Near-field linear sampling RCS measurement method based on adaptive time-domain gating

Abstract

This invention discloses a near-field linear sampling RCS measurement method based on adaptive time-domain gating. The steps are as follows: acquiring continuous echo signals from the target and the calibration body; performing phase center correction on the echo data acquired through near-field sampling; determining the estimated adaptive distance between the calibration phase center and the origin of the coordinate system according to different measurement positions, selecting a gate function, and performing time gating on the corrected echo signal to achieve adaptive time-domain gating; acquiring the two-dimensional plane spectrum of the target and the calibration body; compensating the two-dimensional plane spectrum using a scanning probe; and obtaining the near-field measurement result of the target's RCS. This invention combines adaptive time-domain gating with near-field linear measurement, avoiding the problem that the general time-domain gating range in existing technologies is difficult to effectively filter noise, reducing measurement time, and improving measurement accuracy.

Description

Technical Field

[0001] This invention belongs to the field of measurement technology, and more specifically relates to a near-field linear sampling RCS (Radar Cross Section) measurement method based on adaptive time-domain gating in the field of electromagnetic measurement technology. This invention can be used to obtain the radar cross section of a target by measurement and calculation. Background Technology

[0002] In the field of radar detection and target identification, radar cross section (RCS) is a physical quantity reflecting the scattering characteristics of the object under test. With the development of radar technology, RCS measurement technology is indispensable for various objects, including aircraft, tanks, and missiles as common targets. RCS measurement can generally be divided into far-field measurement, compact-field measurement, and near-field measurement methods, depending on the measurement site. For electrically large targets, far-field RCS measurement requires a very long test site and high-power test equipment, and the measurement accuracy is easily affected by the test environment. Compact-field measurement can significantly shorten the test distance, but the required parabolic surface is expensive, and the equipment operation and maintenance costs are high. Near-field measurement, as an emerging technology, has advantages such as short test distance, low investment cost, indoor operation, strong confidentiality, high measurement accuracy, large information capacity, and all-weather operation. The near-field measurement method involves acquiring scattering data within the near-radiation zone of the target using a scanning probe, and then extrapolating the data through certain data processing methods to obtain the target's far-field RCS. Currently, SAR imaging measurement methods can obtain not only the far-field RCS of a target but also its own scattering characteristics, making them widely used in calculating electromagnetic scattering problems. However, this method requires consideration of imaging resolution, necessitating the use of broadband signals for scanning, which increases the data volume, placing excessive demands on computer memory and significantly increasing computation time. Circular scanning, compared to linear scanning, not only requires consideration of turntable accuracy but also necessitates a substantial amount of measurement time.

[0003] The Institute of Electronics, Chinese Academy of Sciences, disclosed a method for measuring the backscattering cross section (RCS) based on two-dimensional near-field imaging using line-track scanning in its patent application, "Method for Measuring Backscattering Cross Section Based on Two-Dimensional Near-Field Imaging Using Line Track Scanning" (application date: August 28, 2014, application number: 201410432104.X, publication number: CN104199026A). The method's implementation steps are as follows: First, within a selected frequency range, the transmitting and receiving antennas perform line-track scanning to acquire scattering measurement data of the target under test; second, background cancellation is performed on the acquired data; third, T phase differences are taken within a preset value range and interval, and these T phase differences are used to perform phase compensation on the true scattering measurement data of the target under test after background cancellation, and imaging is then performed; fourth, the effective scattering coefficient of the target is extracted from the optimally focused two-dimensional scattering image; fifth, the target under test is replaced with a calibration object, and steps one, two, three, and four are repeated; sixth, the true radar cross section (RCS) value of the target under test is calculated. Although this method uses techniques such as phase compensation and background cancellation to effectively improve measurement accuracy, it still has a shortcoming: it ignores the influence of field echoes on the measurement results, resulting in poor measurement accuracy.

[0004] The Beijing Institute of Environmental Characteristics disclosed a clutter suppression method for near-field RCS measurement based on InSAR technology in its patent application, "Clutter Suppression Method for Linear Scanning Near-Field RCS Measurement Based on InSAR Technology" (Application Date: 2016.12.09, Application No.: 201611131827.1, Publication No.: CN106526547A). The method mainly involves the following steps: First, performing a linear scan of the target under two different altitude conditions to obtain two two-dimensional images of the target; second, determining the height of each scattering source of the target based on the height difference between the two linear scans and the phase difference between the two two-dimensional images; third, filtering the target based on the height of each scattering source, and reconstructing the filtered scattering sources to obtain the clutter-suppressed target RCS. Although this method can effectively suppress clutter echoes and improve measurement accuracy, it still has three shortcomings: First, when using InSAR technology after a straight-line scan, the image resolution must be considered. If the resolution is too high, aliasing will occur, distorting the image and significantly reducing the measurement results; conversely, a low resolution will greatly increase the measurement time. Second, this method does not consider probe delay and its own radiation characteristics after acquiring near-field data, and directly processes the sampled data, leading to deviations in the echo signal expression and thus errors in the final target RCS near-field measurement. Third, because this method does not consider the different backgrounds at different measurement locations and only uses a general time-domain gating range, the background noise can cause deviations in the data acquired during sampling, resulting in certain errors in the final target RCS near-field measurement. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a near-field linear sampling RCS measurement method based on adaptive time-domain gating. This method solves the problems of long measurement time and large computer memory requirements under broadband scanning, as well as the technical problems of reduced measurement accuracy caused by ignoring the influence of the scanning probe and the delay in probe sampling in the prior art, and the technical problems of reduced measurement accuracy caused by ignoring the different background noise at different linear measurement positions.

[0006] To achieve the above objectives, the present invention proposes a method that directly calculates the RCS of the object under test using near-field linear measurement and two-dimensional plane spectrum transformation, without the need for imaging technology. This eliminates the need for broadband scanning to meet resolution requirements, significantly reducing measurement time and computer memory usage. Since the echo signal requires a cable connection for acquisition in actual measurements, the phase center is not located at the antenna position. The offset is determined by generating a one-dimensional range image from the echo signal, and phase correction is performed to move the phase center to the antenna position, satisfying the assumptions of linear near-field to far-field conversion technology. This greatly reduces the impact of phase center offset caused by probe "delay" on the measurement results. Furthermore, since the probe output is proportional to its radiation characteristics in actual measurements, probe compensation is achieved by dividing the probe's two-dimensional plane spectrum by the probe's output plane spectrum, significantly reducing the influence of the probe's own radiation characteristics on the measurement results. Since the background noise distribution varies in the linear scanning position, using a general time-domain gating range will not effectively filter out the noise due to positional changes, thus affecting the measurement results. By using different time-domain gating ranges according to different measurement positions, the reduction in measurement accuracy caused by changes in the position of background noise can be effectively reduced.

[0007] To achieve the above objectives, the technical solution adopted by the present invention includes the following steps:

[0008] Step 1: Acquire continuous echo signals of the target and calibration body under uniform linear sampling:

[0009] Step 1.1: Use a scanning probe to perform uniform linear sampling on the target under test, the calibration body, and the empty background to obtain discrete echo signals of the target under test, the calibration body, and the empty background under uniform linear sampling at L sampling points under background noise. Where Δx represents the uniform linear sampling interval, c represents the speed of light, f represents the operating frequency of the scanning probe, and L represents the total number of uniform linear sampling points. x Indicates the scanning path length of the scanning probe;

[0010] Step 1.2: Calculate the difference between the discrete echo data of the target under test, the calibration body and the empty background at each straight sampling point to obtain the discrete echo signal of the target under test and the discrete echo signal of the calibration body.

[0011] Step 1.3: Transform the discrete echo signal of the target under test and the discrete echo signal of the calibration body into the continuous echo signal of the target under test and the continuous echo signal of the calibration body, respectively.

[0012] Step 2: Perform phase center correction on the continuous echo signal of the target under test and the continuous echo signal of the calibration body respectively:

[0013] Step 2.1, calculate the phase shift of the continuous echo signals of the target and the calibration body according to the following formula:

[0014]

[0015] Among them, R del t represents the phase shift of the echo signal. peak d represents the time from the issuance of the sampling command to the receipt of the echo data. mea R represents the radius of the target object to be measured. mea This indicates the distance from the scanning probe to the geometric center of the target being measured;

[0016] Step 2.2: Use the phase offset to correct the continuous echo signal of the target under test and the continuous echo signal of the calibration body respectively, to obtain the corrected continuous echo signal of the target under test and the corrected continuous echo signal of the calibration body.

[0017] Step 3: Perform time gating on the continuous echo signal of the corrected target and the continuous echo signal of the corrected calibration body, respectively.

[0018] Step 3.1, calculate the estimated adaptive distance from the calibration phase center to the coordinate origin at each measurement location according to the following formula:

[0019]

[0020] Among them, R adp,n x represents the estimated adaptive distance between the calibration phase center and the origin at the nth measurement position in a Cartesian coordinate system. n This represents the x-axis coordinate value of the nth measurement position in a Cartesian coordinate system.

[0021] Step 3.2, calculate the gate function for each measurement location according to the following formula:

[0022]

[0023] Among them, G n (x n R0) represents the gate function expression for the nth measurement position in a Cartesian coordinate system, R k R represents the distance from the k-th point on the gate function to the phase center, |·| represents the absolute value operation, and R gate Indicates the width of the gate function;

[0024] Step 3.3: Calculate the continuous echo signal of the target under test after time gating and the continuous echo signal of the calibration body after time gating;

[0025] Step 4: Calculate the two-dimensional plane spectrum of the target under test and the two-dimensional plane spectrum of the calibration body using the continuous echo signals from the time-gated target and calibration body, respectively, according to the following formula:

[0026]

[0027]

[0028] Where, A0(k) x ,f), A1(k x f) represent the two-dimensional plane spectra of the target and the calibration body, respectively, and k x k y Let k represent the two-dimensional plane spectral coordinates respectively. x Axis coordinates, k y axis coordinate value, e () This indicates an exponential operation with the natural logarithm as the base, j represents the imaginary unit, and π represents pi. These represent the continuous echo signals of the target under test and the calibration body after time gating, respectively.

[0029] Step 5: Compensate for the two-dimensional plane spectrum of the target under test and the two-dimensional plane spectrum of the calibration body using a scanning probe.

[0030] Step 5.1: Obtain the two-dimensional plane spectrum of the scanning probe in the local coordinate system according to the following formula:

[0031]

[0032] in, E represents the two-dimensional plane spectrum of the scanning probe in the local coordinate system. T E R These represent the far-field sectional radiation patterns of the transmitting and receiving ends of the scanning probe, respectively. The angle of observation of the scanning probe is represented by , and cos(·) represents the cosine function;

[0033] Step 5.2, according to the following formula, obtain the two-dimensional plane spectrum of the scanning probe in the Cartesian coordinate system:

[0034]

[0035] Among them, P TR (k x f) represents the two-dimensional plane spectrum of the scanning probe in a Cartesian coordinate system;

[0036] Step 5.2: According to the following formula, obtain the two-dimensional plane spectrum of the target under test and the two-dimensional plane spectrum of the calibration body after compensation.

[0037]

[0038]

[0039] in, These represent the two-dimensional plane spectra of the compensated object under test and the calibration body, respectively.

[0040] Step 6, obtain the near-field measurement results of the target's RCS:

[0041] Step 6.1: Perform linear near-field to far-field transformation on the two-dimensional plane spectrum of the compensated target and the two-dimensional plane spectrum of the compensated calibration body respectively, and obtain the relative radar cross section of the target and the relative radar cross section of the calibration body respectively.

[0042] Step 6.2: According to the following formula, calibrate the relative radar cross section of the target under test using the relative radar cross section of the calibration body, and obtain the far-field absolute radar cross section of the target under test:

[0043]

[0044] in, This represents the far-field absolute radar cross section of the target obtained under near-field linear measurement. These represent the relative radar cross-sections of the object under test and the calibration object, respectively. Represents the absolute radar cross-section of the calibration body.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] First, this invention, through near-field linear measurement and two-dimensional planar spectral transformation, can directly calculate the RCS of the object under test without imaging, avoiding the problems of long calculation time and large computer memory requirements under broadband scanning. This allows the invention to use narrowband signals for scanning, significantly reducing the time spent in the measurement process.

[0047] Secondly, this invention moves the reference phase center to the antenna position by moving the echo signals of the target under test and the calibration body respectively, thereby achieving phase center correction and probe compensation by dividing the two-dimensional plane spectrum of the probe by the two-dimensional plane spectrum of the target under test. This avoids the influence of the sampling delay of the probe in the prior art and the radiation characteristics of the probe itself on the data acquired during the sampling process. This invention can effectively reduce the influence of the probe on the measurement results and improve the measurement accuracy.

[0048] Third, this invention employs adaptive time-domain gating technology on the echo signals of the target and the calibration body. Specifically, it calculates the estimated adaptive distance between the phase center and the origin of the coordinate system at different linear scanning positions, and then uses a gate function to perform time gating on the echo signals. This avoids the problem of reduced measurement accuracy caused by using a universal time-domain gating range when the measurement position and background environment differ in existing technologies. This allows the invention to reduce the impact of background noise on the measurement results and ensure the accuracy of far-field extrapolation results. Attached Figure Description

[0049] Figure 1 is a flow chart of the present invention;

[0050] Figure 2 This is a simulation diagram of the present invention. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] Reference Figure 1 The steps for implementing the embodiments of the present invention will be described in further detail below.

[0053] Step 1: Obtain the continuous echo signals of the target and the calibration body under uniform linear sampling.

[0054] Step 1.1: Use a scanning probe to perform uniform linear sampling on the target under test, the calibration body, and the empty background to obtain discrete echo signals of the target under test, the calibration body, and the empty background under uniform linear sampling at L sampling points under background noise. Where Δx represents the uniform linear sampling interval, and c represents the speed of light. f L represents the operating frequency of the scanning probe, and L represents the total number of uniform linear sampling points. x This indicates the length of the scanning path of the scanning probe.

[0055] Step 1.2: Calculate the difference between the discrete echo data of the target under test, the calibration body and the empty background at each straight sampling point to obtain the discrete echo signal of the target under test and the discrete echo signal of the calibration body.

[0056] Step 1.3: Transform the discrete echo signal of the target under test and the discrete echo signal of the calibration body into the continuous echo signal of the target under test and the continuous echo signal of the calibration body, respectively.

[0057] The Nyquist theorem transforms the discrete echo signals of the target and the calibration body into continuous echo signals of the target and the calibration body, respectively, using the following equation:

[0058]

[0059]

[0060] Where U0(x,f) and U1(x,f) represent the continuous echo signal of the target under test and the continuous echo signal of the calibration body, respectively. 0l ′、U 1l Let x' and x' represent the discrete echo data of the l-th sampling point of the target and the calibration body under uniform linear sampling, respectively, where l = 1, 2, 3, ..., L, sin() represents the sine function, π represents pi, and x' represents the x-axis coordinate value of the l-th sampling point in the Cartesian coordinate system.

[0061] The aforementioned uniform linear sampling is a near-field linear measurement technique. To prevent the sampled discrete echo signals from overlapping and becoming distorted when reconstructing continuous echo signals, it is necessary to... When acquiring near-field linear data in the xoy plane, the size of the target in the vertical direction (z-axis) must satisfy the far-field condition, while the target in the horizontal direction (xoy plane) does not need to satisfy the far-field condition. The far-field condition is a necessary condition for a spherical wave emitted by a point wave source to be considered a plane wave at a field point (a point other than the point wave source). Therefore, R must be satisfied. mea >2D z 2 f / c, where R mea Dz represents the distance from the scanning probe to the geometric center of the target under test, and Dz represents the size of the target under test in the z-axis direction. Since the scanning coverage of the scanning probe is limited, there exists an effective far-field RCS angular domain for the target under test, and the boundary angle of this angular domain is determined by the following formula:

[0062]

[0063] Where, θ eff The effective angle represents the scan coverage area, arctan(·) represents the arctangent function, and L m D represents half of the total scanning length of the scanning probe. x This indicates the size of the target to be measured in the x-axis direction.

[0064] In an embodiment of the present invention, a microwave anechoic chamber is used to perform near-field linear measurements along the x-axis using a scanning probe in a Cartesian coordinate system. First, the relevant parameters for measurement are determined: the operating frequency of the scanning probe is f = 10 GHz; the uniform linear sampling interval Δx ≤ 0.0075, meaning the distance between two adjacent sampling points is no greater than 0.0075 m; and the target size in the z-axis direction is 0.1 m. Based on the above formula, the following can be calculated: That is, the distance from the scanning probe to the geometric center of the target being measured is greater than Next, uniform linear sampling is performed on the target under test, the calibration body, and the empty background to obtain the discrete echo signal U of L sampling points of the target under test, the calibration body, and the empty background under background noise. 0l ={U 01 U 02 ,...,U 0l ,...,U 0L}、U 1l ={U 11 U 12 ,...,U 1l ,...,U 1L} and U 2l ={U 21 U 22 ,...,U 2l ,...,U 2L}, where l∈{1,2,...,L}. Then, the differences between the discrete echo signal of the target under test, the discrete echo center of the calibration body, and the discrete echo signal of the empty background are calculated to achieve background cancellation, thus obtaining the discrete echo data U' of the target under test. 0l ={U' 01 ,U' 02 ,...,U' 0l ,...,U' 0L Discrete echo data U' of the calibration body 1l ={U' 11 ,U' 12 ,...,U' 1l ,...,U' 1L Finally, the discrete echo signals of the target and the calibration body are transformed into continuous echo signals of the target and the calibration body, respectively, using the Nyquist theorem. This is achieved by the following equation.

[0065] Step 2: Perform phase center correction on the continuous echo signal of the target under test and the continuous echo signal of the calibration body respectively.

[0066] Step 2.1, calculate the phase shift of the continuous echo signals of the target and the calibration body according to the following formula:

[0067]

[0068] Among them, R del t represents the phase shift of the echo signal. peak d represents the time from the issuance of the sampling command to the receipt of the echo data. mea R represents the radius of the target object to be measured. mea This indicates the distance from the scanning probe to the geometric center of the target being measured.

[0069] Step 2.2: Use the phase offset to correct the continuous echo signal of the target under test and the continuous echo signal of the calibration body respectively, to obtain the corrected continuous echo signal of the target under test and the corrected continuous echo signal of the calibration body.

[0070] The step-off method is used to correct the continuous echo signals of the target under test and the calibration body respectively, resulting in the corrected continuous echo signals of the target under test and the calibration body. This is achieved by the following formula:

[0071]

[0072]

[0073] Wherein, U0'(x,f) and U1'(x,f) represent the continuous echo signal of the target under test after correction and the continuous echo signal of the calibration body after correction, respectively.

[0074] In this embodiment of the invention, since the LNF2FFT assumes the reference phase center is located at the antenna position, but in actual measurements, it is difficult to determine the appropriate length of the connecting cable, phase center correction is required. The phase offset R of the echo signals from the target and the calibration body is obtained by calculating the radius of the target, adding the distance from the transmitted signal to the leading edge of the object's illumination front, and subtracting the distance from the scanning probe to the geometric center of the target. del And through R del The phase centers of the target echo signal U0(x,f) and the calibration body echo signal U1(x,f) are corrected respectively to obtain the corrected target echo signal U0'(x,f) and calibration body echo signal U1'(x,f).

[0075] Step 3: Perform time gating on the continuous echo signal of the corrected target and the continuous echo signal of the corrected calibration body, respectively.

[0076] Step 3.1, calculate the estimated adaptive distance from the calibration phase center to the coordinate origin at each measurement location according to the following formula:

[0077]

[0078] Among them, R adp,n x represents the estimated adaptive distance between the calibration phase center and the origin at the nth measurement position in a Cartesian coordinate system. n This represents the x-axis coordinate value of the nth measurement position in a Cartesian coordinate system.

[0079] Step 3.2, calculate the gate function for each measurement location according to the following formula:

[0080]

[0081] Among them, G n (x n R0) represents the gate function expression for the nth measurement position in a Cartesian coordinate system, R k R represents the distance from the k-th point on the gate function to the phase center, |·| represents the absolute value operation, and R gate This indicates the width of the gate function.

[0082] Step 3.3: Calculate the continuous echo signal of the target under test after time gating and the continuous echo signal of the calibration body after time gating.

[0083] The continuous echo signals of the target under test after time gating and the calibration body after time gating are calculated separately by the following formula:

[0084]

[0085]

[0086] in, These represent the continuous echo signal of the target under test after time gating and the continuous echo signal of the calibration body after time gating, respectively.

[0087] In an embodiment of the present invention, the estimated adaptive distance R between the phase center and the origin is determined at the nth measurement position in the calculation plane rectangular coordinate system. adp,n The origin of the coordinate system differs from the origin in the existing gate function gating process. It is a variable that changes with the measurement position and can be determined through R... adp,n Determine the location of the origin of the dynamic coordinate system, which is the center location of the gate function. This is based on the set width R of the gate function. gate The final gate function expression is calculated because the dynamic change of the coordinate origin enables the dynamic change of the gate function, which better solves the problem of different background noise at different measurement positions that is difficult to remove.

[0088] Step 4: Calculate the two-dimensional plane spectrum of the target under test and the two-dimensional plane spectrum of the calibration body using the continuous echo signals from the time-gated target and calibration body, respectively, according to the following formula:

[0089]

[0090]

[0091] Where, A0(k) x ,f), A1(k x f) represent the two-dimensional plane spectra of the target and the calibration body, respectively, and kx k y Let k represent the two-dimensional plane spectral coordinates respectively. x Axis coordinates, k y axis coordinate value, e (·) This indicates an exponential operation with the natural logarithm as the base, j represents the imaginary unit, and π represents pi. These represent the continuous echo signals of the target under test and the calibration body after time gating, respectively.

[0092] Echo signal of the target under test after time gating calibrator echo signal Two-dimensional plane wave mode expansions were performed separately to obtain the two-dimensional plane wave spectrum A0(k) of the target under test. y The two-dimensional plane spectrum A1(k) of the calibration body and f) y ,f).

[0093] Step 5: Compensate the two-dimensional plane spectrum of the target under test and the two-dimensional plane spectrum of the calibration body by scanning the probe.

[0094] Step 5.1: Obtain the two-dimensional plane spectrum of the scanning probe in the local coordinate system according to the following formula:

[0095]

[0096] in, E represents the two-dimensional plane spectrum of the scanning probe in the local coordinate system. T E R These represent the far-field sectional radiation patterns of the transmitting and receiving ends of the scanning probe, respectively. represents the observation angle of the scanning probe, and cos(·) represents the cosine function.

[0097] Step 5.2, according to the following formula, obtain the two-dimensional plane spectrum of the scanning probe in the Cartesian coordinate system:

[0098]

[0099] Among them, P TR (k x f) represents the two-dimensional plane spectrum of the scanning probe in a Cartesian coordinate system.

[0100] Step 5.3: According to the following formula, obtain the compensated two-dimensional plane spectrum of the target under test and the compensated two-dimensional plane spectrum of the calibration body respectively:

[0101]

[0102]

[0103] in, These represent the two-dimensional plane spectra of the measured object and the calibration body after compensation, respectively.

[0104] The relationship between the local coordinate system and the global coordinate system (Cartesian coordinate system) is as follows: x = -x′, y = -y′, where x and y represent the x-axis and y-axis coordinates of the coordinate point in the global coordinate system, respectively, and x′ and y′ represent the x-axis and y-axis coordinates of the coordinate point in the local coordinate system, respectively.

[0105] In an embodiment of the present invention, the far-field sectional pattern E of the transmitting and receiving ends of the scanning probe is shown. T and E R By performing variable substitution, the probe's two-dimensional plane spectrum in local coordinates is obtained. Then, a coordinate transformation is performed to obtain the probe's two-dimensional plane spectrum P in global coordinates. TR In engineering practice, since the probe output is proportional to the probe's far-field pattern, the two-dimensional plane spectrum P of the scanning probe in global coordinates is obtained. TR Compensation is achieved by dividing the two-dimensional plane spectra of the target and the calibration body by A0 and A1, respectively, to obtain the compensated two-dimensional plane spectra of the target and the calibration body passing through the probe.

[0106] Step 6: Obtain the near-field measurement results of the target RCS.

[0107] Step 6.1: Perform linear near-field to far-field transformation on the two-dimensional plane spectrum of the compensated target and the two-dimensional plane spectrum of the compensated calibration body to obtain the relative radar cross section of the target and the relative radar cross section of the calibration body, respectively.

[0108] Linear near-field to far-field transformation is performed on the compensated two-dimensional plane spectrum of the target under test and the compensated two-dimensional plane spectrum of the calibration body to obtain the relative radar cross section of the target under test and the relative radar cross section of the calibration body, respectively, by the following formula:

[0109]

[0110]

[0111] in, These represent the relative radar cross sections of the target and the calibration object, respectively. The observation angle represents the relative radar cross-section, and k represents the wavenumber of the scanning probe's operating frequency f.

[0112] Step 6.2: According to the following formula, calibrate the relative radar cross section of the target under test using the relative radar cross section of the calibration body, and obtain the far-field absolute radar cross section of the target under test:

[0113]

[0114] in, This represents the far-field absolute radar cross section of the target obtained under near-field linear measurement. These represent the relative radar cross-sections of the object under test and the calibration object, respectively. Represents the absolute radar cross-section of the calibration body.

[0115] The effects of this invention will be further illustrated below with simulation experiments:

[0116] 1. Simulation experimental conditions:

[0117] The measurement platform of this invention is the standard microwave anechoic chamber of Xi'an University of Electronic Science and Technology.

[0118] The simulation experiment hardware platform of this invention is as follows: the processor is an Intel Xeon Gold 6240 CPU with a main frequency of 2.6GHz and the memory is 32GB.

[0119] The software platform for the simulation experiment of this invention is: Windows 10 operating system, Matlab R2019b.

[0120] 2. Simulation content and result analysis.

[0121] The two curved metal plates used in the simulation experiment of this invention are a simplified scattering model. The model material is an ideal conductor. The dimensions of both metal plates are 0.25 × 0.001 × 0.1 m, and the included angle between the two metal plates is 30°. The operating frequency of the probe is f = 10 GHz, and the radius r of the spherical calibration body is... sph =111.8mm, place the probe at a distance R from the object to be measured. mea At a position of 1m, set the scanning path x = -1.1~1.1m, the sampling interval Δx = 0.007m, the number of scanning points L = 315, and scan along the x-axis.

[0122] The simulation experiment of this invention uses the present invention and existing technology (MoM) to analyze the scattering model and obtain the radar cross section of the target model under test, such as... Figure 2 As shown.

[0123] In the simulation experiments of this invention, the existing technology used refers to:

[0124] The low-order method of moments (MoM) proposed by R.F. Harrington et al. in "Field Computing by Moment Methods" is abbreviated as MoM.

[0125] The following combination Figure 2 The effects of the present invention will be further described.

[0126] Figure 2 The horizontal axis represents the angle of the far-field RCS of the target under test at the probe's operating frequency, and the vertical axis represents the radar cross section of the target object. Figure 2 The solid lines in the diagram represent radar cross section curves obtained using existing technologies, while the dashed lines represent radar cross section curves obtained using the method of this invention. Figure 2 The upper left corner of the image shows the two curved metal plates of the target object used in this embodiment of the invention. It can be seen that the theoretical value and the measurement result are basically consistent.

Claims

1. A near-field linear sampling RCS measurement method based on adaptive time-domain gating, characterized in that, The measurement method involves uniformly sampling the target, calibration object, and background using a scanning probe, calculating the estimated adaptive distance from the calibration phase center to the origin at each measurement location, and obtaining the relative radar cross-section of the target and the calibration object. The steps of this method are as follows: Step 1: Acquire continuous echo signals of the target and calibration body under uniform linear sampling: Step 1.1: Use a scanning probe to perform uniform linear sampling on the target under test, the calibration body, and the empty background to obtain discrete echo signals of the target under test, the calibration body, and the empty background under uniform linear sampling at L sampling points under background noise. Where Δx represents the uniform linear sampling interval, c represents the speed of light, f represents the operating frequency of the scanning probe, and L represents the total number of uniform linear sampling points. x Indicates the scanning path length of the scanning probe; Step 1.2: Calculate the difference between the discrete echo data of the target under test, the calibration body and the empty background at each straight sampling point to obtain the discrete echo signal of the target under test and the discrete echo signal of the calibration body. Step 1.3: Transform the discrete echo signal of the target under test and the discrete echo signal of the calibration body into the continuous echo signal of the target under test and the continuous echo signal of the calibration body, respectively. Step 2: Perform phase center correction on the continuous echo signal of the target under test and the continuous echo signal of the calibration body respectively: Step 2.1, calculate the phase shift of the continuous echo signals of the target and the calibration body according to the following formula: Among them, R del t represents the phase shift of the echo signal. peak d represents the time from the issuance of the sampling command to the receipt of the echo data. mea R represents the radius of the target object to be measured. mea This indicates the distance from the scanning probe to the geometric center of the target being measured; Step 2.2: Use the phase offset to correct the continuous echo signal of the target under test and the continuous echo signal of the calibration body respectively, to obtain the corrected continuous echo signal of the target under test and the corrected continuous echo signal of the calibration body. Step 3: Perform time gating on the continuous echo signal of the corrected target and the continuous echo signal of the corrected calibration body, respectively. Step 3.1, calculate the estimated adaptive distance from the calibration phase center to the coordinate origin at each measurement location according to the following formula: Among them, R adp,n x represents the estimated adaptive distance between the calibration phase center and the origin at the nth measurement position in a Cartesian coordinate system. n This represents the x-axis coordinate value of the nth measurement position in a Cartesian coordinate system. Step 3.2, calculate the gate function for each measurement location according to the following formula: Among them, G n (x n R0) represents the gate function expression for the nth measurement position in a Cartesian coordinate system, R k R represents the distance from the k-th point on the gate function to the phase center, |·| represents the absolute value operation, and R gate Indicates the width of the gate function; Step 3.3: Calculate the continuous echo signal of the target under test after time gating and the continuous echo signal of the calibration body after time gating; Step 4: Calculate the two-dimensional plane spectrum of the target under test and the two-dimensional plane spectrum of the calibration body using the continuous echo signals from the time-gated target and calibration body, respectively, according to the following formula: Where, A0(k) x ,f), A1(k x f) represent the two-dimensional plane spectra of the target and the calibration body, respectively, and k x k y Let k represent the two-dimensional plane spectral coordinates respectively. x Axis coordinates, k y axis coordinate value, e (·) This indicates an exponential operation with the natural logarithm as the base, j represents the imaginary unit, and π represents pi. These represent the continuous echo signals of the target under test and the calibration body after time gating, respectively. Step 5: Compensate for the two-dimensional plane spectrum of the target under test and the two-dimensional plane spectrum of the calibration body using a scanning probe. Step 5.1: Obtain the two-dimensional plane spectrum of the scanning probe in the local coordinate system according to the following formula: in, E represents the two-dimensional plane spectrum of the scanning probe in the local coordinate system. T E R These represent the far-field sectional radiation patterns of the transmitting and receiving ends of the scanning probe, respectively. The angle of observation of the scanning probe is represented by , and cos(·) represents the cosine function; Step 5.2, according to the following formula, obtain the two-dimensional plane spectrum of the scanning probe in the Cartesian coordinate system: Among them, P TR (k x f) represents the two-dimensional plane spectrum of the scanning probe in a Cartesian coordinate system; Step 5.2: According to the following formula, obtain the two-dimensional plane spectrum of the target under test and the two-dimensional plane spectrum of the calibration body after compensation. in, These represent the two-dimensional plane spectra of the compensated object under test and the calibration body, respectively. Step 6, obtain the near-field measurement results of the target's RCS: Step 6.1: Perform linear near-field to far-field transformation on the two-dimensional plane spectrum of the compensated target and the two-dimensional plane spectrum of the compensated calibration body respectively, and obtain the relative radar cross section of the target and the relative radar cross section of the calibration body respectively. Step 6.2: According to the following formula, calibrate the relative radar cross section of the target under test using the relative radar cross section of the calibration body, and obtain the far-field absolute radar cross section of the target under test: in, This represents the far-field absolute radar cross section of the target obtained under near-field linear measurement. These represent the relative radar cross-sections of the object under test and the calibration object, respectively. Represents the absolute radar cross-section of the calibration body.

2. The near-field linear sampling RCS measurement method based on adaptive time-domain gating according to claim 1, characterized in that, The transformation of the discrete echo signal of the target under test and the discrete echo signal of the calibration body into the continuous echo signal of the target under test and the continuous echo signal of the calibration body, respectively, as described in step 1.3, is achieved by the following formula: Where U0(x,f) and U1(x,f) represent the continuous echo signal of the target under test and the continuous echo signal of the calibration body, respectively. 0l ′、U 1l ' and ' represent the discrete echo data of the l-th sampling point of the target and the calibration body under uniform linear sampling, respectively, l = 1, 2, 3, ..., L, sin(·) represents the sine function, and x' represents the x-axis coordinate value of the l-th sampling point in the Cartesian coordinate system.

3. The near-field linear sampling RCS measurement method based on adaptive time-domain gating according to claim 2, characterized in that, The step 2.2, which involves using phase offset to correct the continuous echo signals of the target under test and the calibration body respectively, yields the corrected continuous echo signals of the target under test and the calibration body, achieved by the following formula: Wherein, U′0(x,f) and U′1(x,f) represent the continuous echo signal of the target under test after correction and the continuous echo signal of the calibration body after correction, respectively.

4. The near-field linear sampling RCS measurement method based on adaptive time-domain gating according to claim 3, characterized in that, The calculation of the continuous echo signal of the target under test after time gating and the continuous echo signal of the calibration body after time gating, as described in step 3.3, is achieved by the following formula: in, These represent the continuous echo signal of the target under test after time gating and the continuous echo signal of the calibration body after time gating, respectively.

5. The near-field linear sampling RCS measurement method based on adaptive time-domain gating according to claim 1, characterized in that, The linear near-field to far-field transformation performed on the compensated two-dimensional plane spectrum of the target under test and the compensated two-dimensional plane spectrum of the calibration body, as described in step 6.1, to obtain the relative radar cross section of the target under test and the relative radar cross section of the calibration body, is achieved by the following formula: in, These represent the relative radar cross sections of the target and the calibration object, respectively. The observation angle represents the relative radar cross-section, and k represents the wavenumber of the scanning probe's operating frequency f.

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