Orthogonal magnetic antenna system shipborne ground wave radar target direction finding method based on multi-moment amplitude-frequency information

Abstract

The invention relates to an orthogonal magnetic antenna system shipborne ground wave radar target direction finding method based on multi-moment amplitude-frequency information, and belongs to the technical field of high-frequency ground wave radar direction finding. The method comprises the following steps: acquiring radar time domain data, a target detection result and attitude data of a shipborne platform in a heading change period, and extracting a target echo according to the target detection result; the method comprises the following steps: performing time-frequency analysis on a target echo to obtain a Doppler and amplitude information time sequence, and framing according to a fixed frame length to construct a single-frame Doppler frequency shift change sequence; obtaining an initial estimation value of a target azimuth by using two-channel amplitude response characteristics of an orthogonal magnetic antenna and adopting an amplitude comparison algorithm; and further combining attitude data to generate a theoretical Doppler frequency shift change sequence, carrying out matching search through a least square criterion to obtain single-frame azimuth accurate estimation, and carrying out smooth processing on a multi-frame result to output a stable azimuth. The method has the advantages of high direction finding precision and strong robustness under the condition of target echo broadening.

Description

Technical Field

[0001] This invention relates to the field of high-frequency ground wave radar direction finding technology, specifically to a target direction finding method for shipborne ground wave radar based on an orthogonal magnetic antenna system with multi-time amplitude-frequency information. Background Technology

[0002] High-frequency surface wave radar (HFSWR), with its 3-30MHz electromagnetic waves propagating along the sea surface, can achieve long-range, wide-area detection beyond visual range and has the ability to continuously track the movement of targets, making it a core technology for large-scale maritime target early warning and monitoring. Compared with shore-based HFSWRs, shipborne HFSWRs, utilizing the mobility and ease of deployment of shipborne platforms, have unique advantages in long-range maritime early warning and monitoring.

[0003] Currently, shipborne ground-wave radar has achieved long-range target detection at distances exceeding 100 kilometers. However, due to limitations in space and complex environments on shipborne platforms, high-precision direction finding remains a challenge. The essence of this problem lies in the contradiction between traditional direction-finding modes and shipborne application scenarios: First, limited space on shipborne platforms prevents the deployment of large array antennas, and traditional array-based direction-finding methods relying on element phase differences suffer from weak direction-finding performance due to insufficient aperture. Second, existing research often considers shipborne platform motion as a negative interference factor, while techniques utilizing platform motion, such as synthetic aperture radar, are more suitable for high-speed platforms, offering limited improvement in direction-finding performance for low-speed shipborne shortwave frequencies. Therefore, it is urgent to break through the traditional array amplitude-phase dependent direction-finding mode and explore new ideas and methods for non-array ground-wave radar direction finding suitable for space-constrained shipborne scenarios.

[0004] An orthogonal magnetic antenna is a co-located, non-array antenna. The radiation pattern of a single magnetic antenna is figure-eight shaped, and the amplitude and phase of the two channels are complementary. Figure 2 As shown, its amplitude and phase information can be used for azimuth estimation, providing a new option for target orientation finding of space-constrained shipborne ground-wave radar. Furthermore, our research found that when the shipborne platform is navigating, changes in the platform's heading alter the target's azimuth in the radar and its angle with the platform's heading, resulting in a corresponding observable Doppler frequency shift in the target echo, such as... Figure 3 As shown, the target's location information is "encoded" in the frequency shift feature.

[0005] Therefore, to improve the direction finding performance of shipborne ground wave radar, it is necessary to develop a direction finding method that integrates the amplitude and Doppler information of the target. This method should be based on an orthogonal magnetic antenna with complementary amplitude and phase characteristics. By observing the target at multiple times and leveraging the high Doppler resolution of the ground wave radar, the target's azimuth information can be "decoded." This is crucial for promoting the practical application of non-array shipborne ground wave radar. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] This invention aims to provide a target orientation method for shipborne ground wave radar based on orthogonal magnetic antenna system with multi-time amplitude-frequency information. It utilizes the Doppler frequency shift variation law of target echo caused by the bow change of the shipborne platform and combines the amplitude response characteristics of orthogonal magnetic antenna to achieve accurate estimation of target azimuth.

[0008] (II) Technical Solution

[0009] A target direction finding method for a shipborne ground-wave radar based on multi-time amplitude-frequency information using an orthogonal magnetic antenna system includes the following steps:

[0010] S1. Acquisition of Observation Data

[0011] The observation data includes radar time-domain data, target detection results, and attitude data collected by the shipborne platform during a period of observation when the bow changes. Based on the target detection results, the radar time-domain data is correlated and matched to extract the time-domain data corresponding to the target, which is then used as input for subsequent processing.

[0012] S2, Expand target information extraction

[0013] The time-domain data corresponding to the target is subjected to time-frequency analysis to extract the time series of Doppler information and the time series of amplitude information. The observation time is divided into frames according to a fixed frame length to obtain the Doppler sequence and amplitude sequence of each frame. The Doppler information of adjacent sampling points in a single frame is differentially analyzed to obtain the Doppler frequency shift change sequence of that frame.

[0014] S3. Initial azimuth estimation based on amplitude information

[0015] Based on a single-frame amplitude sequence, the initial estimate θ0 of the target azimuth angle is calculated using the orthogonal amplitude response characteristics of the two channels of the orthogonal magnetic antenna through an amplitude comparison algorithm.

[0016] S4. Precise location estimation based on Doppler information

[0017] Based on attitude data, the bow change angle Δα and platform velocity v of the shipborne platform within one frame are obtained. shipBased on the relationship between the target's Doppler frequency shift and azimuth angle, a theoretical Doppler frequency shift sequence for the frame is generated for different candidate azimuth angles. The measured Doppler frequency shift sequence is matched with the theoretical Doppler frequency shift sequence, and the least squares error is used as the cost function to search for candidate azimuth angles that minimize the cost function within a preset angle search interval. These candidate azimuth angles are then used as the target azimuth estimation results for the frame. An azimuth time series sequence is constructed using the target azimuth estimation results obtained from multiple consecutive observations. The azimuth time series sequence is then smoothed to output the accurate azimuth estimation results for the target.

[0018] Step S2, the time-frequency analysis and processing, includes: performing continuous wavelet transform on the corresponding matched time-domain data to obtain the time-frequency distribution, and using synchronous extraction transform to rearrange and sharpen the time-frequency distribution.

[0019] In step S2, the frequency and amplitude of the peak point of the time-frequency distribution at each moment are taken as the Doppler estimate and amplitude estimate for that moment, respectively, to form the time series of the Doppler information and the time series of the amplitude information.

[0020] In step S2, the number of sampling points per frame is 512.

[0021] Before the heading change in step S4, the Doppler information of the target is as follows:

[0022]

[0023] Among them, v ship Let λ represent the velocity of the shipborne platform at this moment, θ represent the wavelength, and θ represent the angle between the target and the shipborne platform. target θ represents the velocity of the target at this moment. target The angle between the target's velocity direction and the line connecting the target and the shipborne platform is given. After the heading changes, the target's Doppler information is as follows:

[0024]

[0025] Therefore, the relationship between the target's Doppler frequency shift and the azimuth angle is obtained as follows:

[0026] .

[0027] The preset angle search interval mentioned in step S4 is reduced to [θ0-10°, θ0+10°] based on the initial estimated value θ0.

[0028] The smoothing process described in step S4 includes any one or more combinations of moving average filtering, median filtering, exponentially weighted average filtering, or Kalman filtering.

[0029] (III) Beneficial Effects

[0030] The advantages of this invention are as follows:

[0031] This invention addresses the problem of decreased accuracy in traditional direction finding caused by the motion of shipborne platforms, which leads to Doppler broadening and amplitude reduction in target echoes. It proposes a direction finding method based on an orthogonal magnetic antenna-based shipborne ground-wave radar, fusing multi-time Doppler and amplitude information. This method not only meets the stringent spatial requirements of shipborne platforms but also overcomes the limitations of traditional static observation and the constraints of array amplitude-dependent direction finding modes, thus improving direction finding performance for distant targets. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the basic process of the present invention.

[0033] Figure 2 This is the antenna pattern of the orthogonal magnetic antenna of the present invention.

[0034] Figure 3 The figure shows the simulation results of the Doppler frequency shift of the target under the heading change condition of the present invention.

[0035] Figure 4 The diagram shows the bow-to-head change of the present invention.

[0036] Figure 5 The figure shows the simulation results of the direction finding method of the present invention. Detailed Implementation

[0037] To make the objectives, contents, and advantages of the present invention clearer, the following description is provided in conjunction with the appendix. Figure 1 The specific embodiments of the present invention will be described in further detail below.

[0038] Step 1: Acquisition of observation data.

[0039] The observation data includes radar time-domain data, target detection results, and attitude data collected by the shipborne platform during a period of observation when the bow changes. Based on the target detection results, the radar time-domain data is correlated and matched to extract the time-domain data corresponding to the target, which is then used as input for subsequent processing.

[0040] Step 2: Expand target information extraction.

[0041] The movement of the shipborne platform causes the target echo to broaden in the Doppler dimension and decrease in amplitude. In order to make full use of the information of the broadened target in the Doppler dimension, the radar time-domain data is subjected to time-frequency analysis processing.

[0042] In some embodiments, time-frequency analysis is performed on the time-domain data corresponding to the target using continuous wavelet transform to obtain the time-frequency distribution. To improve frequency resolution, a synchronous extraction transform is further used to rearrange and sharpen the time-frequency distribution. The frequency and amplitude of the peak point of the time-frequency distribution at each moment are taken as the estimation result for that moment, thereby obtaining the time series of Doppler information and the time series of amplitude information.

[0043] Based on the time series of Doppler information and the time series of amplitude information, the observation time is divided into frames of fixed frame length to obtain frame-by-frame Doppler and amplitude sequences. The Doppler information of adjacent sampling points within a single frame is differentially analyzed to obtain the Doppler frequency shift sequence for that frame. An initial azimuth estimate is then performed based on the single-frame Doppler frequency shift sequence and amplitude sequence. In some embodiments, the number of sampling points per frame is 512.

[0044] Step 3: Initial azimuth estimation based on amplitude information.

[0045] When a single far-field signal source is incident, the echo signal received by the orthogonal magnetic antenna satisfies the following model:

[0046]

[0047] In the formula, X(t) = [x1(t), x2(t)] T This represents the echo signals received by the two channels of the orthogonal magnetic antenna; t is the time variable; A(θ) = [cos(θ),sin(θ)] T The vector representing the orthogonal magnetic antenna is denoted by ; S(t) represents the far-field signal from a single incident direction; N(t) = [n1(t), n2(t)] T This represents the noise signal received by the two channels.

[0048] Since the two channels of the orthogonal magnetic antenna have orthogonal amplitude response characteristics, an amplitude comparison algorithm is used to process the single-frame amplitude sequence, and the initial estimate of the target azimuth angle θ0 is calculated using the arctangent function.

[0049]

[0050] Step 4: Precise azimuth estimation based on Doppler information.

[0051] Since amplitude information is easily affected by the motion of the shipboard platform, the error is large when using amplitude information alone for direction finding. Therefore, the Doppler frequency shift sequence is further used to achieve accurate azimuth estimation.

[0052] The heading change angle of the shipborne platform within one frame is denoted as Δα. A schematic diagram of the heading change is shown below. Figure 4 As shown, the Doppler information of the target before the heading change is:

[0053]

[0054] Among them, v ship Let λ represent the velocity of the shipborne platform at this moment, θ represent the wavelength, and θ represent the angle between the target and the shipborne platform. target θ represents the velocity of the target at this moment. target This represents the angle between the target's velocity direction and the line connecting the target and the shipborne platform. After the heading changes, the target's Doppler information is as follows:

[0055]

[0056] This yields the relationship between the target's Doppler frequency shift and the azimuth angle:

[0057]

[0058] As shown above, there is a functional relationship between the Doppler frequency shift and θ. Using the platform's attitude information, Δα and v within this time period can be obtained. ship Therefore, θ can be obtained from the Doppler frequency shift change of the target echo. Regarding the solution of θ, directly substituting the formula relating Doppler frequency shift change and azimuth angle can easily lead to over-reliance on the accuracy of Doppler information extraction. Therefore, a time series of Doppler frequency shift changes is used for estimation. Specifically, based on the relationship between the target's Doppler frequency shift change and azimuth angle, a theoretical Doppler frequency shift change sequence for the frame is generated for different candidate target azimuth angles. The measured Doppler frequency shift change sequence is matched with the theoretical Doppler frequency shift change sequence, and the least squares error is used as the cost function. A parameter solution that minimizes the cost function is searched within a preset angle search interval, and the corresponding θ is used as the target azimuth estimation result for that frame. To reduce computational load, the search interval can be narrowed to [θ0-10°, θ0+10°] based on the initial estimated value θ0 obtained in step 3.

[0059] Considering the continuous nature of target azimuth changes over a short period, an azimuth time series is constructed using the initial azimuth estimation results obtained from multiple consecutive observations. This azimuth time series is then smoothed to suppress random noise and occasional outliers, ultimately outputting a high-precision and stable target azimuth estimation result. In some embodiments, the smoothing process includes any one or more combinations of moving average filtering, median filtering, exponentially weighted average filtering, or Kalman filtering.

[0060] Example

[0061] To verify the effectiveness of the direction-finding method, this invention relates to and has conducted simulation experiments. The platform speed was set to 5 m / s, the heading change was 10°, the target distance was 80 km, the speed was 0 m / s, and the azimuth angle was 45°. Figure 5The corresponding simulation results are shown in the figure. The minimum value is 44.8°, which is the final direction finding result, reflecting the effectiveness of the present invention.

[0062] The above embodiments of the present invention are merely examples for clearly illustrating 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 neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A target direction finding method for a shipborne ground-wave radar based on an orthogonal magnetic antenna system with multi-time amplitude-frequency information, characterized in that, Includes the following steps: S1. Observation data acquisition: The observation data includes radar time-domain data, target detection results, and attitude data collected by the shipborne platform during an observation period when the bow direction changes; the radar time-domain data is correlated and matched based on the target detection results to extract the time-domain data corresponding to the target; S2. Target information extraction: Time-frequency analysis is performed on the time-domain data corresponding to the target to extract the time series of Doppler information and the time series of amplitude information; the observation time is divided into frames according to a fixed frame length to obtain the Doppler sequence and amplitude sequence of each frame, and the Doppler information of adjacent sampling points in a single frame is differentially divided to obtain the Doppler frequency shift change sequence of that frame. S3. Initial azimuth estimation based on amplitude information: Based on a single frame amplitude sequence, the initial estimated value θ0 of the target azimuth angle is calculated by using the orthogonal amplitude response characteristics of the two channels of the orthogonal magnetic antenna through the amplitude comparison algorithm. S4. Accurate azimuth estimation based on Doppler information: Based on attitude data, the bow change angle Δα and platform velocity v of the shipborne platform within one frame are obtained. ship Based on the relationship between the target Doppler frequency shift change and the azimuth angle, a theoretical Doppler frequency shift change sequence for the frame is generated for different candidate azimuth angles; the measured Doppler frequency shift change sequence is matched with the theoretical Doppler frequency shift change sequence, and the least squares error is used as the cost function to search for candidate azimuth angles that minimize the cost function within a preset angle search interval, and these candidate azimuth angles are used as the target azimuth estimation result for the frame; A target azimuth estimation result is constructed using the target azimuth estimation result obtained from multiple consecutive observations. The target azimuth estimation result is then output after smoothing the target azimuth estimation result.

2. The target direction finding method for a shipborne ground-wave radar based on an orthogonal magnetic antenna system with multi-time amplitude-frequency information as described in claim 1, characterized in that, Step S2, the time-frequency analysis and processing, includes: performing continuous wavelet transform on the time-domain data that corresponds to and matches the target to obtain the time-frequency distribution, and using synchronous extraction transform to rearrange and sharpen the time-frequency distribution.

3. The target direction finding method for a shipborne ground-wave radar based on an orthogonal magnetic antenna system with multi-time amplitude-frequency information as described in claim 1, characterized in that, In step S2, the frequency and amplitude of the peak point of the time-frequency distribution at each moment are taken as the Doppler estimate and amplitude estimate for that moment, respectively, to form the time series of the Doppler information and the time series of the amplitude information.

4. The target direction finding method for a shipborne ground-wave radar based on an orthogonal magnetic antenna system with multi-time amplitude-frequency information as described in claim 1, characterized in that, In step S2, the number of sampling points per frame is 512.

5. The target direction finding method for a shipborne ground-wave radar based on an orthogonal magnetic antenna system with multi-time amplitude-frequency information as described in claim 1, characterized in that, Before the heading change in step S4, the Doppler information of the target is as follows: Among them, v ship Let λ represent the velocity of the shipborne platform at this moment, θ represent the wavelength, and θ represent the angle between the target and the shipborne platform. target θ represents the velocity of the target at this moment. target The angle between the target's velocity direction and the line connecting the "target-shipborne platform" is given. After the heading changes, the target's Doppler information is as follows: Therefore, the relationship between the target's Doppler frequency shift and the azimuth angle is obtained as follows: 。 6. The target direction finding method for a shipborne ground-wave radar based on an orthogonal magnetic antenna system with multi-time amplitude-frequency information as described in claim 1, characterized in that, The preset angle search interval mentioned in step S4 is reduced to [θ0-10°, θ0+10°] based on the initial estimated value θ0.

7. The target direction finding method for a shipborne ground wave radar based on an orthogonal magnetic antenna system with multi-time amplitude-frequency information as described in claim 1, characterized in that, The smoothing process described in step S4 includes any one or more combinations of moving average filtering, median filtering, exponentially weighted average filtering, or Kalman filtering.

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