Radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation

Abstract

The present invention discloses a radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation, which relates to the field of radar information processing technology. The method comprises: S1. constructing a random initial phase modulation signal radar echo model based on positive and negative LFM pulse signals to obtain a desired echo; S2. performing random initial phase elimination on the desired echo based on a reference function to obtain the desired echo after random initial phase elimination; S3. performing range ambiguity suppression based on matched filtering on the desired echo after random initial phase elimination. The random initial phase modulation signal based on positive and negative LFM of the present invention can simultaneously combine the advantages of both positive and negative LFM-based and random initial phase modulation-based methods to suppress range ambiguity. At the same time, the random initial phase modulation signal technology is used to perform random initial phase modulation on the transmitted pulse, which can reduce the correlation between the interference signal and the transmitted signal echo, thereby improving the anti-interference performance of the SAR imaging radar.

Description

Technical Field

[0001] The present invention relates to the field of radar information processing technology, and in particular to a radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation. Background Art

[0002] Wide-area Synthetic Aperture Radar (SAR) imaging technology can utilize high-flying trajectories to detect targets over a wide range, providing target designation for precision strikes. Under conditions where the trajectory is high and the distance is greater than the angle of incidence, wide-area, wide-swath imaging requires a low pulse repetition frequency (PRF) to avoid range ambiguity. However, achieving high azimuth resolution in SAR imaging requires a high pulse repetition frequency (PRF) to avoid azimuth ambiguity. In traditional single-channel SAR systems, range and azimuth ambiguity are difficult to reconcile. When a high PRF is used to ensure high azimuth resolution, echoes from different transmitted pulses within the swath alias within the receiving window, resulting in range ambiguity in the imaging result and the appearance of false targets in the image, hindering further research such as target detection. The operating altitude, range, and angle of incidence of wide-area SAR imaging differ significantly from those of traditional missile-borne SAR imaging, making range and azimuth ambiguity particularly prominent. The bandwidth is much larger than the information bandwidth.

[0003] Linear frequency modulation (LFM) signals have advantages such as a bandwidth much larger than the information bandwidth, insensitivity to Doppler shift, and ease of engineering implementation. Therefore, they are often used as transmit signals in traditional SAR. Based on this, range ambiguity has been suppressed from the perspective of waveform optimization design. Mittermayer J. first proposed that alternating positive and negative LFM signals can suppress range ambiguity in SAR imaging. Positive and negative LFM signals also have the advantage of being easy to implement. Studies have shown that positive and negative LFM signals have good range ambiguity suppression effects for point target imaging, but are less effective for distributed target imaging. In practice, ground or sea surface SAR targets are typically modeled as distributed targets rather than point targets. Waveform optimization methods that employ phase modulation on LFM signals offer another approach to range ambiguity suppression. Dall J. et al. proposed an azimuth phase encoding technique. By encoding the azimuth of the transmitted signal, the ambiguous signal echo can be filtered out in the azimuth frequency domain to remove some of the ambiguity energy. After analyzing the principle of range ambiguity suppression, they found that this method relies too heavily on a high repetition rate. Within the repetition rate range commonly used in practical applications, this technique has very limited range ambiguity suppression.

[0004] Therefore, it is an urgent problem for those skilled in the art to propose a radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation to solve the difficulties existing in the existing technology. Summary of the Invention

[0005] In view of this, the present invention provides a radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation, and proposes a waveform optimization method for random initial phase modulation of positive and negative LFM signals, which can realize radar range ambiguity suppression.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation includes the following steps:

[0008] S1. Construct a random initial phase modulation signal radar echo model based on positive and negative LFM pulse signals to obtain the expected echo;

[0009] S2. Perform random initial phase elimination on the desired echo based on the reference function to obtain the desired echo after random initial phase elimination;

[0010] S3. Perform range ambiguity suppression based on matched filtering on the expected echo after random initial phase elimination.

[0011] In the above method, optionally, the expression of the expected echo in S1 is:

[0012]

[0013] Among them, s exp (τ, μ) is the expected echo, μ is the azimuth time, τ is the range time, H r is the frequency modulation slope, f0 is the signal carrier frequency, ρ a (·),ρ r (·) is the antenna pattern function in azimuth and range directions, is the initial modulation phase that changes randomly between pulses, R(μ) is the distance from the target to the radar, μ c is the beam center crossing time.

[0014] In the above method, optionally, the specific content of performing random initial phase elimination on the desired echo based on the reference function in S2 is:

[0015] The desired echo is multiplied by the reference function to eliminate the random initial phase, and the random initial phase of the desired echo is completely eliminated.

[0016] In the above method, optionally, the specific content of performing range ambiguity suppression based on matched filtering on the desired echo after random initial phase elimination in S3 is:

[0017] If the expected echo is a transmitted signal echo with a negative frequency modulation slope, then the frequency modulation slope of the adjacent ambiguous echo is positive.

[0018] The desired echo and the blurred echo are respectively multiplied by the matched filter in the frequency domain for pulse compression; then they are respectively converted into time domain signals through inverse Fourier transform; the processing results of the desired echo and the processing results of the blurred echo are respectively obtained to suppress the range ambiguity.

[0019] In the above method, optionally, the matched filters used for the desired echo and the blurred echo during pulse compression processing are:

[0020]

[0021] Among them, f τ is the distance frequency, T r is the pulse repetition period, j 2 is -1.

[0022] The above method is optional. The core principle of the random initial phase modulation signal to suppress range ambiguity is that the blurred echo caused by its random residual phase is not accumulated, but the amplitude value of the blurred echo relative to the expected echo is not reduced.

[0023] It can be seen from the above technical solution that, compared with the prior art, the present invention provides a radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation, which has the following beneficial effects: the random initial phase modulation signal based on positive and negative LFM of the present invention can simultaneously combine the advantages of both positive and negative LFM-based and random initial phase modulation-based methods to suppress range ambiguity, and at the same time, utilize the random initial phase modulation signal technology to perform random initial phase modulation on the transmitted pulse, which can reduce the correlation between the interference signal and the transmitted signal echo, thereby improving the anti-interference performance of the SAR imaging radar. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0025] Figure 1 A flow chart of a radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation provided by the present invention;

[0026] Figure 2 A distributed ship target simulation scene diagram provided by an embodiment of the present invention;

[0027] Figure 3A schematic diagram of the simulation results of a ship target using an LFM signal provided by an embodiment of the present invention;

[0028] Figure 4 A schematic diagram of the amplified result of the LFM signal real target imaging provided by an embodiment of the present invention;

[0029] Figure 5 A schematic diagram of a false target caused by LFM signal range ambiguity provided by an embodiment of the present invention;

[0030] Figure 6 Schematic diagram of the simulation results of ship targets with positive and negative LFM signals provided by an embodiment of the present invention;

[0031] Figure 7 A schematic diagram of the amplified results of positive and negative LFM signals of a real target provided by an embodiment of the present invention;

[0032] Figure 8 Schematic diagram of a false target caused by range ambiguity of positive and negative LFM signals provided by an embodiment of the present invention;

[0033] Figure 9 A schematic diagram of ship target simulation results based on the random initial phase modulation signal of positive and negative LFM provided in an embodiment of the present invention;

[0034] Figure 10 A schematic diagram of the amplified result of real target imaging using a random initial phase modulation signal based on positive and negative LFM provided by an embodiment of the present invention;

[0035] Figure 11 Schematic diagram of false targets generated by range ambiguity of random initial phase modulation signals based on positive and negative LFM provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] Reference Figure 1 As shown, the present invention discloses a radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation, comprising the following steps:

[0038] S1. Construct a random initial phase modulation signal radar echo model based on positive and negative LFM pulse signals to obtain the expected echo;

[0039] S2. Perform random initial phase elimination on the desired echo based on the reference function to obtain the desired echo after random initial phase elimination;

[0040] S3. Perform range ambiguity suppression based on matched filtering on the expected echo after random initial phase elimination.

[0041] Furthermore, the expression of the expected echo in S1 is:

[0042]

[0043] Among them, s exp (τ, μ) is the expected echo, μ is the azimuth time, τ is the range time, H r is the frequency modulation slope, f0 is the signal carrier frequency, ρ a (·),ρ r (·) is the antenna pattern function in azimuth and range directions, is the initial modulation phase that changes randomly between pulses, R(μ) is the distance from the target to the radar, μ c is the beam center crossing time.

[0044] Furthermore, the specific content of performing random initial phase elimination on the desired echo based on the reference function in S2 is:

[0045] The desired echo is multiplied by the reference function to eliminate the random initial phase, and the random initial phase of the desired echo is completely eliminated.

[0046] Furthermore, the specific content of the range ambiguity suppression based on matched filtering for the desired echo after the random initial phase elimination in S3 is:

[0047] If the expected echo is a transmitted signal echo with a negative frequency modulation slope, then the frequency modulation slope of the adjacent ambiguous echo is positive.

[0048] The desired echo and the blurred echo are respectively multiplied by the matched filter in the frequency domain for pulse compression; then they are respectively converted into time domain signals through inverse Fourier transform; the processing results of the desired echo and the processing results of the blurred echo are respectively obtained to suppress the range ambiguity.

[0049] Furthermore, the matched filters used for the desired echo and the blurred echo during pulse compression processing are:

[0050]

[0051] Among them, f τ is the distance frequency, T r is the pulse repetition period, j 2 is -1.

[0052] Furthermore, the core principle of the random initial phase modulation signal to suppress range ambiguity is that the blurred echo caused by its random residual phase does not accumulate, but does not reduce the amplitude value of the blurred echo relative to the expected echo.

[0053] In a specific embodiment, the specific content is as follows

[0054] Step (1): Construction of radar echo model of random initial phase modulation signal based on positive and negative LFM.

[0055] The core principle of random initial phase modulation signals in suppressing range ambiguity lies in the fact that the ambiguous echoes caused by the random residual phase do not accumulate, but the amplitude of the ambiguous echo relative to the desired echo is not reduced. Considering that transmitting positive and negative LFM pulse signals can suppress the amplitude of a single ambiguous echo, random initial phase modulation is combined with positive and negative LFM signals to suppress range ambiguity. The radar transmission signal is expressed as:

[0056]

[0057] Where μ is the azimuth time, τ is the range time, H r is the frequency modulation slope, f0 is the signal carrier frequency, ρ a (·),ρ r (·) is the antenna pattern function in azimuth and range directions, is the initial modulation phase that varies randomly between pulses.

[0058] If the expected echo is the echo of the negative LFM pulse signal, the expected echo S exp The expression of (τ, μ) is:

[0059]

[0060] Among them, R(μ) is the distance from the target to the radar, μ c is the beam center crossing time.

[0061] When the expected echo modulation frequency is negative, the adjacent fuzzy echo s amb The frequency modulation slope of (τ, μ) is positive:

[0062]

[0063] Step (2): random initial phase elimination of the expected echo based on the reference function.

[0064] Desired echo and ambiguous echo prior and reference function Multiplication is used to eliminate the random initial phase. The random initial phase of the desired echo can be completely eliminated, but the fuzzy echo cannot be completely eliminated and there is still a residual phase. The fuzzy echo is transformed into the range frequency domain using the stationary phase principle. The expression is:

[0065]

[0066] Step (3): Range ambiguity suppression based on matched filtering.

[0067] The expected echo is the transmitted signal echo with a negative frequency modulation. The matched filter used in the pulse compression processing is:

[0068]

[0069] The result of pulse compression by multiplying the fuzzy echo with the matched filter in the frequency domain is:

[0070]

[0071] After the range frequency domain matched filtering and then the inverse Fourier transform, it can be converted to the time domain signal to obtain the processing result of the fuzzy echo:

[0072]

[0073] The above operation is also performed on the desired echo. However, the random initial phase of the desired echo can be completely eliminated by the reference function, and the filter used for pulse compression is also matched. For comparison, the processing results of the desired echo are also obtained:

[0074]

[0075] Comparing the processing results of the fuzzy echo and the expected echo, it is found that the amplitude of the fuzzy echo time domain signal is reduced by After emitting a random initial phase modulated LFM pulse signal and de-phase-modulating it with a reference function, the blurred echo has a residual phase with random characteristics. This results in that when the pulse accumulation in the imaging area is completed, all the desired echoes can be accumulated at the same phase center, but the blurred echoes are irregularly distributed at the random residual phase. Therefore, the random initial phase modulation signal based on positive and negative LFM can combine the advantages of both positive and negative LFM and random initial phase modulation to suppress range ambiguity.

[0076] In another specific embodiment, the set SAR imaging simulation parameters are shown in Table 1.

[0077] Table 1 SAR imaging simulation parameters

[0078] Imaging parameters Simulation values Imaging parameters Simulation values Pulse repetition rate 5000Hz Sampling frequency <![CDATA[1.2×10 8 Hz]]> Pulse width <![CDATA[4×10 -5 s]]> Pulse bandwidth <![CDATA[8×10 7 Hz]]> Azimuth sampling points 5000 wavelength 0.0182m Azimuth beamwidth 1.2° Antenna gain 39dB Range beamwidth 2.2°

[0079] Figure 2 It is a distributed ship target simulation scene diagram; Figure 3 This is a schematic diagram of the simulation results of LFM signal ship target; Figure 4 This is a schematic diagram of the result after the LFM signal real target imaging is magnified; Figure 5 Schematic diagram of false targets caused by LFM signal range ambiguity; Figure 6 This is a schematic diagram of the simulation results of ship targets with positive and negative LFM signals; Figure 7 This is a schematic diagram of the amplified results of the real target imaging of the positive and negative LFM signals; Figure 8 Schematic diagram of false targets caused by range ambiguity of positive and negative LFM signals; Figure 9 Schematic diagram of the simulation results of ship targets based on the random initial phase modulation signal of positive and negative LFM; Figure 10 This is a schematic diagram of the amplified result of real target imaging based on the random initial phase modulation signal of positive and negative LFM; Figure 11 Schematic diagram of false targets generated by range ambiguity of random initial phase modulation signals based on positive and negative LFM.

[0080] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation, characterized in that: The following steps are involved: S1. Construct a random initial phase modulation signal radar echo model based on positive and negative LFM pulse signals to obtain the expected echo; S2. Perform random initial phase elimination on the desired echo based on the reference function to obtain the desired echo after random initial phase elimination; S3. Perform range ambiguity suppression based on matched filtering on the expected echo after random initial phase elimination.

2. The radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation according to claim 1 is characterized in that: The expression of the expected echo in S1 is: Among them, S exp (τ, μ) is the expected echo, μ is the azimuth time, τ is the range time, H r is the frequency modulation slope, f0 is the signal carrier frequency, ρ a (·),ρ r (·) is the antenna pattern function in azimuth and range directions, is the initial modulation phase that changes randomly between pulses, R(μ) is the distance from the target to the radar, μ c is the beam center crossing time.

3. The radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation according to claim 1 is characterized in that: The specific content of random initial phase elimination of the expected echo based on the reference function in S2 is: The desired echo is multiplied by the reference function to eliminate the random initial phase, and the random initial phase of the desired echo is completely eliminated.

4. The radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation according to claim 1 is characterized in that: The specific content of the range ambiguity suppression based on matched filtering for the expected echo after random initial phase elimination in S3 is: If the expected echo is a transmitted signal echo with a negative frequency modulation slope, then the frequency modulation slope of the adjacent ambiguous echo is positive. The desired echo and the blurred echo are respectively multiplied by the matched filter in the frequency domain for pulse compression; then they are respectively converted into time domain signals through inverse Fourier transform; the processing results of the desired echo and the processing results of the blurred echo are respectively obtained to suppress the range ambiguity.

5. The radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation according to claim 4 is characterized in that: The matched filters used for the desired echo and the fuzzy echo in pulse compression processing are: Among them, f τ is the distance frequency, T r is the pulse repetition period, j 2 is -1.

6. A radar range ambiguity suppression method based on positive and negative LFM random initial phase modulation according to any one of claims 1 to 5, characterized in that: The core principle of random initial phase modulation signal to suppress range ambiguity is that the ambiguous echo caused by its random residual phase does not accumulate, but does not reduce the amplitude of the ambiguous echo relative to the expected echo.

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