Constant-beam-width beam forming method based on vector combination array

Abstract

The invention provides a constant-beam-width beam forming method based on a vector combination array, which aims at the problem of receiving broadband signals by an underwater acoustic measurement array, combines a vector nested linear array and a sound pressure circular array into the vector combination array, and can be used for measuring broadband radiation noise of an underwater acoustic target. Constant-beam-width beam forming based on a combined array is divided into three parts, namely a measurement beam width calculation part, a vector nested array constant-beam-width beam forming part and combined array constant-beam-width beam forming part, beam width changes under different frequencies are compensated through frequency weighting according to the nested array principle, and particularly, the beam width change under different frequencies is compensated through frequency weighting. A nested array is formed by constructing sub-arrays with different intervals, the main lobe beam width is ensured to be constant by adopting a method of linearly combining a sub-array directivity function, and in a signal processing process, a single linear array is subdivided into a plurality of different sub-arrays for operation, so that the complexity of the combined array is reduced, and the number of processing channels is also reduced.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic target measurement, in particular to a constant beamwidth beamforming method based on a vector combination array. Background Art

[0002] The measurement of underwater acoustic target radiation noise plays an important role in the fields of marine resource development and environmental protection. By analyzing the noise characteristics of underwater acoustic targets, it can be used for target identification and positioning. The radiation noise of underwater acoustic targets is composed of the superposition of line spectrum and broadband continuous spectrum, so it is necessary to carry out broadband measurement method research on the radiation noise of underwater acoustic targets.

[0003] In the process of underwater acoustic target measurement, if the main beam of the measurement array is too wide relative to the measurement target, it will receive too much background noise and reduce the array gain; if the main beam is too narrow, it will not be able to completely cover the underwater acoustic target, and it will not be able to obtain effective information on its radiation noise and the true sound source level. Therefore, it is very important to study the measurement system in which the main lobe beam width does not change with frequency.

[0004] Traditionally, the single hydrophone method or the linear array method is used to measure the radiated noise of moving underwater acoustic targets. The single hydrophone method is easy to implement and has a simple principle. It can perform normal measurements on targets with high sound source levels, but it cannot provide array gain and cannot suppress the interference of marine environmental noise, making it difficult to meet the needs of measuring the radiated noise of low-noise underwater acoustic targets. The horizontal linear array has an obvious ability to suppress traffic noise in space, but does not have sufficient array gain to suppress sea surface environmental noise or seabed reflection noise, which will reduce the stability of the radiated noise measurement results under shallow sea conditions. Although the vertical linear array can reduce the influence of sea surface noise and multi-path interference, the array aperture is limited by the sea depth, which is not conducive to wide-band radiated noise testing in shallow waters. The planar array has directional measurement capabilities, but the application aperture is large in the low-frequency band and is not easy to deploy.

[0005] The constant beamwidth beamformer of the base array can be implemented in the frequency domain and the time domain. The core of the Chebyshev weighting method, the spatial resampling method and the FIR method is to divide the broadband signal into different sub-bands, apply different weights to each sub-band, and keep the main lobe width consistent on the measurement band. However, most of these methods are implemented in the form of scalar linear arrays, and it is difficult to avoid the "left and right ambiguity" problem that exists in linear array signal processing.

[0006] In summary, although the traditional underwater acoustic target radiation noise measurement method can achieve a constant beam width, it has problems such as insufficient array gain, aperture limitation and "left and right ambiguity" when dealing with low-noise targets and complex marine environments, making it difficult to ensure measurement accuracy and stability. Especially in shallow water and low-frequency applications, the limitations of these methods are more prominent. Summary of the invention

[0007] Aiming at the problem of receiving broadband signals by underwater acoustic measurement array, the present invention combines vector nested linear array and sound pressure circular array into vector combination array, and proposes a constant beamwidth beamforming method, which can be used for broadband radiated noise measurement of underwater acoustic targets.

[0008] The vector hydrophone picks up the sound pressure and three mutually orthogonal particle velocity information in the underwater sound field at the same point. Its particle velocity channel has a dipole directivity that is independent of frequency, so it can achieve full-space unambiguous orientation of the target and obtain performance equivalent to that of a four-element sound pressure array system. Compared with the sound pressure array of the same formation, the vector array has higher array gain and better target detection and estimation capabilities.

[0009] The technical solution of the present invention is:

[0010] The constant beamwidth beamforming method based on vector combination array comprises the following steps:

[0011] Step 1: Calculate the measurement beam width;

[0012] The main lobe width of the measurement beam is calculated according to the height of the hydroacoustic target and the distance between the measurement point and the target;

[0013] Step 2: Form a vector nested array constant beam width beam response;

[0014] Step 2.1: Divide the set working frequency bandwidth into K frequency sub-bands. Adjacent frequency sub-bands have the same frequency endpoint values. For a certain frequency sub-band [f l ~f h ], a set of vector nested linear arrays is formed by two linear arrays with different array element spacings;

[0015] Step 2.2: Calculate the beam response B of the low-frequency linear array L (f,θ);

[0016] Step 2.3: Calculate the beam response B of the high-frequency linear array H (f,θ);

[0017] Step 2.4: Perform frequency weighting on the beam responses of the high-frequency linear array and the low-frequency linear array respectively to obtain the beam response output result B(f,θ) of the group of vector nested linear arrays;

[0018] Step 2.5: Based on the beam response output of the vector nested linear array obtained in step 2.4, calculate the constant beam width beam response B of the vector nested linear array. vector (f,θ);

[0019] Step 3: Form the combined array constant beamwidth beam response:

[0020] Step 3.1: N equally spaced array elements form a sound pressure circular array with a radius of r. Calculate the beam response B of the sound pressure circular array. circle (θ);

[0021] Step 3.2: Calculate the array steering vectors of the sound pressure circular array and the vector nested linear array in the combined array;

[0022] Step 3.3: Calculate the received signals of each element of the sound pressure circular array and each element of the vector nested linear array in the combined array, and then calculate the mutual coordination direction of the combined array;

[0023] Step 3.4: Calculate the beam response of the combined array according to the steering vector of the combined array;

[0024] Step 3.5: construct a low-frequency combination base array and a high-frequency combination base array respectively; the low-frequency combination base array is composed of a low-frequency linear array and a sound pressure circular array, and the high-frequency combination base array is composed of a high-frequency linear array and a sound pressure circular array;

[0025] Step 3.6: Calculate the beam responses of the low-frequency combined array and the high-frequency combined array respectively;

[0026] Step 3.7: Calculate the frequency weighting function of the combined array, and obtain the constant beamwidth beam response of the combined array in the frequency sub-band based on the frequency weighting function of the combined array.

[0027] Furthermore, the main lobe width of the measurement beam in step 1 is expressed as:

[0028]

[0029] Among them, H is the height of the hydroacoustic target itself; L is the distance between the measurement point and the target.

[0030] Furthermore, in step 2.2, according to the low frequency f l The design spacing is d l =λ l / 2 M-element linear array is used as the low-frequency linear array SA1 of the vector nested linear array, where λ l For low frequency f l The corresponding wavelength, M is the set value, the beam response of the low-frequency linear array is B L (f,θ) is:

[0031]

[0032] Where, θ is the measurement beam scanning angle; θ p is the known desired direction of the main beam; f is the frequency of the received target signal;

[0033] In step 2.3, according to the high frequency f h The design spacing is dh =λ h / 2 M-element linear array is used as the high-frequency linear array SA2 of the vector nested linear array, where λ h For high frequency f h Corresponding wavelength, beam response of high frequency linear array B H (f,θ) is:

[0034]

[0035] The beam response output result B(f,θ) of the set of vector nested linear arrays obtained in step 2.4 is:

[0036] B(f,θ)=L(f)B L (f,θ)+H(f)B H (f,θ)

[0037] Wherein, L(f) and H(f) are the frequency weighting coefficients of the low-frequency linear array and the high-frequency linear array, respectively.

[0038] Furthermore, the low-frequency linear array frequency weighting coefficient L(f) and the high-frequency linear array frequency weighting coefficient H(f) are calculated according to the formula

[0039]

[0040]

[0041] Calculated.

[0042] Furthermore, in step 2.5, the vector nested linear array constant beam width beam response B vector (f,θ) is:

[0043]

[0044] Furthermore, in step 3.1, the beam response B of the sound pressure circular array circle (θ) is:

[0045] B circle (θ)=|w H (θ)a(θ)|=|a H (θ p )Q -1 a(θ)|

[0046] Where w(θ) = Q -1 a(θ p ) is the weighting vector under the condition of maximum array gain; a(θ) is the scanning vector; Q is the normalized noise covariance matrix; a(θ p ) is the circular array steering vector.

[0047] Furthermore, the circular array steering vector a(θ p ) is expressed as:

[0048]

[0049] Where λ is the wavelength of the received signal and n is the number of the nth array element.

[0050] Furthermore, in step 3.2, the array steering vectors of the sound pressure circular array and the vector nested linear array in the combined array are:

[0051]

[0052]

[0053] Among them, a circle_n (θ) is the steering vector of the nth element of the sound pressure circular array; a v_m (θ) is the steering vector of the mth element of the vector nested linear array; d is the element spacing;

[0054] The received signals of each element of the sound pressure circular array in the combined base array and the received signals of each element of the vector nested linear array in step 3.3 are:

[0055] x circle_n (t) = a circle_n (θ s )s(t)+n pn (t)

[0056] x line_m (t) = a v_m (θ s )s(t)+n vm (t)

[0057] Among them, x circle_n (t) is the sound pressure hydrophone receiving signal corresponding to the nth array element in the sound pressure circular array; x line_m (t) is the vector hydrophone receiving signal corresponding to the mth array element in the vector nested linear array; s(t) is the far-field incident signal, n pn (t) and n vm (t) is the noise signal;

[0058] The beam response of the combined array in step 3.4 is:

[0059] B(θ s )=w H (θ s ) c (θ s )

[0060] Among them, w(θ s ) is the weight vector, ac (θ s ) is the steering vector of the combined matrix.

[0061] Furthermore, the steering vector a of the combined matrix c (θ s )for:

[0062]

[0063] a circle (θ s )=[a circle_1 (θ s ),...,a circle_n (θ),...,a circle_N (θ s )] T

[0064] a v (θ s )=[a v_1 (θ s ),...,a v_m (θ),...,a v_M (θ s )] T .

[0065] Furthermore,

[0066] The beam response B of the low frequency combined array in step 3.6 L (f,θ) and the beam response of the high frequency combined array B H (f,θ) is:

[0067] B L (f,θ)=B circle (f,θ)B L (f,θ)

[0068] B H (f,θ)=B circle (f,θ)B H (f,θ)

[0069] The frequency weighting function of the combined matrix in step 3.7 is:

[0070]

[0071] Beneficial Effects

[0072] The present invention realizes broadband constant beamwidth beamforming by combining vector nested linear array and acoustic pressure circular array. From the perspective of array design, this combination gives full play to the advantages of both. On the one hand, the vector hydrophone array can capture and combine directional underwater acoustic target radiation noise signals with four receiving channels. A single vector hydrophone can not only achieve full-space unambiguous orientation, but also its performance is comparable to that of a four-element acoustic pressure array sonar system. Furthermore, the vector nested array shows stronger resistance to "left and right ambiguity" and higher processing gain than the acoustic pressure array of the same formation. On the other hand, the uniform circular array can receive signals from all directions of space without dead angles by virtue of its unique geometric characteristics, effectively avoiding signal ambiguity caused by improper formation or layout. At the same time, it can also effectively suppress ocean background noise and significantly improve array gain. From the perspective of beamforming, the present invention utilizes the principle of nested arrays to compensate for beamwidth changes at different frequencies by frequency weighting. Specifically, a nested array is formed by constructing subarrays with different spacings, and a method of linearly combining the directivity functions of the subarrays is used to ensure that the main lobe beamwidth is constant. During the signal processing process, this algorithm subdivides a single linear array into multiple different sub-arrays for calculation, which not only reduces the complexity of the combined array, but also reduces the number of processing channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 This is a diagram of the combined base array of the present invention;

[0074] Figure 2 : are directivity diagrams of two sub-arrays according to an embodiment of the present invention, wherein (a) is the directivity diagram of the low-frequency sub-array, and (b) is the directivity diagram of the high-frequency sub-array;

[0075] Figure 3 : are constant beamwidth beam patterns of the nested linear array according to an embodiment of the present invention, wherein (a) is a scalar nested linear array constant beamwidth beam pattern, and (b) is a vector nested linear array constant beamwidth beam pattern;

[0076] Figure 4 : is the directivity diagram of the sound pressure circular array of an embodiment of the present invention;

[0077] Figure 5 1 are directivity diagrams of a low-frequency combination array and a high-frequency combination array according to an embodiment of the present invention, wherein (a) is the directivity diagram of the low-frequency combination array, and (b) is the directivity diagram of the high-frequency combination array;

[0078] Figure 6 1 and 2 are combined array constant beamwidth beam patterns in two linear array cases according to an embodiment of the present invention, wherein (a) is a combined array constant beamwidth beam pattern, and (b) is a vector combined array constant beamwidth beam pattern. DETAILED DESCRIPTION

[0079] The invention proposes a constant beamwidth beamforming method based on a combined array consisting of a vector nested linear array and an acoustic pressure circular array. This method not only has the characteristic of resisting 180-degree blur, but also can realize broadband constant beamwidth beamforming while obtaining a larger array gain.

[0080] The first part of the present invention calculates the optimal main beam width by measuring the size of the target and the distance between the measuring array and the target, and this width is the -3dB beam width used subsequently; the second part constructs a vector nested linear array, takes the -3dB beam width calculated in the first part as the target width, and uses a linear combination method to achieve constant beamwidth beamforming of the array; the third part constructs a combined array composed of a vector nested linear array and a sound pressure circular array, uses a conventional beamforming method to obtain the directivity function of the sound pressure circular array, and then combines the sound pressure circular array with the low-frequency sub-array and the high-frequency sub-array constructed in the second part to construct a combined array, and after obtaining two directivity functions respectively, a linear combination method is used to achieve the constant beamwidth of the combined array.

[0081] The present invention specifically comprises the following steps:

[0082] Step 1: Calculate the measurement beamwidth:

[0083] The main lobe width of the measurement beam is calculated based on the height H of the hydroacoustic target and the distance L between the measurement point and the target:

[0084]

[0085] Step 2: Form a vector nested array constant beamwidth beam response:

[0086] Step 2.1: Divide the set working frequency bandwidth into K frequency sub-bands, and adjacent frequency sub-bands have the same frequency endpoint value; for a certain frequency sub-band [f l ~f h ], a set of vector nested linear arrays is formed by two linear arrays with different array element spacings, and the beam responses of the low-frequency linear array and the high-frequency linear array of the vector nested linear array corresponding to the frequency sub-band are obtained through steps 2.2 and 2.3.

[0087] Step 2.2: According to the low frequency f l The design spacing is d l =λ l / 2 M-element linear array is used as the low-frequency linear array SA1 of the vector nested linear array, where λ l For low frequency f l The corresponding wavelength, M is the set value, calculate the beam response B of the low-frequency linear array L (f,θ) is:

[0088]

[0089] Where, θ is the measurement beam scanning angle; θ p is the known desired direction of the main beam; f is the frequency of the received target signal.

[0090] Step 2.3: According to the high frequency f h The design spacing is d h =λ h / 2 M-element linear array is used as the high-frequency linear array SA2 of the vector nested linear array, where λ h For high frequency f h Corresponding wavelength, calculate the beam response B of the high-frequency linear array H (f,θ) is:

[0091]

[0092] Step 2.4: After assigning appropriate amplitude weights to the high-frequency linear array and the low-frequency linear array, linear combination is performed. That is, the beam responses of the high-frequency linear array and the low-frequency linear array are frequency-weighted to obtain the beam response output result of the nested linear array group:

[0093] B(f,θ)=L(f)B L (f,θ)+H(f)B H (f,θ) (4)

[0094] Among them, L(f) and H(f) are the frequency weighting coefficients of the low-frequency linear array and the high-frequency linear array respectively;

[0095] The specific frequency weighting coefficient is calculated as follows:

[0096] The beam response B(f,θ) obtained after frequency weighting should satisfy:

[0097]

[0098] Where D(f,θ c ) is the directivity factor;

[0099] The frequency weighting functions corresponding to the low-frequency linear array SA1 and the high-frequency linear array SA2 are obtained as follows:

[0100]

[0101] If we assume that θ p = 0, that is, when the target is in the horizontal direction of the array, then take

[0102]

[0103] Where c is the underwater sound speed;

[0104] It can be seen that L(f) and H(f) are a set of frequency filters that weight the beam responses of the two linear arrays according to the frequency variation.

[0105] Step 2.5: Perform combined signal processing on the vector hydrophone sound pressure channel and the three velocity channels, where the orthogonal joint velocity is expressed as:

[0106]

[0107] Where s(t) is the far-field incident signal, (p(t)+v c (t))v c (t) Normalized directivity of this combination Signal processing applied to vector nested linear arrays.

[0108] Since the vector array beamforming conforms to the product theorem, that is, the vector array beam response is equal to the product of the non-directional beam response (that is, B(f,θ) obtained in step 2.4) and the directivity function of the vector array itself, the constant beam width beam response of the vector nested linear array can be calculated as:

[0109]

[0110] Step 3: Form the combined array constant beamwidth beam response:

[0111] Step 3.1: N equally spaced array elements form a sound pressure circle array with a radius of r. The position vector of the nth array element relative to the origin (center of the circle) is p n =[rcosα,rsinα], where α is the angle between the array element and the coordinate origin relative to the x-axis, and the beam response B of the sound pressure circular array is calculated. circle (θ), the specific steps are:

[0112] Under far-field plane wave conditions, θ p is the expected direction of the main beam, then the received signal of the circular array is expressed as:

[0113] X=a(θ p )s(t)+n(t) (10)

[0114] Where s(t) is the far-field incident signal; n(t) is the received noise; a(θ p ) is the circular array steering vector, expressed as:

[0115]

[0116] Where, λ is the wavelength of the received signal; n is the number of the nth array element;

[0117] Array gain (AG) is defined as the ratio of the output signal-to-noise ratio of the base array to the output signal-to-noise ratio of the reference array element. max =a(θ p ) H Q-1 a(θ p ), the beam response of the sound pressure circular array is:

[0118] B circle (θ)=|w H (θ)a(θ)|=|a H (θ p )Q -1 a(θ)| (12)

[0119] Where w(θ) = Q -1 a(θ p ) is the weighting vector under the condition of maximum array gain; a(θ) is the scanning vector; Q is the normalized noise covariance matrix.

[0120] Step 3.2: Calculate the array steering vector of the sound pressure circular array and vector nested linear array in the combined array:

[0121]

[0122] Among them, a circle_n (θ) is the steering vector of the nth element of the sound pressure circular array; a v_m (θ) is the steering vector of the mth element of the vector nested linear array; d is the element spacing.

[0123] Step 3.3: Calculate the sound pressure in the combined array, the circular array element receiving signal, and the vector nested linear array element receiving signal:

[0124]

[0125] Among them, x circle_n (t) is the sound pressure hydrophone receiving signal corresponding to the nth array element in the sound pressure circular array; x line_m (t) is the vector hydrophone receiving signal corresponding to the mth array element in the nested linear array; s(t) is the far-field incident signal, n pn (t) and n vm (t) is the noise signal;

[0126] Then, calculate the mutual coordination direction R of the combined matrix:

[0127]

[0128] Among them, a circle (θ s )=[a circle_1 (θ s ),...,a circle_n (θ),...,a circle_N (θ s )] T ,

[0129] a v (θ s )=[a v_1 (θ s ),...,a v_m (θ),...,a v_M (θ s )] T and a c (θ s ) is the steering vector of the combined matrix; σ s is the signal power, σ nm is the noise power.

[0130] Step 3.4: According to the conventional beamforming algorithm, the weight vector is w = a(θ s ) / MN, the beam response of the combined array is calculated as:

[0131] B(θ s )=w H (θ s ) c (θ s ) (16)

[0132] Step 3.5: Similar to Step 2.2 and Step 2.3, construct a low-frequency combination array and a high-frequency combination array respectively, where the low-frequency combination array CA1 is composed of an array element spacing d l The low-frequency vector linear array and the sound pressure circular array are combined, and the high-frequency combination base array CA2 is composed of array elements with a spacing of d h The high-frequency vector linear array and the sound pressure circular array are combined. The horizontal linear array and the horizontal circular array are placed independently. The positions are as shown in the attached figure. Figure 1 As shown, the horizontal linear array is fixed in the middle of the water body by buoys and sinking devices, and the circular array is placed horizontally on one side of the linear array. A rectangular coordinate system is drawn in the underwater environment. The linear array and the circular array have distances on the z-axis and x-axis, and the direct distance between the two arrays is known.

[0133] Step 3.6: Similar to steps 2.2 and 2.3, calculate the beam response B of the low-frequency combination array respectively. L (f,θ) and the beam response of the high frequency combined array B H (f,θ):

[0134]

[0135] Step 3.7: Similar to step 2.4, calculate the frequency weighting function of the combined matrix as:

[0136]

[0137] The constant beam width beam response of the combined array in the frequency sub-band is obtained by calculating the frequency weighting function of the combined array.

[0138] The following takes an octave as an example and further describes the constant beamwidth beamforming method of the present invention in conjunction with the accompanying drawings. In this example, the combined array is composed of a 7-element vector nested linear array and an 8-element sound pressure circular array. The combined array array diagram is shown in the attached figure. Figure 1 As shown, the specific steps are:

[0139] Step 1: Calculate the measurement beamwidth:

[0140] The measurement distance is 50m, the hydroacoustic target parameter H is 12m, and the optimal main lobe width is 14 according to formula (1).

[0141] Step 2: Form a vector nested array constant beamwidth beam response:

[0142] The signal processing frequency band is 1000Hz~2000Hz, which is transformed into a sub-band. Two vector nested sub-arrays are constructed. The array element spacing between the low-frequency sub-array and the high-frequency sub-array is d l =λ l / 2 = 0.75 and d h =λ h / 2=0.375.

[0143] According to formula (2) and (3), the directivity function of the low-frequency sub-array and the beam response of the high-frequency sub-array are calculated respectively. The directivity diagrams of the two sub-arrays are shown in the attached figure. Figure 2 shown.

[0144] The frequency weighting function is calculated according to formula (6), and then the frequency weighting function calculated by formula (6) is substituted into formula (4) to obtain the beam response output result of the vector nested linear array.

[0145] The constant beam width beam response of the vector nested linear array is calculated according to formula (9), as shown in the following figure: Figure 3 shown.

[0146] Step 3: Forming a combined array constant beamwidth wave

[0147] The beam response of the 8-element sound pressure circular array is calculated according to formula (12). The radius of the sound pressure circular array is 0.5m. Its directivity diagram is shown in the attached figure. Figure 4 shown.

[0148] According to formula (17), the beam response of the low-frequency combined array and the beam response of the high-frequency combined array are calculated respectively. The directivity diagrams of the two combined arrays are shown in the attached figure. Figure 5 shown.

[0149] Step 3.3: Calculate the frequency weighting function of the combined array according to formula (18) to obtain the constant beamwidth beam patterns of the combined array in the two linear array cases, as shown in the attached figure. Figure 6 shown.

[0150] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. A constant beamwidth beamforming method based on a vector combination array, characterized in that: The following steps are involved: Step 1: Calculate the measurement beam width; The main lobe width of the measurement beam is calculated according to the height of the hydroacoustic target and the distance between the measurement point and the target; Step 2: Form a vector nested array constant beam width beam response; Step 2.1: Divide the set working frequency bandwidth into K frequency sub-bands. Adjacent frequency sub-bands have the same frequency endpoint values. For a certain frequency sub-band [f l ~f h ], a set of vector nested linear arrays is formed by two linear arrays with different array element spacings; Step 2.2: Calculate the beam response B of the low-frequency linear array L (f,θ); Step 2.3: Calculate the beam response B of the high-frequency linear array H (f,θ); Step 2.4: Perform frequency weighting on the beam responses of the high-frequency linear array and the low-frequency linear array respectively to obtain the beam response output result B(f,θ) of the group of vector nested linear arrays; Step 2.5: Based on the beam response output of the vector nested linear array obtained in step 2.4, calculate the constant beam width beam response B of the vector nested linear array. vector (f,θ); Step 3: Form the combined array constant beamwidth beam response: Step 3.1: N equally spaced array elements form a sound pressure circular array with a radius of r. Calculate the beam response B of the sound pressure circular array. circle (θ); Step 3.2: Calculate the array steering vectors of the sound pressure circular array and the vector nested linear array in the combined array; Step 3.3: Calculate the received signals of each element of the sound pressure circular array and each element of the vector nested linear array in the combined array, and then calculate the mutual coordination direction of the combined array; Step 3.4: Calculate the beam response of the combined array according to the steering vector of the combined array; Step 3.5: construct a low-frequency combination base array and a high-frequency combination base array respectively; the low-frequency combination base array is composed of a low-frequency linear array and a sound pressure circular array, and the high-frequency combination base array is composed of a high-frequency linear array and a sound pressure circular array; Step 3.6: Calculate the beam responses of the low-frequency combined array and the high-frequency combined array respectively; Step 3.7: Calculate the frequency weighting function of the combined array, and calculate the constant beamwidth beam response of the combined array in the frequency sub-band based on the frequency weighting function of the combined array.

2. The constant beamwidth beamforming method based on vector combination array according to claim 1, characterized in that: The main lobe width of the measurement beam in step 1 is expressed as: Among them, H is the height of the hydroacoustic target itself; L is the distance between the measurement point and the target.

3. The constant beamwidth beamforming method based on vector combination array according to claim 1, characterized in that: In step 2.2, according to the low frequency f l The design spacing is d l =λ l / 2 M-element linear array is used as the low-frequency linear array SA1 of the vector nested linear array, where λ l For low frequency f l The corresponding wavelength, M is the set value, the beam response of the low-frequency linear array is B L (f,θ) is: Where, θ is the measurement beam scanning angle; θ p is the known desired direction of the main beam; f is the frequency of the received target signal; In step 2.3, according to the high frequency f h The design spacing is d h =λ h / 2 M-element linear array is used as the high-frequency linear array SA2 of the nested linear array group, where λ h For high frequency f h Corresponding wavelength, beam response of high frequency linear array B H (f,θ) is: The beam response output result B(f,θ) of the set of vector nested linear arrays obtained in step 2.4 is: B(f,θ)=L(f)B L (f,θ)+H(f)B H (f,θ) Wherein, L(f) and H(f) are the frequency weighting coefficients of the low-frequency linear array and the high-frequency linear array, respectively.

4. The constant beamwidth beamforming method based on vector combination array as claimed in claim 3, characterized in that: The low-frequency linear array frequency weighting coefficient L(f) and the high-frequency linear array frequency weighting coefficient H(f) are calculated according to the formula Calculated.

5. The constant beamwidth beamforming method based on vector combination array as claimed in claim 1, characterized in that: In step 2.5, the vector nested linear array constant beam width beam response B vector (f,θ) is:

6. The constant beamwidth beamforming method based on vector combination array according to claim 1, characterized in that: In step 3.1, the beam response B of the sound pressure circular array circle (θ) is: B circle (θ)=|w H (θ)a(θ)|=|a H (i p )Q -1 a(θ)| Where w(θ) = Q -1 a(θ p ) is the weighting vector under the condition of maximum array gain; a(θ) is the scanning vector; Q is the normalized noise covariance matrix; a(θ p ) is the circular array steering vector.

7. The constant beamwidth beamforming method based on vector combination array according to claim 6, characterized in that: The circular array steering vector a(θ p ) is expressed as: Where λ is the wavelength of the received signal and n is the number of the nth array element.

8. The constant beamwidth beamforming method based on vector combination array as claimed in claim 1, characterized in that: In step 3.2, the array steering vectors of the sound pressure circular array and the vector nested linear array in the combined array are: Among them, a circle_n (θ) is the steering vector of the nth element of the sound pressure circular array; a v_m (θ) is the steering vector of the mth element of the vector nested linear array; d is the element spacing; The received signals of each element of the sound pressure circular array in the combined base array and the received signals of each element of the vector nested linear array in step 3.3 are: x circle_n (t)=a circle_n (θ s )s(t)+n pn (t) x line_m (t)=a v_m (θ s )s(t)+n vm (t) Among them, x circle_n (t) is the sound pressure hydrophone receiving signal corresponding to the nth array element in the sound pressure circular array; x line_m (t) is the vector hydrophone receiving signal corresponding to the mth array element in the vector nested linear array; s(t) is the far-field incident signal, n pn (t) and n vm (t) is the noise signal; The beam response of the combined array in step 3.4 is: B(θ s )=w H (i s )a c (i s ) Among them, w(θ s ) is the weight vector, a c (θ s ) is the steering vector of the combined array.

9. The constant beamwidth beamforming method based on vector combination array as claimed in claim 1, characterized in that: The steering vector a of the combined matrix c (θ s )for: a circle (i s )=[a circle_1 (i s ),...,a circle_n (θ),...,a circle_N (i s )] T a v (i s )=[a v_1 (i s ),...,a v_m (θ),...,a v_M (i s )] T 。 10. The constant beamwidth beamforming method based on vector combination array according to claim 1, characterized in that: The beam response B of the low frequency combined array in step 3.6 L (f,θ) and the beam response of the high frequency combined array B H (f,θ) is: B L (f,θ)=B circle (f,θ)B L (f,θ) B H (f,θ)=B circle (f,θ)B H (f,θ) The frequency weighting function of the combined matrix in step 3.7 is:

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