A monopole crossed-loop antenna signal direction finding method combining amplitude ratio and variable step-size MUSIC

Abstract

The application relates to a single-pole cross-ring antenna signal direction finding method combining amplitude comparison and variable step size MUSIC, which mainly comprises the following steps: obtaining an initial estimated angle through an amplitude comparison algorithm; if the angle is located in a cross-angle domain of a ring antenna, the high-precision characteristic of the amplitude comparison algorithm in the angle domain is utilized to directly take the angle as a final result, so that the direction finding performance of the angle domain is improved; if the angle is not located in the cross-angle domain, the initial estimated result is further utilized to reduce the spectral peak search range of a MUSIC algorithm, and a variable step size mode is adopted to search a spatial spectrum function, so that the direction finding resolution of the MUSIC algorithm is improved, and the calculation complexity is reduced. The application utilizes two direction finding algorithms of amplitude comparison and MUSIC, realizes high-precision direction finding in the cross-angle domain of the ring antenna, shows higher resolution success rate, effectively improves direction finding efficiency, and has important application value in the fields of high-frequency radar sea current detection and short-wave communication.

Description

Technical Field

[0001] This invention relates to the field of signal direction finding technology, specifically to a method for signal direction finding using a monopole cross-loop antenna with combined amplitude ratio and variable step size MUSIC. Background Technology

[0002] High-frequency radars are deployed on coastal land and islands to provide dynamic observation of the sea surface and ship surveillance. Early high-frequency radars mostly used uniform antenna arrays to receive echoes, but these arrays were bulky, difficult to maintain, and required large installation sites. In recent years, high-frequency radars have gradually adopted portable antennas, a typical example being the CODAR SeaSonde series radars equipped with monopole cross-loop antennas. A monopole cross-loop antenna consists of a vertically polarized omnidirectional reference antenna and two mutually orthogonal loop antennas. It has advantages such as small size, mobility, ease of installation and maintenance, and wide application scenarios, and is widely used in radar, radio reconnaissance, sonar, and communications. Radar systems using monopole cross-loop antennas have become an important part of my country's ocean current detection system, and the accuracy of its Direction of Arrival (DOA) estimation is crucial for the high-precision inversion of flow fields by portable high-frequency radars.

[0003] The monopole cross-loop antenna is a portable antenna with a common phase center. It estimates the direction of arrival (ROA) based on the amplitudes of the signals received on the monopole and the two loop antennas. The amplitude comparison algorithm utilizes the orthogonal amplitude response characteristics of the two loops to solve for the azimuth angle by comparing the amplitudes of the two loops of the monopole cross-loop antenna. This algorithm is computationally simple and has strong real-time performance. Currently, monopole cross-loop antennas typically use the Multiple Signal Classification (MUSIC) algorithm to estimate the signal's angle of arrival. This algorithm decomposes the covariance matrix of the received signal from the monopole cross-loop antenna to obtain the signal subspace and noise subspace, and uses the orthogonality of the two subspaces to construct a spatial spectrum function to achieve super-resolution direction finding. However, under complex conditions such as low signal-to-noise ratio, its azimuth estimation performance significantly degrades. Furthermore, the traditional MUSIC algorithm uses a fixed step size for spectral peak search, making it difficult to balance direction finding accuracy and computational complexity. While a large step size reduces the computational burden, it cannot guarantee high-precision estimation; conversely, a small step size improves resolution but increases computational complexity. Therefore, current single direction finding algorithms cannot simultaneously achieve both accuracy and computational complexity, resulting in low computational efficiency. There is an urgent need for a signal direction finding method that can integrate the advantages of different direction finding algorithms and balance direction finding accuracy and computational efficiency. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] This invention aims to provide a direction finding method for monopole cross-loop antenna signals that combines amplitude comparison and variable step size MUSIC, achieving accurate estimation and simple calculation of the cross-angle domain of the loop antenna. It combines the high direction finding accuracy of the MUSIC algorithm with the low computational cost of the amplitude comparison algorithm, thus achieving high-precision and high-efficiency DOA estimation.

[0006] (II) Technical Solution

[0007] This invention includes the following steps:

[0008] Step 1: Initial estimation of the signal angle based on the amplitude comparison algorithm.

[0009] The initial estimated angle is obtained by performing an arctangent operation on the amplitude of the two antenna loops using an amplitude comparison algorithm on the obtained monopole cross-loop antenna output signal.

[0010] Step 2: Signal angle determination.

[0011] Using the initial estimated angle obtained in step one, based on the error characteristics of the amplitude comparison algorithm, it is determined whether the initial estimated angle is within the ring antenna cross angle domain. If the initial estimated angle is within the ring antenna cross angle domain, the initial estimated result will be retained as the final direction finding result. If the initial estimated angle is not within the ring antenna cross angle domain, a fine measurement using the variable step size MUSIC algorithm is required.

[0012] Step 3: Detailed angle measurement using the variable step size MUSIC algorithm.

[0013] Using the initial estimated angle obtained in step one as the center and the random error caused by noise in the amplitude comparison algorithm as the radius, the initial spectral peak search interval of the MUSIC algorithm is constructed.

[0014] Within the initial peak search interval, peak search is performed based on the MUSIC spatial spectral function with a step size of 1°, and the slope value corresponding to each angle within the initial peak search interval is calculated using the slope formula.

[0015] Find the angle at which the slope value first falls below 0. Since the spectral peak is to the left of the angle at which the slope is less than zero, take two points forward as the starting point of the variable step size search interval. Starting from the initial angle, introduce a variable step size function and perform a variable step size iterative search until the slope value falls below 0 again. The angle at which the slope is less than 0 is the final DOA estimation result.

[0016] (III) Beneficial Effects

[0017] The advantages of this invention are as follows:

[0018] This invention combines amplitude comparison and variable step size MUSIC algorithms, retains the direction finding results of the amplitude comparison algorithm in the cross-angle domain of the ring antenna, improves the direction finding performance in this domain, narrows the search range of the MUSIC algorithm, and introduces a variable step size strategy to search the spatial spectrum function, avoiding exhaustive search in the entire angle domain, thereby improving the direction finding resolution of the MUSIC algorithm while reducing computational complexity. Attached Figure Description

[0019] Figure 1 The present invention provides a flow chart for the direction finding method using the combined amplitude comparison and MUSIC algorithm.

[0020] Figure 2 The CLM antenna pattern provided for this invention.

[0021] Figure 3 An angular characteristic diagram of the direction-finding error of the amplitude comparison algorithm provided by this invention.

[0022] Figure 4 The diagram shows the direction finding results of three algorithms using measured data, as provided by this invention. Detailed Implementation

[0023] 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.

[0024] Step 1: Initial estimation of the signal angle based on the amplitude comparison algorithm.

[0025] The initial estimated angle is obtained by performing an arctangent operation on the amplitude of the two antenna loops using an amplitude comparison algorithm on the obtained monopole cross-loop antenna output signal.

[0026] Specifically, the flowchart of the monopole cross-loop antenna signal direction finding method based on the combined amplitude comparison and variable step size MUSIC algorithm is as follows: Figure 1 As shown, the monopole cross-loop antenna consists of three elements with common phase centers, including two orthogonal loop antennas and one monopole antenna. The radiation pattern of the monopole cross-loop antenna is shown in the figure. Figure 2 As shown, the monopole antenna has equal gain for signals from any azimuth angle, and the signal strength received by the two loop antennas in the horizontal direction is sinusoidally or cosinely related to the azimuth angle. The output signal of the monopole cross-loop antenna is:

[0027] ,

[0028] in, The true azimuth angle of the incident signal. This is the steering vector for the monopole cross-loop antenna; For the incident signal, , The output signals of ring A, ring B, and monopole C are... Additive white Gaussian noise for each channel;

[0029] Based on the orthogonal amplitude response characteristics of the monopole cross-loop antenna, the initial estimated angle is obtained by calculating the output signal of the monopole cross-loop antenna using the arctangent function through the amplitude comparison algorithm. :

[0030] .

[0031] Step 2: Signal angle determination.

[0032] The cross-angle domain of the ring antenna is determined based on the direction-finding error characteristics of the amplitude comparison algorithm.

[0033] Specifically, because the amplitude comparison algorithm, when using the arctangent function, is less affected by noise in the cross-angle domain of the ring antenna, the difference in the amplitude response of the two rings is small, and the error is robust to noise. However, in the non-cross-angle domain, the difference in the amplitude response of the two rings is significant, and noise easily leads to deviations in the arctangent calculation, causing the error to increase sharply. The characteristics of the direction-finding error of the amplitude comparison algorithm as a function of angle are as follows: Figure 3 As shown, the direction finding error of the amplitude comparison algorithm exhibits symmetry and periodicity about 45°. The cross angles of the ring antenna are 45°, 135°, 225°, and 315°. The threshold range can be adjusted according to the direction finding accuracy.

[0034] Using the initial estimated angle obtained in step one, determine the initial estimated angle. Is it located in the cross-angle domain of the ring antenna?

[0035] Specifically, if the initial estimated angle If it is located within the cross-angle domain of the ring antenna, then it will be retained. As the final direction finding result, if If the angle is not within the cross-angle domain of the ring antenna, proceed to step three to perform detailed angle measurement using the variable step size MUSIC algorithm.

[0036] Step 3: Detailed angle measurement using the variable step size MUSIC algorithm.

[0037] Output signal of monopole cross-loop antenna The covariance matrix is ​​constructed using the following formula:

[0038] ,

[0039] in, These represent the mathematical expectation and the conjugate transpose operation, respectively. This is the steering vector for the monopole cross-loop antenna. The signal covariance matrix, The noise power of the output signal. It is an identity matrix.

[0040] The output covariance matrix is ​​decomposed into eigenvalues ​​to obtain the corresponding signal subspace and noise subspace:

[0041] ,

[0042] in, These are the diagonal matrices corresponding to the eigenvalues ​​of the signal subspace and the noise subspace, respectively. These are the signal subspace and the noise subspace, respectively.

[0043] Based on the orthogonality of the two subspaces, a spatial spectral function is constructed:

[0044] ,

[0045] DOA estimation is achieved by searching for spectral peaks using the MUSIC spectral operator, which iterates through the entire angular range.

[0046] Using the initial estimated angle obtained in step one Centered on the random direction-finding error of the amplitude comparison algorithm Using the radius, determine the initial spectral peak search interval for the MUSIC algorithm:

[0047] ,

[0048] in The calculation formula is:

[0049] ,

[0050] in, The half-power beamwidth of the monopole cross-loop antenna is 65.5°, and SNR is the signal-to-noise ratio of the output signal.

[0051] In the initial peak search interval The initial spectral peak search of the MUSIC algorithm is performed with a large step size of 1°, and the slope formula is used:

[0052] ,

[0053] Calculate the slope value at each point within the initial spectral peak search interval, where, The peak value of the angle spectrum at the (i+1)th point. The angular spectrum peak value is the i-th point.

[0054] Determine the starting point for the variable step size peak search and perform a variable step size iterative search.

[0055] Specifically, find the angle at which the slope value first becomes less than zero within the initial spectral peak search interval. Since the spectral peak is to the left of the angle corresponding to the slope being less than zero, take two points forward to obtain the starting value of the variable step size search interval. ,by To use the initial value, introduce a variable step size function:

[0056] ,

[0057] according to The variable step size iterative search is performed until the slope value is less than zero again, and the angle corresponding to the slope being less than zero is taken as the final DOA estimation result.

[0058] The direction finding results are measured using root mean square error and computational complexity.

[0059] Specifically, the direction-finding accuracy is calculated using the root mean square error (RMSE) formula:

[0060] ,

[0061] Where W is the number of experiments. Let w be the estimated DOA value for the w-th experiment. This represents the actual angle of incidence.

[0062] Specifically, the method presented in this paper utilizes a monopole cross-loop antenna and a single-frequency signal source for experiments. Both are deployed in an open square to create a relatively ideal experimental environment. The transmitter is located in the cross-angle domain of the loop antenna, while the receiver uses the monopole cross-loop antenna to acquire IQ data. Gaussian white noise with different signal-to-noise ratios is added to the acquired data, and the processed signals are then subjected to direction finding using three different algorithms. Figure 4 The results show the root mean square error of DOA estimation for three algorithms under different signal-to-noise ratios. The computation time of the proposed method is reduced by more than three times compared to the MUSIC algorithm. The results show that the proposed method can adaptively select the method to achieve high-efficiency direction finding and meet the direction finding requirements of CLM antenna signals.

Claims

1. A method for direction finding of a monopole cross-loop antenna signal by combining amplitude tapering and variable step size MUSIC, characterized in that, The method comprises the following steps: (1) based on the amplitude comparison algorithm signal angle initial estimation, the output signal of the acquired monopole cross loop antenna is subjected to arctangent operation by using the amplitude comparison algorithm to obtain an initial estimated angle; (2) signal angle discrimination, based on the error characteristics of the amplitude comparison algorithm, it is judged whether the initial estimated angle obtained in step (1) is in the cross angle domain of the loop antenna, if the initial estimated angle is in the cross angle domain of the loop antenna, the initial estimation result is retained as the final direction finding result, if the initial estimated angle is not in the cross angle domain of the loop antenna, variable step MUSIC algorithm fine measurement is needed; (3) variable step MUSIC algorithm angle fine measurement, the initial estimated angle obtained in step (1) is taken as the center, and the random error caused by the amplitude comparison algorithm is taken as the radius, and an initial spectral peak search interval of the MUSIC algorithm is constructed; in the initial spectral peak search interval, a spectral peak is searched based on the MUSIC spatial spectrum function with a step of 1°, and the slope value corresponding to each angle in the initial spectral peak search interval is calculated by using the slope formula; the angle corresponding to the first time when the slope value is less than 0 is found, since the spectral peak value is on the left side of the angle corresponding to the slope less than 0, two points are taken as the starting values of the variable step search interval, and the variable step function is introduced from the starting angle as the starting point, and the variable step iterative search is performed until the slope value is less than 0 again, and the angle corresponding to the slope less than 0 is the final DOA estimation result.

2. The method according to claim 1, wherein, The initial estimation of the signal angle based on the amplitude comparison algorithm comprises: (1) the output signal of the monopole cross loop antenna is: ， wherein, is the true azimuth angle of the incident signal, is the monopole crossed loop antenna steering vector; is the incident signal, , is the output signal of loop A, loop B, monopole C, is the additive white Gaussian noise of each channel; (2) The initial estimated angle is obtained by using the amplitude comparison algorithm The specific formula is as follows: 。 3. The method according to claim 1, wherein, The signal angle discrimination comprises: (1) the cross angle of the loop antenna is 45°, 135°, 225° and 315°, and the domain value range can be adjusted according to the direction finding accuracy, when the amplitude comparison algorithm is operated by using the arctangent function, the difference between the amplitude responses of the double loop is small in the cross angle domain of the loop antenna, the error is robust to noise, in the non-cross angle domain, the difference between the amplitude responses of the double loop is significant, the noise easily leads to the deviation of the arctangent operation, and the error sharply increases; (2) If the initial estimated angle is in the loop antenna crossing angle domain, then the initial estimated angle will be retained as the final direction finding result, if is not in the loop antenna crossing angle domain, then step (3) is entered to perform variable step size MUSIC algorithm fine measurement.

4. The method according to claim 1, wherein, The variable step MUSIC algorithm angle fine measurement comprises: (1) For the monopole cross-loop antenna output signal The covariance matrix is constructed, and the specific formula is as follows: ， wherein denote the mathematical expectation and the conjugate transpose operation, respectively, is the monopole cross-loop antenna steering vector, is the signal covariance matrix, is the noise power of the output signal, is the identity matrix; The output covariance matrix is subjected to eigenvalue decomposition to obtain corresponding signal subspaces and noise subspaces: ， wherein are diagonal matrices corresponding to the eigenvalues of the signal and noise subspaces, respectively, are the signal and noise subspaces, respectively. Based on the orthogonal characteristics of the two subspaces, a spatial spectrum function is constructed: ， The DOA estimation is realized by searching the spectral peak by using the MUSIC spectral operator through traversing the entire angle range; (2) the initial spectral peak search range of the MUSIC algorithm is: ， wherein is the random direction finding error of the amplitude comparison algorithm, in particular: ， wherein, is the half-power beamwidth of the monopole cross-loop antenna, and SNR is the signal-to-noise ratio of the output signal. (3) The initial spectrum peak search of the MUSIC algorithm, in the initial spectrum peak search interval is searched with a large step of 1°, and the slope formula is used: ， calculating the slope value of each point in the initial spectrum peak search interval, wherein, is the angle spectrum peak value of the first point, is the angle spectrum peak value of the first point; (4) Detailed analysis of the variable step size MUSIC algorithm: Find the angle at which the slope first becomes less than zero within the initial spectral peak search interval. Since the spectral peak is to the left of the angle at which the slope becomes less than zero, take the values ​​of the two points forward to obtain the starting value of the variable step size search interval. ,by Starting with this, we introduce a variable step size function: ， The variable step size iterative search is performed in a manner according to The variable step size iterative search is performed in a manner according to The variable step size iterative search is performed in a manner according to

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