A rotating target detection method for a range walking whirling electromagnetic wave radar

Abstract

The application relates to a rotating target detection method of a distance walking vortex electromagnetic wave radar, which comprises the following steps: obtaining target echo signals of two OAM modes; respectively adopting an improved Radon-Fourier transform to process the target echo signals of the two OAM modes, so as to obtain power spectrum diagrams of three-dimensional spaces of the target echo signals of the two OAM modes in coupling Doppler frequency f a , a radial velocity rough estimation value and target distance; searching for peak values in the three-dimensional space power spectrum corresponding to the target echo signals of the two OAM modes respectively, so as to obtain a first coupling Doppler frequency estimation value, a second coupling Doppler frequency estimation value, a first radial velocity rough estimation value and a second radial velocity rough estimation value, and then calculating a radial velocity v r and a tangential velocity v t ; judging whether the radial velocity v r is blurred or not, and if blurred, performing a deblurring processing on the radial velocity v r . Compared with one-dimensional velocity estimation of a traditional radar, the application provides additional target velocity features, and better target classification and identification performance can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of new radar signal processing technology, specifically relating to a method for detecting rotating targets using range-moving vortex electromagnetic wave radar. Background Technology

[0002] Unlike traditional plane electromagnetic waves, vortex electromagnetic waves, through modulation of orbital angular momentum (OAM), possess unique characteristics such as ring beams, spiral wavefronts, and orthogonality of OAM modes. Over the past decade, these unique properties have garnered significant attention in fields such as wireless communication, remote sensing, and topographic altimetry.

[0003] In the radar field, vortex electromagnetic waves have applications in synthetic aperture radar (SAR) imaging, SAR interferometry, and infrared imaging, significantly improving imaging capabilities compared to plane waves. However, these applications neglect the target Doppler effect of vortex electromagnetic waves. The target Doppler effect of vortex electromagnetic waves consists of two parts: a linear Doppler shift similar to that of plane waves and a rotational Doppler shift related to the OAM mode. The rotational Doppler shift has been successfully measured in optics. Optical research shows that the rotational Doppler shift differs from the traditional linear Doppler shift. In the radio frequency field, phase measurement methods have been proposed to detect the rotational Doppler shift. In the microwave field, time-frequency analysis methods are used to estimate the velocity and acceleration of rotating targets; however, most existing rotating target detection methods only consider targets with constant distance over the observation time. However, when the Doppler shift is relatively small, a longer observation time is required to obtain sufficient Doppler frequency resolution. In such cases, range travel may occur, requiring further investigation. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a range-moving vortex electromagnetic wave radar rotating target detection method. This method overcomes the range-moving problem in parameter estimation, achieves high-precision two-dimensional velocity estimation, and obtains high-precision radial and tangential velocities of the rotating target.

[0005] The technical solution of this invention is: a method for detecting rotating targets using range-moving vortex electromagnetic wave radar, the method comprising the following steps:

[0006] The radar transmits two OAM mode vortex electromagnetic wave signals in a pulse manner in sequence, and obtains target echo signals in two OAM modes.

[0007] The target echo signals of the two OAM modes were processed by an improved Radon-Fourier transform to obtain the coupled Doppler frequency shift of the target echo signals of the two OAM modes. Rough estimate of radial velocity Target distance Power spectrum in three-dimensional space;

[0008] The first coupled Doppler frequency shift estimate is obtained by searching for the peak values ​​in the three-dimensional power spectrum corresponding to the target echo signals of the two OAM modes respectively. Second Coupled Doppler Frequency Shift Estimate Coarse estimate of the first radial velocity Coarse estimate of the second radial velocity ;

[0009] The first coupled Doppler frequency shift estimate Second Coupled Doppler Frequency Shift Estimate Substituting the Doppler frequency shift estimate into the relationship between radial and tangential velocities, the radial velocity is calculated. and tangential velocity ;

[0010] Determine radial velocity Does blurring occur? If blurring occurs, then for radial velocity... Perform defuzzing to obtain the true value of the radial velocity; otherwise, the radial velocity... This is the true value of the radial velocity.

[0011] Preferably, the target echo signals of the two OAM modes are respectively:

[0012]

[0013]

[0014] in,

[0015]

[0016]

[0017] in, It is a time variable. OAM mode The corresponding target echo signal, OAM mode The corresponding target echo signal, The signal amplitude of the target echo signal. The instantaneous azimuth difference of the target. For tangential velocity, Radial velocity, , It is the wavelength of the target echo signal. For the target pitch angle, The time difference between the received signal and the transmitted signal. The unit impulse function, The pulse repetition time, For the first OAM mode, For the second OAM mode, The radius of the circular array; The number of modes is The first kind of Bessel function; The number of modes is The first kind of Bessel function;

[0018] Preferably, the improved Radon-Fourier transform is:

[0019]

[0020] in, The power of the target echo signal, This is a rough estimate of the radial velocity. For the coupling Doppler frequency shift, For the target distance, The length of the observation time window, For the target echo signal, This is a rough estimate of the radial velocity;

[0021]

[0022] in, It is a filter function based on the improved Radon-Fourier transform.

[0023] Preferably, the radial velocity and tangential velocity are calculated using the following formulas:

[0024]

[0025] in, For the first OAM mode The corresponding Doppler frequency shift of the target echo signal, For the second OAM mode The corresponding Doppler frequency shift of the target echo signal, The wavelength of the target echo signal.

[0026] Preferably, the method for determining whether the radial velocity is ambiguous is as follows:

[0027] If the coarse estimate of the radial velocity is greater than the maximum unambiguous velocity (MUS), then radial velocity ambiguity is considered to have occurred; otherwise, radial velocity ambiguity has not occurred.

[0028] Preferably, the maximum unambiguous speed is:

[0029]

[0030] Wherein, PRF is the pulse repetition frequency of the target echo signal. It is the wavelength of the target echo signal.

[0031] Preferably, the actual radial velocity for:

[0032]

[0033] in, It is a fuzzy number.

[0034] Preferably, the fuzzy number for:

[0035]

[0036] in, This indicates the floor function.

[0037] Another technical solution of the present invention is: an electronic device, comprising:

[0038] Memory: Used to store computer-readable instructions; and

[0039] A processor for executing the computer-readable instructions to perform the above-described methods.

[0040] Another technical solution of the present invention is: a computer storage medium storing a computer program thereon, wherein the computer program is executed by a processor to implement the above-described method.

[0041] The advantages of this invention compared to the prior art are as follows:

[0042] (1) This invention derives a Doppler frequency shift model related to radial velocity and tangential velocity. By analyzing the correspondence between Doppler frequency shift and OAM mode, a pulse signal with dual OAM mode is designed, which lays the foundation for decoupling of Doppler frequency shift of vortex electromagnetic waves and has high practical value.

[0043] (2) This invention proposes an improved Radon-Fourier transform to estimate the coupled Doppler frequency shift while compensating for distance travel.

[0044] (3) The present invention uses a decoupling method to estimate the coupled Doppler frequency in order to obtain estimates of the tangential velocity and the radial velocity respectively.

[0045] (4) The present invention makes a judgment on the ambiguity of radial velocity and designs an ambiguity resolution process. Attached Figure Description

[0046] Figure 1 This is a flowchart of the rotating target detection method of the range-walking vortex electromagnetic wave radar according to an embodiment of the present invention.

[0047] Figure 2 This is a signal diagram of the time-distance plane after matched filtering in an embodiment of the present invention.

[0048] Figure 3(a) shows an embodiment of the present invention. Distance of the improved Radon-Fourier transform result Two-dimensional cross-sectional view;

[0049] Figure 3(b) shows an embodiment of the present invention. Improved Radon-Fourier Transform Results - Two-dimensional cross-sectional view;

[0050] Figure 3(c) shows an embodiment of the present invention. Improved Radon-Fourier Transform Results - Two-dimensional cross-sectional view of the distance plane.

[0051] Figure 4(a) shows an embodiment of the present invention. Distance of the improved Radon-Fourier transform result Two-dimensional cross-sectional view.

[0052] Figure 4(b) shows an embodiment of the present invention. Improved Radon-Fourier Transform Results - Two-dimensional cross-sectional view.

[0053] Figure 4(c) shows an embodiment of the present invention. Improved Radon-Fourier Transform Results - Two-dimensional cross-sectional view of the distance plane.

[0054] Figure 5 This is a Doppler frequency shift estimation diagram for the target of an embodiment of the present invention. Detailed Implementation

[0055] The present invention will now be described in further detail.

[0056] The application scenarios of this invention are as follows:

[0057] First, a Doppler frequency shift model related to radial and tangential velocities is derived. By analyzing the correspondence between Doppler frequency shift and OAM modes, a dual-OAM mode pulse signal is designed. Then, an improved Radon-Fourier transform is proposed to estimate the coupled Doppler frequency shift while compensating for range travel. Furthermore, a decoupling method is used to estimate the coupled Doppler frequency to obtain estimates for tangential and radial velocities separately. Finally, ambiguity in the radial velocity is addressed, and a deambiguation process is designed. Compared to traditional one-dimensional velocity estimation, this provides additional target velocity features, resulting in better target classification and recognition performance.

[0058] The implementation steps of this invention are as follows:

[0059] Step 1: The radar transmits two OAM mode vortex electromagnetic wave signals in pulse mode in sequence to obtain target echo signals in two OAM modes.

[0060] Vortex electromagnetic waves are typically generated by circular arrays. Consider a vortex array... N A circular array with antennas placed at equal intervals, the transmitted signal of the nth array element can be given in the following way.

[0061] (1)

[0062] in, It is a time variable. It is the center frequency of the transmitted signal. It is the azimuth angle of the nth array element. It is the waveform of the transmitted signal. It is the number of OAM modes of the transmitted signal.

[0063] On the receiver, the same phase weighting is applied to the target echo. Then, Echo of the target at an arbitrary point , can be written as

[0064] (2)

[0065] When N is large enough

[0066]

[0067] in

[0068] (3)

[0069] (4)

[0070] in, It is the radius of the circular array. This is a reference time delay. , It's the wavelength. It is the azimuth angle of the nth array element. It is the modal number The first kind of Bessel function, It is the target pitch angle. Let the initial azimuth of the target be... The instantaneous azimuth difference of the target refers to the difference between the target's current azimuth and its initial azimuth. It is radial velocity. It is the tangential velocity. For the target distance, For the target pitch angle, The target azimuth angle;

[0071] Under normal circumstances, , It can be approximated as

[0072] (5)

[0073] After down-conversion and matched filtering, the expression for the received target echo is:

[0074] (6)

[0075] in, The signal amplitude of the target echo signal. It is a unit impulse function.

[0076] In equation (6), both radial and tangential velocities can cause a phase shift related to the Doppler effect. Therefore, in vortex electromagnetic wave radar, the Doppler phase shift... It consists of two parts, represented as

[0077] (7)

[0078] In equation (7), the first term is the conventional Doppler phase caused by radial motion, and the second term is related to the tangential velocity. It can be seen that in the case of vortex electromagnetic waves, these two Doppler effects are coupled. Because the two Doppler phase components are coupled, the true value of velocity information cannot be obtained for moving target detection.

[0079] To achieve decoupled Doppler estimation, this invention designs pulse signals with different OAM modes. According to the Doppler phase shift formula (7) for vortex electromagnetic waves, the corresponding Doppler frequency shift can be obtained as follows:

[0080] (8)

[0081] In the above formula, only the second term is related to the OAM mode. Therefore, by adjusting the OAM mode, the rotational Doppler frequency shift changes, while the radial Doppler frequency shift remains unchanged. In the design of this invention, the radar transmits two OAM modes sequentially in pulse mode. and In the receiver, the echoes of the two modes are separated in the pulse signal. Therefore, two echo signals with different rotational Doppler shifts and the same radial Doppler shift can be obtained. The signals of the two OAM modes can be written as:

[0082] (9)

[0083] (10)

[0084] in,

[0085]

[0086]

[0087] in, It is a time variable. For the first OAM mode The corresponding target echo signal, OAM mode The corresponding target echo signal, The signal amplitude of the target echo signal. Let the initial azimuth of the target be... The instantaneous azimuth difference of the target refers to the difference between the target's current azimuth and its initial azimuth. For tangential velocity, Radial velocity, , It is the wavelength of the target echo signal. The pitch angle of the target. The time difference between the received signal and the transmitted signal. The unit impulse function, The pulse repetition time, This is the first OAM mode. This is the first OAM mode. Let be the radius of the circular array. The number of modes is The first kind of Bessel function; The number of modes is The first kind of Bessel function;

[0088] Step 2 involves applying an improved Radon-Fourier transform to the target echo signals of the two OAM modes to obtain the coupled Doppler frequency shifts of the target echo signals of the two OAM modes. Rough estimate of radial velocity Target distance Power spectrum in three-dimensional space.

[0089] The rotational Doppler frequency shift is relatively small, requiring long observation times to extract this Doppler component. However, it has been found that long observation times introduce distance travel effects. Traditional time-frequency analysis methods are ineffective under distance travel. To overcome this problem, this invention proposes an improved Radon-Fourier transform.

[0090] The traditional Radon-Fourier transform is shown as

[0091] (11)

[0092] in

[0093] (12)

[0094] in, The power of the target echo signal, This is a rough estimate of the radial velocity. For the coupling Doppler frequency shift, For the target distance, The length of the observation time window, For the target echo signal, This is a rough estimate of the radial velocity;

[0095] As shown above, the filtering function In the traditional Radon-Fourier transform, the Doppler frequency shift depends only on the radial velocity. However, when using vortex electromagnetic waves, the Doppler shift is a combination of tangential and radial Doppler effects. To make the filtering function... This invention proposes an improved filtering function to compensate for the coupling Doppler frequency shift effect. , represented as

[0096] (13)

[0097] in It is a filter function based on the improved Radon-Fourier transform.

[0098] Since the tangential velocity is independent of the target distance, the range gate search in the improved Radon-Fourier transform is the same as that in the original Radon-Fourier transform. Therefore, the improved Radon-Fourier transform result for a pulse signal is given by the following formula:

[0099] (14)

[0100] in, This is a rough estimate of the radial velocity. This is the Doppler frequency shift for coupling.

[0101] Step 3 obtains the first coupled Doppler frequency shift estimate by searching for the peak values ​​in the three-dimensional spatial power spectra corresponding to the target echo signals of the two OAM modes respectively. Second Coupled Doppler Frequency Shift Estimate Coarse estimate of the first radial velocity Coarse estimate of the second radial velocity .

[0102] By searching three-dimensional space Two coupled Doppler frequency shift estimation results can be obtained. and Based on equation (8), the relationship between the Doppler frequency shift estimation result and the velocity is as follows:

[0103] (15)

[0104] The radial and tangential velocities can be estimated by solving a system of two linear equations, as follows:

[0105] (16)

[0106] in, For the first OAM mode The corresponding Doppler frequency shift of the target echo signal, For the second OAM mode The corresponding Doppler frequency shift of the target echo signal, The wavelength of the target echo signal.

[0107] Step 4: Estimate the first coupled Doppler frequency shift. Second Coupled Doppler Frequency Shift Estimate Substituting the Doppler frequency shift estimate into the relationship between radial and tangential velocities, the radial velocity is calculated. and tangential velocity .

[0108] To reduce the computational cost of the improved Radon-Fourier Transform, a low pulse repetition frequency (PRF) should be used. However, a lower PRF results in a lower maximum unambiguous velocity (MUS), which can lead to radial velocity ambiguity during decoupling. In signal processing, if the improved Radon-Fourier Transform estimates... If the velocity is greater than the maximum unambiguous velocity MUS, radial velocity ambiguity is considered to have occurred; otherwise, radial velocity ambiguity has not occurred. To resolve the ambiguity issue, the maximum unambiguous velocity MUS and... Calculate the fuzzy number Its formula is:

[0109] (17)

[0110] in, It is the maximum unambiguous speed MUS. This indicates the floor function.

[0111] So, the actual radial velocity We can obtain:

[0112] (18)

[0113] in, It is a fuzzy number.

[0114] The effects of the present invention will be further illustrated below using simulation data.

[0115] Radar parameters are shown in Table 1. The radar transmits two OAM modes sequentially in pulse mode. In the following simulation, a motion parameter of... , and original distance The target is a signal-to-noise ratio (SNR) of 0 dB before the matched filter. Figure 2 The image of the matched-filtered signal on the time-distance plane is shown. From Figure 2 As can be seen, distance movement occurs when the observation time is long. Then, the two pulse signals with different OAM modes are separated. Figures 3(a) to 3(c) show... The improved Radon-Fourier transform results are shown in three two-dimensional profiles. After applying the improved Radon-Fourier transform, the target parameters are clearly estimated. Figures 4(a) to 4(c) illustrate this. The improved Radon-Fourier transform results at that time.

[0116] Table 1. Radar Parameters

[0117]

[0118] Furthermore, to decouple the coupled Doppler frequency shift, the pulse-by-pulse strategy of this invention is employed. Based on the results of Figures 3(a) to 3(c) and Figures 4(a) to 4(c), the Doppler frequency shift estimate of the target can be extracted, such as... Figure 5 As shown. Due to the variation of the OAM mode, the estimation of the Doppler frequency shift is different. Substituting the estimation results into equation (16), the estimated results of the tangential velocity and radial velocity are 315.73 m / s and -0.503 m / s, respectively. According to the parameters in Table 1, the MUS in the improved Radon-Fourier transform process is 1.5 m / s, which is much smaller than the coarse estimate of the radial velocity obtained in Figures 3(a)~3(c) and 4(a)~4(c). This means that velocity ambiguity occurs. Then, the true value obtained through the ambiguity solution process is 99.997 m / s. In addition, the estimation errors of the tangential and radial velocities are 5.24% and 0.003%, respectively.

[0119] In summary, this invention solves the velocity estimation problem in target recognition after imaging. Compared with traditional radar which only has radial one-dimensional velocity estimation capability, vortex electromagnetic wave radar has two-dimensional velocity estimation capability. By fully exploiting the characteristics of this system, the distance travel problem in parameter estimation is overcome, and high-precision two-dimensional velocity estimation is achieved.

[0120] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for detecting rotating targets using a range-traveling vortex electromagnetic wave radar, characterized in that... Includes the following steps: The radar transmits two OAM mode vortex electromagnetic wave signals in a pulse manner in sequence, and obtains target echo signals in two OAM modes. The target echo signals of the two OAM modes were processed by an improved Radon-Fourier transform to obtain the coupled Doppler frequency shift of the target echo signals of the two OAM modes. Rough estimate of radial velocity Target distance Power spectrum in three-dimensional space; The first coupled Doppler frequency shift estimate is obtained by searching for the peak values ​​in the three-dimensional power spectrum corresponding to the target echo signals of the two OAM modes respectively. Second Coupled Doppler Frequency Shift Estimate Coarse estimate of the first radial velocity Coarse estimate of the second radial velocity ; The first coupled Doppler frequency shift estimate Second Coupled Doppler Frequency Shift Estimate Substituting the Doppler frequency shift estimate into the relationship between radial and tangential velocities, the radial velocity is calculated. and tangential velocity ; Determine radial velocity Does blurring occur? If blurring occurs, then for radial velocity... Perform defuzzing to obtain the true value of the radial velocity; otherwise, the radial velocity... This is the true value of the radial velocity; The target echo signals of the two OAM modes are as follows: in, in, It is a time variable. OAM mode The corresponding target echo signal, OAM mode The corresponding target echo signal, The signal amplitude of the target echo signal. This represents the vortex azimuth difference between the array antenna and the target. For tangential velocity, Radial velocity, , It is the wavelength of the target echo signal. For the target pitch angle, The time difference between the received signal and the transmitted signal. The unit impulse function, The pulse repetition time, For the first OAM mode, For the second OAM mode, The radius of the circular array; The number of modes is The first kind of Bessel function; The number of modes is The first kind of Bessel function; The radial velocity and tangential velocity are calculated using the following formulas: in, The wavelength of the target echo signal.

2. The method for detecting rotating targets using a range-traveling vortex electromagnetic wave radar according to claim 1, characterized in that... The improved Radon-Fourier transform is: in, The power of the target echo signal, This is a rough estimate of the radial velocity. For the coupling Doppler frequency shift, For the target distance, The length of the observation time window, For the target echo signal; in, It is a filter function based on the improved Radon-Fourier transform.

3. The method for detecting rotating targets using a range-traveling vortex electromagnetic wave radar according to claim 1, characterized in that... The method for determining whether radial velocity is ambiguous is as follows: If the coarse estimate of the radial velocity is greater than the maximum unambiguous velocity (MUS), then radial velocity ambiguity is considered to have occurred; otherwise, radial velocity ambiguity has not occurred.

4. The method for detecting rotating targets using a range-traveling vortex electromagnetic wave radar according to claim 1, characterized in that... The maximum unambiguous speed is: Wherein, PRF is the pulse repetition frequency of the target echo signal. It is the wavelength of the target echo signal.

5. The method for detecting rotating targets using a range-traveling vortex electromagnetic wave radar according to claim 1, characterized in that... Actual radial velocity for: in, It is a fuzzy number.

6. A method for detecting rotating targets using a range-traveling vortex electromagnetic wave radar according to claim 5, characterized in that... The fuzzy number for: in, This indicates the floor function.

7. An electronic device, characterized in that, include: Memory: Used to store computer-readable instructions; as well as A processor for executing the computer-readable instructions to perform the method as described in any one of claims 1 to 6.

8. A computer storage medium, characterized in that... It stores a computer program, which is executed by a processor to implement the method of any one of claims 1 to 6.

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