Dynamic beamforming method based on uniform circular frequency diversity array sonar

Abstract

This invention relates to the field of array signal processing, specifically to a dynamic beamforming method for a uniform circular frequency diversity array sonar. The method includes: constructing a uniform circular frequency diversity array; configuring nonlinear frequency offsets in the form of natural logarithms for each array element; and transmitting a multi-carrier composite signal for each element, composed of multiple logarithmically offset single-frequency signals superimposed; calculating the complex weighting coefficients of each single-frequency signal based on the desired beam pointing and desired distance; and synthesizing a dynamic beam. This invention eliminates the phenomenon of periodic grating lobes in the beam over distance through nonlinear multi-carrier frequency offset design, solving the range-azimuth coupling problem; simultaneously, through the multi-carrier superposition mechanism, it significantly suppresses sidelobe levels and energy tails, improving the system's anti-interference capability; the constructed beam model strictly follows the physical laws of sound wave propagation, accurately characterizing the dynamic propagation characteristics of the beam.

Description

Technical Field

[0001] This invention relates to the field of array signal processing, and more specifically to a dynamic beamforming method based on a uniform circular frequency diversity array sonar. Background Technology

[0002] Frequency Diversity Array (FDA), as a novel array signal processing technology, has attracted widespread attention in the fields of radar and sonar detection since its inception. Unlike traditional phased array technology, FDA introduces small frequency differences on each transmitting element of the array to form time-varying beams that are dependent on range and azimuth, thereby providing resolution in the range dimension and offering a new technical approach for multi-target detection and anti-jamming.

[0003] To fully leverage the spatial symmetry of the array, researchers combined the FDA with a uniform circular array, proposing the Uniform Circular Frequency Diverse Array (UCFDA). The UCFDA is geometrically isotropic, making it suitable for omnidirectional detection scenarios. It demonstrates significant potential, particularly in clutter suppression and signal-to-interference-plus-noise ratio (SNR) enhancement, providing a promising engineering solution for underwater sonar systems.

[0004] However, existing UCFDA sonar beamforming technology still has several core defects, hindering its transformation into a high-performance, high-reliability engineering system. For example, the traditional linear frequency offset design used by Sarah et al. in the paper "An investigation into uniform circularfrequency diverse array (UCFDA) radars" (published in Remote Sensing Letters, 2015, 6(9): 707-714) results in a periodic distribution of the beam in the range dimension, producing grating lobes and causing severe coupling between the target range and azimuth, making it difficult to achieve accurate two-dimensional resolution. The single-carrier logarithmic frequency offset proposed by Khan et al. in the paper "Frequency diverse array radar with logarithmically increasing frequency offset" (published in IEEE Antennas and Wireless Propagation Letters, 2015, 14: 499-502) can alleviate the coupling problem between the target range and azimuth, but the range dimension sidelobe level is high, the beam tail is obvious, the anti-interference capability is weak, and it is easily affected by underwater clutter and noise. The traditional linear frequency offset design used by Liao et al. in the paper "Frequency diverse array radar with logarithmically increasing frequency offset" can alleviate the coupling problem between the target range and azimuth, but the beam tail is high, the anti-interference capability is weak, and it is easily affected by underwater clutter and noise. The scheme proposed in "beam pattern synthesis using symmetrical logarithmic frequency offsets for target indication" (published in IEEE Transactions on Antennas and Propagation, 2019, 67(5): 3505-3509) confuses the signal generation time with the time variable during signal propagation, incorrectly canceling the two and attempting to eliminate beam time-varying characteristics, resulting in a serious disconnect between the theoretical model and the physical reality of sound wave propagation. In addition, the existing method lacks a flexible adjustment mechanism between range resolution, sidelobe suppression effect and system complexity, making it difficult to adapt to the dynamic requirements of different detection distances and environmental noise.

[0005] To address the aforementioned issues, various improvement schemes have been proposed in this field, such as optimization methods based on iterative least mean square algorithms or second-order cone programming. While these methods can achieve point beamforming to some extent, they often neglect the time characteristics of signal propagation and the inherent time-varying nature of the beam. Other research has attempted to combine time modulation with nonlinear frequency offset, but this has not effectively solved the sidelobe suppression problem and has instead increased the complexity of system implementation.

[0006] Therefore, there is an urgent need in this field for a dynamic beamforming method that can effectively decouple distance and azimuth, significantly suppress sidelobes, strictly follow the principles of sound propagation, and has good adjustment flexibility. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention proposes a dynamic beamforming method based on a uniform circular frequency diversity array sonar. By introducing a nonlinear multi-carrier frequency offset design and combining it with precise time variable modeling, the method solves the range-azimuth coupling problem, significantly suppresses beam sidelobes, and achieves flexible and controllable beam performance, thereby improving the detection accuracy and anti-interference capability of UCFDA sonar in complex underwater environments.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention proposes a dynamic beamforming method based on a uniform circular frequency diversity array sonar, comprising the following steps:

[0010] S1. Construct a uniform circular frequency diversity array, wherein the uniform circular frequency diversity array is composed of... The array elements are evenly distributed in a radius of [missing information]. On the circumference of the circle, the reference frequency of the uniform circular frequency diversity array is ;

[0011] S2. Configure nonlinear element frequency offsets for each element in the uniform circular frequency diversity array, where the element frequency offset configured for the m-th element is... Generated based on a nonlinear function. ;

[0012] S3. Transmit a multi-carrier composite signal to each of the array elements, wherein the multi-carrier composite signal is composed of L single-frequency signals with different frequencies superimposed on each other; wherein, the first... The first of the array elements The frequency of a single-frequency signal From reference frequency The frequency offset of the corresponding array element and carrier sequence number Related carrier frequency offset Sure; , ;

[0013] S4. For each array element, based on the desired beam pointing azimuth angle... and expected distance Calculate the complex weighting coefficients for each single-frequency signal;

[0014] S5. Synthesize a dynamic beamline based on the element frequency offset of each array element, the carrier frequency offset of each array element, and the complex weighting coefficient of each single-frequency signal.

[0015] Furthermore, in S1, the radius The calculation formula is:

[0016]

[0017]

[0018] In the formula, This is the radius adjustment coefficient. , The spacing between array elements is The radius of the time array, Reference frequency The corresponding wavelength.

[0019] Furthermore, the radius adjustment coefficient The value range is 0.75 to 0.95.

[0020] Furthermore, in S2, the array element frequency offset Based on the natural logarithm function, the calculation formula is:

[0021]

[0022] In the formula, It is the first constant with a fixed frequency.

[0023] Furthermore, in S3, the carrier frequency offset Based on the natural logarithm function, the calculation formula is:

[0024]

[0025] In the formula, It is the second constant with a fixed frequency.

[0026] Furthermore, in S3, the first The first of the array elements The frequency of a single-frequency signal The calculation formula is:

[0027] .

[0028] Furthermore, in S4, the first The first of the array elements A single-frequency signal, its complex weighting coefficients The calculation formula is:

[0029]

[0030] In the formula, The imaginary unit, For the first The azimuth angle of each array element The pulse width. >0, This represents the speed at which sound waves propagate in water.

[0031] Furthermore, in S5, the dynamic beam pattern The calculation formula is:

[0032]

[0033] In the formula, The azimuth of the observation point. The distance between the observation point and the center of the array. The observation time.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] (1) This invention eliminates the phenomenon of periodic grating lobes in the beam in terms of range by using nonlinear frequency offset design and multi-carrier superposition mechanism, thereby solving the range-azimuth coupling problem caused by traditional linear frequency offset and enabling accurate two-dimensional resolution of target range and azimuth. At the same time, the complementary effect between multiple carriers effectively reduces beam sidelobe level and energy tail, significantly enhancing the system's anti-clutter and anti-interference performance in complex underwater environments.

[0036] (2) In the theoretical modeling, the present invention strictly distinguishes the time variables in the signal generation and propagation process, so that the synthesized beam can correctly present the characteristics of dynamic propagation with time and space, strictly follow the physical law of sound wave propagation in water medium, avoid the theoretical defects and simulation distortion caused by the confusion of time variables in the prior art, and provide a reliable theoretical basis for engineering implementation.

[0037] (3) The present invention uses the total number of carriers as a key adjustable parameter. By adjusting this parameter, a dynamic balance and optimized configuration can be achieved between range resolution, sidelobe suppression level and system implementation complexity. This enables the system to flexibly select the optimal working mode according to the actual needs of different detection scenarios (such as long-range search and short-range identification) and environmental conditions (such as noise and clutter intensity), which significantly improves the practical value and deployment flexibility of the method. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the uniform circular frequency diversity array in an embodiment of the present invention;

[0039] Figure 2The sonar transmission beam pattern obtained using traditional linear frequency offset;

[0040] Figure 3 Two-dimensional sonar transmission beammaps at different observation times obtained using single-carrier logarithmic frequency offset;

[0041] Figure 4 Projection and cross-sectional views of the sonar transmission beam pattern obtained using single-carrier logarithmic frequency offset at t=2.0s;

[0042] Figure 5 The two-dimensional sonar transmission beam patterns obtained at different observation times when using the dynamic beamforming method proposed in the embodiments of the present invention and L=4;

[0043] Figure 6 When L=4 and t=2.0s, the projection and cross-sectional views of the sonar transmission beam pattern obtained by the dynamic beamforming method proposed in this embodiment of the invention are shown.

[0044] Figure 7 The two-dimensional sonar transmission beam patterns obtained at different observation times when using the dynamic beamforming method proposed in this embodiment of the invention and L=16;

[0045] Figure 8 The projection and cross-sectional views of the sonar transmission beammap obtained by the dynamic beamforming method proposed in this embodiment of the invention when L=16 and t=2.0s are shown. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Example

[0048] This embodiment proposes a dynamic beamforming method based on a uniform circular frequency diversity array sonar, which is performed according to the following steps:

[0049] S1, Reference Figure 1 A geometric and signal model of a uniform circular frequency diversity array is established. In this model, the x-axis and y-axis are established in the array plane with the center of the array circle as the origin O. Isotropic array elements are uniformly distributed in a radius of [missing information]. On the circumference of the circle. The reference frequency of the uniform circular frequency diversity array is The radius of the array Determined by the following formula:

[0050]

[0051]

[0052]

[0053] In the formula, This indicates the speed at which sound waves travel in water. This represents the radius adjustment coefficient. , The element spacing is represented as The radius of the time array, Reference frequency The corresponding wavelength.

[0054] For the main beam distance section, when the element spacing is less than At that time, as the radius decreases, the main lobe width of the beam pattern in the angular dimension will increase; while when the element spacing is greater than or equal to As the radius increases, the main lobe width of the angular beam pattern narrows, but the side lobe height increases, and some side lobes appear that are close to the main lobe height. Therefore, in order to balance the main lobe width and side lobe height, The preferred value range is 0.75 to 0.95.

[0055] In the uniform circular frequency diversity array, the first ( ) azimuth angle of each array element , The preferred values ​​are 8~64.

[0056] In this embodiment, =16, =10KHz, =1500m / s, =0.93.

[0057] S2. Configure nonlinear array element frequency offset:

[0058] To eliminate the range-dimensional periodic grating lobes caused by traditional linear frequency offset, a nonlinear element frequency offset is configured for each element in the uniform circular frequency diversity array. This element frequency offset is generated based on the natural logarithm function, where is the th... Array element frequency offset configured for each array element , The calculation formula is:

[0059]

[0060] In the formula, This represents a first fixed frequency variation constant, in this embodiment, =5Hz.

[0061] S3. Configure multi-carrier composite signal and carrier frequency offset:

[0062] For each element in the uniform circular frequency diversity array, a multi-carrier composite signal is transmitted. The multi-carrier composite signal is composed of L superimposed single-frequency signals with different frequencies; the value of L is preferably 4 to 16; wherein, the first... The first of the array elements ( The frequency of a single-frequency signal From reference frequency The frequency offset of the corresponding array element and carrier sequence number Related carrier frequency offset Determined; to satisfy the narrowband signal assumption, ,Right now .

[0063] in, Based on the natural logarithm function, the calculation formula is:

[0064]

[0065] In the formula, This represents the second fixed frequency variation constant, in this embodiment, =5Hz.

[0066] The calculation formula is:

[0067] .

[0068] S4. For each array element, based on the desired beam pointing azimuth angle... and expected distance Calculate the complex weighting coefficients for each single-frequency signal, for the . The first of the array elements A single-frequency signal, its complex weighting coefficients The calculation formula is:

[0069]

[0070] In the formula, Represents the imaginary unit. Indicates the pulse width. >0.

[0071] In this embodiment, = , =900m, =1s.

[0072] S5. Based on the frequency offset of each array element, the frequency offset of each carrier, and the complex weighting coefficients of each single-frequency signal, synthesize the dynamic beam pattern. .

[0073] No. The transmission signal of each array element It can be represented as:

[0074]

[0075] When satisfied <0.1 At that time, all array elements reach the far field signal It can be represented as:

[0076]

[0077] The first exponent term on the right side of the equal sign in the equation This describes the propagation process of sound waves; the second exponential summation term... This reflects the beam characteristics in the azimuth plane.

[0078] therefore, The calculation formula is:

[0079]

[0080] In the above formula, This represents the azimuth angle of the observation point, which is the angle between the line connecting the observation point and the center O of the circle and the positive x-axis in the array plane. This represents the distance between the observation point and the center of the array. The observation time.

[0081] To illustrate the beneficial effects of the present invention, the sonar beammaps under the traditional linear frequency offset (Scheme-1), the single-carrier logarithmic frequency offset (Scheme-2), and the nonlinear multi-carrier (Scheme-3) of this embodiment were simulated and compared. The results are as follows:

[0082] Figure 2 The sonar transmission beam pattern obtained using scheme-1 is shown. Figure 2 In the diagram, 'a' represents the three-dimensional transmission beam pattern. Figure 2 In the diagram, b represents the two-dimensional transmission beam pattern. Figure 2 In this context, 'c' represents the distance-dimensional beammap of the desired angular cross section. Figure 2 In the d-axis, the angular beam pattern represents the distance between the main beams and the cross-section. Figure 2 a and Figure 2As can be seen from b in the figure, the beam energy appears periodically in the distance dimension, forming grating lobes; Figure 2 The presence of c further confirms this periodicity, with a period of approximately c / =150m. Therefore, Scheme-1 suffers from severe range-azimuth coupling.

[0083] Figure 3 Two-dimensional transmission beammaps at different observation times obtained using scheme-2 are shown; Figure 3 'a' in t Two-dimensional transmitted beam pattern at 0.5s. Figure 3 b in t Two-dimensional transmit beam pattern at 0.75s. Figure 3 c in t Two-dimensional transmit beam pattern at 1.0s. Figure 3 d in t Two-dimensional transmitted beam pattern at 2.0s. Figure 3 As can be seen, although the grating lobes are eliminated and the beam appears as dots, the beam pattern formed by Scheme-2 has obvious energy tails in its sidelobe region.

[0084] Figure 4 Showing t At 2.0s, the projection and cross-sectional views of the sonar beam pattern obtained using Scheme-2; Figure 4 In this diagram, 'a' represents the angular beam projection. Figure 4 In the diagram, b represents the angular beam pattern of the desired distance section. Figure 4 In this context, 'c' represents the range-dimensional beam projection diagram. Figure 4 In this context, d represents the distance-dimensional beammap of the desired angular cross-section. From... Figure 4 c and Figure 4 As can be seen from d, the maximum sidelobe level of the beam is as high as about 0.48, and the energy decays slowly in the non-main lobe direction. This indicates that although Scheme-2 solves the coupling problem, its sidelobe suppression capability is insufficient, and it is easily affected by clutter and noise in the actual complex underwater environment.

[0085] Figure 5 It demonstrates the adoption of scheme-3 and L Two-dimensional transmission beam patterns obtained at different observation times when =4; Figure 5 'a' in t Two-dimensional transmitted beam pattern at 0.5s. Figure 5 b in t Two-dimensional transmit beam pattern at 0.75s. Figure 5 c in t Two-dimensional transmit beam pattern at 1.0s. Figure 5 d in t Two-dimensional transmit beam pattern at 2.0s.

[0086] Figure 6 Showing L =4, t At 2.0s, the projection and cross-sectional views of the sonar beam pattern obtained using Scheme-3; Figure 6 In this diagram, 'a' represents the angular beam projection. Figure 6 In the diagram, b represents the angular beam pattern of the desired distance section. Figure 6 In this context, 'c' represents the range-dimensional beam projection diagram. Figure 6 In this context, d represents the distance-dimensional beam pattern of the desired angular cross section.

[0087] Figure 7 It demonstrates the adoption of scheme-3 and L Two-dimensional transmission beam patterns obtained at different observation times when =16; Figure 7 'a' in t Two-dimensional transmitted beam pattern at 0.5s. Figure 7 b in t Two-dimensional transmit beam pattern at 0.75s. Figure 7 c in t Two-dimensional transmit beam pattern at 1.0s. Figure 7 d in t Two-dimensional transmit beam pattern at 2.0s.

[0088] Figure 8 Showing L =16, t At 2.0s, the projection and cross-sectional views of the sonar beam pattern obtained using Scheme-3; Figure 8 In this diagram, 'a' represents the angular beam projection. Figure 8 In the diagram, b represents the angular beam pattern of the desired distance section. Figure 8 In this context, 'c' represents the range-dimensional beam projection diagram. Figure 8 In this context, d represents the distance-dimensional beam pattern of the desired angular cross section.

[0089] from Figure 5 and Figure 7 As can be seen, the beam pattern formed by Scheme-3 is a clear dot pattern, with the grating lobes completely eliminated, successfully achieving decoupling. Simultaneously, the main lobe of the beam dynamically moves along the distance dimension with observation time, conforming to the laws of sound propagation.

[0090] from Figure 6 c and Figure 8 As can be seen from 'c', the energy outside the main lobe decays rapidly, while the side lobes are effectively suppressed. Figure 6 b in Figure 6 d in Figure 8 b in Figure 8 The d in the text corresponds to the Figure 4 b in Figure 4 Compared to d in the original text, this effect can be quantified, and the quantification results are shown in Table 1.

[0091] Table 1. Comparison of UCFDA sonar beam performance under different frequency offset schemes

[0092]

[0093] As can be seen from Table 1, the method proposed in this invention achieves significant optimization in beam synthesis performance:

[0094] (1) Effective improvement in range resolution. When L=16, the main lobe width in the range dimension is compressed from 105m in scheme-2 to 75m, and the resolution is improved by about 28.6%;

[0095] (2) The sidelobe suppression effect is outstanding. When L=16, the maximum sidelobe level drops significantly from 0.48 to 0.16, a reduction of 66.7%, and the system's ability to resist clutter and interference is significantly enhanced;

[0096] (3) The azimuth performance remained stable. The main lobe width in the angular dimension remained at 17.0, indicating that the change in the number of carriers L did not affect the azimuth resolution.

[0097] (4) Flexible and adjustable performance. The total number of carriers L is a key adjustable parameter. The main lobe width and side lobe level in the range dimension can be flexibly adjusted by increasing or decreasing the value of L. Thus, in practical applications, dynamic optimization and balance can be achieved between beam performance and system complexity according to the requirements of different detection scenarios.

[0098] The specific embodiments of the present invention are provided to enable those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0099] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A dynamic beamforming method based on a uniform circular frequency diversity array sonar, characterized in that, Includes the following steps: S1. Construct a uniform circular frequency diversity array, wherein the uniform circular frequency diversity array is composed of... The array elements are evenly distributed in a radius of [missing information]. On the circumference of the circle, the reference frequency of the uniform circular frequency diversity array is ; S2. Configure a nonlinear element frequency offset for each element in the uniform circular frequency diversity array, which is the first element. Array element frequency offset configured for each array element Generated based on a nonlinear function. ; S3. Transmit a multi-carrier composite signal to each of the array elements, wherein the multi-carrier composite signal is composed of L single-frequency signals with different frequencies superimposed on each other; wherein, the first... The first of the array elements The frequency of a single-frequency signal From reference frequency The frequency offset of the corresponding array element and carrier sequence number Related carrier frequency offset Sure; , ; S4. For each array element, based on the desired beam pointing azimuth angle... and expected distance Calculate the complex weighting coefficients for each single-frequency signal; S5. Synthesize a dynamic beamline based on the element frequency offset of each array element, the carrier frequency offset of each array element, and the complex weighting coefficient of each single-frequency signal.

2. The dynamic beamforming method based on a uniform circular frequency diversity array sonar according to claim 1, characterized in that, In S1, the radius The calculation formula is: In the formula, This is the radius adjustment coefficient. , The spacing between array elements is The radius of the time array, Reference frequency The corresponding wavelength.

3. The dynamic beamforming method based on a uniform circular frequency diversity array sonar according to claim 2, characterized in that, Radius adjustment coefficient The value range is 0.75 to 0.

95.

4. The dynamic beamforming method based on a uniform circular frequency diversity array sonar according to claim 1, characterized in that, In S2, the array element frequency offset Based on the natural logarithm function, the calculation formula is: In the formula, It is the first constant with a fixed frequency.

5. The dynamic beamforming method based on a uniform circular frequency diversity array sonar according to claim 1, characterized in that, In S3, the carrier frequency offset Based on the natural logarithm function, the calculation formula is: In the formula, It is the second constant with a fixed frequency.

6. The dynamic beamforming method based on a uniform circular frequency diversity array sonar according to claim 1, characterized in that, In S3, the first The first of the array elements The frequency of a single-frequency signal The calculation formula is: 。 7. The dynamic beamforming method based on a uniform circular frequency diversity array sonar according to claim 2, characterized in that, In S4, no. The first of the array elements A single-frequency signal, its complex weighting coefficients The calculation formula is: In the formula, The imaginary unit, For the first The azimuth angle of each array element The pulse width. >0, This represents the speed at which sound waves propagate in water.

8. The dynamic beamforming method based on a uniform circular frequency diversity array sonar according to claim 7, characterized in that, In S5, dynamic beam pattern The calculation formula is: In the formula, The azimuth of the observation point. The distance between the observation point and the center of the array. The observation time.

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