Stepping frequency through-wall imaging array arrangement experiment platform and rapid behind-wall human body imaging method

Abstract

The invention belongs to the technical field of electromagnetic wave detection and imaging, and relates to a step-frequency through-wall imaging array arrangement experimental platform and a rapid imaging method for a human body behind a wall. The step-frequency through-wall imaging array arrangement experimental platform provided by the invention comprises an antenna array plate, a movable array bracket and an antenna bracket, the platform is compatible with horizontal polarization, vertical polarization and circular polarization ultra-wideband through-wall antennas, supports data acquisition modes such as single-transmitting and single-receiving, single-transmitting and multi-receiving and time-division multi-transmitting and multi-receiving, breaks through the geometric constraint of a traditional fixed array, and can verify the influence of factors such as different polarization combinations and array element arrangement on human body imaging behind the wall. According to the rapid imaging method for the human body behind the wall, the dielectric constant and the thickness of the wall can be estimated, a wall refraction model is established, a through-wall electromagnetic wave refraction path is calculated, weak human body scattering signals behind the wall are extracted, phase compensation and three-dimensional imaging are rapidly carried out, imaging grating lobe suppression is carried out, and finally three-dimensional real-time imaging and target positioning of a human body target behind the wall are achieved.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave detection and imaging technology, and relates to a step-frequency through-wall imaging array arrangement experimental platform and a method for rapid imaging of the human body behind a wall. Background Technology

[0002] Through-wall radar imaging technology utilizes the penetrating power of low-frequency electromagnetic waves to achieve non-invasive perception of targets within enclosed spaces by analyzing the interaction between electromagnetic waves and building media and targets behind walls. Compared to optical and infrared technologies, it offers advantages such as all-weather operation, strong penetration, and concealment, making it irreplaceable in critical fields such as security monitoring and disaster relief. Traditional narrow-pulse systems, due to limitations in signal time-bandwidth product, inherently present a contradiction between detection range and resolution, failing to meet the high-precision and rapid detection requirements in complex scenarios. While stepped-frequency continuous wave radar achieves high resolution through synthesized large bandwidth, it also imposes more stringent constraints on the array antenna arrangement, element spacing, and aperture structure. To systematically study the impact of array arrangement on azimuth resolution, side-mounted horizontal imaging quality, and other aspects, there is an urgent need for a highly flexible array arrangement experimental platform and a rapid imaging method for people behind walls, thereby providing reliable experimental evidence and data support for through-wall radar imaging scenarios.

[0003] Traditional through-wall radars often employ mechanically moving single antennas or small-scale arrays for point-by-point scanning, resulting in significant data acquisition time and making it difficult to meet real-time sensing requirements in dynamic target detection scenarios. Furthermore, existing arrays typically use regular, fixed arrangements such as uniform linear arrays, whose rigid geometric layout makes it difficult to dynamically adjust the spatial position and aperture shape of array elements. This design flaw limits research into the correlation between array parameters and imaging performance. Currently, there is a lack of a rapidly reconfigurable through-wall imaging array deployment platform that supports the rapid deployment of arbitrary array types, restricting the research and verification of optimal through-wall imaging array configuration schemes.

[0004] The penetrating disturbance of electromagnetic waves by walls mainly manifests as third-order physical effects: refraction distortion, multipath reflection, and penetration attenuation. Reflection at the wall interface induces multipath coupling between the transmitted signal and the target echo, causing aliasing interference in the time and frequency domains. Penetration attenuation due to dielectric loss significantly weakens the scattering intensity of the target behind the wall. These coupling effects trap the target signal in a low signal-to-noise ratio predicament caused by wall reflection noise and path loss, greatly increasing the difficulty of detecting and separating weak targets. The refraction effect forces imaging algorithms to accurately calculate the dual-medium propagation path of electromagnetic waves through the wall and design a high-precision phase compensation model accordingly. This process relies on solving high-dimensional equations, leading to a sharp increase in computational complexity and severely restricting real-time imaging capabilities and experimental iteration efficiency. Summary of the Invention

[0005] The purpose of this invention is to solve the problems existing in the prior art and to provide a step-frequency through-wall imaging array layout experimental platform and a method for rapid imaging of the human body behind a wall.

[0006] The technical solution provided by this invention is as follows: a step-frequency through-wall imaging array arrangement experimental platform, comprising an antenna array board, a movable array bracket, and an antenna bracket; the antenna array board is mounted on the movable array bracket; wherein, the antenna array board is provided with equally spaced wiring holes; screw fixing holes are provided around the wiring holes for fixing the antenna bracket; the antenna bracket is fixed to the antenna array board by screws.

[0007] Preferably, the upper surface of the antenna bracket is provided with a slot compatible with single-polarized or dual-polarized antennas; the lower surface of the antenna bracket is mounted on the array plate in a horizontal, vertical or 45-degree rotation manner.

[0008] Furthermore, the present invention also provides a method for rapid imaging of a human body behind a wall, the method comprising: Step 1: Using multiple transmitting and receiving antennas on the experimental platform, electromagnetic wave signals are transmitted and received in a stepped frequency manner to obtain the raw echo data of the target behind the wall. The expression for this data is: ; in, The starting frequency, For frequency step size, For frequency index ( ), At the speed of light, and The first The first transmitting antenna and the first The total distance of the electromagnetic wave propagation path from each receiving antenna to the target; Step 2: Process the raw echo data to identify static wall reflection echoes and dynamic human target echoes; Step 3: Divide the space behind the wall into X×Y×Z pixels according to the three dimensions of azimuth, range, and pitch. Then, perform range compensation and superposition on the one-dimensional range signals obtained from different array transceiver antennas to image the target.

[0009] Preferably, in step three, imaging is performed using a direct frequency domain projection algorithm, specifically including: By searching for the reflected echo locations on the first and second surfaces of the wall, and using Fresnel's refraction formula to estimate the dielectric constant and thickness of the wall, and determining the incident and exit points of the electromagnetic wave within the wall, the total propagation path distance of the electromagnetic wave after penetrating the wall can be accurately calculated. ; In the formula , , These represent the three distances of the electromagnetic wave before, during, and after it passes through the wall; Let be the dielectric constant of the wall. for or ; The calculated , Substitute the direct frequency domain projection algorithm and calculate the imaging results: .

[0010] Preferably, in step three, a frequency-domain one-dimensional backpropagation (BP) imaging algorithm is used for imaging, specifically including: The one-dimensional distance is calculated using the improved inverse Fourier formula: ; In the formula, ; The length of the array; The time-domain data is obtained from the discrete inverse Fourier transform; For frequency domain data; Substitute the calculated one-dimensional distance into the following formula to calculate the imaging result: .

[0011] Preferably, the distances from all transmitting and receiving antennas to each pixel in the space behind the wall are pre-calculated and stored. During imaging, the pre-stored distance values ​​are directly called to superimpose the signals and obtain the imaging result.

[0012] Preferably, an equivalent array center distance matrix is ​​constructed: the original canvas is expanded in the width and height directions to form an equivalent spatial canvas; the center point of the equivalent canvas is equivalent to the center of the antenna array; the distance from the array center to each pixel in the equivalent canvas is pre-calculated, and the distance from each antenna to the spatial canvas forms a distance matrix; the corresponding distance is taken out from the distance matrix during imaging calculation.

[0013] The step-frequency through-wall imaging array arrangement experimental platform provided by this invention is compatible with horizontally polarized, vertically polarized, and circularly polarized ultra-wideband through-wall antennas. It can freely test antenna arrays with various topologies such as linear arrays, area arrays, and sparse arrays. It supports data acquisition methods such as single-transmit single-receive, single-transmit multiple-receive, and time-division multiple-transmit multiple-receive. It breaks through the geometric constraints of traditional fixed arrays and can verify the influence of different polarization combinations and array element arrangements on human body imaging behind walls. The rapid human body imaging method behind walls can estimate the dielectric constant and thickness of the wall, establish a wall refraction model, calculate the refraction path of electromagnetic waves through the wall, extract weak human body scattering signals behind the wall, quickly perform phase compensation and three-dimensional imaging, and perform imaging grating lobe suppression. Finally, it can realize three-dimensional real-time imaging and target localization of human targets behind walls, which can accelerate the research and verification of optimal array configuration schemes for through-wall imaging. Attached Figure Description

[0014] Figure 1 This is a front view of the experimental platform for the arrangement of a stepped-frequency through-wall imaging array provided in an embodiment of the present invention; Figure 2 This is a side view of the experimental platform for the arrangement of a stepped-frequency through-wall imaging array provided in this embodiment of the invention; Figure 3 This is a schematic diagram of the antenna support; Figure 4 This is a schematic diagram of a single-polarized antenna and its support frame. Figure 5 This is a schematic diagram of the combination of a dual-polarized antenna and its support frame; Figure 6 This is a schematic diagram of the combination of a dual-polarized antenna and an array support. Figure 7 This is a schematic diagram of the combination of a dual-polarized antenna and an array support. Figure 8 This is a schematic diagram of a stepped-frequency imaging array; Figure 9 It is a static echo; Figure 10 It is a dynamic echo Figure 11 It is a slice in the center distance matrix of the equivalent array corresponding to different antennas. Detailed Implementation

[0015] To more clearly understand the technical content of this invention, its solution will now be described in detail with reference to the accompanying drawings and specific embodiments. The accompanying drawings show a preferred embodiment of this invention, but its scope of protection is not limited thereto, and can be flexibly adjusted according to specific usage requirements in practical applications. This embodiment aims to help those skilled in the art to fully and deeply understand the inventive concept of this solution.

[0016] Example 1: This example provides an experimental platform for arranging a stepped-frequency through-wall imaging array, such as... Figure 1 and Figure 2 As shown, the antenna array board 1 is made of FR4 material and is connected to a movable array bracket 2 made of metal. The antenna array board 1 has 1.1cm diameter wiring holes 3 spaced 2.5cm apart. Around the wiring holes are screw holes 4, also spaced 2.5cm apart, for fixing the antenna bracket 5. The wiring hole area is 80cm x 80cm, and the M4 screw area is 82.5cm x 82.5cm, allowing for antenna installation in 33 x 33 positions.

[0017] Antenna bracket 5 Figure 3 As shown, the antenna bracket 5 has a slot on its upper surface that is compatible with both single-polarized and dual-polarized antennas, and 12 screw holes on its lower surface. The upper eight holes are located at the vertices of a 2.5cm square, rotated 45 degrees horizontally and 45 degrees. The lower four holes are located at the two vertices of the rectangles containing the two squares, forming two rectangles 5cm long and 2.5cm wide with the screw holes at the two square vertices. When the antenna bracket is mounted horizontally, vertically, or rotatably on the antenna array board, simply align the screw holes on the corresponding rectangles with the screw holes on the array board, insert the screws, and tighten the nuts at the back of the antenna array board. Therefore, it supports horizontal, vertical, and 45-degree rotatable mounting on the antenna array board 1. A schematic diagram of its combination with single-polarized and dual-polarized Vivaldi antennas is shown below. Figure 4 , Figure 5 As shown in the diagram, the antenna array board is mounted on the antenna array board. Figure 6 and Figure 7 As shown, it supports the installation of various arrays.

[0018] Example 2: Based on the step-frequency through-wall imaging array arrangement experimental platform of Example 1 above, this example provides a method for rapid imaging of the human body behind a wall, as follows: (1) Stepped frequency imaging principle The formula for step-frequency transmitted signals is: (1); in, Indicates the first The amplitude of each signal component; The initial frequency; This is the frequency step size; The imaginary unit; These are serial number variables, corresponding to different frequency points.

[0019] A schematic diagram of area array step frequency imaging is shown below. Figure 8 As shown in the figure, the step frequency signal is generated by... One antenna transmits, One antenna receives, antenna , The distance to the target is , Then the target's echo signal is: (2).

[0020] The phase of the echo signal is related to the target distance. By calculating the distance from different locations in space to the antenna and performing distance compensation and superposition on the signals, the target can be imaged. The calculation formula for the direct frequency domain projection algorithm is as follows: (3).

[0021] (2) Through-wall imaging principle Microwave echoes penetrating the wall, such as Figure 9 and Figure 10 As shown, the static echo, in sequence, consists of the direct wave from the antenna, the reflected echo from the first and second surfaces of the wall, and remains unchanged over time. The dynamic echo is the human body echo, which changes over time. The refraction path conforms to Fresnel's equation: (4); In the formula , These are the dielectric constants of air and the wall, respectively. , This represents the angle between the electromagnetic wave and the normal. (5); In the formula , , These represent the three distances of the electromagnetic wave before, during, and after it passes through the wall.

[0022] For the one-dimensional range signals obtained from different array transceiver antennas, the echoes from the first and second surfaces of the wall are retrieved by searching for the maximum value in the region. A matrix is ​​constructed using Fresnel's formula to estimate the dielectric constant and thickness of the wall, and the incident and exit points of the wall are obtained. Formula (5) is then used to calculate... , and the calculated , Substituting the value into formula (3) will enable the imaging of the target behind the wall.

[0023] Example 3: This example provides an accelerated imaging method, as detailed below: The inverse Fourier transform is shown in formula (6): (6); In the formula, For time-domain data obtained from discrete inverse Fourier transform, For frequency domain data; This is the array length.

[0024] The frequency domain one-dimensional BP imaging algorithm can be derived into a modified form of the inverse Fourier formula through formula (7): (7); In the formula, .

[0025] The frequency domain one-dimensional BP imaging algorithm can be derived into the form of the inverse Fourier formula, as shown in formula (7). Therefore, the superimposed imaging of a single signal at different positions can be approximated by the modified form of the inverse Fourier.

[0026] To address the problem of excessive computational complexity in calculating the distance from each signal to each pixel, a memory-optimized index lookup technique is implemented. This technique reduces the computational complexity required for imaging by pre-calculating the distance and loading it into memory.

[0027] Memory-optimized distance index lookup technology behind the wall: Pre-storing the distance of M×N signals to each pixel on the canvas requires memory of size M×N×X×Y×Z. By splitting the distance corresponding to each signal into the superposition of the distances of two antennas, only the distances from different transmitting and receiving antennas to the wall need to be pre-stored, thus optimizing the memory usage to (M+N)×X×Y×Z.

[0028] The space behind the wall is divided into X×Y×Z pixels according to three dimensions: azimuth, range, and pitch. The distance from the antenna to each pixel behind the wall is calculated according to formula (5). Substituting this into formula (3) yields the imaging result, but the computational complexity is O(M×N×K×X×Y×Z). One-dimensional distances are quickly calculated according to formula (7). The distances are pre-calculated and stored in memory. Substituting this into formula (8) optimizes the imaging speed to O(M×N×X×Y×Z). (8).

[0029] Equivalent array center distance matrix: such as Figure 11 As shown, let the width, height, and length of the spatial canvas be W, H, and L respectively, and the width and height of the antenna array be W. A H A Construct a structure with a width, height, and length of W+W. A H+H A Given an equivalent spatial canvas of L, calculate the distance from the array center to each pixel in the equivalent spatial canvas. Then, the distance from each antenna to the spatial canvas only needs to be extracted from a slice of the distance matrix from the equivalent array center. This further optimizes the memory footprint to (1 + W). A / W)(1+ H A / H)×W×H.

Claims

1. An experimental platform for arranging a stepped-frequency through-wall imaging array, characterized in that: The device includes an antenna array board, a movable array bracket, and an antenna bracket. The antenna array board is mounted on the movable array bracket. The antenna array board has equally spaced wiring holes. Screw holes are provided around the wiring holes for fixing the antenna bracket. The antenna bracket is fixed to the antenna array board with screws. The upper surface of the antenna bracket has a slot compatible with single-polarized or dual-polarized antennas. The lower surface of the antenna bracket is mounted on the array board in a horizontal, vertical, or 45-degree rotation manner.

2. A method for rapid imaging of a human body behind a wall, characterized in that, The method includes: Step 1: Using multiple transmitting and receiving antennas on the experimental platform described in claim 1, electromagnetic wave signals are transmitted and received in a stepped frequency manner to obtain the original echo data of the target behind the wall, the expression of which is: ； in, The starting frequency, For frequency step size, For frequency index ( ), At the speed of light, and The first The first transmitting antenna and the first The total distance of the electromagnetic wave propagation path from each receiving antenna to the target; Step 2: Divide the space behind the wall into X×Y×Z pixels according to three dimensions: azimuth, range, and pitch. Then, perform range compensation and superposition on the one-dimensional range signals obtained from different array transceiver antennas to image the target.

3. The rapid imaging method for a human body behind a wall according to claim 2, characterized in that, In step two, the direct frequency domain projection algorithm is used for imaging, specifically including: By searching for the reflected echo locations on the first and second surfaces of the wall, and using Fresnel's refraction formula to estimate the dielectric constant and thickness of the wall, and determining the incident and exit points of the electromagnetic wave within the wall, the total propagation path distance of the electromagnetic wave after penetrating the wall can be accurately calculated. ； In the formula , , These represent the three distances of the electromagnetic wave before, during, and after it passes through the wall; Let be the dielectric constant of the wall. for or ; The calculated , Substituting into the direct frequency domain projection algorithm, the imaging results are calculated: ； in, , These refer to the number of transmitting antennas and the number of receiving antennas, respectively.

4. The rapid imaging method for a human body behind a wall according to claim 2, characterized in that, In step two, a frequency-domain one-dimensional backpropagation (BP) imaging algorithm is used for imaging, specifically including: The one-dimensional distance is calculated using the improved inverse Fourier formula: ； In the formula, ; The length of the array; The time-domain data is obtained from the discrete inverse Fourier transform; For frequency domain data; Substitute the calculated one-dimensional distance into the following formula to calculate the imaging result: 。 5. The rapid imaging method for a human body behind a wall according to claim 4, characterized in that, The distances from all transmitting and receiving antennas to each pixel in the space behind the wall are pre-calculated and stored. During imaging, the pre-stored distance values ​​are directly called to superimpose the signals and obtain the imaging result.

6. The rapid imaging method for a human body behind a wall according to claim 5, characterized in that, Constructing an equivalent array center distance matrix: Expand the original canvas in both width and height directions to increase the size of the antenna array, forming an equivalent spatial canvas; the center point of the equivalent canvas is equivalent to the center of the antenna array; pre-calculate the distance from the array center to each pixel in the equivalent canvas, and the distance from each antenna to the spatial canvas forms a distance matrix; during imaging calculation, extract the corresponding distance from this distance matrix.

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