A method for suppressing narrow-band radio frequency interference in low-frequency synthetic aperture radar based on Gaussian function

Abstract

The invention provides a method for suppressing narrowband radio frequency interference of a low-frequency synthetic aperture radar based on a Gaussian function. The method firstly performs a two-dimensional Fourier transform on an echo signal received by a low-frequency SAR to obtain an echo signal in a two-dimensional frequency domain; secondly, a 3δ method is used to detect whether a radio frequency interference signal exists, the position where the maximum value of the radio frequency interference signal is located is found, and a two-dimensional Gaussian function is set with the position as the center; then, the two-dimensional Gaussian function is multiplied with the two-dimensional echo signal to extract the radio frequency interference signal at the position, and the extracted radio frequency interference signal is subtracted from the two-dimensional echo signal to complete the suppression of the radio frequency interference signal at the position; then, the 3δ method is repeatedly used to detect and set a new two-dimensional Gaussian function to extract and eliminate the radio frequency interference signal until all the radio frequency interference signals are eliminated; finally, the two-dimensional frequency domain signal is transformed into a two-dimensional time domain to complete the suppression of the narrowband radio frequency interference signal.

Description

Technical Field

[0001] The present invention relates to the field of radar technology, and more specifically, to a method for suppressing narrow-band radio frequency interference of a low-frequency synthetic aperture radar based on a Gaussian function. Background Art

[0002] Synthetic aperture radar (SAR) acquires target information by actively emitting and receiving electromagnetic waves. Therefore, compared with optical and infrared observation methods, SAR is not restricted by weather, light and other conditions, and has broad application prospects in both military and civilian applications. Compared with high-frequency SAR systems, low-frequency SAR has a lower operating frequency and a longer wavelength, so it has a strong penetrating ability and can detect and image hidden targets in the woods, inside buildings and under the surface. Therefore, low-frequency SAR detection technology plays an increasingly important role in national economic construction, environmental detection and protection, and modern warfare.

[0003] However, there are a lot of radio frequency interference signals such as broadcasting, television, and mobile communications in the low-frequency SAR working frequency band, which have a great impact on the detection capability and imaging quality of the low-frequency SAR system. These radio frequency interference signals are generally narrow-band and high-power (much higher than the power of the SAR echo signal), and it is difficult to determine whether there is a radio frequency interference signal in the echo in the time domain.

[0004] At present, the RF interference suppression methods used for low-frequency SAR imaging processing mainly include parametric methods and non-parametric methods. The parametric method first establishes a model of the RF interference signal, then estimates the parameters of the model to reconstruct the RF interference signal, and finally subtracts the estimated RF interference signal from the echo signal to complete the suppression of the RF interference signal. The parametric method has a good suppression effect on the RF interference signal, but it has a large amount of calculation, so it is difficult to ensure the real-time performance of RF interference suppression. At the same time, since the modeling of the RF interference signal is based on the assumption that the signal is stable, and as the electromagnetic environment becomes more and more complex, the RF interference signal shows more and more non-stationary, so the parametric method is difficult to accurately model the RF interference signal and estimate the parameters of the signal model. Although the non-parametric method has a poor suppression effect on the RF interference signal, its method is simple, easy to implement, and has high efficiency, and can basically meet the real-time suppression of the RF interference signal. Therefore, the use of non-parametric methods to suppress RF interference signals will have a wider range of applications.

[0005] The notch method is a traditional non-parametric RF interference suppression method, which is simple and efficient, but it will cause the target echo signal to lose a lot of energy, which seriously affects the quality of low-frequency SAR imaging. RF interference signals generally have narrowband characteristics in the range frequency domain and azimuth frequency domain. Therefore, this characteristic of RF interference signals can be used to set filters, which will achieve better filtering effects and reduce the loss of target echo signals, thereby achieving effective suppression of low-frequency SAR RF interference signals. Summary of the invention

[0006] The invention provides a Gaussian function-based low-frequency synthetic aperture radar narrow-band radio frequency interference suppression method with good radio frequency interference suppression effect.

[0007] In order to achieve the above technical effects, the technical solution of the present invention is as follows:

[0008] A method for suppressing narrow-band radio frequency interference of a low-frequency synthetic aperture radar based on a Gaussian function comprises the following steps:

[0009] S1: transform the echo signal into two-dimensional frequency domain;

[0010] S2: Setting a two-dimensional Gaussian function to extract and eliminate radio frequency interference signals;

[0011] S3: transform the two-dimensional frequency domain signal after eliminating the radio frequency interference signal into the two-dimensional time domain.

[0012] Furthermore, the specific process of step S1 is:

[0013] Assume that the echo signal received by the low-frequency SAR system is x(t,τ), where t is the slow time and τ is the fast time. Perform a two-dimensional Fourier transform on it to obtain a two-dimensional frequency domain signal X(f,f τ ).

[0014] Furthermore, in step S2, first, the 3δ method is used in the two-dimensional frequency domain to detect whether the radio frequency interference signal exists. If it exists, the position of the maximum value of the radio frequency interference signal is found; then, a two-dimensional Gaussian function is set with the position of the maximum value as the center, and the two-dimensional Gaussian function is multiplied with the two-dimensional echo signal to extract the radio frequency interference signal; finally, the extracted radio frequency interference signal is subtracted from the two-dimensional echo signal to complete the suppression of the radio frequency interference signal at this position; the 3δ method is repeatedly used to detect the data obtained in the previous step and set a new two-dimensional Gaussian function to extract and eliminate the radio frequency interference signal until all radio frequency interference signals are eliminated.

[0015] Furthermore, the specific process of step S3 is:

[0016] The two-dimensional frequency domain signal after eliminating the radio frequency interference signal is subjected to a two-dimensional inverse Fourier transform to obtain a two-dimensional time domain echo signal after radio frequency interference suppression, thereby finally completing the suppression of the narrowband radio frequency interference signal.

[0017] Furthermore, in step S1, since the RF interference signal has narrowband characteristics in both the distance and azimuth frequency domains, compared with only transforming it to the distance frequency domain or the azimuth frequency domain, transforming the echo signal to the two-dimensional frequency domain can concentrate the energy of the RF interference signal more, thereby better extracting the RF interference signal and achieving better RF interference suppression effect.

[0018] Furthermore, the specific process of step S2 is:

[0019] S21: Calculate the two-dimensional frequency domain signal X(f,f τ ) and standard deviation δ, the detection threshold can be set as:

[0020]

[0021] S22: if there is a radio frequency interference signal, find the position of the maximum value of the radio frequency interference signal and set a two-dimensional Gaussian function with the position as the center. When setting the two-dimensional Gaussian function, the bandwidth of the part of the position that is greater than the threshold can be detected as a reference for the function width;

[0022] S23: multiplying the two-dimensional frequency domain echo signal by the two-dimensional Gaussian function to extract the radio frequency interference signal, and subtracting the extracted radio frequency interference signal from the two-dimensional frequency domain echo signal to suppress the radio frequency interference signal at the position;

[0023] S24: Repeat the 3δ method to detect the new data obtained in S21-S23 and set a new two-dimensional Gaussian function to extract and eliminate the radio frequency interference signal until all the radio frequency interference signals are eliminated.

[0024] Furthermore, step S3 is to transform the two-dimensional frequency domain echo signal after eliminating the radio frequency interference signal into the two-dimensional time domain to obtain the final echo signal after radio frequency interference suppression.

[0025] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0026] The present invention firstly performs a two-dimensional Fourier transform on an echo signal received by a low-frequency SAR to obtain an echo signal in a two-dimensional frequency domain; secondly, a 3δ method is used to detect whether a radio frequency interference signal exists, the position where the maximum value of the radio frequency interference signal is located is found, and a two-dimensional Gaussian function is set with the position as the center; then, the two-dimensional Gaussian function is multiplied with the two-dimensional echo signal to extract the radio frequency interference signal at the position, and the extracted radio frequency interference signal is subtracted from the two-dimensional echo signal to complete the suppression of the radio frequency interference signal at the position; then, the 3δ method is repeatedly used to detect and set a new two-dimensional Gaussian function to extract and eliminate the radio frequency interference signal until all the radio frequency interference signals are eliminated; finally, the two-dimensional frequency domain signal is transformed into a two-dimensional time domain to complete the suppression of the narrowband radio frequency interference signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of the method of the present invention;

[0028] Figure 2 This is the imaging result of the point target before and after adding the RF interference signal;

[0029] Figure 3 is the two-dimensional frequency domain and two-dimensional Gaussian function of the echo signal;

[0030] Figure 4 These are the imaging results after suppressing the radio frequency interference signal using the traditional notch method and the present invention. DETAILED DESCRIPTION

[0031] The drawings are for illustrative purposes only and should not be construed as limiting the present patent;

[0032] In order to better illustrate the present embodiment, some parts in the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product;

[0033] It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0034] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0035] A method for suppressing narrow-band radio frequency interference of a low-frequency synthetic aperture radar based on a Gaussian function comprises the following steps:

[0036] S1: transform the echo signal into two-dimensional frequency domain;

[0037] S2: Setting a two-dimensional Gaussian function to extract and eliminate radio frequency interference signals;

[0038] S3: transform the two-dimensional frequency domain signal after eliminating the radio frequency interference signal into the two-dimensional time domain.

[0039] The specific process of step S1 is:

[0040] Assume that the echo signal received by the low-frequency SAR system is x(t,τ), where t is the slow time and τ is the fast time. Perform a two-dimensional Fourier transform on it to obtain a two-dimensional frequency domain signal X(f,f τ ).

[0041] In step S2, first, the 3δ method is used in the two-dimensional frequency domain to detect whether the RF interference signal exists. If it exists, the position of the maximum value of the RF interference signal is found; then, a two-dimensional Gaussian function is set with the position of the maximum value as the center, and the two-dimensional Gaussian function is multiplied with the two-dimensional echo signal to extract the RF interference signal; finally, the extracted RF interference signal is subtracted from the two-dimensional echo signal to complete the suppression of the RF interference signal at that position; the 3δ method is repeatedly used to detect all signals and set a new two-dimensional Gaussian function to extract and eliminate the RF interference signal until all RF interference signals are eliminated.

[0042] The specific process of step S3 is:

[0043] The two-dimensional frequency domain signal after eliminating the radio frequency interference signal is subjected to a two-dimensional inverse Fourier transform to obtain a two-dimensional time domain echo signal after radio frequency interference suppression, thereby finally completing the suppression of the narrowband radio frequency interference signal.

[0044] In step S1, since the RF interference signal has narrowband characteristics in both the distance and azimuth frequency domains, compared with only transforming it to the distance frequency domain or the azimuth frequency domain, transforming the echo signal to the two-dimensional frequency domain can concentrate the energy of the RF interference signal more, thereby better extracting the RF interference signal and achieving better RF interference suppression effect.

[0045] The specific process of step S2 is:

[0046] S21: Calculate the two-dimensional frequency domain signal X(f,f τ ) and standard deviation δ, the detection threshold can be set as:

[0047]

[0048] S22: if there is a radio frequency interference signal, find the position of the maximum value of the radio frequency interference signal and set a two-dimensional Gaussian function with the position as the center. When setting the two-dimensional Gaussian function, the bandwidth of the part of the position that is greater than the threshold can be detected as a reference for the function width;

[0049] S23: multiplying the two-dimensional frequency domain echo signal by the two-dimensional Gaussian function to extract the radio frequency interference signal, and subtracting the extracted radio frequency interference signal from the two-dimensional frequency domain echo signal to suppress the radio frequency interference signal at the position;

[0050] S24: Repeat the 3δ method to detect the new data obtained in S21-S23 and set a new two-dimensional Gaussian function to extract and eliminate the radio frequency interference signal until all the radio frequency interference signals are eliminated.

[0051] Step S3 is to transform the two-dimensional frequency domain echo signal after eliminating the radio frequency interference signal into the two-dimensional time domain to obtain the final echo signal after radio frequency interference suppression.

[0052] like Figure 1 As shown, the whole process is divided into three steps: the first step is to transform the echo signal into the two-dimensional frequency domain; the second step includes detecting the RF interference signal, setting the Gaussian function and multiplying it by the two-dimensional echo signal to extract the RF interference signal and eliminate the RF interference signal; the third step is to transform the two-dimensional frequency domain signal after eliminating the RF interference signal into the two-dimensional time domain, and finally complete the suppression of narrowband RF interference.

[0053] The Gaussian function-based low-frequency SAR narrowband radio frequency interference suppression method of the present invention is verified through simulation experiments, and the effectiveness of the present invention is demonstrated by theoretical analysis and simulation experiment results.

[0054] In the simulation experiment, the parameters of the low-frequency SAR system and the radio frequency interference signal of the present invention are shown in the following table:

[0055] parameter value parameter value Radar signal center frequency 600MHz RF interference signal frequency [620, 607, 585] MHz Radar signal sampling frequency 200MHz Pulse repetition frequency 200Hz Radar signal bandwidth 100MHz Radar signal pulse width 1μs Radar speed 100m / s Radar altitude 300m

[0056] Figure 2 is the result of imaging the original point target (i.e. without adding the RF interference signal) and after adding the narrowband RF interference signal. Figure 2 (a) is the imaging result of the point target when no RF interference signal is added. Figure 2 (b) is the imaging result of the point target after adding the narrowband RF interference signal. Figure 3 It can be seen that adding narrowband RF interference signals will have a serious impact on imaging.

[0057] Figure 3 (a) is the imaging result after the echo signal is transformed into the two-dimensional frequency domain. Figure 3 (b) Figure 3 The Gaussian function is set at the center of the RF interference signal with the highest amplitude in (a). Figure 3 (a) It can be seen that the RF interference signal has a narrowband characteristic in the two-dimensional frequency domain, and its amplitude is much larger than the amplitude of the SAR echo signal.

[0058] Figure 4 It is the imaging result after suppressing the narrowband radio frequency interference signal by using the traditional notch method and the method of the present invention respectively. Figure 4 (a) is the imaging result after suppressing narrowband RF interference signal using traditional notch method. Figure 4 (b) is the imaging result after suppressing the narrowband radio frequency interference signal using the method of the present invention. Figure 4 It can be seen that the traditional notch method and the method of the present invention have a suppressive effect on narrowband RF interference signals and can filter out most of the RF interference signals. Figure 4 (a) and Figure 4 (b) It can be seen that after the conventional notch filter method suppresses the narrowband RF interference signal, there are still a lot of residual interference signals in the imaging result, while after the method of the present invention suppresses the narrowband RF interference signal, there are almost no residual interference signals in the imaging result. Therefore, the method of the present invention has a better suppression effect on the narrowband RF interference signal and can improve the imaging quality of SAR.

[0059] The following table calculates the signal-to-interference ratio (i.e., the ratio of the target echo signal energy to the residual interference signal energy in the imaging result) of the imaging result after the traditional notch method and the method of the present invention suppress narrowband RF interference signals. By comparing the following table, it can be seen that the signal-to-interference ratio of the imaging result after the method of the present invention suppresses narrowband RF interference signals is better than that of the traditional notch method, indicating that the method of the present invention has better narrowband RF interference signal suppression performance:

[0060] index Traditional notch method Method of the present invention Signal-to-interference ratio (dB) 7.4169 11.0799

[0061] The same or similar reference numerals correspond to the same or similar components;

[0062] The positional relationships described in the drawings are only for illustrative purposes and should not be construed as limiting the present patent.

[0063] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for suppressing narrowband radio frequency interference of low-frequency synthetic aperture radar based on Gaussian function, characterized in that: The following steps are involved: S1: transform the echo signal into two-dimensional frequency domain; S2: Setting a two-dimensional Gaussian function to extract and eliminate radio frequency interference signals; S3: transforming the two-dimensional frequency domain signal after eliminating the radio frequency interference signal into the two-dimensional time domain; The specific process of step S1 is: Assume that the echo signal received by the low-frequency SAR system is x(t,τ), where t is the slow time and τ is the fast time. Perform a two-dimensional Fourier transform on it to obtain a two-dimensional frequency domain signal X(f,f τ ); In the step S2, first, the 3δ method is used in the two-dimensional frequency domain to detect whether the radio frequency interference signal exists. If it exists, the position of the maximum value of the radio frequency interference signal is found; then, a two-dimensional Gaussian function is set with the position of the maximum value as the center, and the two-dimensional Gaussian function is multiplied with the two-dimensional echo signal to extract the radio frequency interference signal; finally, the extracted radio frequency interference signal is subtracted from the two-dimensional echo signal to complete the suppression of the radio frequency interference signal at this position; the 3δ method is repeatedly used to detect all signals and set a new two-dimensional Gaussian function to extract and eliminate the radio frequency interference signal until all radio frequency interference signals are eliminated.

2. The Gaussian function-based low-frequency synthetic aperture radar narrowband radio frequency interference suppression method according to claim 1, characterized in that: The specific process of step S3 is: The two-dimensional frequency domain signal after eliminating the radio frequency interference signal is subjected to a two-dimensional inverse Fourier transform to obtain a two-dimensional time domain echo signal after radio frequency interference suppression, thereby finally completing the suppression of the narrowband radio frequency interference signal.

3. The Gaussian function-based low-frequency synthetic aperture radar narrowband radio frequency interference suppression method according to claim 2, characterized in that: In step S1, since the RF interference signal has narrowband characteristics in both the distance and azimuth frequency domains, compared with only transforming it to the distance frequency domain or the azimuth frequency domain, transforming the echo signal to the two-dimensional frequency domain can concentrate the energy of the RF interference signal more, thereby better extracting the RF interference signal and achieving better RF interference suppression effect.

4. The Gaussian function-based low-frequency synthetic aperture radar narrowband radio frequency interference suppression method according to claim 3 is characterized in that: The specific process of step S2 is: S21: Calculate the two-dimensional frequency domain signal X(f,f τ ) and standard deviation δ, the detection threshold can be set as: ； S22: if there is a radio frequency interference signal, find the position of the maximum value of the radio frequency interference signal and set a two-dimensional Gaussian function with the position as the center. When setting the two-dimensional Gaussian function, the bandwidth of the part of the position that is greater than the threshold can be detected as a reference for the function width; S23: multiplying the two-dimensional frequency domain echo signal by the two-dimensional Gaussian function to extract the radio frequency interference signal, and subtracting the extracted radio frequency interference signal from the two-dimensional frequency domain echo signal to suppress the radio frequency interference signal at the position; S24: Repeat the 3δ method to detect the new data obtained in S21-S23 and set a new two-dimensional Gaussian function to extract and eliminate the radio frequency interference signal until all the radio frequency interference signals are eliminated.

5. The Gaussian function-based low-frequency synthetic aperture radar narrowband radio frequency interference suppression method according to claim 4 is characterized in that: Step S3 is to transform the two-dimensional frequency domain echo signal after eliminating the radio frequency interference signal into the two-dimensional time domain to obtain the final echo signal after radio frequency interference suppression.

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