A method for identifying the azimuth of the near field of a whirling electromagnetic wave

Abstract

A vortex electromagnetic wave near field azimuth identification method is provided. Four kinds of vortex electromagnetic waves with different modes are set to detect a target, four groups of echo data are obtained, two-by-two interference processing is performed on the four groups of echo data, the phase generated by the target slant range is eliminated, six groups of echo phases after interference are extracted, six groups of theoretical phases are constructed, and a search algorithm is used to obtain a high-precision target azimuth angle which makes the sum of absolute values of errors between the echo phases after interference and the theoretical phases minimum. The present application can complete azimuth identification only by using four modes under the condition of ensuring measurement accuracy, is more efficient, and is more in line with the demand of rapid direction finding of near field detector.

Description

Technical Field

[0001] This invention relates to a highly efficient and accurate near-field orientation identification method for vortex electromagnetic waves based on multimodal baselines. Background Technology

[0002] With the development of modern air defense, the next generation of directional identification not only requires near-field detectors to provide target distance information, but also needs to have the ability to estimate the target's azimuth to achieve accurate target positioning. Traditional radio near-field detectors typically use amplitude and phase methods for angle measurement, both of which have drawbacks such as low accuracy or weak noise resistance. Summary of the Invention

[0003] The purpose of this invention is to provide a vortex electromagnetic wave near-field orientation identification method to meet the high-efficiency and high-precision angle measurement requirements of radio near-field detectors for aerial targets.

[0004] To achieve the above objectives, the present invention provides a method for near-field orientation identification of vortex electromagnetic waves, comprising:

[0005] Step S1: Set up four types of vortex electromagnetic waves with different modes to detect the target and obtain four sets of echo data;

[0006] Step S2: Perform interferometry on each pair of the four sets of echo data to eliminate the phase generated by the target slant range and extract the six sets of echo phases after interferometry.

[0007] Step S3: Construct six sets of theoretical phases and use a search algorithm to obtain a high-precision target azimuth angle that minimizes the sum of the absolute values ​​of the errors between the echo phase after interference and the theoretical phase.

[0008] Step S1 includes:

[0009] Step S1.1: This invention employs a multi-transmitter, single-receiver mode, using a uniform circular antenna array to generate vortex electromagnetic waves. N identical isotropic transmitting antennas are set up, with each element uniformly distributed within a radius of [missing information]. On the circumference of a circle, a single antenna element located at the center receives the target echo. A spherical coordinate system is established with the receiving antenna as the origin, and point p is the target. The distance from the receiving antenna to the target. The pitch angle is [value], and the pitch angle range is [value]. , The target azimuth angle, the azimuth angle range is... ;

[0010] The number of generated orbital angular momentum modes are respectively , , , Four types of vortex electromagnetic waves were used to irradiate the target, among which... The baseline for both modes;

[0011] The direction of the main lobe of the Bessel function is the same as the direction of the main lobe of the vortex wave.

[0012]

[0013] in, For modal number, The array radius is , For wavelength, Represents the first kind of Bessel function, ;

[0014] Get the mode number Given [1, 50], calculate the main lobe pointing direction for each mode. Perform a three-segment linear fit:

[0015]

[0016] Given the target pitch angle In this case, calculate the beam pointing position. Find the corresponding fitted values.

[0017]

[0018] Based on the fitted values And the fitting formula, from which the corresponding number of modes is derived. ;

[0019] Step S1.2: Determine the number of modes Then, three modal baselines were set. , , Azimuth measurements were performed, and four sets of echo data were obtained as follows:

[0020]

[0021] Step S2 includes:

[0022] Step S2.1: Based on the modal number and three modal baselines , , By constructing a compensated phase and compensating for the first term on the right-hand side of the equation for the echo data, we obtain:

[0023]

[0024] in, represents an imaginary number, ;

[0025] Step S2.2: Eliminate the influence of the first exponential term on the right side of the equation of the echo data by echo interferometry with different mode numbers, and extract the phase after interferometry. :

[0026] .

[0027] Step S3 includes:

[0028] Step S3.1: Set the search azimuth vector The search scope is The search interval is 0.1°, and the number of searches is [number missing]. Based on the known number of modes and modal baselines, six sets of theoretical phases are constructed. :

[0029]

[0030] Step S3.2: Construct the theoretical phase With the extracted interference phase Subtracting these yields six sets of phase error vectors:

[0031]

[0032] Step S3.3: Sum the absolute values ​​of the six error vectors, and search for the vector that minimizes the sum of the absolute values ​​of the errors. This is the high-precision azimuth angle we are looking for:

[0033] .

[0034] This invention addresses the high-efficiency and high-precision angle measurement requirements of near-field detectors by proposing a high-efficiency and high-precision near-field azimuth identification method based on a multi-mode baseline electromagnetic vortex. It utilizes only four different orbital angular momentum modes of vortex electromagnetic waves for detection, performs interferometry processing on the echo results to eliminate phase caused by the target slant range, extracts the effective phase containing azimuth information, and uses a search algorithm to obtain the high-precision target azimuth, thus improving the angle measurement accuracy of near-field detectors. This invention employs vortex electromagnetic waves based on a multi-mode baseline, whose wavefront has a special spiral structure and is continuously changing. This characteristic gives it angular diversity and azimuth resolution capabilities. Compared to traditional amplitude and phase methods for angle measurement, this invention better meets the high-precision angle measurement requirements of radio near-field detectors for aerial targets. Compared to other algorithms with more modes, this invention can complete azimuth identification using only four modes while ensuring measurement accuracy, resulting in higher efficiency and better meeting the needs of near-field detectors for rapid direction finding. Attached Figure Description

[0035] Figure 1This is a flowchart of the method of the present invention.

[0036] Figure 2 This is a diagram of the geometric model of a vortex wave near-field detector.

[0037] Figures 3(a) and 3(b) are comparison diagrams of beam directions for different baseline modes. Figure 3(a) shows the beam direction for different baseline modes. A comparison of beam directions with a modal baseline of ±1, Figure 3(b) shows the beam direction with a modal number of... With modal baseline , Comparison diagram of beam direction at different times.

[0038] Figure 4 It is modal The beam pattern when the modal baselines are 1, -28, and -29 (i.e., the number of modes in the four groups are 14, 15, -14, and -15 respectively).

[0039] Figure 5 This is a diagram showing the results of multimodal azimuth angle measurement of a long baseline.

[0040] Figure 6 This is a schematic diagram of the azimuth angle measurement error over 1000 Monte Carlo measurements. Detailed Implementation

[0041] The following is based on Figures 1-6 The preferred embodiments of the present invention will be described in detail below.

[0042] In recent years, vortex electromagnetic wave imaging detection has become a research hotspot for many scholars. Unlike classical plane waves, the signal in the vortex electromagnetic wave detection area exhibits significant spatial fluctuations. Different targets within the beam generate different electromagnetic excitations at the same distance, resulting in echoes containing more target information. Compared to traditional radar imaging detection, it offers better noise and interference resistance. Combining the advantages of vortex electromagnetic waves, developing a high-efficiency and high-precision near-field orientation identification method based on multi-mode baselines can improve the angle measurement capability of near-field detectors.

[0043] like Figure 1 As shown, the present invention provides a method for near-field orientation identification of vortex electromagnetic waves, comprising:

[0044] Step S1: Set up four types of vortex electromagnetic waves with different modes to detect the target and obtain four sets of echo data;

[0045] The specific steps of step S1 are as follows:

[0046] Step S1.1, as follows Figure 2As shown, this invention employs a multi-transmit, single-receive mode, using a uniform circular antenna array to generate vortex electromagnetic waves. It sets up N identical isotropic transmitting antennas, with each element uniformly distributed within a radius of [missing information]. On the circumference of a circle, a single antenna element located at the center receives the target echo. A spherical coordinate system is established with the receiving antenna as the origin, and point p is the target. The distance from the receiving antenna to the target. The pitch angle is [value], and the pitch angle range is [value]. , The target azimuth angle, the azimuth angle range is... .

[0047] The number of generated orbital angular momentum modes are respectively , , , Four types of vortex electromagnetic waves irradiate the target, among which This serves as the baseline for both modes.

[0048] The direction of the main lobe of a vortex electromagnetic wave is related to the array radius, signal frequency, and mode number. The direction of the main lobe can be accurately represented by the Bessel function; that is, the direction of the main lobe of the Bessel function is the direction of the vortex wave's main lobe.

[0049]

[0050] in, For modal number, The array radius is , For wavelength, Represents the first kind of Bessel function, .

[0051] Get the mode number Given [1, 50], calculate the main lobe pointing direction for each mode. To improve accuracy, a three-segment linear fit is performed:

[0052]

[0053] Given the target pitch angle In this case, calculate the beam pointing position. Find the corresponding fitted values.

[0054]

[0055] Based on the fitted values And the fitting formula, from which the corresponding number of modes is derived. .

[0056] Step S1.2: Determine the number of modes After that, three modal baselines need to be determined. , , .

[0057] For different modes to have overlapping beamwidth coverage areas, they must overlap to have the same detection area. As shown in Figures 3(a) and 3(b), the overlap of beamwidth coverage areas for adjacent modes (i.e., baseline 1) is greater than 50%, while the overlap is 100% when modes are opposite. Therefore, when determining the number of modes... Subsequently, five modal baselines can meet the detection requirements, namely: , , As the baseline continues to expand, the beam coverage of the mode and the mode The overlap of beam coverage is small, and targets in the same area may not be detected.

[0058] Near-field detectors typically operate within a pitch angle range of 30° to 60°. A pitch angle of 40° is chosen, along with the array radius... At that time, calculate the corresponding modal number. With a value of 14, the calculated main lobe width is approximately 10°, covering a range of 34.1° to 44.1°. This is achieved when using the minimum modal baseline. (Mode number 15) When measuring the target azimuth, the beam coverage range is 31.4°~40.7°, which is consistent with the mode number of... The overlap of the beamwidth coverage area is approximately 67%, which meets the detection requirements.

[0059] Assume the angle measurement error is Different baselines The angle measurement range is The angle measurement error is When the modal baseline is 1, there is no angular ambiguity, but the angular measurement error is relatively large; when the modal baseline is a long baseline, the angular measurement accuracy is high, but when the absolute value of the azimuth angle is greater than 1, the angular measurement accuracy is relatively high. In some cases, ambiguity in angle measurement leads to increased angle measurement error. Therefore, using long-segment baseline multimode vortex electromagnetic waves for detection can solve the ambiguity problem and improve the accuracy of angle measurement.

[0060] To meet the detection requirements and angle measurement accuracy, this invention selects four of the five feasible modal baselines for high-precision angle measurement. , , , Azimuth angle measurements were performed (i.e., four sets of mode numbers were 14, 15, -14, and -15). Taking a single target as an example, the four sets of echo data were obtained as follows:

[0061]

[0062] in, represents an imaginary number, .

[0063] Step S2: Perform interferometry on each pair of the four sets of echo data to eliminate the phase generated by the target slant range and extract the six sets of echo phases after interferometry.

[0064] The specific steps of step S2 are as follows:

[0065] Step S2.1, number of modes and three modal baselines , , All parameters are known. A compensation phase is constructed to compensate for the first term on the right-hand side of the equation for the echo data, resulting in:

[0066]

[0067] The first item in the results of steps S2.2 and S1.2 is the target slant range phase, which is related to the orbital angular momentum mode number. It is irrelevant; by processing echoes with different mode numbers, the influence of the first exponential term on the right-hand side of the equation for the echo data can be eliminated, and the phase after interferometry can be extracted. :

[0068]

[0069] Step S3: Construct six sets of theoretical phases and use a search algorithm to obtain a high-precision target azimuth angle that minimizes the sum of the absolute values ​​of the errors between the interferometric echo phase and the theoretical phase;

[0070] The specific steps of step S3 are as follows:

[0071] Step S3.1: Set the search azimuth vector The search scope is The search interval is 0.1°, and the number of searches is [number missing]. Based on the known number of modes and modal baselines, six sets of theoretical phases are constructed. :

[0072]

[0073] Step S3.2: Construct the theoretical phase With the extracted interference phase Subtracting these yields six sets of phase error vectors:

[0074]

[0075] Step S3.3: Sum the absolute values ​​of the six error vectors, and search for the vector that minimizes the sum of the absolute values ​​of the errors. This is the high-precision azimuth angle we are looking for:

[0076]

[0077] Figure 3(a) shows the modal number of... A comparison of beam directions with a modal baseline of ±1, Figure 3(b) shows the beam direction with a modal number of... With modal baseline , The beam direction comparison diagram shows that the overlap of the beam width coverage area of ​​adjacent modes (i.e., the baseline is ±1) is greater than 50%, and the overlap of the beam width coverage area is 100% when the modes are opposite, which meets the requirements of vortex wave detection. Figure 4 For the selected mode Beam patterns with modal baselines of 1, -28, and -29 (i.e., four sets of mode numbers of 14, 15, -14, and -15, respectively), and beam directions for mode 14 and mode -14. Figure 1 The beam coverage is consistent, and the coverage areas of modes 15 and -15 overlap with those of modes 14 and -14 by approximately 67%, which meets the detection requirements. Figure 5 To set the interferometric phase measurement error to 10°, the modal baseline... , , When the signal frequency band is selected as the Ku band, the results of long-segment baseline multimodal angle measurement using this invention are shown in the figure. Combining the advantages of large angle measurement range of small-mode baseline and high angle measurement accuracy of large-mode baseline, this method can achieve ambiguity-free high-precision measurement of azimuth within a 360° range, with an angle measurement accuracy of 0.27°. Figure 6 The angle measurement results from 1000 Monte Carlo simulations show that the present invention has high angle measurement accuracy and a small error fluctuation range.

[0078] This invention addresses the high-efficiency and high-precision angle measurement requirements of near-field detectors by proposing a high-efficiency and high-precision near-field azimuth identification method based on a multi-mode baseline electromagnetic vortex. It utilizes only four different orbital angular momentum modes of vortex electromagnetic waves for detection, performs interferometry processing on the echo results to eliminate phase caused by the target slant range, extracts the effective phase containing azimuth information, and uses a search algorithm to obtain the high-precision target azimuth, thus improving the angle measurement accuracy of near-field detectors. This invention employs vortex electromagnetic waves based on a multi-mode baseline, whose wavefront has a special spiral structure and is continuously changing. This characteristic gives it angular diversity and azimuth resolution capabilities. Compared to traditional amplitude and phase methods for angle measurement, this invention better meets the high-precision angle measurement requirements of radio near-field detectors for aerial targets. Compared to other algorithms with more modes, this invention can complete azimuth identification using only four modes while ensuring measurement accuracy, resulting in higher efficiency and better meeting the needs of near-field detectors for rapid direction finding.

[0079] It should be noted that, in the embodiments of the present invention, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the embodiments and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0080] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for near-field orientation identification of vortex electromagnetic waves, characterized in that, Include: Step S1: Set up four types of vortex electromagnetic waves with different modes to detect the target and obtain four sets of echo data; Step S1.1: Adopting a multi-transmit single-receiver mode, a uniform circular antenna array is used to generate vortex electromagnetic waves. N identical isotropic transmitting antennas are set up, with each array element uniformly distributed in a radius of [missing information]. On the circumference of a circle, a single antenna element located at the center receives the target echo. A spherical coordinate system is established with the receiving antenna as the origin, and point p is the target. The distance from the receiving antenna to the target. The pitch angle is [value], and the pitch angle range is [value]. , The target azimuth angle, the azimuth angle range is... ; The number of generated orbital angular momentum modes are respectively , , , The four types of vortex electromagnetic waves irradiate the target; The direction of the main lobe of the Bessel function is the same as the direction of the main lobe of the vortex wave. in, For modal number, The array radius is , For wavelength, Represents the first kind of Bessel function; Get the mode number Given [1, 50], calculate the main lobe pointing direction for each mode. Perform a three-segment linear fit: Given the target pitch angle In this case, calculate the beam pointing position. Find the corresponding fitted values. Based on the fitted values And the fitting formula, from which the corresponding number of modes is derived. ; Step S1.2: Determine the number of modes Then, three modal baselines were set. , , Azimuth measurements were performed, and four sets of echo data were obtained as follows: Step S2: Perform interferometry on each pair of the four sets of echo data to eliminate the phase generated by the target slant range and extract the six sets of echo phases after interferometry. Step S3: Construct six sets of theoretical phases and use a search algorithm to obtain a high-precision target azimuth angle that minimizes the sum of the absolute values ​​of the errors between the echo phase after interference and the theoretical phase.

2. The vortex electromagnetic wave near-field orientation identification method as described in claim 1, characterized in that, Step S2 includes: Step S2.1: Based on the modal number and three modal baselines , , By constructing a compensated phase and compensating for the first term on the right-hand side of the equation for the echo data, we obtain: Step S2.2: Eliminate the influence of the first exponential term on the right side of the equation of the echo data by echo interferometry with different mode numbers, and extract the phase after interferometry. : 。 3. The vortex electromagnetic wave near-field orientation identification method as described in claim 2, characterized in that, Step S3 includes: Step S3.1: Set the search azimuth vector The search scope is The search interval is 0.1°, and the number of searches is [number missing]. Based on the known number of modes and modal baselines, six sets of theoretical phases are constructed. : Step S3.2: Construct the theoretical phase With the extracted interference phase Subtracting these yields six sets of phase error vectors: Step S3.3: Sum the absolute values ​​of the six error vectors, and search for the vector that minimizes the sum of the absolute values ​​of the errors. This is the high-precision azimuth angle we are looking for: 。

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