A method for estimating the azimuth angle of high-frequency over-the-horizon radar signals based on optimized layout of multiple orthogonal dual magnetic antennas

Abstract

This invention relates to a method for estimating the azimuth angle of high-frequency over-the-horizon radar signals based on an optimized layout of multiple orthogonal dual magnetic antennas. The method includes: constructing a compact optimized layout adapted to a shipborne platform using two centrally co-located and orthogonally placed magnetic antennas as basic units; and proposing an azimuth angle estimation method based on this layout: first, using information from the ship's Automatic Identification System (AIS) to perform amplitude and phase calibration on the received signal; then, normalizing the signal's magnitude; finally, using an ideal steering vector and a multi-signal classification algorithm to estimate the direction of arrival (DOA) of the target signal. This method inherits the target detection performance advantages of magnetic antennas while effectively adapting to the spatial constraints of shipborne platforms. The proposed azimuth angle estimation method effectively eliminates the influence of environmental interference on signal reception, achieving azimuth estimation for weak target signals, and providing key technical support for the practical application of small shipborne high-frequency over-the-horizon radar.

Description

Technical Field

[0001] This invention relates to the field of high-frequency over-the-horizon radar azimuth estimation technology, specifically to a high-frequency over-the-horizon radar signal azimuth estimation method based on the optimized layout of multiple orthogonal dual magnetic antennas. Background Technology

[0002] High-frequency over-the-horizon (HFOTHR) radars play a crucial role in marine environmental awareness and maritime security due to their over-the-horizon, all-weather, and wide-area coverage capabilities for monitoring sea surface currents and maritime targets. Compared to shore-based HFOTHRs, shipborne HFOTHRs can flexibly select observation areas based on platform mobility, covering distant ocean areas that are difficult for traditional shore-based systems to reach, thus becoming an important development direction for HFOTHR technology. However, the spatial limitations of shipborne platforms pose significant challenges to the selection of antenna systems and the achievement of optimal system performance.

[0003] Currently, based on the different receiving antennas, HFOTHR systems can be broadly classified into two categories: large-array radars and compact radars. While large-array radars can achieve high azimuth resolution through multiple large antennas, their bulky size makes them difficult to deploy on space-constrained shipboard platforms. Compact radars, on the other hand, with their small size and simple structure, exhibit unique advantages in scenarios such as mobile observation and temporary deployment. Existing compact HFOTHR systems mainly employ monopole cross-loop antennas and magnetic antennas. The spatially co-located three-element structure of monopole cross-loop antennas is mature in ocean current observation, but its signal-to-noise ratio (SNR) is low, making it difficult to meet the stringent requirements for detecting weak targets. Magnetic antennas exhibit superior anti-interference and high SNR characteristics in target detection; however, while a single magnetic antenna has a certain degree of directivity, in practical applications, multiple magnetic antennas are usually required to work collaboratively in a half-wavelength configuration, using the signal phase difference between multiple antennas to achieve direction finding. This undoubtedly increases the space occupied by the antenna layout.

[0004] As small shipborne platforms increasingly demand miniaturization and deployment flexibility from HFOTHR systems, the development of antenna-co-located HFOTHR systems has become an urgent need. However, currently, only monopole cross-loop antenna systems can achieve this. On the other hand, compact HFOTHR systems using magnetic antennas have demonstrated excellent performance in detecting weak targets at sea, providing important technical references for solving the detection challenges of shipborne platforms. Therefore, developing a receiving antenna layout that inherits the performance advantages of magnetic antennas in target detection while meeting the stringent space requirements of shipborne platforms, and simultaneously constructing an azimuth estimation method adapted to this antenna layout, is crucial for advancing the practical application of small shipborne HFOTHR systems. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] The present invention aims to provide an optimized layout of multiple orthogonal dual magnetic antennas suitable for high-frequency over-the-horizon radar, and to develop a corresponding signal azimuth estimation method based on this layout, so as to achieve the technical objective of meeting the stringent space requirements of shipborne platforms and significantly improving the direction finding accuracy of weak targets at sea.

[0007] (II) Technical Solution

[0008] A method for estimating the azimuth angle of high-frequency over-the-horizon radar signals based on the optimized layout of multiple orthogonal dual magnetic antennas includes two core components: optimized layout design of multiple orthogonal dual magnetic antennas and azimuth angle estimation based on this layout.

[0009] (1) The optimized layout design of multiple orthogonal dual magnetic antennas includes:

[0010] ① Construction of the basic unit of orthogonal dual magnetic antenna: Select two magnetic antennas with identical performance parameters, and place them in a state where the two magnetic antennas are centrally located and orthogonal to each other. The corresponding ideal steering vector is represented as [cos(θ), sin(θ)]. T , where θ represents the incident azimuth angle of the target signal.

[0011] ② Determine the layout suitable for the shipborne platform: Select N sets of orthogonal dual magnetic antennas, stacked vertically with a central co-location, where N is a positive integer, and maintain the angular spacing between each magnetic antenna at π / 2N. The ideal steering vector for the entire antenna layout is:

[0012]

[0013] The above formula contains 2N terms, which correspond to the response characteristics of the target signal by the 2N magnetic antennas.

[0014] (2) The azimuth estimation based on this layout includes:

[0015] ① Amplitude and phase error correction: The known information of the Automatic Identification System (AIS) is used to correct the amplitude and phase error of the received signals of each channel. The specific implementation process includes associating and matching HFOTHR data with AIS data, estimating the error matrix using AIS information and compensating for it.

[0016] ② Modulus normalization: Divide the received signal of each magnetic antenna by the environmental influence factor to eliminate the interference of the shipborne platform environment on the received signal.

[0017] ③ Super-resolution direction finding based on multiple orthogonal dual magnetic antennas: The received signal after modulus normalization is used to estimate the azimuth angle using the multiple signal classification (MUSIC) algorithm, where the steering vector required by the algorithm is calculated according to the ideal steering vector.

[0018] The modulus normalization step is implemented as follows:

[0019] Let D(θ) be the influence coefficient of the shipborne platform environmental factors on the antenna pattern of each magnetic antenna. Then the actual antenna pattern expression of each magnetic antenna is:

[0020]

[0021] When a single far-field signal source is incident on this antenna configuration, the echo signals received by each magnetic antenna satisfy the following model:

[0022]

[0023] In the formula, X(t) = [x1(t), x2(t), ..., x N (t),...,x 2N (t)] T , representing the echo signals received by 2N magnetic antennas; t is the time variable; S(t) represents the far-field signal from a single incident direction; N(t) = [n1(t), n2(t), ..., n N (t),...,n 2N (t)] T , representing the noise signal received by 2N magnetic antennas.

[0024] Furthermore, expanding X(t) yields:

[0025]

[0026] In the actual operating scenarios of high-frequency over-the-horizon radar, the signal-to-noise ratio of the target signal is high. Ignoring the influence of noise on the target signal, the above formula can be further simplified to:

[0027]

[0028] Furthermore, the environmental impact factor is defined as C, and its specific expression is denoted as:

[0029]

[0030] Dividing the received signal from each magnetic antenna by C, we get:

[0031]

[0032] When the received signal is normalized using the above-mentioned modulus normalization operation, the interference of environmental influence D(θ) on the received signal can be eliminated.

[0033] (III) Beneficial Effects

[0034] The advantages of this invention are as follows:

[0035] This invention innovatively proposes a compact receiving antenna layout adapted to shipborne platforms, using orthogonal dual magnetic antennas as the basic unit, and proposes an azimuth estimation method based on this layout. It inherits the performance advantages of magnetic antennas in target detection, meets the stringent space requirements of shipborne platforms, and simultaneously constructs an azimuth estimation method adapted to this antenna layout, effectively eliminating the influence of environmental interference on signal reception, and ultimately achieving azimuth estimation for weak target signals. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the basic process of the present invention.

[0037] Figure 2 This is a schematic diagram of a set of orthogonal magnetic antennas according to the present invention.

[0038] Figure 3 This is an ideal antenna pattern for a set of orthogonal magnetic antennas according to the present invention.

[0039] Figure 4 This is the ideal antenna pattern for the three sets of orthogonal magnetic antennas of the present invention.

[0040] Figure 5 The figure shows the simulation results of RMSE as a function of signal-to-noise ratio when estimating DOA for the three sets of orthogonal magnetic antennas of the present invention. Detailed Implementation

[0041] 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.

[0042] To address the challenge of balancing space requirements with azimuth estimation accuracy in compact HFOTHR systems using magnetic antennas, this invention proposes a high-frequency over-the-horizon radar signal azimuth estimation method based on an optimized layout of multiple orthogonal dual magnetic antennas. The method comprises two core components: "optimized layout design of multiple orthogonal dual magnetic antennas" and "azimuth estimation based on this layout".

[0043] This layout uses "orthogonal dual magnetic antennas" as the basic unit: two magnetic antennas with identical performance parameters (operating frequency band, impedance, amplitude, phase, size, etc.) are selected, such as... Figure 2 As shown, a single basic unit consists of two magnetic antennas, which are arranged in a centrally co-located and orthogonal configuration. The ideal antenna pattern is shown in the figure. Figure 3 As shown, the corresponding ideal steering vector can be expressed as [cos(θ), sin(θ)] T , where θ represents the incident azimuth angle of the target signal.

[0044] Based on this, a layout adapted to the shipborne platform is constructed: N groups of orthogonal dual magnetic antennas are selected and stacked vertically in a centrally co-located manner, where N is a positive integer, and the angular spacing between each magnetic antenna is maintained at π / 2N. The steering vector of the entire antenna layout is:

[0045]

[0046] The above formula contains 2N terms, which correspond to the response characteristics of the target signal by the 2N magnetic antennas.

[0047] The azimuth estimation based on this layout specifically includes the following steps:

[0048] Step 1: Amplitude and phase error correction.

[0049] Although all magnetic antennas maintain consistent design specifications and manufacturing processes, factors such as transmission cable losses and manufacturing errors in electronic components can cause amplitude and phase deviations in the received signals from each antenna. Failure to eliminate these errors will directly lead to inaccurate signal azimuth estimation. Therefore, amplitude and phase error correction is necessary for all received signals acquired by the magnetic antennas.

[0050] This invention uses known information from AIS to correct amplitude and phase errors in the received signals of each channel. The specific implementation process is as follows:

[0051] (1) Associate and match HFOTHR data with AIS data;

[0052] (2) Use AIS information to estimate the error matrix and compensate for it.

[0053] The specific implementation methods of the above steps can be referred to the existing technology, and will not be elaborated here.

[0054] Step 2: Modulus normalization.

[0055] In practical applications, environmental factors on shipboard platforms (such as metal railings and decks) can interfere with the electromagnetic field distribution of magnetic antennas, causing severe distortion of the antenna pattern. The stronger the environmental interference, the greater the distortion. Directly using an ideal pattern to calculate the azimuth will result in significant estimation errors. Therefore, to ensure the accuracy of azimuth calculations, it is necessary to further eliminate the influence of environmental changes on the directivity of each magnetic antenna.

[0056] Since all magnetic antennas are centrally located, the interference from the shipboard platform's environmental factors on the received signals of each magnetic antenna is consistent. Let D(θ) be the influence coefficient of this consistent interference on the antenna pattern. Then, the actual antenna pattern expression for each magnetic antenna is:

[0057]

[0058] When a single far-field signal source is incident on this antenna configuration, the echo signals received by each magnetic antenna satisfy the following model:

[0059]

[0060] In the formula, X(t) = [x1(t), x2(t), ..., x N (t),...,x 2N (t)] T , representing the echo signals received by 2N magnetic antennas; t is the time variable; S(t) represents the far-field signal from a certain incident direction; N(t) = [n1(t), n2(t), ..., n N (t),...,n 2N (t)] T , representing the noise signal received by 2N magnetic antennas.

[0061] Furthermore, expanding X(t), we get:

[0062]

[0063] In actual HFOTHR operating scenarios, the signal-to-noise ratio of the target signal is high, and the influence of noise on the target signal is negligible. Therefore:

[0064]

[0065] Furthermore, the environmental impact factor is defined as C, and its specific expression is denoted as:

[0066]

[0067] Modulus normalization is performed on X(t): The received signal from each magnetic antenna is divided by C to obtain the normalized signal X. ’ (t), the expression is:

[0068]

[0069] The above normalization operation can eliminate the interference of environmental influence D(θ) on the received signal, laying the foundation for subsequent azimuth estimation.

[0070] Step 3: Super-resolution direction finding based on multiple orthogonal dual magnetic antennas.

[0071] The X obtained after step 2 ’ (t) The azimuth angle of the target signal is estimated using the Multiple Signal Classification (MUSIC) algorithm. The steering vector required by the algorithm is calculated according to the ideal steering vector defined above in this invention. The specific process is as follows:

[0072] (1) Calculation of signal covariance matrix

[0073] Based on the normalized received signal matrix X from step 2 ’ (t), calculate the covariance matrix of the signal, the formula is:

[0074]

[0075] In the formula, K is the number of snapshots, [ ] H This indicates the conjugate transpose operation.

[0076] (2) Perform eigenvalue decomposition on the covariance matrix

[0077] Eigenvalue decomposition of the covariance matrix R yields the signal subspace and noise subspace, as shown in the formula:

[0078]

[0079] In the formula, U S For the estimation of the signal subspace, Λ S U is a diagonal matrix of signal eigenvalues. N For the estimation of the noise subspace, Λ N This is a diagonal matrix of noise eigenvalues.

[0080] (3) Spatial spectrum search

[0081] Using the spatial spectrum search principle of the MUSIC algorithm, the spatial spectral power corresponding to each azimuth angle is calculated, and the angle corresponding to the maximum spectral power is taken as the final estimated azimuth angle of the target signal. The formula is as follows:

[0082]

[0083]

[0084] In the formula, P MUSIC (θ) represents the spatial spectral power corresponding to the azimuth angle θ. Let arg be the azimuth angle of the target signal. θ max represents the solution that makes P MUSIC (θ) is the operation corresponding to the maximum value of missing θ.

[0085] Example

[0086] When N=3 is selected, this layout consists of 6 magnetic antennas, and the ideal antenna pattern is as follows. Figure 4 As shown, its ideal steering vector is specifically:

[0087]

[0088] In this embodiment, to verify the effectiveness of the layout and the appropriate azimuth estimation method, the present invention relates to and conducts simulation experiments: randomly generating amplitude and phase errors, pattern errors and mutual coupling errors, and conducting 200 Monte Carlo experiments based on the error model to ensure the statistical reliability of the results. Figure 5 The curve of the root mean square error (RMSE) of azimuth angle estimation as a function of the signal-to-noise ratio at the receiving end is given, which can intuitively reflect the estimation accuracy of this method under different signal-to-noise ratio conditions.

[0089] 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 high-frequency over-the-horizon radar signal azimuth angle estimation method based on a multi-orthogonal double magnetic antenna optimized layout, characterized in that, Comprise: "Multi-orthogonal dual magnetic antenna optimization layout design" and "azimuth angle estimation based on the layout" two parts of the core content, including the following steps: (1) The multi-orthogonal dual magnetic antenna optimization layout design includes: Orthogonal dual magnetic antenna basic unit construction: select two magnetic antennas with consistent performance parameters, place the two pairs of magnetic antennas in a central co-site and orthogonal state, and the corresponding ideal steering vector is represented as [cos(θ), sin(θ)] T , wherein θ represents the incident azimuth angle of the target signal; Adapt to the layout of the ship-borne platform: select N sets of orthogonal dual magnetic antennas to be centrally co-located and stacked, N is a positive integer, keep the angle interval between each magnetic antenna π / 2N, the ideal steering vector of the whole antenna layout is: ， The above formula contains 2N terms, respectively corresponding to the response characteristics of 2N magnetic antennas to the target signal; (2) The azimuth angle estimation based on the layout includes: Amplitude and phase error correction: use the known information of the ship automatic identification system to correct the amplitude and phase error of each channel received signal, the specific implementation process includes associating and matching high-frequency over-the-horizon radar data with ship automatic identification system data, estimating the error matrix using ship automatic identification system information and compensating; Modulus normalization: divide the received signal of each magnetic antenna by the environmental impact factor to eliminate the interference of the ship-borne platform environment on the received signal; Super-resolution direction finding based on multi-orthogonal dual magnetic antenna: the received signal after modulus normalization is used to estimate the azimuth angle by multiple signal classification algorithm, wherein the steering vector required by the algorithm is calculated according to the ideal steering vector of the whole antenna layout.

2. The method of claim 1, wherein, The modulus normalization is implemented as follows: Let the influence coefficient of the ship-borne platform environmental factors on the antenna pattern of each magnetic antenna be D(θ), then the actual antenna pattern expression of each magnetic antenna is: ； When a single far-field signal source is incident on the antenna layout, the echo signals received by each magnetic antenna satisfy the following model: ， where X(t) = [x1(t), x2(t),..., x N (t),..., x 2N (t)] T represents the echo signals received by the 2N magnetic antennas; t is the time variable; S(t) represents the far-field signal from a single incident direction; N(t) = [n1(t), n2(t),..., n N (t),..., n 2N (t)] T represents the noise signals received by the 2N magnetic antennas. Further, expand X(t) to get: ； In the actual working scene of high-frequency over-the-horizon radar, the signal-to-noise ratio of the target signal is high, and the influence of noise signal on the target signal is ignored, so the above formula is further simplified as: ； Further, define the environmental impact factor C, and its specific expression is: ； Divide the received signal of each magnetic antenna by C to get: ， When the received signal is subjected to the modulus normalization operation described above, the interference of the environmental impact D(θ) on the received signal can be eliminated.

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