A method for calibrating amplitude error of direction-finding array based on calibration source rotation

Abstract

To address the amplitude mismatch problem between parallel data acquisition channels in high-precision direction finding, the present invention discloses a method for calibrating the amplitude error of a direction-finding array based on calibration source rotation. This method eliminates the need to obtain the precise direction of the incident signal from an auxiliary calibration source. Instead, it calibrates the amplitude mismatch between array elements by controlling and measuring the rotation angle of the array to be calibrated. This method reduces the accuracy requirements for the calibration source during calibration of traditional array direction-finding systems, enabling its application in complex, large-scale production environments.

Description

Technical Field

[0001] The present invention relates to wireless high-precision direction-finding technology, and specifically discloses a direction-finding array amplitude error calibration method based on calibration source rotation, belonging to the technical field of calculation, estimation or counting. Background Art

[0002] Array signal processing is an important research branch in the field of signal processing. It mainly involves placing multiple sensors at different locations in space to form a sensor array. Traditional array signal processing mainly receives and processes spatial signal fields in parallel, such as Figure 1 As shown, the purpose is to extract the characteristic parameters of the array received signal and suppress interference and noise or information of no interest.

[0003] Since array signal processing relies on the parallel acquisition of multiple channel signals, its accuracy is limited by various errors between channels, such as amplitude mismatch, phase mismatch, array element mutual coupling, etc.

[0004] Considering a direction-finding array consisting of M antennas, according to the existing array error model, we can obtain:

[0005] X(t)=ΓAS(t)+N(t)

[0006] Where X(t) is the M*1-dimensional snapshot vector data, i.e., the collected signals of the M antennas in the direction-finding array; N(t) is the M*1-dimensional array noise vector; S(t) is the N*1-dimensional incident signal amplitude vector, where the incident signal contains N signal sources; A is the M*N-dimensional array flow matrix. Γ is an M*M-dimensional diagonal matrix, and the elements on the diagonal are the amplitude errors between channels. If only the amplitude error is considered, the elements on the diagonal of Γ are all real numbers. If antenna 1 in the antenna array is used as a reference, then

[0007] Γ=diag{1,ρ1,...,ρ M-1}

[0008] Among them, ρ i is a complex number representing the amplitude error of the i-th antenna relative to antenna 1, |ρ i | represents the amplitude error, arg(ρ i ) represents the phase error. |*| represents the operation of taking the absolute value of a complex number, and arg(*) represents the operation of taking the complex angle.

[0009] Traditional single-auxiliary calibration requires placing a calibration source with a known incident signal direction within the direction-finding system calibration environment. In this case, N is 1 in the array error model, and the array flow matrix in A is precisely known. Therefore, the inter-channel amplitude and phase error Γ can be obtained from the measured X(t). The array error model is simplified to:

[0010] X(t)=Γa(θ s )s(t)+N(t)

[0011] Obtaining the covariance matrix of the above data, we can get:

[0012] R xx ′=E(x(t)x * (t))=δ s 2 Γa(θ s )a H (θ s )Γ * +δ n 2 I

[0013] Among them, θ s is the known precise direction of the auxiliary signal source, δ s 2 is the power of the incident signal source, δ n 2 is the noise signal power.

[0014] Perform eigenvalue decomposition on the above covariance matrix to obtain the largest eigenvalue. The corresponding eigenvector is the eigenvector of the signal space. If the array antenna is a uniform linear array (ULA), the eigenvector of the signal space can be expressed as:

[0015]

[0016] Where λ0 is the direction finding signal wavelength, L is the ULA array spacing, and ρ i are the diagonal elements in Γ, that is, the error to be calibrated.

[0017] At this time, when the position of the auxiliary calibration source is known:

[0018]

[0019] Therefore, by comparing e max and a(θ s ) can obtain the array error.

[0020] It can be observed that the accuracy of the traditional auxiliary calibration source method depends on the incident signal direction θ of the auxiliary calibration source. s Therefore, in order to ensure the accuracy of θ s The array error calibration system is often more complicated and is generally difficult to use alone in a large-scale production process with complex environments. Summary of the Invention

[0021] The invention aims to solve the above-mentioned shortcomings of the background technology and provide a method for calibrating the amplitude error of a direction-finding array based on the rotation of a calibration source, without the need to accurately obtain the direction of the incident signal θ of the auxiliary calibration source. s In this case, a method of calibrating the amplitude error of the direction-finding system array element by obtaining the turntable rotation angle was invented, which solved the technical problem of high-precision calibration of the element amplitude error in a simple engineering production environment.

[0022] The present invention achieves the above-mentioned purpose by adopting the following technical solutions.

[0023] By observing the above a(θ s ) and e max It can be seen that when θ s Unknown, but very close to 0, there is an approximation:

[0024]

[0025] According to the above properties, in θ s When the accuracy cannot be guaranteed, we can rotate the array to be calibrated on a small scale near the incident angle of 0, and accurately measure the angle of array rotation with a goniometer to calibrate the array error.

[0026] The specific principles are as follows:

[0027] First, place a calibration source in the calibration environment and the array to be calibrated on a turntable. At this point, the precise position of the incident signal direction cannot be guaranteed, that is, the size of θ1 cannot be determined, but it can be confirmed that θ1 is very close to 0.

[0028] At this time, through the array measurement principle, the signal space characteristic vector at this time can be obtained as:

[0029]

[0030] Then rotate the turntable by a small angle to θ2. At this point, the incident signal is still close to 0. At this point, through the array measurement principle, the signal space characteristic vector at this time can be obtained as:

[0031]

[0032] The angle of rotation is measured by an angle meter, that is: θ2-θ1=Δθ.

[0033] At this point, conjugate multiplication of the two obtained signal space feature vectors can be obtained:

[0034]

[0035] Therefore, when the turntable is rotated before and after, the traditional spatial spectrum estimation algorithm is used to obtain emax,2 and e max,1 , and when Δθ is obtained by high-precision goniometer measurement, the amplitude error of the array can be estimated according to the above formula |ρ i What needs to be ensured is that the directions θ2 and θ1 of the incident signals from the auxiliary source are approximately close to 0 before and after the rotation.

[0036] The present invention adopts the above-mentioned technical solution, which has the following beneficial effects: It does not require obtaining the precise incident signal direction of the auxiliary calibration source. By controlling and measuring the rotation angle of the array to be calibrated, the signal space characteristic vectors before and after the turntable are obtained, and the amplitude mismatch between the array elements is calibrated. This reduces the high-precision requirements for the calibration source direction during calibration of traditional array direction-finding systems. Furthermore, the amplitude mismatch of the array direction-finding system is calibrated by easily and accurately measuring the relative rotation angle. The calibration scheme proposed in this patent can reduce the requirements for array amplitude error calibration systems, making this technology applicable to large-scale production processes in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the linear array antenna parallel receiver direction finding model.

[0038] Figure 2 Schematic diagram of the calibration system before rotation.

[0039] Figure 3 Schematic diagram of the calibration system after rotation.

[0040] Figure 4 This is a flow chart of the method for calibrating the amplitude error of an array element in a direction-finding system based on calibration source rotation proposed in the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0042] The present invention proposes a method for calibrating the amplitude error of a direction finding system array element based on the rotation of a calibration source, such as Figure 4 As shown, it includes the following 6 steps.

[0043] Step 1: Place the array antenna to be calibrated on a turntable, and place an auxiliary calibration source 1 meter away. The auxiliary calibration source is roughly perpendicular to the antenna array. The incident direction angle of the auxiliary calibration source is θ1. θ1 can be unknown and can be close to 0. Before rotating the turntable, calibrate the system as follows: Figure 2 As shown;

[0044] Step 2: Obtain the collected signal X(t) from each antenna and calculate the autocorrelation matrix of X(t), i.e. the covariance matrix of X(t). After decomposing the eigenvalues of the covariance matrix of X(t), the eigenvector e corresponding to the maximum eigenvalue is obtained. max,1 ;

[0045] Step 3: Rotate the turntable on which the array antenna to be calibrated is placed by a small angle until the incident angle of the auxiliary calibration source is θ2. θ2 may be unknown and still be approximately close to 0. After the turntable is rotated, the system is calibrated as follows: Figure 3 As shown;

[0046] Step 4: Use a high-precision goniometer to measure the angular difference Δθ between the incident direction of the auxiliary calibration source before and after the turntable rotates.

[0047] Step 5: Obtain the data collected by the array antenna to be calibrated when the incident direction angle of the auxiliary calibration source is θ2 through direction finding technology, calculate the autocorrelation matrix of the collected signal of the array antenna to be calibrated when the incident direction angle of the auxiliary calibration source is θ2, and obtain the eigenvector e corresponding to the maximum eigenvalue after decomposing the eigenvalue of the autocorrelation matrix. max,2 ;

[0048] Step 6: Calculate the amplitude mismatch between each channel of the array antenna to be calibrated |ρ by formula (1) i |.

[0049] The above embodiments are merely illustrative of the present invention. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, those skilled in the art may make partial changes thereto. All other embodiments that are consistent with the spirit of the invention and are obtained by those skilled in the art without inventive effort are intended to fall within the scope of protection of the present invention.

Claims

1. A method for calibrating the amplitude error of a direction-finding array based on calibration source rotation, characterized in that: The steps include: Step 1: Place the array antenna to be calibrated on a turntable and place an auxiliary calibration source in an area outside the turntable. The auxiliary calibration source is perpendicular to the antenna array. The incident direction angle of the auxiliary calibration source before rotating the turntable is referred to as the first incident direction angle. The first incident direction angle is unknown and close to 0. Step 2, obtaining the acquisition signal of the array antenna to be calibrated when the incident direction angle of the auxiliary calibration source in front of the rotating turntable is the first incident direction angle through the direction finding technology, and calculating the covariance matrix of the acquisition signal of the array antenna to be calibrated when the incident direction angle of the auxiliary calibration source in front of the rotating turntable is the first incident direction angle, performing eigenvalue decomposition on the covariance matrix of the acquisition signal of the array antenna to be calibrated when the incident direction angle of the auxiliary calibration source in front of the rotating turntable is the first incident direction angle, and obtaining the eigenvector corresponding to the maximum eigenvalue of the covariance matrix of the acquisition signal of the array antenna to be calibrated in front of the rotating turntable; Step 3: Rotate the turntable on which the array antenna to be calibrated is placed by a small angle. After the turntable is rotated, the auxiliary calibration source is still perpendicular to the antenna array. The incident direction angle of the auxiliary calibration source after the turntable is rotated is recorded as the second incident direction angle. The second incident direction angle is unknown and close to 0. Step 4, measuring the turntable rotation angle difference, where the turntable rotation angle difference is the difference between the second incident direction angle and the first incident direction angle; Step 5, obtaining the acquisition signal of the array antenna to be calibrated when the incident direction angle of the auxiliary calibration source behind the rotating turntable is the second incident direction angle by using the direction finding technology, calculating the covariance matrix of the acquisition signal of the array antenna to be calibrated when the incident direction angle of the auxiliary calibration source behind the rotating turntable is the second incident direction angle, performing eigenvalue decomposition on the covariance matrix of the acquisition signal of the array antenna to be calibrated when the incident direction angle of the auxiliary calibration source behind the rotating turntable is the second incident direction angle, and obtaining the eigenvector corresponding to the maximum eigenvalue of the covariance matrix of the acquisition signal of the array antenna to be calibrated after the rotating turntable; Step 6: Calculate the amplitude mismatch between the channels of the array antenna to be calibrated based on the eigenvector corresponding to the maximum eigenvalue of the covariance matrix of the signal collected by the array antenna to be calibrated before the turntable is rotated, the eigenvector corresponding to the maximum eigenvalue of the covariance matrix of the signal collected by the array antenna to be calibrated after the turntable is rotated, and the turntable rotation angle difference measured in step 4.

2. The method for calibrating the amplitude error of a direction-finding array based on calibration source rotation according to claim 1, wherein: In step 4, a high-precision goniometer is used to measure the rotation angle difference of the turntable.

3. The method for calibrating the amplitude error of a direction-finding array based on calibration source rotation according to claim 1, wherein: The step 6 adopts Calculate the amplitude mismatch between each channel of the array antenna to be calibrated, where: is the conjugate matrix of the eigenvector corresponding to the maximum eigenvalue of the covariance matrix of the signal collected by the array antenna to be calibrated before the rotating turntable, e max,2 is the eigenvector corresponding to the maximum eigenvalue of the covariance matrix of the signal collected by the array antenna to be calibrated after the turntable is rotated, θ1 is the first incident direction angle, θ2 is the second incident direction angle, Δθ is the turntable rotation angle difference, λ0 is the direction finding signal wavelength, L is the ULA linear array spacing, M is the number of antennas included in the array antenna to be calibrated, ρ2 is the amplitude error of the second antenna relative to the reference antenna, ρ M-1 is the amplitude error of the M-1th antenna relative to the reference antenna.

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