A microwave correlation forward-looking imaging method based on random frequency modulation

Abstract

The application discloses a microwave correlation forward-looking imaging method based on random frequency modulation, which comprises the following steps: S1, arranging multiple frequency hopping radar antennas in a specific distribution to form a frequency hopping radar array, and setting a target imaging area; S2, constructing a space-time random radiation field by independently transmitting random frequency hopping signals and receiving antenna random sampling through each frequency hopping radar antenna, and sampling echoes at random time intervals after the target is sighted; S3, judging the randomness of the space-time random radiation field, and processing the space-time random radiation field by using a least square method if the randomness of the space-time random radiation field is insufficient; and S4, performing compression correlation processing on the echoes obtained by the sight and the space-time random radiation field, and realizing target imaging. The application has good azimuth resolution and anti-interference performance, is simple to realize, and has strong engineering application potential.

Description

Technical Field

[0001] This invention relates to the field of radar signal processing technology, and more specifically, to a microwave-correlated forward-looking imaging method based on random frequency modulation. Background Technology

[0002] The radar field is becoming increasingly mature, with synthetic aperture radar and Doppler sharpening technology being the most widely used. However, conventional radar imaging methods generally suffer from imaging blind spots, specifically forward-looking imaging. Forward-looking imaging is inextricably linked to aerial reconnaissance and mapping, making it a critical issue that must be addressed. The difference between forward-looking imaging and conventional radar imaging lies in the fact that the detection area in forward-looking imaging is directly in front of the radar platform's direction of movement. Conventional radars struggle to obtain usable Doppler information from targets in this area, thus hindering the achievement of good azimuth resolution. Therefore, the key to forward-looking imaging lies in improving its azimuth / elevation resolution without relying on Doppler information. Currently, domestic research in the field of forward-looking radar is flourishing, encompassing multiple imaging directions. Among these, a novel radar imaging method that does not rely on Doppler information—microwave correlation imaging—possesses significant potential for forward-looking imaging.

[0003] Microwave correlation imaging originates from classical correlation imaging in optics. Optical correlation imaging utilizes the principle of quantum correlation to image the target by correlating two spatially correlated light beams; it is also known as "ghost imaging." Microwave correlation imaging borrows this principle, extending the idea of ​​optical correlation to the microwave field, thus forming microwave correlation imaging technology.

[0004] However, domestic research in the field of microwave correlated forward-looking imaging still needs further development. Li Chunli, Shi Jiakang, and others from Xi'an University of Electronic Science and Technology have studied GPU-based hardware implementation of microwave correlated forward-looking imaging, while Ruan Feng, Mu Jia, and others mainly study random phase modulation microwave correlated forward-looking imaging based on phased array radar. Most domestic research on microwave correlated forward-looking imaging focuses on random phase modulation-based methods, neglecting the inherent phase modulation limitations of phased array radar, thus requiring further improvement in the practicality of random phase modulation-based microwave correlated forward-looking imaging. To address these issues, it is indeed necessary to propose a microwave correlated forward-looking imaging method based on random frequency modulation. Summary of the Invention

[0005] The purpose of this invention is to provide a microwave-correlated forward-looking imaging method based on random frequency modulation to overcome the shortcomings of the existing technology.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A microwave-correlated forward-looking imaging method based on stochastic frequency modulation includes the following steps:

[0008] S1. Arrange multiple frequency-hopping radar antennas in a specific distribution to form a frequency-hopping radar array, and set the target imaging area;

[0009] S2. Construct a spatiotemporal random radiation field by independently transmitting random frequency-hopping signals through each frequency-hopping radar antenna and randomly sampling the receiving antenna. After staring at the target, sample the echo at random moments between pulses.

[0010] S3. Determine the randomness of the spatiotemporal random radiation field. If the randomness of the spatiotemporal random radiation field is insufficient, use the least squares method to process it and obtain an approximate solution.

[0011] S4. Compress and correlate the echo obtained by staring in step S2 with the spatiotemporal random radiation field in step S2 or step S3 to achieve target imaging.

[0012] Further, step S1 specifically involves: arranging the frequency hopping radars into a row of antennas at equal intervals along the direction of the aircraft wings to form a frequency hopping radar array, and setting the target imaging area as a diamond-shaped area.

[0013] Further, step S2 specifically includes:

[0014] S20. Let the location of the target scattering point be... And the signal frequency of the i-th transmitting antenna is f i (t) and its antenna position vector is There is an array of M transmitting antennas, where t is the sampling time, j is an imaginary number, c is the speed of light, and E0 is the field strength amplitude. Then, the incident field strength E from the i-th transmitting antenna to the imaging target region... si for:

[0015]

[0016] The incident field strength of the entire antenna array on the imaging region is obtained as follows:

[0017]

[0018] The random radiation field of the target region is obtained as follows:

[0019]

[0020] S21. During microwave-correlated forward-looking imaging, the target scattering characteristic is σ. After the random radiation field illuminates the target imaging area, an echo is generated and received by the frequency-hopping radar array, resulting in the target echo E. r for:

[0021]

[0022] S22. The target scattering characteristics can be obtained through inversion as follows:

[0023]

[0024] To ensure the randomness of the spatiotemporal random radiation field in the time dimension, sampling time t is randomly selected between pulses. q ,q=1,…,Q;

[0025] S23. Sample at random times within each pulse to reduce the correlation of the radiation field in the time dimension, and transform it into the following matrix, where e is noise:

[0026]

[0027] Furthermore, step S3 specifically includes:

[0028] Ignoring noise for now, the transformed matrix S23 is simplified to obtain:

[0029] E r =E s σ is estimated using the least squares method, and both sides of the equation are multiplied by E. s H ,get:

[0030] E s H E r =E s H E s σ

[0031] When E s When the column is full, then E s H E s Since it is a non-singular matrix, the least squares method can directly calculate a unique solution:

[0032]

[0033] When E s When the number of columns is less than 10, If it cannot be solved directly, then the principal component decomposition method is used to solve E. s To refactor, first convert E s Singular value decomposition yields: E s =UDV H Where D is a Q×N Vickers diagonal matrix, and U and V are Q×Q and N×N unitary matrices respectively, truncating D and U into N×N square matrices D′ and U′, we can reconstruct the following:

[0034] Therefore, an approximate solution is obtained: In this function, inv() inverts the matrix, processes the spatiotemporal random radiation array using the least squares estimation method, and then performs compression correlation to obtain a unique or approximate solution for the target scattering characteristic distribution, thus completing the imaging of the target.

[0035] Compared with existing technologies, the advantages of this invention are as follows: This invention provides a microwave correlation forward-looking imaging method based on random frequency modulation. First, multiple frequency-hopping radar antennas are used to form a radar array with a specific arrangement. Each antenna generates a random frequency-hopping signal to synthesize a pulse. Multiple pulses are used to stare at the target area. Then, the random time of each pulse is sampled to form a spatiotemporal random radiation field. The spatiotemporal radiation field with insufficient randomness is subjected to least squares estimation processing. After compression correlation operation on the echo and the spatiotemporal random radiation field, the target scattering characteristic network is finally obtained, realizing forward-looking area imaging. It has good azimuth resolution and anti-interference ability, and is simple to implement, with strong engineering application potential. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart of the microwave-correlated forward-looking imaging method based on random frequency modulation of the present invention.

[0038] Figure 2 This is a schematic diagram of the imaging geometry for the application scenario of this invention.

[0039] Figure 3 This invention relates to a single-pulse random frequency-modulated radiation field.

[0040] Figure 4 This is the spatiotemporal random radiation field of the present invention.

[0041] Figure 5 This is the result of random frequency modulated microwave correlation imaging according to the present invention.

[0042] Figure 6 A comparison of two imaging methods after introducing interference into this invention. Detailed Implementation

[0043] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0044] See Figure 1 and Figure 2 As shown, this embodiment discloses a microwave correlation forward-looking imaging method based on random frequency modulation, including the following steps:

[0045] Step S1: Arrange multiple frequency-hopping radar antennas in a specific distribution to form a frequency-hopping radar array, and set the target imaging area.

[0046] Specifically, such as Figure 2 A frequency-hopping radar array is formed by arranging antennas at equal intervals along the direction of the aircraft's wings. This constitutes a multi-transmitter, single-receiver configuration, which can effectively suppress left-right ambiguity. It is also simple in structure and highly practical. At the same time, the target imaging area is changed from a typical square area to a rhomboid area. This can effectively reduce the spatial correlation of the random radiation field generated by the radar array facing the aircraft's wings in each scattering unit, thereby improving the imaging effect.

[0047] Step S2: Construct a spatiotemporal random radiation field by independently transmitting random frequency-hopping signals through each frequency-hopping radar antenna and randomly sampling through the receiving antenna. After staring at the target, sample the echo at random moments between pulses.

[0048] Specifically, to further improve randomness, the specific arrangement of the transmitting antennas is considered during the simulation process. Step S2 includes:

[0049] Step S20: Let the position of the target scattering point be... And the signal frequency of the i-th transmitting antenna is f i (t) and its antenna position vector is There is an array of M transmitting antennas, where t is the sampling time, j is an imaginary number, c is the speed of light, and E0 is the field strength amplitude. Then, the incident field strength E from the i-th transmitting antenna to the imaging target region... si for:

[0050]

[0051] The incident field strength of the entire antenna array on the imaging region is obtained as follows:

[0052]

[0053] The random radiation field of the target region is obtained as follows:

[0054]

[0055] Step S21: During microwave-correlated forward-looking imaging, the target scattering characteristic is σ. After the random radiation field illuminates the target imaging area, an echo is generated and received by the frequency-hopping radar array, resulting in the target echo E. r for:

[0056]

[0057] Step S22: The target scattering characteristics can be obtained through inversion as follows:

[0058]

[0059] To ensure the randomness of the spatiotemporal random radiation field in the time dimension, sampling time t is randomly selected between pulses. q ,q=1,…,Q;

[0060] Step S23: Sample at random times within each pulse to reduce the correlation of the radiation field in the time dimension, and transform it into the following matrix, where e is noise:

[0061]

[0062] Step S3: Determine the randomness of the spatial random radiation field. If the randomness of the spatiotemporal random radiation field is insufficient, use the least squares method to process it and obtain an approximate solution.

[0063] Ignoring noise for now, the transformed matrix formula (6) is simplified to:

[0064] E r =E s σ+e (7)

[0065] When solving for the target scattering characteristic distribution, the influence of noise is temporarily ignored. Therefore, the only case where equation (7) has a solution is rank(E). s ) = rank(E s E r In other words, if we want the matrix to have a solution, first E s The number of rows must be no less than the number of columns, meaning the number of equations in a system of linear equations must be no less than the number of unknowns. Secondly, E... s The row rank(E) must be satisfied. s ) equals the column number, otherwise even if it meets the rank(E) condition, it will not be true. s ) = rank(E s E r This approach yields only infinite solutions, which are meaningless for imaging. However, in actual imaging, the above conditions are often not fully met. Therefore, in such cases, least squares estimation can be used to solve the problem.

[0066] Multiply both sides of the above formula by E. s H (This is a common technique in the least squares method), resulting in:

[0067] E s H E r =E sH E s σ (8)

[0068] When E s When the column is full, then E s H E s Since it is a non-singular matrix, the least squares method can directly calculate a unique solution:

[0069]

[0070] When E s When the number of columns is less than 10, If it cannot be solved directly, then the principal component decomposition method is used to solve E. s To refactor, first convert E s Singular value decomposition yields:

[0071] E s =UDV H (10)

[0072] Where D is a Q×N Vickers diagonal matrix, and D and U are truncated, with U and V being Q×Q and N×N unitary matrices respectively, D and U are truncated into N×N square matrices D′ and U′, and reconstructed to obtain:

[0073]

[0074] Therefore, an approximate solution is obtained:

[0075]

[0076] In this function, inv() inverts the matrix, processes the spatiotemporal random radiation array using the least squares estimation method, and then performs compression correlation to obtain a unique or approximate solution for the target scattering characteristic distribution, thus completing the imaging of the target.

[0077] S4. Compress and correlate the echo obtained by staring in step S2 with the spatiotemporal random radiation field in step S2 or step S3 to achieve target imaging.

[0078] To verify the effectiveness of this invention, a preliminary verification of the proposed method is conducted below using simulation. It should be understood that the simulation described herein is for illustrative purposes only and is not intended to limit the invention. Assume the frequency-hopping signal bandwidth B = 1 GHz and the pulse duration T... p =2µs, carrier frequency f0 = 10GHz, sampling rate f s =5MHz, 24 antennas, 500m planar distance, and an imaging area of ​​40×40 meters. The simulation results and analysis are as follows.

[0079] Figure 3It is a single-pulse random amplitude modulation radiation field, mainly representing the state of the radiation field of a single pulse on an imaging plane of 40×40 meters. Figure 4 This is the total spatiotemporal radiation field. The rows represent the number of pulses, and each row represents the radiation field intensity generated by each pulse in the entire imaging area. The columns represent each imaging scattering unit, and each column represents the radiation field intensity of each scattering unit in multiple pulses. It can be seen that the radiation field as a whole has a snowflake pattern, which represents extremely high randomness. Figure 5 The imaging result is a microwave-correlated forward-looking imaging with random frequency modulation. The result shows that the effect is relatively clear and basically meets the expectations.

[0080] To further demonstrate the robustness of this method, it is compared with random phase-modulated microwave correlated forward-looking imaging under the same conditions, and the comparison is made under two different interference conditions: noise coherent interference and frequency fretting interference. Figure 6 Figure (a) shows the construction of point, line, and rectangular detection targets; Figure (b) shows the imaging effect after introducing white noise; Figures (c) and (e) show random phase modulation imaging after introducing two types of interference respectively; Figures (d) and (f) show random frequency modulation imaging after introducing two types of interference respectively. As can be seen from the figures, the false alarm rate of random phase modulation-based imaging is higher than that of random frequency modulation-based imaging. Under the same noise power, microwave forward-looking imaging based on random frequency modulation has higher anti-interference capability than microwave forward-looking imaging based on random phase modulation.

[0081] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, the patent owner may make various modifications or alterations within the scope of the appended claims, as long as they do not exceed the protection scope described in the claims of the present invention, they shall be within the protection scope of the present invention.

Claims

1. A microwave correlation forward-looking imaging method based on random frequency modulation, characterized in that, Includes the following steps: S1. Arrange multiple frequency-hopping radar antennas in a specific distribution to form a frequency-hopping radar array, and set the target imaging area; S2. Construct a spatiotemporal random radiation field by independently transmitting random frequency-hopping signals through each frequency-hopping radar antenna and randomly sampling the receiving antenna. After staring at the target, sample the echo at random moments between pulses. S3. Determine the randomness of the spatiotemporal random radiation field. If the randomness of the spatiotemporal random radiation field is insufficient, use the least squares method to process it and obtain an approximate solution. S4. Compress and correlate the echo obtained by staring in step S2 with the spatiotemporal random radiation field in step S2 or step S3 to achieve target imaging.

2. The microwave correlation forward-looking imaging method based on random frequency modulation according to claim 1, characterized in that, Step S1 specifically involves arranging the frequency-hopping radar antennas at equal intervals along the direction of the aircraft wings to form a frequency-hopping radar array, and setting the target imaging area as a diamond-shaped area.

3. The microwave correlation forward-looking imaging method based on random frequency modulation according to claim 1, characterized in that, Step S2 specifically includes: S20. Let the location of the target scattering point be... And the signal frequency of the i-th transmitting antenna is f i (t) and its antenna position vector is There is an array of M transmitting antennas, where t is the sampling time, j is the imaginary number, c is the speed of light, and E0 is the field strength amplitude; then the incident field strength E from the i-th transmitting antenna to the imaging target region is... si for: The incident field strength of the entire antenna array on the imaging region is obtained as follows: The random radiation field of the target region is obtained as follows: S21. During microwave-correlated forward-looking imaging, the target scattering characteristic is σ. After the random radiation field illuminates the target imaging area, an echo is generated and received by the frequency-hopping radar array, resulting in the target echo E. r for: S22. The target scattering characteristics can be obtained through inversion as follows: To ensure the randomness of the spatiotemporal random radiation field in the time dimension, sampling time t is randomly selected between pulses. q ,q=1,…,Q; S23. Sample at random times within each pulse to reduce the correlation of the radiation field in the time dimension, and transform it into the following matrix, where e is noise:

4. The microwave correlation forward-looking imaging method based on random frequency modulation according to claim 3, characterized in that, Step S3 specifically includes: Ignoring noise for now, the transformed matrix S23 is simplified to obtain: E r =E s σ is estimated using the least squares method, and both sides of the equation are multiplied by E. s H ,get: AND s H AND r =And s H AND s σ When E s When the column is full, then E s H E s Since it is a non-singular matrix, the least squares method can directly calculate a unique solution: When E s When the number of columns is less than 10, If it cannot be solved directly, then the principal component decomposition method is used to solve E. s To refactor, first convert E s Singular value decomposition yields: E s =UDV H Where D is a Q×N Vickers diagonal matrix, and U and V are Q×Q and N×N unitary matrices respectively, truncating D and U into N×N square matrices D′ and U′, we can reconstruct the following: Therefore, an approximate solution is obtained: In this function, inv() inverts the matrix, processes the spatiotemporal random radiation array using the least squares estimation method, and then performs compression correlation to obtain a unique or approximate solution for the target scattering characteristic distribution, thus completing the imaging of the target.

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