Ultra-low sidelobe waveform design method for airborne weather avoidance radar

Abstract

The application provides a kind of waveform design method of airborne weather anti-collision radar with ultra-low sidelobe, comprising: frequency modulation curve design; Transmit waveform design; Design signal power spectrum, obtain signal amplitude modulation according to signal power spectrum, design filter frequency response according to signal amplitude modulation.The application helps to improve the accuracy of airborne weather anti-collision radar on weather target reflectivity factor calculation and the detection probability of high voltage line.Compared with general NLFM waveform, the waveform proposed in the application does not need amplitude modulation when transmitting, can transmit with full power, increases the transmission efficiency, and is easier to implement in engineering.

Description

Technical Field

[0001] This invention relates to the field of radar technology, and specifically to a method for designing ultra-low sidelobe waveforms for an airborne weather collision avoidance radar. Background Technology

[0002] Airborne weather collision avoidance radar can detect and warn of weather, terrain, and low-altitude obstacles in front of an aircraft, ensuring flight safety. Hazardous weather, high-voltage lines, and high-voltage towers are two important types of targets detected by weather collision avoidance radar. Since weather targets are usually large-area volume targets, the sidelobes of radar echoes from highly reflective weather can "block" the radar echoes from surrounding weakly reflective clouds, leading to larger errors in estimating the echo power of weakly reflective clouds and inaccurate calculation of the reflectivity factor. Similarly, when detecting high-voltage lines, the strong scattering of radar echoes from high-voltage towers results in high radar echo power, and their high range sidelobes can "overwhelm" the weak high-voltage line signals near the tower, causing missed and false detections of high-voltage lines, thus affecting the detection and identification of high-voltage lines. Therefore, designing a radar waveform with ultra-low sidelobes is of great significance for improving the detection performance of airborne weather collision avoidance radar.

[0003] Traditional linear frequency modulation (LFM) waveform pulse compression results in a high range sidelobe, with a peak sidelobe level (PSL) that can only reach a maximum of -13.4dB. Windowing techniques can reduce this to around -30dB, which is very disadvantageous for weak target detection because the main lobe of a weak target signal is likely to be overwhelmed by the sidelobe of a strong target, leading to missed detections and false detections. Summary of the Invention

[0004] In view of this, embodiments of this specification provide an ultra-low sidelobe waveform design method for an airborne weather collision avoidance radar to solve the problems of missed and false detections of targets.

[0005] This specification provides the following technical solution in its embodiments: a method for designing ultra-low sidelobe waveforms for airborne weather collision avoidance radar, comprising: frequency modulation curve design; transmission waveform design; designing signal power spectrum; obtaining signal amplitude modulation based on signal power spectrum; and designing filter frequency response based on signal amplitude modulation.

[0006] Furthermore, according to the formula Design the frequency modulation curve, among which, For signal bandwidth, For signal duration, Values , Values t represents time.

[0007] Furthermore, integrating the formula for the frequency modulation curve yields the phase modulation of the signal, specifically: .

[0008] Furthermore, the transmitted signal waveform is represented as follows: ,in, .

[0009] Furthermore, the signal power spectrum is designed to be Gaussian in shape, specifically as follows: ,in, .

[0010] Furthermore, signal amplitude modulation is obtained based on the instantaneous phase principle according to the signal power spectrum, specifically as follows: ,in, This is the amplitude modulation required for the signal.

[0011] Furthermore, on And signals without amplitude modulation Zeros are padded at the beginning and end to make both lengths three times the signal length, specifically: ; .

[0012] Furthermore, regarding the signal after zero padding... Perform Fourier transform to obtain ,right Perform Fourier transform to obtain Then the frequency response of the filter for ,in, for . conjugate.

[0013] Compared with the prior art, the beneficial effects that at least one of the technical solutions adopted in the embodiments of this specification can achieve include at least the following: the present invention helps to improve the accuracy of airborne meteorological collision avoidance radar in calculating the reflectivity factor of meteorological targets and the detection probability of high-voltage lines. Compared with the general NLFM waveform, the waveform proposed in this invention does not require amplitude modulation during transmission, can be transmitted at full power, increases transmission efficiency, and is easier to implement in engineering. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart illustrating an embodiment of the present invention; Figure 2This is a schematic diagram of the frequency modulation curve shape of the present invention; Figure 3 This is a schematic diagram of the transmitted waveform shape of the present invention; Figure 4 This is a schematic diagram of the frequency response of the filter of the present invention; Figure 5 This is a schematic diagram of the waveform of the target object after passing through the filter; Figure 6 A schematic diagram comparing the waveform processing results of existing technologies with those of this invention; Figure 7 This is a schematic diagram showing the change in signal-to-noise ratio of a weak signal with relative intensity. Detailed Implementation

[0016] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] like Figure 1 As shown in the figure, this embodiment of the invention provides a method for designing ultra-low sidelobe waveforms for airborne weather collision avoidance radar. The specific steps are as follows: Step 1: Frequency modulation curve design.

[0019] Design the signal frequency modulation according to equation (1): (1) in, For signal bandwidth, For signal duration, Pick , Pick t represents time.

[0020] Step 2: Design the transmission waveform.

[0021] (a) Integrating equation (1) yields the phase modulation of the signal, as shown in equation (2): (2) (b) According to equation (2), the transmitted signal waveform can be expressed as: (3) The transmitted signal waveform can be generated according to formula (3).

[0022] Step 3: Receiver Filter Design. Filter design consists of the following three sub-steps: Signal power spectrum design; The signal power spectrum is designed to be Gaussian in shape, as shown in equation (4): (4) in, .

[0023] Determine the signal amplitude modulation from the power spectrum; According to the principle of instantaneous phase, we have: (5) In equation (5), For the amplitude modulation required by the signal, For phase modulation of the signal, Indicates to By taking the second derivative and substituting equations (2) and (4), we can obtain the required signal amplitude modulation to achieve the predetermined power spectrum: (6) Design the filter frequency response based on signal amplitude modulation; Simulation experiments show that increasing the filter length can improve the PSL. To obtain a longer filter response without amplitude modulation of the transmitted signal, the first step is to... And signals without amplitude modulation Pad the signals with zeros at the beginning and end to make their length three times the signal length. Let the zero-padding signals be... and The corresponding Fourier transforms are respectively and Then we have: (7) (8) Filter frequency response It can be obtained from the following formula: (9) After the above steps, the filter is designed. In engineering implementation, the transmitted signal is generated and transmitted according to equation (3). After the receiver filter is designed in advance according to step 3, the echo signal passes through the designed filter and the output signal can achieve ultra-low sidelobe. As can be seen from equation (3), the transmitted signal does not need amplitude modulation and the transmission efficiency can be guaranteed.

[0024] With bandwidth pulse width Taking waveform parameters with a sampling rate of 125MHz as an example, the design implementation involves the following steps: 1. Frequency modulation curve design The frequency modulation curve parameters are designed as follows: , Then the formula for the frequency modulation curve is: ; The designed frequency modulation curve shape is as follows Figure 2 As shown.

[0025] 2. Transmit Waveform Design (a) Integrating the mathematical expression of the frequency modulation curve, we obtain the phase modulation of the signal as: ; (b) Based on phase modulation, the transmitted signal waveform is obtained as follows: ; The designed transmitted signal waveform in the time domain is as follows: Figure 3 As shown.

[0026] 3. Receiver Filter Design (a) Signal power spectrum design.

[0027] Based on the signal parameters, the signal power spectrum is designed as follows: ; (b) Determine the signal amplitude modulation based on the power spectrum.

[0028] Based on the instantaneous phase principle, the signal amplitude modulation is obtained as follows: ; (c) Design the filter response based on the signal amplitude modulation.

[0029] 1) Zero padding for the signal;

[0030] ; 2) Calculate the Fourier transform of the signal after zero-padding; The Fourier transform is obtained digitally in a computer, and the mathematical description of the calculation process is as follows: ; in, .

[0031] 3) Filter frequency response design; Filter frequency response It can be obtained by the following formula: ; After substituting the values, the frequency response of the filter is obtained as follows: Figure 4 As shown.

[0032] To verify the ultra-low sidelobe effect of the proposed solution, a target was set at 3 km. The waveform and receiving filter designed in the proposed solution were used. The time-domain waveform of the target after passing through the receiving filter is as follows: Figure 5 As shown.

[0033] Depend on Figure 5 It can be seen that after the transmitted waveform passes through the filter, its sidelobe level is low, with a PSL of approximately -77dB.

[0034] To verify the performance of the waveform designed in this implementation scheme for detecting small targets near a large target, an experiment compared the target processing results of the traditional LFM waveform and the waveform designed in this invention. Two targets were set up in the experiment, with distances of 3 km and 2.6 km, and signal-to-noise ratios of 55 dB and 0 dB, respectively. A BLACKMAN window was applied to the LFM waveform to minimize sidelobes. The results of processing the LFM waveform and the NLFM waveform designed in this invention are shown below. Figure 6 As shown: Depend on Figure 6 The comparison shows that for small targets at 2.6 km, the traditional LFM waveform cannot detect them because the sidelobes are too high and are submerged. However, after waveform processing designed in this invention, the target is clearly visible with a signal-to-noise ratio greater than 15 dB, and can obviously be detected.

[0035] Figure 7 The following diagram illustrates how the signal-to-noise ratio (SNR) of weak signals detected by the conventional LFM waveform and the waveform of this invention varies with the relative SNR of two targets, one strong and one weak: Depend on Figure 7 It can be seen that this invention improves the detection capability of weak signals when the strong signal is more than 35dB stronger than the weak signal, and the signal-to-noise ratio of the weak signal is improved by more than 10dB compared to the traditional LFM waveform, thus increasing the detection probability. In high-voltage line detection scenarios, this invention achieves a false alarm probability of... When the actual signal-to-noise ratio of a high-voltage line is less than 15dB, the detection probability can be increased by at least 30%.

[0036] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical solutions, and technical solutions in this invention can be freely combined and used.

Claims

1. A method for designing ultra-low sidelobe waveforms for an airborne weather collision avoidance radar, characterized in that, include: Frequency modulation curve design is based on the formula Design the frequency modulation curve, among which, For signal bandwidth, For signal duration, Values , Values t is time; The transmitted waveform design involves integrating the frequency modulation curve formula to obtain the signal phase modulation, which can then be represented as: ,in, ; Design the signal power spectrum, obtain the signal amplitude modulation based on the signal power spectrum, and design the filter frequency response based on the signal amplitude modulation. The designed signal power spectrum is Gaussian in shape, specifically: ,in, ; Signal amplitude modulation is obtained based on the instantaneous phase principle according to the signal power spectrum, specifically as follows: ,in, For amplitude modulation of the signal; right And signals without amplitude modulation Zeros are padded at the beginning and end to make both lengths three times the signal length, specifically: ; ； Signals after zero padding Perform Fourier transform to obtain ,right Perform Fourier transform to obtain Then the frequency response of the filter for ,in, for . conjugate.

2. The ultra-low sidelobe waveform design method for airborne weather collision avoidance radar according to claim 1, characterized in that, Phase modulation specifically refers to: 。

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