A squint radar linear frequency modulation signal distance space variation Doppler correction method

Abstract

The application provides a squint radar linear frequency modulation signal distance space variation Doppler correction method, which comprises the following steps: obtaining a time delay correction value Δτ(τ) corresponding to each distance unit relative to a scene center according to a Doppler center f d (R i ) of each distance unit i ); performing linear fitting to obtain a linear fitting first-order term coefficient α and a constant term β; performing distance linear space variation time delay correction; obtaining a distance space variation Doppler correction signal and performing distance compression to obtain a distance space variation Doppler correction distance compression result The application provides a distance space variation Doppler effect compensation strategy, which eliminates target distance positioning errors caused by squint observation.

Description

Technical Field

[0001] This invention relates to a range-space-varying Doppler correction method for LFM signals of slant-looking radar, belonging to the field of radar technology. Background Technology

[0002] When observing from a high-speed moving platform using a large oblique angle, the observed scene echo exhibits a significant Doppler frequency shift, which is spatially variable with respect to range. When using a linear frequency modulated (LFM) signal system, this spatially variable Doppler frequency shift causes different range deviations for targets at different distances, resulting in range-direction positioning errors. This effect is known as range-Doppler coupling in LFM. Furthermore, when the Doppler frequency shift is large relative to the LFM signal bandwidth, the matched filter mismatch reduces the target compression gain, thus degrading target observation performance. When the instantaneous coverage area in the pitch direction is large, the Doppler characteristics of target echoes also change at different ranges, leading to altered LFM pulse compression offsets for targets at different distances. Currently, there is no literature describing compensation for the range-variable Doppler coupling effect. Summary of the Invention

[0003] This invention addresses the range-space-variable Doppler coupling effect in oblique-looking radar observations by constructing a range-direction space-variable Doppler model and obtaining a range-direction linear space-variable Doppler correction function through integration. This function is then continuously corrected in a single step, avoiding range segmentation and ensuring consistent correction effects across all range cells.

[0004] The technical solution of this invention is:

[0005] A method for range-space-varying Doppler correction of linear frequency modulated signals from a squint radar, comprising:

[0006] 1) Calculate the Doppler center f for each distance cell. d (R i According to the Doppler center f of each distance unit d (R i ), to obtain the time delay correction value Δτ(τ) corresponding to each distance unit relative to the scene center. i );

[0007] 2) Based on the time delay correction value Δτ(τ) obtained in step 1) for each distance cell i Perform linear fitting and solve for the coefficients α of the first-order term and the constant term β of the linear fitting.

[0008] 3) Based on the linear term coefficient α and constant term β obtained in step 2), construct the distance-direction linear spatially variable time delay correction function corresponding to each distance unit;

[0009] 4) Based on the range-directed linear spatially varying time delay correction function obtained in step 3), obtain the range-directed spatially varying Doppler corrected signal.

[0010] 5) The range-varying Doppler corrected signal obtained in step 4) Range compression was performed to obtain the range compression result after range-to-space-variable Doppler correction. Complete the calibration method.

[0011] Preferably, the Doppler center f of each range cell is calculated using the radar platform's position and velocity, and the radar antenna's azimuth and viewing angle. d (R i ).

[0012] Preferably, each distance unit corresponds to a time delay correction value Δτ(τ). i Specifically:

[0013]

[0014] Where i is the label of the distance cell; R i τ represents the slant distance of the i-th distance unit relative to the scene center; i For each distance unit, the time delay relative to the scene center, K r The modulation frequency of a linear frequency modulated signal;

[0015] Preferably, the expression for linear fitting is: Δτ(τ i )=ατ i +β.

[0016] Preferably, the distance-oriented linear spatial time delay correction function is characterized as a linear frequency modulation signal.

[0017] Preferably, the distance-direction linear spatially varying time delay correction function corresponding to each distance unit is specifically:

[0018] h(τ i )=exp(j2πβK r τ i +jπαK r τ i 2 ),

[0019] Where h(τ) i ) represents the distance-directed linear spatial time-varying delay correction function value; j is the imaginary unit.

[0020] Preferably, the range-varying Doppler corrected signal Specifically:

[0021]

[0022] Wherein, s(τ) i () represents the echo pulse received by the slanting radar.

[0023] The advantages of this invention compared to the prior art are:

[0024] Range-to-space-variable compensation typically employs a range-block processing method, where each range sub-block is corrected using the Doppler at its center. This increases processing complexity, and the correction effect at the edges of range sub-blocks is inferior to that at the center. This invention, however, uses a unified correction function to achieve one-time correction of the range-to-space-variable Doppler, avoiding the operational complexity of range-block processing and the poor correction effect at the edges of range sub-blocks. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the observation geometry of a slant-looking radar;

[0026] Figure 2 A simulation example of the Doppler range variation curve under the observation geometry of a squint radar;

[0027] Figure 3 The following is the implementation flow of the method of the present invention;

[0028] Figure 4 The effect of echo correction using scene-center Doppler (all point targets);

[0029] Figure 5 To demonstrate the effect of echo correction using scene-center Doppler ( Figure 4 (Proximal local magnification);

[0030] Figure 6 To demonstrate the effect of echo correction using scene-center Doppler ( Figure 4 (Enlarged view of the middle section);

[0031] Figure 7 To demonstrate the effect of echo correction using scene-center Doppler ( Figure 4 (Extreme local magnification);

[0032] Figure 8 Doppler-induced shift in pulse pressure peak;

[0033] Figure 9 Echo correction effect (all point targets) is achieved using Doppler echo that varies with distance.

[0034] Figure 10 Echo correction effect using spatially varying Doppler with distance ( Figure 9 (Proximal local magnification);

[0035] Figure 11 Echo correction effect using spatially varying Doppler with distance ( Figure 9 (Enlarged view of the middle section);

[0036] Figure 12 Echo correction effect using spatially varying Doppler with distance ( Figure 9 (Extreme local magnification). Detailed Implementation

[0037] To better understand the above technical solutions, the technical solutions of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.

[0038] A range-space-variable Doppler correction method for linear frequency modulation (LFM) signals from a squint radar is proposed. Based on the radar observation geometry, range-space-variable Doppler parameters are calculated, and then these parameters are used to perform Doppler compensation on the echo. For example... Figure 3 As shown, it includes the following steps:

[0039] 1) Calculate the Doppler center f of each range cell using the radar platform's position and velocity, and the radar antenna's azimuth and viewing angle. d (R i ).

[0040] Where i is the label of the distance cell; R i Let represent the slant distance of the i-th distance unit relative to the scene center. Then, the time delay correction value relative to the scene center... τ i For each distance unit, the time delay relative to the scene center, K r The frequency modulation of the LFM signal;

[0041] 2) Based on the time delay correction value Δτ(τ) obtained in step 1) for each distance cell i A linear fit is performed to obtain Δτ(τ). i )=ατ i +β, solve to obtain the coefficients α of the first-order term and the constant term β of the linear fit;

[0042] 3) Based on the linear coefficient α and constant term β obtained in step 2), construct the range-direction linear space-varying time delay correction function corresponding to each range unit; the range-direction linear space-varying time delay correction function corresponding to each range unit is specifically as follows:

[0043] h(τ i )=exp(j2πβK r τ i +jπαK r τi 2 ),

[0044] The function h(τ) i ) is a linear frequency modulated signal. Where h(τ) i ) represents the distance-directed linear spatial time-varying delay correction function value; j is the imaginary unit.

[0045] 4) Based on the distance-oriented linear space-varying time delay correction function h(τ) obtained in step 3), i ), will the echo pulse s(τ) i ) and h(τ i Multiplying these together yields the range-space-variable Doppler-corrected (Doppler corresponds to time delay) positive signal.

[0046]

[0047] 5) The range-varying Doppler corrected signal obtained in step 4) Range compression was performed to obtain the range compression result after range-to-space-variable Doppler correction. Complete the correction method. Range compression results after range-to-space Doppler correction. Used for detecting and processing targets detected by radar.

[0048] Example

[0049] A schematic diagram of the observation geometry of a squint radar is shown below. Figure 1 As shown in the figure The radar observation viewpoint is θ, where θ is the azimuth angle. EL R is the elevation beamwidth of the radar antenna; c R n and R f These are the slant distances at the center, near end, and far end of the scene, respectively.

[0050] Using the simulation parameters in Table 1, range-space-variable Doppler correction simulation of the LFM signal of the slant-looking radar was performed.

[0051] Table 1 Operating parameters of the squint radar

[0052]

[0053] Figures 4-7 The image shows the pulse compression results of the echoes. The solid blue line represents the pulse compression results without Doppler correction. It can be seen that the peak positions of each target deviate from their true positions (the vertical bars in the image). The peak position of the central target after compression is approximately 3360.1m closer to its true position than its theoretical position. The calculated result of 3361.3m is basically consistent.

[0054] Simulation example of Doppler range variation curve under the observation geometry of slant-look radar, as shown below. Figure 2 As shown.

[0055] After applying Doppler approximation compensation at the scene center, the peak position of pulse compression (dashed line in the figure) is significantly closer to the true position. However, since the variation of Doppler with distance is ignored, only the peak position of the target at the scene center coincides with the true position. The compression peak position of near targets is farther than the true position, and the compression peak position of far targets is closer than the true target position. The nearest target in the figure is about 178m farther than the true position, which exceeds the range resolution (150m).

[0056] Figure 8 The figure shows the Doppler variation curve of the slant range delay (relative to the scene center), which is mainly expressed as a linear component. The pulse compression result is obtained by correcting the echo using a range-directed linear spatially varying time-shift correction function. Figure 9 Middle Figure 12 The figure shows the dashed lines. For comparison, the traditional Doppler compensation results (scene center Doppler compensation) are also shown in the figure. It can be seen that after applying the range-directed linear spatially varying time-shift correction function, the target compression peaks at the near, middle, and far ends of the scene match the true target positions well, with deviations from the true positions of 13.5m, 7.4m, and 13.5m, respectively, corresponding to range resolution units of 9%, 5%, and 9%.

[0057] The proposed method for range-space-varying Doppler correction of LFM signals from slant-looking radar addresses the range-space-varying Doppler coupling effect during slant-looking radar observation by constructing a range-direction range-varying Doppler model and obtaining a range-direction linear range-varying Doppler correction function through integration. This method performs continuous correction on the echo in a single step, avoiding range segmentation and ensuring consistent correction effects across all range cells. Simultaneously, it significantly reduces range-direction positioning errors, thereby improving the positioning accuracy of the radar.

[0058] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

[0059] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for range-space-varying Doppler correction of linear frequency modulated signals for slant-looking radar, characterized in that, include: 1) Calculate the Doppler center of each distance cell. According to the Doppler center of each distance unit Obtain the time delay correction value corresponding to each distance unit relative to the scene center. ; 2) Based on the time delay correction value obtained in step 1), for each distance unit. Perform linear fitting and solve for the coefficients of the first-order term of the linear fit. and constant term ; 3) Based on the coefficients of the linear term obtained in step 2), and constant term Construct a distance-direction linear spatially variable time delay correction function for each distance unit; 4) Based on the range-directed linear spatially varying time delay correction function obtained in step 3), obtain the range-directed spatially varying Doppler corrected signal. ; 5) The range-varying Doppler corrected signal obtained in step 4) Range compression was performed to obtain the range compression result after range-to-space-variable Doppler correction. Complete the calibration method; Each distance unit corresponds to a time delay correction value. Specifically: Where i is the label of the distance cell; This represents the slant distance of the i-th distance unit relative to the scene center; The time delay for each distance unit relative to the scene center. The modulation frequency of a linear frequency modulated signal; The expression for linear fitting is: ; The distance-oriented linear spatially variable time delay correction function is characterized as a linear frequency modulation signal; The distance-oriented linear spatially varying time delay correction function corresponding to each distance unit is specifically as follows: ， in, This represents the value of the distance-oriented linear space-varying time delay correction function; j is the imaginary unit; Range-directed spatially Doppler corrected signal Specifically: ； in, This refers to the echo pulse received by the slant-looking radar.

2. The method for range-space-varying Doppler correction of linear frequency modulated signals for slant-looking radar according to claim 1, characterized in that, Using the radar platform's position and velocity, and the radar antenna's azimuth and viewing angle, the Doppler center of each range cell is calculated. .

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