnetic surface transmitting sub-arrays and the reconfigurable electromagnetic surface receiving sub-arrays jointly form the cross reconfigurable electromagnetic surface transmitting-receiving total array. In fig. 2a and 2b, different cross modules respectively image corresponding human target regions.
As shown in FIG. 3, the upper plane is the focal plane, R0The distance of the electromagnetic surface from the focal plane can be reconstructed. The x direction (the transverse square of the cross reconfigurable electromagnetic surface array in fig. 2a and 2 b) is the emitting array of the cross reconfigurable electromagnetic surface array, i.e. the N transverse square arrays represent the cross reconfigurable electromagnetic surface emitting subarrays; the y direction (vertical square of the cross reconfigurable electromagnetic surface array in fig. 2a and 2 b) is a receiving array of the cross reconfigurable electromagnetic surface array, i.e. the N vertical square arrays represent cross reconfigurable electromagnetic surface receiving sub-arrays. The transmitting array of the cross reconfigurable electromagnetic surface array and the receiving array of the cross reconfigurable electromagnetic surface array jointly form a cross reconfigurable electromagnetic surface transmitting and receiving total array, N reconfigurable electromagnetic surface transmitting sub-arrays correspond to N reconfigurable electromagnetic surface receiving sub-arrays one by one, and N is a positive integer. Of course, the transverse square of the cross reconfigurable electromagnetic surface array is a receiving array of the cross reconfigurable electromagnetic surface array, namely the N transverse square arrays represent cross reconfigurable electromagnetic surface receiving sub-arrays; the vertical square is an emitting array of the cross reconfigurable electromagnetic surface array, namely, the vertical square array represents a cross reconfigurable electromagnetic surface emitting subarray, and the vertical square is not limited herein. In addition, the spatial structure of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray can be T-shaped, etc., and is not limited herein as long as the transmitting array of the reconfigurable electromagnetic surface array and the receiving array of the reconfigurable electromagnetic surface array are orthogonal in space. When each cross-shaped reconfigurable electromagnetic surface transmit-receive total array works, all reconfigurable electromagnetic surface transmitting sub-arrays and all reconfigurable electromagnetic surface receiving sub-arrays work simultaneously, and high-resolution imaging of a real-time target area is realized in a phased array mode.
In one example, as shown in fig. 3, the N reconfigurable electromagnetic surface emitting sub-arrays may include a transmission feed, a diode phase control array, and an antenna element; the N reconfigurable electromagnetic surface receiving sub-arrays can comprise a receiving feed source, a diode phase control unit and an antenna unit. The array element phases of the reconfigurable electromagnetic surface emitting subarray and the reconfigurable electromagnetic surface receiving subarray can be adjusted by controlling the on-off state of the voltage-controlled diode.
Figures 4a-4d illustrate a sub-array overlay multiplexing schematic of a reconfigurable electromagnetic surface array according to an embodiment of the present disclosure.
The sub-array can be a reconfigurable electromagnetic surface transmitting sub-array or a reconfigurable electromagnetic surface receiving sub-array. Taking the reconfigurable electromagnetic surface receiving array as an example for explanation, as shown in fig. 4a-4d, the reconfigurable electromagnetic surface receiving array may include 4 receiving feed sources, which are a first receiving feed source, a second receiving feed source, a third receiving feed source, and a fourth receiving feed source from left to right. As shown in fig. 4a, the first receiving feed corresponds to the first 6 x 6 antenna element and its diode phase control array (first reconfigurable electromagnetic surface receiving sub-array), as shown in fig. 4b, the second receiving feed corresponds to the second 6 x 6 antenna element and its diode phase control array (second reconfigurable electromagnetic surface receiving sub-array), the first sub-array and the second sub-array are overlapped and multiplexed with the 3 x 6 antenna element and its diode phase control array from left to right 4-6 columns, as shown in fig. 4c, the third receiving feed corresponds to the third 6 x 6 antenna element and its diode phase control array (third reconfigurable electromagnetic surface receiving sub-array), the second sub-array and the third sub-array are overlapped and multiplexed with the 3 x 6 antenna element and its diode phase control array from left to right 7-9 columns, as shown in fig. 4d, the fourth receiving feed source corresponds to a fourth 6 x 6 antenna unit and a diode phase control array thereof (a fourth reconfigurable electromagnetic surface receiving sub-array), and the third sub-array and the fourth sub-array are overlapped and multiplexed with 3 x 6 antenna units and diode phase control arrays thereof in a 10-12 th column from left to right.
Step S12: and aiming at the multichannel transmitting digital wave beam of each reconfigurable electromagnetic surface transmitting subarray and the multichannel receiving digital wave beam of the reconfigurable electromagnetic surface receiving subarray corresponding to the multichannel transmitting digital wave beam, the multichannel transmitting digital wave beam is orthogonal in space to form a multichannel digital synthesis wave beam of a transmitting subarray, and the multichannel digital synthesis wave beam is focused to a corresponding position of a three-dimensional imaging target area to form a transmitting subarray scanning wave beam.
In an example, the on-off state of the diode phase control array of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray can be adjusted, the phases of the antenna elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray are adjusted, and the phases of the multichannel transmitting digital beams and the phases of the multichannel receiving digital beams are adjusted according to the phases of the antenna element elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray to form the transmitting and receiving subarray scanning beams.
In one example, the digital beamforming of the multi-channel transmit signal according to the adjusted transmit feed signal may be spatially orthogonal to the digital beamforming of the multi-channel transmit signal according to the adjusted transmit feed as a multi-channel digital composite beam of the transmit-receive subarray.
Figure 5 illustrates a reconfigurable electromagnetic surface array scanning schematic according to an embodiment of the present disclosure.
As shown in fig. 3, for each reconfigurable electromagnetic surface emitting subarray 16 × 16 antenna elements and diode phase control thereof, the emitting feed source of the reconfigurable electromagnetic surface emitting subarray irradiates the antenna elements, and the phases of the antenna elements are controlled by regulating and controlling the diode phase control array, so that multi-channel emitting digital beams of the emitting subarray are focused on a certain position of an imaging region; digital beam synthesis is performed on the multi-channel transmission digital beam signals by regulating and controlling the phase of the transmission feed source signals, so as to obtain the multi-channel transmission digital scanning beam shown in fig. 5. The 16 x 16 antenna units of the reconfigurable electromagnetic surface receiving subarray corresponding to the reconfigurable electromagnetic surface transmitting subarray with the scale of 16 x 16 focus the multi-channel receiving digital wave beams of the receiving subarray on the same focused area of the transmitting array through the regulation and control of a diode phase control array corresponding to each unit; digital beam synthesis is performed on the multi-channel receiving signals by regulating and controlling the phase of the receiving feed source signal, and a multi-channel receiving digital beam (receiving digital scanning beam) reflected by a receiving target area is shown in fig. 5. The multi-channel transmit digital scanning beam and the multi-channel receive digital scanning beam are spatially orthogonal to a multi-channel digital synthesized beam of the transmit-receive subarray (the transmit-receive synthesized beam in fig. 5), as shown at the center black point of the plane in fig. 5.
Ideal cos is adopted for both the feed source and the radiation pattern of the reconfigurable electromagnetic surface arrayqThe (θ) model, taking the (m, n) element as an example, has the amplitude of the transmit-receive synthesized beam at the focal plane black point as follows:
Figure GDA0002946914970000101
wherein the content of the first and second substances,
Figure GDA0002946914970000102
in order to reconstruct the electromagnetic surface array element path phase,
Figure GDA0002946914970000103
the phase of the reconfigurable electromagnetic surface array unit can be adjusted. If all array units need to be superposed in equal phase at a focusing point, the phase characteristics of the reconfigurable electromagnetic surface array units need to meet the following requirements:
Figure GDA0002946914970000104
because the reconfigurable electromagnetic surface array unit has discrete phase characteristics, the maximum value of the phase state of the reconfigurable electromagnetic surface array unit can be adopted for judgment:
Figure GDA0002946914970000105
according to the method, all array elements of the transmitting subarray and the receiving subarray are traversed, so that all transmitting subarray beams and all receiving subarray beams are orthogonal in space and focused at corresponding positions of a target plane.
Step S13: and performing phase compensation on the overlapped array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, adjusting the phase of a multi-channel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray and the phase of a multi-channel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray, and focusing the multi-channel digital synthesis beams of different transmitting and receiving subarrays to different positions of a three-dimensional imaging target area to obtain a plurality of transmitting and receiving subarray scanning beams.
The traditional phased array forms the cross transceiving array, and can also realize scanning imaging of a target area, but because the scanning range is large, the array element interval is small (half wavelength is optimal), and the number of radio frequency channels is large. The cost and the scanning efficiency of the three-dimensional imaging system are considered, the beam scanning can be realized by adopting a composite beam scanning system and utilizing an undersampling design and controlling the phase of a diode control unit capable of reconstructing the digital electromagnetic surface, and the cost is lower. The wide beam scanning of the sub-array scanning beam is carried out on the target imaging area through the reconfigurable electromagnetic surface transmitting sub-array and the reconfigurable electromagnetic surface receiving sub-array, and DBF (beam combining and transmitting) is adopted for fine scanning in the main lobe range of the transmitting and receiving sub-array, so that high-resolution three-dimensional near-field imaging can be realized.
Taking a reconfigurable electromagnetic surface receiving array as an example, by using a directional diagram product theorem, a total array directional diagram can be represented in a form of a product of a reconfigurable electromagnetic surface receiving sub-array element factor (SA Subarray Pattern) and a multi-channel array factor (SA backup AF Pattern) of the reconfigurable electromagnetic surface receiving sub-array, as shown in fig. 6a, the grating lobe of the DBF can be effectively suppressed. When the reconfigurable electromagnetic surface emitting subarrays and the reconfigurable electromagnetic surface receiving subarrays are arranged in parallel, the equivalent array element spacing is the array length of the reconfigurable electromagnetic surface emitting subarrays or the reconfigurable electromagnetic surface receiving subarrays, and at the moment, when DBF scans, the grating lobes can enter two adjacent zeros of main lobes of the reconfigurable electromagnetic surface emitting subarrays or the reconfigurable electromagnetic surface receiving subarrays, but cannot enter 3dB main lobes. In order to increase the scanning margin of the reconfigurable electromagnetic surface emitting subarray or the reconfigurable electromagnetic surface receiving subarray, the reconfigurable electromagnetic surface emitting subarray and the reconfigurable electromagnetic surface receiving subarray are subjected to overlapping multiplexing undersampling design as shown in fig. 4a to 4d, so that the DBF grating lobe is always outside the main lobe zero point, and the peripheral target interference is further reduced.
By adopting a digital beam synthesis mode that partial array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray are respectively overlapped (the reconfigurable electromagnetic surface transmitting subarray or the reconfigurable electromagnetic surface receiving subarray are overlapped), the reconfigurable electromagnetic surface transmitting or receiving subarray factors formed by multiple channels can be better matched with a reconfigurable electromagnetic surface transmitting or receiving subarray directional diagram, and the grating lobe of the DBF is kept to be always in the side lobe of the reconfigurable electromagnetic surface transmitting or receiving subarray directional diagram. Fig. 6b and 6c show the relationship between the far-field pattern of the reconfigurable electromagnetic surface subarray (transmitting subarray or receiving subarray) and the total array factor of the reconfigurable electromagnetic surface (pattern corresponding to DBF and having a certain scanning angle) when the array elements of the reconfigurable electronic surface receiving subarray and the transmitting subarray are multiplexed theoretically. Fig. 6d shows a comparison of the results of the array elements multiplexing and non-multiplexing of the reconfigurable electronic surface receiving subarrays and the transmitting subarrays in theory, and proves that when the array elements of the reconfigurable electronic surface receiving subarrays and the transmitting subarrays are multiplexed, the DBF grating lobes are obviously suppressed.
And for the reconfigurable electromagnetic surface array working in the near field, a scanning mode of transceiving channel digital beam synthesis is adopted. The reconfigurable electromagnetic surface emitting array needs real beam scanning, the N reconfigurable electromagnetic surface emitting sub-arrays work simultaneously, and the phase management situation when two adjacent reconfigurable electromagnetic surface emitting sub-arrays are overlapped and multiplexed is shown in fig. 7, wherein for N array elements of the multiplexing part of the two adjacent reconfigurable electromagnetic surface emitting sub-arrays, the ith (i is 1,2,3, say, N) is taken for explanation, and the wave path generated by the corresponding two reconfigurable electromagnetic surface emitting sub-array feed sources and the phase distribution required to be compensated can be expressed as follows:
Figure GDA0002946914970000121
wherein k is0Representing the wave number of the corresponding radio frequency,
Figure GDA0002946914970000122
respectively representing the distance from the array element to the corresponding reconfigurable electromagnetic surface emission subarray feed source, (x)i,yi) Representing the horizontal and vertical coordinates of the array element. Theta denotes the pitch angle of the array element to the focus position,
Figure GDA0002946914970000123
indicating the azimuth angle of the array element to the focus position.
In one example, according to the phase distribution of the array element overlapping part of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, phase compensation is carried out on the overlapping part of the reconfigurable electromagnetic surface transmitting subarray or the reconfigurable electromagnetic surface receiving subarray by using a phase matching adjustment method of an average phase. Wherein the average phase may be
Figure GDA0002946914970000124
So as to carry out phase compensation on the overlapped part of the reconfigurable electromagnetic surface transmitting subarray or the reconfigurable electromagnetic surface receiving subarray. The phase compensation can be carried out on the overlapped array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, so that the multichannel digital synthesis wave beams of different transmitting and receiving subarrays are focused to different positions of a three-dimensional imaging target area.
In one example, the multiplexing coincidence rate of the reconfigurable electromagnetic surface subarrays is 50% by adopting the method and interleaving and multiplexing according to the 1/2 array element number of the reconfigurable electromagnetic surface subarrays. The discretization is followed by phase compensation, and factors such as illumination range and propagation loss are considered, and the obtained near field digital beam synthesis results at different positions are shown in fig. 8 a. Fig. 8b is the digital beam synthesis result under the condition that the reconfigurable electromagnetic surface subarray unit is not multiplexed. As can be seen from fig. 8a and 8b, the DBF scanning accuracy can be maintained to a certain extent by using the reconfigurable electromagnetic surface subarray element multiplexing technology in combination with an average phase compensation method, and the grating lobe influence is effectively reduced.
In one example, in order to further improve the beam pointing accuracy and reduce the side lobe level, the particle swarm optimization is adopted to optimize the sub-array side lobe by taking the average phase as the initial phase matching. The cost function with low sidelobe and low grating lobe as the optimization target can be expressed by the following formula:
Figure GDA0002946914970000131
wherein the content of the first and second substances,|F(xi,yi) I represents a two-dimensional near-field directional diagram generated by the ith multiplexing array element, ML(xi,yi) Representing the lower envelope, M, of the i-th array element for which a directional diagram is desiredU(xi,yi) Indicating that the ith array element expects to get the upper envelope of the pattern. Compared with the pointing accuracy of a subarray wave beam, the influence of low sidelobe on imaging quality is more critical, and because the particle swarm algorithm is sensitive to initial value setting, the phase matching result of the averaging method is used as an optimized initial phase, so that the robustness of an iterative process can be improved.
Step S14: and dividing the three-dimensional imaging target area into a plurality of parallel sections, and combining wide beam scanning of the scanning beams of the transmitting and receiving subarrays and narrow beam scanning of the multichannel digital synthesis beams in the main lobe of the transmitting and receiving subarrays on each parallel section to obtain three-dimensional imaging of the three-dimensional imaging target area.
In one example, a target scene is divided into a plurality of parallel cross sections, each flat cross section is focused by adopting a dynamic depth of field multi-focusing technology, and near-field three-dimensional imaging of a target area can be obtained by combining wide beam scanning of the transceiver sub-array and fine scanning (narrow beam scanning) of the multi-channel digital synthesis beam in a main lobe of the transceiver sub-array on each parallel cross section. Fig. 10 is a schematic diagram of a reconfigurable electromagnetic surface array working in a near-field focusing mode to form a focused spot on a target plane, where the reconfigurable electromagnetic surface array is a cross array and the spot (sub-array scanning beam) is defined as the area covered by the 3dB main lobe of the transmit-receive sub-array. The reconfigurable electromagnetic surface array adopts self-adaptive focusing scanning, and can realize ultra-large depth of field. As shown in fig. 11, the position of the parallel cross section of the lens can be changed by 10cm as a step, and the diameter of the observation spot of the three-dimensional imaging plane is set within ± 5cm of the focusing plane, so as to realize dynamic focusing in a large distance range between the center and the edge of the plane, and realize high-resolution near-field three-dimensional imaging.
The reconfigurable electromagnetic surface array is constructed according to a three-dimensional imaging target area, the reconfigurable electromagnetic surface array comprises N reconfigurable electromagnetic surface transmitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays, the N reconfigurable electromagnetic surface transmitting sub-arrays and the N reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence and are orthogonal in space, part of array elements of the adjacent reconfigurable electromagnetic surface transmitting sub-arrays or the adjacent reconfigurable electromagnetic surface receiving sub-arrays are overlapped, and N is a positive integer; aiming at a multichannel transmitting digital beam of each reconfigurable electromagnetic surface transmitting subarray and a multichannel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray corresponding to the multichannel transmitting digital beam, the multichannel transmitting digital beam is orthogonal in space to form a multichannel digital synthesis beam of a transmitting subarray, and the multichannel digital synthesis beam is focused to a corresponding position of a three-dimensional imaging target area to form a transmitting subarray scanning beam; performing phase compensation on overlapped array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, adjusting the phase of a multi-channel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray and the phase of a multi-channel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray, and focusing the multi-channel digital synthesis beams of different transmitting and receiving subarrays to different positions of a three-dimensional imaging target area to obtain a plurality of transmitting and receiving subarray scanning beams; and dividing the three-dimensional imaging target area into a plurality of parallel sections, and combining wide beam scanning of the scanning beams of the transmitting and receiving subarrays and narrow beam scanning of the multichannel digital synthesis beams in the main lobe of the transmitting and receiving subarrays on each parallel section to obtain three-dimensional imaging of the three-dimensional imaging target area. The space scanning times can be reduced by several orders of magnitude, the advantages of a sparse array and real beam imaging are integrated, the passing-through type rapid security inspection when the flow of people is large can be realized, and the human body is rapidly scanned and imaged.
In a possible implementation mode, a non-uniform fast fourier transform algorithm can be used to obtain a multichannel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray and a multichannel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray corresponding to the multichannel transmitting digital beam, and the multichannel transmitting digital beam and the multichannel receiving digital beam are orthogonal in space to form a multichannel digital synthesis beam of the transmitting subarray and the receiving subarray.
The fast DBF algorithm is usually based on a far-field signal model and cannot be directly applied to near-field imaging; the delay-and-sum (delay-and-sum) algorithm can achieve near-field focusing, but is too computationally expensive to be suitable for fast implementation of the algorithm. The invention provides a near-field spherical wave front phase compensation method, which is characterized in that series expansion approximation is carried out on an electromagnetic wave propagation path in a Fresnel region of an antenna array, and spherical wave front phase is compensated by multiplying a matching function. And a digital beam forming algorithm is adopted to realize rapid dynamic focusing at different distances.
A near-field beam forming algorithm based on non-uniform fast Fourier transform (NUFFT) can be applied to the non-uniform sparse array element sampling condition, a foundation is laid for follow-up antenna array sparse research, and the calculation complexity of a DBF algorithm is far lower than that of a delay-accumulation algorithm. The wave beams of the reconfigurable electromagnetic surface transmitting array and the reconfigurable electromagnetic surface receiving array are orthogonal and focused, and a one-dimensional wave beam forming algorithm is considered. The reconfigurable electromagnetic surface receiving array is taken as an example, and a near-field multi-channel digital synthetic beam algorithm based on NUFFT is introduced.
As shown in fig. 9, the transmitting signal is s (t), and the total number of the reconfigurable electromagnetic surface transmitting linear arrays is M0And each antenna unit (diode unit) is positioned in a reconfigurable electromagnetic surface subarray. The m antenna unit in the transmitting linear array receives (r)0One-way signal of the target at θ) is s (t- τ (r)0M, θ)), wherein
Figure GDA0002946914970000151
Let the transmit signal frequency be f, the near-field direction diagram corresponding to the transmit antenna array can be represented as:
Figure GDA0002946914970000152
for the near field case, the target imaging region is typically located in the Fresnel region of the transmit array (0.96D < r)0≤D22 λ), the target time delay can be fresnel approximated under a least squares estimate:
Figure GDA0002946914970000153
substituting into the near field pattern formula yields:
Figure GDA0002946914970000154
let thetastartAnd thetaendThe initial angle and the end angle formed for the digital synthesis beam are stepped by N angles at equal intervals.
Any scan angle therein can be expressed as:
sin theta ═ p delta s + delta s/2 (N/2 ≦ p ≦ N/2-1), where
Figure GDA0002946914970000155
Order to
Figure GDA0002946914970000161
ωm＝-2πfxmΔ s/c, which can be further expressed as:
Figure GDA0002946914970000162
due to w'm(r0) Is non-uniformly distributed, and B (r)0,θp) The near field digital beamforming may be done based on one-dimensional NUFFT for uniform distribution.
Having described embodiments of the present disclosure, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen in order to best explain the principles of the embodiments, the practical application, or improvements made to the technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims (7)

1. A method of three-dimensional imaging based on an array of reconfigurable electromagnetic surfaces, the method comprising:
the reconfigurable electromagnetic surface array is constructed according to a three-dimensional imaging target area, and comprises N reconfigurable electromagnetic surface transmitting sub-arrays and N reconfigurable electromagnetic surface receiving sub-arrays, wherein the N reconfigurable electromagnetic surface transmitting sub-arrays and the N reconfigurable electromagnetic surface receiving sub-arrays are in one-to-one correspondence and are orthogonal in space, part of array elements of the adjacent reconfigurable electromagnetic surface transmitting sub-arrays or the adjacent reconfigurable electromagnetic surface receiving sub-arrays are overlapped, and N is a positive integer;
aiming at that a multichannel transmitting digital beam of each reconfigurable electromagnetic surface transmitting subarray and a multichannel receiving digital beam of a reconfigurable electromagnetic surface receiving subarray corresponding to the multichannel transmitting digital beam are orthogonal in space and synthesized into a multichannel digital synthesis beam of a transmitting and receiving subarray, and focusing the multichannel digital synthesis beam to a corresponding position of a three-dimensional imaging target area is a transmitting and receiving subarray scanning beam;
performing phase compensation on overlapped array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, adjusting the phase of a multi-channel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray and the phase of a multi-channel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray, and focusing the multi-channel digital synthesis beams of different transmitting and receiving subarrays to different positions of a three-dimensional imaging target area to obtain a plurality of transmitting and receiving subarray scanning beams;
and dividing the three-dimensional imaging target area into a plurality of parallel sections, and combining wide beam scanning of the scanning beams of the transmitting and receiving subarrays and narrow beam scanning of the multichannel digital synthesis beams in the main lobe of the transmitting and receiving subarrays on each parallel section to obtain three-dimensional imaging of the three-dimensional imaging target area.
2. The three-dimensional imaging method according to claim 1, wherein the reconfigurable electromagnetic surface emitting subarray comprises a transmission feed, a diode phase control array and an antenna element;
the reconfigurable electromagnetic surface receiving subarray comprises a receiving feed source, a diode phase control array and an antenna unit.
3. The three-dimensional imaging method of claim 2, wherein said adjusting phases of the multi-channel transmit digital beams of the reconfigurable electromagnetic surface transmit sub-array and the multi-channel receive digital beams of the reconfigurable electromagnetic surface receive sub-array comprises:
and adjusting the on-off state of the diode phase control array of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, adjusting the phases of the antenna units of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, and adjusting the phase of the multichannel transmitting digital beam and the phase of the multichannel receiving digital beam according to the phases of the antenna unit array elements of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray to form a transmitting-receiving subarray scanning beam.
4. The three-dimensional imaging method according to claim 2, wherein the digital beamforming of the multi-channel transmission signals according to the adjustment of the phase of the transmission feed signal and the digital beamforming of the multi-channel transmission signals according to the adjustment of the phase of the transmission feed are spatially orthogonal as a multi-channel digital synthesized beam of the transmit-receive subarray.
5. The three-dimensional imaging method according to claim 1, wherein the phase compensation of the overlapping array elements of the reconfigurable electromagnetic surface transmit sub-array and the reconfigurable electromagnetic surface receive sub-array comprises:
and according to the phase distribution of the array element overlapping parts of the reconfigurable electromagnetic surface transmitting subarray and the reconfigurable electromagnetic surface receiving subarray, carrying out phase compensation on the array element overlapping parts of the reconfigurable electromagnetic surface transmitting subarray or the reconfigurable electromagnetic surface receiving subarray by using a phase matching adjustment method of an average phase.
6. Three-dimensional imaging method according to claim 1,
and obtaining a multichannel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray and a multichannel receiving digital beam of the reconfigurable electromagnetic surface receiving subarray corresponding to the multichannel transmitting digital beam of the reconfigurable electromagnetic surface transmitting subarray by using a non-uniform fast Fourier transform algorithm, wherein the multichannel transmitting digital beam and the multichannel receiving digital beam are orthogonal in space to form a multichannel digital synthesis beam of the transmitting subarray.
7. A method of three-dimensional imaging according to claim 1 wherein the total array of reconfigurable electro-magnetic surfaces is cross-shaped, T-shaped, r-shaped.
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