Large aperture array near field target passive direction finding and ranging method

Abstract

The application discloses a large-aperture array near-field target passive direction-finding and ranging method, and belongs to the technical field of underwater acoustic detection and array signal processing.The application solves the problems of low azimuth estimation precision and large calculation amount of the existing near-field target passive positioning method.The application utilizes the spectrum peak broadening property of the near-field target spatial spectrum estimation under a far-field model, and proposes a far-near field target discrimination method.The application sets a ranging step, adopts a coarse focusing scanning mode and a fine focusing scanning mode, obtains the near-field target azimuth and distance at the narrowest spectrum peak width of the spatial spectrum, and significantly improves the azimuth estimation precision.Moreover, the application directly realizes the far-near field discrimination of the target on the basis of the long-range one-dimensional azimuth spectrum, and does not need to pass through two-dimensional spatial scanning to realize the far-near field discrimination of the target, so that the calculation amount of the far-near field discrimination of the target is significantly reduced.The application can be applied to the near-field target passive direction-finding and ranging.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of underwater acoustic detection and array signal processing, and particularly relates to a large-aperture array near-field target passive direction-finding and ranging method. BACKGROUND

[0002] In order to obtain better spatial processing performance, modern sonar systems develop towards large-scale and large-aperture sonar arrays. Due to the increase of the array aperture relative to the target distance, the gain and resolution of the far-field target will be significantly improved. However, with the increase of the array aperture, the near-field spatial coverage of the array will also increase significantly. When the near-field target is compensated, the far-field plane wave compensation assumption is no longer met, and directly using the far-field compensation model for direction estimation will cause the gain and direction-finding performance to decrease seriously, and the near-field compensation model needs to be used. Therefore, the far-field and near-field discrimination problem of the large-aperture array target detection is very important.

[0003] However, the current research on target far-field and near-field discrimination is relatively less, and the following documents mainly carry out research work on passive positioning of near-field targets:

[0004] Document 1: Ji Qing, Cheng Jinfang, Xiao Dawei. Research on near-field small target positioning algorithm based on vector array [J]. Ship Science and Technology, 2018, 40(07): 105-109.

[0005] Document 2: Mei Jidan, Shi Wenpei, Ma Chao, et al. Near-field deconvolution focusing beamforming acoustic image measurement [J]. Acta Acustica, 2020, 45(01): 15-28.

[0006] Document 3: Jia Xiaoyun, Wang Xiujing, Hu Ye. Pipe defect sound source positioning based on MVDR near-field focusing beamforming [J]. Journal of Tianjin University of Science and Technology, 2021, 36(06): 37-43.

[0007] Document 4: Shang Zhigang, Qu Xinghe, Qiao Gang, et al. Beam deconvolution positioning of far-field and near-field mixed sources [J]. Acta Acustica, 2023, 48(03): 447-458.

[0008] Document 1, Document 2 and Document 3 mainly carry out research on near-field source positioning methods, and realize passive positioning of near-field targets through two-dimensional spatial scanning, but they are based on near-field focusing scanning, and the calculation amount of the positioning method is large.

[0009] Document 4 proposes a high-resolution azimuth estimation processing method in the case of a far-near field mixed source, the main purpose of which is to solve the problem of high-resolution processing of multiple targets in the case of far-near field mixed multiple targets, and to improve the azimuth estimation accuracy to a certain extent, but cannot realize the far-near field discrimination of the target, so the spatial spectrum estimation is still affected by the far-near field mixed source, and therefore the accuracy of the azimuth estimation of the near-field target is still limited.

[0010] In summary, the existing near-field target passive positioning method has the problems of spatial spectrum estimation affected by far-near field mixed sources and large amount of calculation, and a new target passive positioning method is urgently needed to solve the problem. SUMMARY

[0011] The purpose of the present application is to solve the problems of low azimuth estimation accuracy and large amount of calculation of the existing near-field target passive positioning method, and a large-aperture array near-field target passive direction-finding and ranging method is proposed.

[0012] The technical scheme adopted by the present application to solve the above technical problems is: a large-aperture array near-field target passive direction-finding and ranging method, which specifically comprises the following steps:

[0013] Step one, obtaining an array far-field beam forming beam width calculation model according to the natural directivity of the uniform linear array;

[0014] Step two, initializing the time t=0;

[0015] Step three, performing far-field beam forming on the array receiving signal at time t to obtain a far-field azimuth spectrum, and then obtaining the coarse measurement angle of each target to be measured and the azimuth spectrum peak width of each target to be measured according to the far-field azimuth spectrum;

[0016] Step four, initializing the number of targets to be measured n=1;

[0017] Step five, inputting the coarse measurement angle of the nth target to be measured into the array far-field beam forming beam width calculation model, comparing the calculated beam width with the azimuth spectrum peak width of the nth target to be measured, and making a near-far field decision for the nth target to be measured;

[0018] Step six, if the nth target to be measured is located in the near field, step seven is continued;

[0019] If the nth target to be measured is located in the far field, the coarse measurement angle is directly taken as the azimuth estimation result of the nth target to be measured; then n=n+1 is set, and step five is returned to be executed;

[0020] Step seven, performing near-field focusing scanning on the nth target to be measured to obtain the azimuth spectrum peak width corresponding to each scanning distance, i.e. the main lobe width corresponding to each scanning distance of the nth target to be measured;

[0021] determining the azimuth initial value and the distance initial value of the nth target to be measured according to the main lobe width corresponding to each scanning distance;

[0022] Step eight, determining the scanning interval of the near-field focusing fine scanning according to the azimuth initial value and the distance initial value of the nth target to be measured, performing the near-field focusing fine scanning in the determined scanning interval, and obtaining the final azimuth and distance of the nth target to be measured;

[0023] Step nine, judging whether n reaches the maximum number of near-field targets;

[0024] If yes, step ten is performed;

[0025] If no, n is set to n+1, and the step five is returned to be performed;

[0026] Step ten, setting t to t+1, and returning to perform the step three.

[0027] Further, the uniform linear array is specifically: taking the positive east direction as the positive direction of the x axis and taking the positive north direction as the positive direction of the y axis, each array element is uniformly arranged at equal intervals on the positive half axis of the x axis, and the distance between adjacent two array elements is d.

[0028] Further, the specific process of the step one is:

[0029] the target incident azimuth is defined as the included angle in the north-east direction, and the incident azimuth of the kth target is denoted as θ k , k=1, 2, …, K, K is the number of incident targets, and for the incident azimuth θ k of the kth target, the natural directivity G(θ) of the uniform linear array is:

[0030]

[0031] wherein, M is the number of array elements, and |·| represents taking the absolute value;

[0032] according to |G(θ)| 2 =1 / 2, the array far-field beam forming beam width calculation model corresponding to the incident azimuth of the kth target is obtained as:

[0033]

[0034] wherein, θ DT is the array far-field beam forming beam width corresponding to the incident azimuth of the kth target, and λ is the signal wavelength.

[0035] Further, the array receiving signal at the tth moment is:

[0036]

[0037] Where x(t) represents the array received signal at time t, s(t) represents the target signal received by the array at time t, n(t) represents the noise signal received by the array at time t, and a(θ) k ) represents angle θ k The corresponding array steering vector.

[0038] Furthermore, the specific process of step three is as follows:

[0039] Step 3.1. Within θ∈[-90°,90°], perform far-field beamforming on the array received signal x(t) to obtain the far-field azimuth spectrum p(θ):

[0040] p(θ)=a(θ) H Ra(θ)

[0041] Where R represents the covariance matrix, R = E[x(t)x H [(t)], E[·] represents the expectation, x H (t) is the conjugate transpose of x(t), and a(θ) is the array steering vector corresponding to the scanning angle θ on the azimuth scan grid. H It is the conjugate transpose of a(θ);

[0042]

[0043] Where e is the base of the natural logarithm, j is the imaginary unit, and the superscript T represents the transpose;

[0044] Step 3.2: Locate the maximum peak position of each local spectral peak in the far-field azimuth spectrum p(θ). Take the angle corresponding to the maximum peak position of each local spectral peak as the coarse angle of each target to be measured, and record the coarse angle of the k-th target to be measured as θ. k ′;

[0045] Taking the position of the maximum peak of any local spectral peak as an example, the method for calculating the width of the azimuth spectral peak of the target under test is as follows:

[0046] The azimuth corresponding to the 3 dB drop to the left of the maximum peak position of this local spectral peak is denoted as θ. L Let θ be the azimuth corresponding to the 3 dB drop to the right of the maximum peak position of this local spectral peak. R Then, the position of the maximum peak of this local spectral peak corresponds to the azimuth spectral peak width Δθ of the target under test as:

[0047] Δθ=|θ R -θ L |

[0048] Similarly, the azimuth spectral peak width of the target under test is obtained from the position of the maximum peak of each local spectral peak.

[0049] Further, the specific process of the step five is:

[0050] For any one to be measured target, the coarse measurement angle of the to be measured target is brought into the array far field beam forming beam width calculation model to obtain the corresponding beam width θ of the to be measured target DT , and the corresponding θ of the to be measured target is compared with the azimuth spectrum peak width Δθ of the to be measured target: DT

[0051] If Δθ≥ε·θ DT , ε is the decision threshold, then the to be measured target is located in the near field;

[0052] Otherwise, Δθ<ε·θ DT , the to be measured target is located in the far field.

[0053] Further, the specific process of the step seven is:

[0054] Step seven one, distance grid division is performed in the search interval θ∈[-90°,90°], wherein D represents the array aperture, D=(M-1)d;

[0055] Then, the near field focusing scanning is respectively performed on the nth to be measured target at each distance, the corresponding azimuth spectrum of each scanning distance is obtained, and then the main lobe width corresponding to each scanning distance is obtained according to the azimuth spectrum;

[0056] Step seven two, the main lobe widths corresponding to the scanning distances are sorted in the order from small to large according to the main lobe widths:

[0057] If the smallest main lobe width corresponds to only one scanning distance, the scanning distance corresponding to the smallest main lobe width is taken as the distance initial value of the to be measured target, and the spectrum peak of the azimuth spectrum obtained when the distance initial value is taken as the scanning distance is obtained, and the angle corresponding to the obtained spectrum peak is taken as the azimuth initial value of the to be measured target;

[0058] If the smallest main lobe width corresponds to multiple scanning distances, the azimuth spectrum power drop degree under each scanning distance corresponding to the smallest main lobe width is calculated, the scanning distance with the maximum azimuth spectrum power drop degree is taken as the distance initial value of the to be measured target, and the angle corresponding to the spectrum peak of the azimuth spectrum obtained when the distance initial value is taken as the scanning distance is taken as the azimuth initial value of the to be measured target;

[0059] The calculation method of the azimuth spectrum power drop degree is:

[0060] Taking the azimuth spectrum under any one scanning distance as an example, the peak power of the azimuth spectrum is denoted as P max ​To the left of the grid point where the peak power is located, the power corresponding to the grid point at an interval of 1° from the grid point where the peak power is located is denoted as P. -1° To the right of the grid point where the peak power is located, the power corresponding to the grid point at an interval of 1° from the grid point where the peak power is located is denoted as P. 1° Then the degree of decrease in the azimuth spectral power ΔP is:

[0061] ΔP=(|P max -P -1° |+|P max -P 1° |) / 2.

[0062] Furthermore, the azimuth spectrum in step seven-one is:

[0063] Taking the i-th scan distance as an example, the i-th scan distance r i The corresponding azimuth spectrum p(θ,r) i )for:

[0064] p(θ,r i )=a(θ,r i ) H Ra(θ,r i )

[0065] Where a(θ,r) i ) represents the array steering vector at the i-th scan distance, and the array steering vector a(θ,r) i The i′th scan orientation θ i′ The guiding vector a(θ) below i′ ,r i )for:

[0066]

[0067] Where, when M is odd, N = (M-1) / 2, and when M is even, N = M / 2, a(θ) i′ ,r i )∈C 2N×1 γ i′ and φ i′ They are represented as follows:

[0068]

[0069] Furthermore, the specific process of step eight is as follows:

[0070] Find the scanning distance in step seven that is closest to the initial distance value but less than the initial distance value, and then find the scanning distance in step seven that is closest to the initial distance value but greater than the initial distance value. Use the found scanning distances as the lower limit and upper limit of the distance for near-field focusing fine scanning, respectively.

[0071] The azimuth initial value is brought into the beam width calculation model to obtain a beam width calculation result, and a difference between the azimuth initial value and the beam width calculation result is taken as a lower limit of an angle of the near-field focusing fine scanning, and a sum of the azimuth initial value and the beam width calculation result is taken as an upper limit of the angle of the near-field focusing fine scanning;

[0072] The near-field focusing fine scanning is performed in the scanning interval, and a near-field focusing azimuth spectrum corresponding to each scanning distance is obtained, and then a main lobe width corresponding to each scanning distance is obtained according to the near-field focusing azimuth spectrum;

[0073] If the minimum main lobe width in each near-field focusing azimuth spectrum corresponds to only one scanning distance, then the scanning distance corresponding to the minimum main lobe width is taken as a final distance value of the target to be measured, and a spectrum peak of the near-field focusing azimuth spectrum obtained when the final distance value is taken as the scanning distance is obtained, and an angle corresponding to the obtained spectrum peak is taken as a final azimuth value of the target to be measured;

[0074] If the minimum main lobe width in each near-field focusing azimuth spectrum corresponds to multiple scanning distances, then a near-field focusing azimuth spectrum power drop degree under each scanning distance corresponding to the minimum main lobe width is calculated, a scanning distance with the maximum near-field focusing azimuth spectrum power drop degree is taken as a final distance value of the target to be measured, and an azimuth corresponding to a spectrum peak of the near-field focusing azimuth spectrum with the maximum power drop degree is taken as a final azimuth value of the target to be measured.

[0075] The present application has the following advantages:

[0076] The present application is aimed at the problem that it is difficult to distinguish far and near source targets to affect spatial spectrum estimation when a large-aperture array is passively detected, and a far and near field target distinguishing method is proposed by using the property that spectrum peak broadening occurs when near-field target spatial spectrum estimation is performed under a far-field model. The present application takes the narrowest spectrum peak width to obtain the near-field target azimuth and distance by setting a ranging step and adopting a coarse focusing scanning first and then fine focusing scanning. The ranging method of the present application can detect multiple targets one by one to obtain the ranging and direction finding results of multiple near-field targets and the direction finding result of a far-field target, and significantly improves the azimuth estimation precision.

[0077] Moreover, the present application directly realizes far and near field target distinguishing on the basis of a one-dimensional far-field azimuth spectrum, and can realize far and near field target distinguishing without two-dimensional spatial scanning, thereby significantly reducing the calculation amount of far and near field target distinguishing. BRIEF DESCRIPTION OF DRAWINGS

[0078] Figure 1 is a flow chart of a large-aperture array near-field target passive direction finding and ranging method of the present application;

[0079] Figure 2 is a schematic diagram of a conventional beam forming array natural directivity.

[0080] Figure 3 is a comparison chart of azimuth spectrum results obtained by focusing scanning at different distances for a 2km near-field target;

[0081] Figure 4 is a far-field azimuth history measurement result for a 2km-4km linear motion near-field target;

[0082] Figure 5 is a coarse measurement result of azimuth and distance for a 2km near-field target;

[0083] Figure 6 is a fine measurement result of azimuth and distance for a 2km near-field target;

[0084] Figure 7 is a range measurement result for a moving target;

[0085] Figure 8 is a direction finding result for a moving target. DETAILED DESCRIPTION

[0086] Embodiment I: in combination with Figure 1 This embodiment describes a large-aperture array near-field target passive direction finding and ranging method, which specifically includes the following steps:

[0087] Step one, obtain an array far-field beam forming beam width calculation model according to the natural directivity of a uniform linear array;

[0088] Step two, initialize the time t=0;

[0089] Step three, perform far-field beam forming on the array received signal at time t to obtain a far-field azimuth spectrum, and then obtain the coarse measurement angle of each target to be measured and the azimuth spectrum peak width of each target to be measured according to the far-field azimuth spectrum;

[0090] Step four, initialize the number of targets to be measured n=1;

[0091] Step five, input the coarse measurement angle of the nth target to be measured into the array far-field beam forming beam width calculation model, compare the calculated beam width with the azimuth spectrum peak width of the nth target to be measured, and make a near-far field decision for the nth target to be measured;

[0092] Step six, if the nth target to be measured is located in the near field, continue to execute step seven;

[0093] If the nth target to be measured is located in the far field, directly use the coarse measurement angle as the azimuth estimation result of the nth target to be measured, and the distance is not measurable; then let n=n+1 and return to execute step five;

[0094] Step seven, performing near-field focusing scanning on the nth target to be detected to obtain the azimuth spectrum peak width corresponding to each scanning distance, that is, to obtain the main lobe width corresponding to each scanning distance of the nth target to be detected;

[0095] According to the main lobe width corresponding to each scanning distance, the azimuth initial value and the distance initial value of the nth target to be detected are determined;

[0096] Step eight, determining the scanning interval of the near-field focusing fine scanning according to the azimuth initial value and the distance initial value of the nth target to be detected, performing the near-field focusing fine scanning in the determined scanning interval, and obtaining the final azimuth and distance of the nth target to be detected;

[0097] Step nine, judging whether n reaches the maximum number of near-field targets;

[0098] If yes, step ten is performed;

[0099] If no, n=n+1 is set, and step five is returned to be executed;

[0100] Step ten, t=t+1 is set, and step three is returned to be executed.

[0101] Specific implementation method two: the difference between the embodiment and the specific implementation method one is that the uniform linear array is specifically: taking the positive east direction as the positive direction of the x axis and taking the positive north direction as the positive direction of the y axis, each array element is uniformly arranged at equal intervals on the positive half axis of the x axis, and the distance between adjacent two array elements is d.

[0102] The other steps and parameters are the same as those in the specific implementation method one.

[0103] Specific implementation method three: the difference between the embodiment and the specific implementation method one or two is that the specific process of step one is:

[0104] The target incident azimuth is defined as the included angle in the north-east direction, and the incident azimuth of the kth target is denoted as θ k , k=1, 2, …, K, K is the number of incident targets, and for the incident azimuth θ k of the kth target, the natural directivity G(θ) of the uniform linear array is:

[0105]

[0106] Wherein, M is the number of array elements, and |·| represents taking the absolute value;

[0107] According to |G(θ)| 2 =1 / 2, that is, |G(θ)| 2 =1 / 2, the θ obtained by deducing the above formula is the beam width, and then the array far-field beam forming beam width calculation model corresponding to the incident azimuth of the kth target is obtained:

[0108]

[0109] wherein θ DT is the array far-field beamforming beamwidth corresponding to the kth target incident direction, λ is the signal wavelength, λ = c / f, c is the underwater sound speed, usually taken as 1500 m / s, and f is the signal frequency.

[0110] The other steps and parameters are the same as those in the first or second embodiment.

[0111] The fourth embodiment is different from any one of the first to third embodiments in that the array receiving signal at the t moment is:

[0112]

[0113] wherein x(t) represents the array receiving signal at the t moment, s(t) represents the target signal received by the array at the t moment, n(t) represents the noise signal received by the array at the t moment, a(θ k ) represents the array steering vector corresponding to the angle θ k .

[0114] The other steps and parameters are the same as those in any one of the first to third embodiments.

[0115] The fifth embodiment is different from any one of the first to fourth embodiments in that the specific process of the step three is:

[0116] Step three one, within θ ∈ [-90°, 90°], the array receiving signal x(t) is subjected to far-field beamforming to obtain a far-field direction spectrum p(θ):

[0117] p(θ) = a(θ) H Ra(θ)

[0118] wherein R represents a covariance matrix, R = E[x(t)x H (t)], E[·] represents expectation, x H (t) is the conjugate transpose of x(t), a(θ) is the array steering vector corresponding to the scanning angle θ on the direction scanning grid, and a(θ) H is the conjugate transpose of a(θ);

[0119]

[0120] wherein e is the base of natural logarithm, j is the imaginary unit, and the upper index T represents transpose.

[0121] Step three two, find the maximum peak position of each local spectrum peak in the far field azimuth spectrum p(θ), take the angle corresponding to the maximum peak position of each local spectrum peak as the coarse measurement angle of each target to be measured, and record the coarse measurement angle of the kth target to be measured as θ k ′

[0122] Take the maximum peak position of any one local spectrum peak as an example, the calculation method of the target azimuth spectrum peak width is:

[0123] Record the azimuth corresponding to the left side of the maximum peak position of the local spectrum peak when it drops by 3dB as θ L Record the azimuth corresponding to the right side of the maximum peak position of the local spectrum peak when it drops by 3dB as θ R Then the azimuth spectrum peak width Δθ of the target corresponding to the maximum peak position of the local spectrum peak is:

[0124] Δθ = |θ R - θ L |

[0125] Similarly, the azimuth spectrum peak width of the target corresponding to the maximum peak position of each local spectrum peak is obtained respectively.

[0126] The other steps and parameters are the same as those in the first to fourth embodiments.

[0127] Figure 2 is a schematic diagram of the natural directivity of a far-field conventional beamforming array with 10 array elements and half-wavelength arraying; according to Figure 2 According to the results, the spectrum peak width of the target of interest is measured, the maximum peak position of the local spectrum peak is found, and the angle θ′ corresponding to the maximum spectrum peak is recorded k = 0°, taking the angle as the coarse measurement angle of the target direction, the azimuths corresponding to the left and right sides of the maximum value when they drop by 3dB are taken as the left and right half-power beamwidth angles respectively, and the difference Δθ = |θ R - θ L |, Δθ is the main lobe width, θ L and θ R are the left and right half-power beamwidth angles respectively.

[0128] It should be noted that when the target is located near the end-fire, the spatial spectrum is periodically extended to two end-fire directions in the range of -90-90° by using the spatial spectrum periodic extension method, and then the left and right 3dB half-power point angles are selected according to the periodically extended spatial spectrum.

[0129] The sixth embodiment is different from the first to fifth embodiments in that the specific process of step five is:

[0130] For any one of the to-be-tested targets, the coarse measurement angle of the to-be-tested target is brought into the array far-field beam forming beam width calculation model to obtain the beam width corresponding to the to-be-tested target DT Then, the corresponding to the to-be-tested target θ DT is compared with the azimuth spectrum peak width Δθ corresponding to the to-be-tested target:

[0131] If Δθ≥ε·θ DT , ε is a decision threshold, then the to-be-tested target is located in the near field;

[0132] Otherwise, Δθ<ε·θ DT , the to-be-tested target is located in the far field.

[0133] The other steps and parameters are the same as one of the first to fifth embodiments.

[0134] Similarly, the method of the embodiment can be used to make near-far field decision for each to-be-tested target respectively. ε is usually greater than 1.5 to prevent the beam width from being affected by the signal-to-noise ratio.

[0135] The seventh embodiment is different from one of the first to sixth embodiments in that the specific process of the seventh step is:

[0136] Step seven one, distance grid division is performed in the search interval θ∈[-90°,90°], wherein D represents the array aperture, D=(M-1)d;

[0137] The present application sets the upper limit of the distance search range as one fourth of the Rayleigh distance (D 2 / λ), and the lower limit as Then, near-field focusing scanning is performed;

[0138] Then, the near-field focusing scanning is performed on the nth to-be-tested target at each distance respectively, the azimuth spectrum corresponding to each scanning distance is obtained, and the main lobe width corresponding to each scanning distance is obtained according to the azimuth spectrum;

[0139] Step seven two, the main lobe widths corresponding to the scanning distances are sorted in the order from small to large according to the main lobe widths:

[0140] If the smallest main lobe width corresponds to only one scanning distance, the scanning distance corresponding to the smallest main lobe width is taken as the distance initial value of the to-be-tested target, and the spectrum peak of the azimuth spectrum obtained when the distance initial value is taken as the scanning distance is obtained, and the angle corresponding to the obtained spectrum peak is taken as the azimuth initial value of the to-be-tested target;

[0141] The ranging error can cause the azimuth spectrum estimation result to have multiple peaks near the target azimuth, so the main lobe width at different distances can be equal, if the smallest main lobe width corresponds to multiple scanning distances, the azimuth spectrum power reduction degree of each scanning distance corresponding to the smallest main lobe width is calculated respectively, the scanning distance with the largest azimuth spectrum power reduction degree is taken as the distance initial value of the target to be measured, and the angle corresponding to the azimuth spectrum peak obtained when the distance initial value is taken as the scanning distance is taken as the azimuth initial value of the target to be measured;

[0142] The calculation method of the azimuth spectrum power reduction degree is as follows:

[0143] Taking the azimuth spectrum at any one scanning distance as an example, the peak power of the azimuth spectrum is denoted as P max On the left side of the grid point where the peak power is located, the power corresponding to the grid point with an interval of 1° from the grid point where the peak power is located is denoted as P -1° On the right side of the grid point where the peak power is located, the power corresponding to the grid point with an interval of 1° from the grid point where the peak power is located is denoted as P 1° Then, the reduction degree ΔP of the azimuth spectrum power is:

[0144] ΔP=(|P max -P -1° |+|P max -P 1° |) / 2.

[0145] The other steps and parameters are the same as those in one of the first to sixth embodiments.

[0146] The higher the power reduction degree, the higher the angle resolution of the azimuth spectrum result, that is, the smaller the ranging error, and a small amount is added to the main lobe width corresponding to the azimuth spectrum with a lower power reduction degree, and the size of the small amount is 1 / 10 of the grid quantization accuracy, and the azimuth and distance corresponding to the narrowest part of the main lobe width are taken as the initial values of the fine scanning.

[0147] Embodiment eight: different from one of the first to seventh embodiments, the azimuth spectrum in step seven is:

[0148] Taking the ith scanning distance as an example, the azimuth spectrum p(θ, r i ) corresponding to the ith scanning distance r i is:

[0149] p i =p(θ,r i )

[0150] p(θ,r i )=a(θ,r i ) H Ra(θ,r i )

[0151] wherein a(θ, r i ) represents the array steering vector at the i-th scanning distance, the i'-th scanning orientation θ i of the array steering vector a(θ, r i′ ) is: i′ i

[0152]

[0153] wherein when M is odd, N = (M-1) / 2, when M is even, N = M / 2, a(θ i′ , r i ) ∈ C 2N×1 , γ i′ and φ i′ are represented as:

[0154]

[0155] The other steps and parameters are the same as one of the first to seventh embodiments.

[0156] The ninth embodiment is different from one of the first to eighth embodiments in that the specific process of the eighth step is:

[0157] The scanning distance closest to the distance initial value and smaller than the distance initial value in the seventh step is found, and the scanning distance closest to the distance initial value and greater than the distance initial value in the seventh step is found, and the found scanning distances are respectively taken as the distance lower limit and the distance upper limit of the near-field focusing fine scanning;

[0158] That is, in each scanning distance corresponding to the orientation initial value, the grid point closest to the grid point where the distance initial value is located is found, and the scanning distance corresponding to the found grid point is taken as the distance interval of the near-field focusing fine scanning;

[0159] The orientation initial value is brought into the beam width calculation model to obtain the beam width calculation result, and the difference between the orientation initial value and the beam width calculation result is taken as the angle lower limit of the near-field focusing fine scanning, and the sum of the orientation initial value and the beam width calculation result is taken as the angle upper limit of the near-field focusing fine scanning;

[0160] The near-field focusing fine scanning is performed in the scanning interval formed by the distance lower limit, the distance upper limit, the angle lower limit and the angle upper limit, the near-field focusing orientation spectrum corresponding to each scanning distance is obtained, and the main lobe width corresponding to each scanning distance is obtained according to the near-field focusing orientation spectrum;

[0161] ​​If the minimum main lobe width in each near-field focusing azimuth spectrum corresponds to one scanning distance, the scanning distance corresponding to the minimum main lobe width is taken as the final distance value of the target to be measured, and the spectrum peak of the near-field focusing azimuth spectrum obtained when the final distance value is taken as the scanning distance is obtained, and the angle corresponding to the obtained spectrum peak is taken as the final azimuth value of the target to be measured;

[0162] If the minimum main lobe width in each near-field focusing azimuth spectrum corresponds to multiple scanning distances, the near-field focusing azimuth spectrum power drop degree under each scanning distance corresponding to the minimum main lobe width is calculated respectively, the scanning distance with the maximum near-field focusing azimuth spectrum power drop degree is taken as the final distance value of the target to be measured, and the azimuth corresponding to the azimuth spectrum spectrum peak of the near-field focusing azimuth spectrum with the maximum power drop degree is taken as the final azimuth value of the target to be measured.

[0163] The other steps and parameters are the same as one of the first to eighth specific embodiments.

[0164] The near-field focusing fine scanning interval is grid divided according to the accuracy requirement of actual direction finding and distance measurement. In general, the grid quantization accuracy is less than 1 / 5 of the measurement accuracy requirement.

[0165] Experimental part

[0166] The array used in the experiment is a 512-element equidistant half-wavelength uniformly distributed linear array, the element spacing is 1.2m, and the sound speed in water is 1500m / s. The azimuth spectrum results obtained by focusing scanning of the 2km near-field target at different distances are compared as shown in Figure 3 The accuracy of the distance estimation of the near-field target affects the azimuth estimation result. When the distance estimation error is large, the spatial spectrum will appear multiple peaks, and then the target azimuth cannot be judged. And it can be known from Figure 3 that the smaller the distance estimation error is, the narrower the spatial spectrum peak width is, which illustrates the feasibility of the method.

[0167] It is assumed that at t=0, a target exists in the space and is incident on the linear array, the near-field moving target incident azimuth is-40°, the distance is 2000m, the signal-to-noise ratio is 10dB, and the target moves away from the receiving array along the north-east direction. The spatial spectrum estimation of the target at each time is obtained Figure 4 . Taking t=0 as an example for analysis, when the far-field model is used for spatial spectrum estimation, the target in the-40° direction occurs spectrum divergence, and according to the far-field target judgment formula, the target is located in the near field.

[0168] The azimuth and distance of the target located in the near field are coarsely measured, the coarse distance grid (interval 1km) is determined in the distance search range, and the azimuth spectrum obtained in the near-field focusing compensation manner is as shown in Figure 5 In order to facilitate analysis, Figure 5Only azimuth spectral maps at different distances within the range of 1–10 km were extracted. (Comparison) Figure 5 The width of the main lobe at different distances was determined, and the azimuth and distance results corresponding to the narrowest point of the main lobe were taken as the initial values ​​for near-field focusing scanning.

[0169] by Figure 5 The orientation and distance dimensions within the Chinese frame serve as the scanning range for near-field focusing fine scanning, such as... Figure 6 As shown. By Figure 6 It can be determined that the near-field target is approximately located at (-40°, 2km). Then, proceed sequentially... Figure 4 The azimuth curve at each moment is processed in the above way to obtain the near-field target azimuth spectrum history and obtain azimuth and distance information.

[0170] Simultaneously, the target's current position and distance information are recorded, resulting in tracking distance history curves and position history curves as shown below. Figure 7 and Figure 8 As shown. The fine scan divides the distance into a fine grid with 5m intervals, by... Figure 7 and Figure 8 It can be seen that the method of the present invention can track the target position, and the magnitude of the ranging error is affected by the accuracy of the distance scanning grid division.

[0171] The above examples of the present invention are merely illustrative of the computational model and process of the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is impossible to exhaustively list all possible implementations here. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for passive direction finding and ranging of a large aperture array near field target, characterized in that, The method specifically comprises the following steps: Step one, obtaining an array far-field beam forming beam width calculation model according to the natural directivity of the uniform linear array; Step two, initializing the time t=0; Step three, performing far-field beam forming on the array receiving signal at the time t to obtain a far-field azimuth spectrum, and then obtaining a coarse measurement angle of each to-be-measured target and a peak width of the azimuth spectrum of each to-be-measured target according to the far-field azimuth spectrum; Step four, initializing the number n of to-be-measured targets to be 1; Step five, inputting the coarse measurement angle of the nth to-be-measured target into the array far-field beam forming beam width calculation model, comparing the calculated beam width with the peak width of the azimuth spectrum of the nth to-be-measured target, and performing near-far field judgment on the nth to-be-measured target; Step six, if the nth to-be-measured target is located in the near field, step seven is continuously executed; if the nth to-be-measured target is located in the far field, the coarse measurement angle is directly taken as the azimuth estimation result of the nth to-be-measured target; then n is set to n+1, and step five is executed again; Step seven, performing near-field focusing scanning on the nth to-be-measured target to obtain a peak width of the azimuth spectrum corresponding to each scanning distance, that is, a main lobe width corresponding to each scanning distance of the nth to-be-measured target; determining an azimuth initial value and a distance initial value of the nth to-be-measured target according to the main lobe width corresponding to each scanning distance; Step eight, determining a scanning interval of near-field focusing fine scanning according to the azimuth initial value and the distance initial value of the nth to-be-measured target, performing near-field focusing fine scanning in the determined scanning interval, and obtaining the final azimuth and distance of the nth to-be-measured target; Step nine, judging whether n reaches the maximum number of near-field targets; if yes, step ten is executed; if no, n is set to n+1, and step five is executed again; Step ten, setting t to t+1, and executing step three again.

2. The method of claim 1, wherein, The uniform linear array specifically comprises: taking the positive east direction as the positive direction of the x axis and the positive north direction as the positive direction of the y axis, and each array element is uniformly arranged at equal intervals on the positive half of the x axis, and the distance between adjacent two array elements is d.

3. The method of claim 2, wherein, The specific process of step one is: The incident azimuth of the target is defined as the angle in the direction of north-northeast, and the incident azimuth of the k-th target is denoted as θ. k k = 1, 2, ..., K, where K is the number of incident targets, and the incident azimuth θ for the k-th target is... k The natural directivity G(θ) of a uniform linear array is: wherein, M is the number of array elements, and |·| represents taking the absolute value; According to |G(θ) 2 =1 / 2, the array far-field beamforming beamwidth calculation model corresponding to the kth target incident orientation is obtained: where θ DT is the array far-field beamforming beamwidth corresponding to the kth target incident direction, and λ is the signal wavelength.

4. The method of claim 3, wherein, The array receiving signal at the time t is: Wherein, x(t) represents the array receiving signal at t moment, s(t) represents the target signal received by the array at t moment, n(t) represents the noise signal received by the array at t moment, a(θ k ) represents the angle θ k Corresponding array steering vector.

5. The method of claim 4, wherein, The specific process of step three is: Step three one, performing far-field beam forming on the array receiving signal x(t) to obtain a far-field azimuth spectrum p(θ) within θ∈[-90°, 90°]: p(0) = a(0) H Ra(0) where R represents a covariance matrix, R = E[x(t)x H (t)], E[·] represents an expectation, x H (t) is a conjugate transpose of x(t), a(θ) is an array steering vector corresponding to a scanning angle θ on a bearing scanning grid, and a(θ) H is a conjugate transpose of a(θ). wherein, e is the base of the natural logarithm, j is the imaginary unit, and the upper index T represents transposition; Step three two, find the maximum peak position of each local spectrum peak in the far field direction spectrum p(θ), take the angle corresponding to the maximum peak position of each local spectrum peak as the coarse measurement angle of each target to be measured, and record the coarse measurement angle of the kth target to be measured as θk k ′; Taking the maximum peak position of any local spectrum peak as an example, the calculation method of the peak width of the azimuth spectrum of the to-be-measured target is: The position corresponding to the 3dB drop left of the maximum peak position of the local spectrum peak is recorded as θ L The position corresponding to the 3dB drop right of the maximum peak position of the local spectrum peak is recorded as θ R The peak width Δθ of the azimuth spectrum peak corresponding to the maximum peak position of the local spectrum peak is: Δθ = |θ R -θ L | Similarly, the peak width of the azimuth spectrum of the to-be-measured target corresponding to the maximum peak position of each local spectrum peak is obtained.

6. The method of claim 5, wherein, The specific process of step five is: For any target to be measured, the coarse angle of the target is substituted into the beamwidth calculation model of the array far-field beamforming to obtain the corresponding beamwidth θ of the target. DT Then, the θ corresponding to the target to be measured DT Compare with the azimuth spectral peak width Δθ corresponding to the target under test: If Δθ ≥ ε θ DT , ε is a decision threshold, then the target under test is in the near field. Otherwise, Δθ < ε θ DT The object under test is located in the far field.

7. The method of claim 6, wherein, The specific process of step seven is: Step seven one, in search interval The distance grid is divided within θ ∈ [-90°, 90°], wherein D represents an array aperture, D = (M-1)d; Then, the near-field focusing scanning is performed on the nth to-be-measured target at each distance, and the azimuth spectrum corresponding to each scanning distance is obtained, and then the main lobe width corresponding to each scanning distance is obtained according to the azimuth spectrum; Step seven two, sorting the main lobe widths corresponding to each scanning distance in the order from small to large: If the minimum main lobe width corresponds to one scanning distance, the scanning distance corresponding to the minimum main lobe width is taken as the distance initial value of the target to be measured, and the spectrum peak of the azimuth spectrum obtained when the distance initial value is taken as the scanning distance is obtained, and the angle corresponding to the obtained spectrum peak is taken as the azimuth initial value of the target to be measured; If the minimum main lobe width corresponds to multiple scanning distances, the azimuth spectrum power drop degree under each scanning distance corresponding to the minimum main lobe width is calculated respectively, the scanning distance with the maximum azimuth spectrum power drop degree is taken as the distance initial value of the target to be measured, and the angle corresponding to the spectrum peak of the azimuth spectrum obtained when the distance initial value is taken as the scanning distance is taken as the azimuth initial value of the target to be measured; The calculation method of the azimuth spectrum power drop degree is: Taking the azimuth spectrum at any one scanning distance as an example, the peak power of the azimuth spectrum is recorded as P max On the left side of the grid point where the peak power is located, the power corresponding to the grid point with an interval of 1° from the grid point where the peak power is located is recorded as P On the right side of the grid point where the peak power is located, the power corresponding to the grid point with an interval of 1° from the grid point where the peak power is located is recorded as P Then the degree of decline of the azimuth spectrum power ΔP is:

8. The method of claim 7, wherein, The azimuth spectrum in step seven is: Taking the ith scan distance as an example, the ith scan distance r i The corresponding azimuth spectrum p(0, r i ) is: p(0, r i ) = a(0, r i ) H Ra(0, r i ) Where a(θ,r) i ) represents the array steering vector at the i-th scan distance, and the array steering vector a(θ,r) i The i′th scan orientation θ i′ The guiding vector a(θ) below i′ ,r i )for: where N = (M-1) / 2 when M is odd and N = M / 2 when M is even, a(θ i′ , i ) e C 2N×1 , γ i′ and φ i′ are given by 9. The method of claim 8, wherein, The specific process of step eight is: The scanning distance closest to the distance initial value and less than the distance initial value in step seven is found, and the scanning distance closest to the distance initial value and greater than the distance initial value in step seven is found, and the found scanning distances are taken as the distance lower limit and the distance upper limit of the near-field focusing fine scanning respectively; The difference between the azimuth initial value and the beam width calculation result is taken as the angle lower limit of the near-field focusing fine scanning, and the sum of the azimuth initial value and the beam width calculation result is taken as the angle upper limit of the near-field focusing fine scanning; The near-field focusing fine scanning is performed in the scanning interval, and the near-field focusing azimuth spectrum corresponding to each scanning distance is obtained respectively, and then the main lobe width corresponding to each scanning distance is obtained according to the near-field focusing azimuth spectrum; If the minimum main lobe width in each near-field focusing azimuth spectrum corresponds to one scanning distance, the scanning distance corresponding to the minimum main lobe width is taken as the final distance value of the target to be measured, and the spectrum peak of the near-field focusing azimuth spectrum obtained when the final distance value is taken as the scanning distance is obtained, and the angle corresponding to the obtained spectrum peak is taken as the final azimuth value of the target to be measured; If the minimum main lobe width in each near-field focusing azimuth spectrum corresponds to multiple scanning distances, the near-field focusing azimuth spectrum power drop degree under each scanning distance corresponding to the minimum main lobe width is calculated respectively, the scanning distance with the maximum near-field focusing azimuth spectrum power drop degree is taken as the final distance value of the target to be measured, and the azimuth corresponding to the spectrum peak of the near-field focusing azimuth spectrum with the maximum power drop degree is taken as the final azimuth value of the target to be measured.

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