Method for reducing MDV by MP-STAP dual-machine cooperation

Abstract

This invention discloses a method for reducing MDV through MP-STAP dual-aircraft collaborative operation, comprising: under given radar system parameters, ensuring that both airborne platforms in the dual-aircraft radar system operate according to a preset mode, including a hybrid baseline configuration in a self-transmitting and self-receiving mode; acquiring clutter data for each platform; compensating the range-Doppler cells of the second airborne platform's clutter data using interpolation shifting to align with the center of the corresponding range-Doppler cells in the clutter data of the first airborne platform, thus obtaining new clutter data for the second airborne platform; acquiring the range-direction clutter signals of both airborne platforms, performing range-direction pre-filtering on each, thus obtaining updated clutter data for both airborne platforms; performing full-array degree-of-freedom joint space-time adaptive processing on the updated clutter data of both airborne platforms, and using the processing result to obtain the reduced MDV value. This invention can utilize the effective aperture of the antennas of both airborne platforms and reduce MDV.

Description

Technical Field

[0001] This invention belongs to the field of radar moving target detection, specifically relating to a method for reducing MDV through MP-STAP dual-machine collaboration. Background Technology

[0002] Low-speed target detection is a component of radar moving target detection. The low speed of low-speed targets (e.g., those with speeds less than 50 m / s) is often due to two reasons: one is that the target itself has a low speed, such as helicopters and rotary-wing drones. The other is that the cosine of the angle between the target's velocity direction and the line of sight is very low, resulting in a very low radial velocity. For example, a missile launched vertically upwards has a low initial velocity, and its predominantly upward flight direction further reduces its radial velocity.

[0003] MDV (minimum detectable velocity) is an important indicator in low-speed target detection. MDV refers to the minimum radial velocity of a target that a radar can detect. It represents the radar system's ability to detect slow-moving targets and provides a lower bound on the range of detectable moving target velocities. When the radial velocity of a target is below the MDV, the target will be obscured by main lobe clutter and cannot be detected, which is also detrimental to subsequent angle measurement and tracking. Reducing the MDV allows targets with relatively low radial velocities to enter the sidelobe clutter region and become easier to detect. In monostatic radar scenarios, space constraints limit the antenna aperture, resulting in lower spatial resolution and thus limited detection capability for slow-moving targets.

[0004] To further improve detection performance, a dual-aircraft collaborative working mode can be adopted, i.e., a dual-aircraft radar system. As the name suggests, a dual-aircraft radar system refers to a system containing two airborne platforms, each of which has signal transmission and reception capabilities. Dual-aircraft collaborative detection has the following advantages: (1) In terms of clutter suppression and detection, the two airborne platforms can be flexibly configured in a dual-aircraft configuration, so that the target will not fall into the main lobe clutter area at the same time, which is beneficial for detection. (2) In terms of anti-jamming, in order to avoid enemy reconnaissance and interference, the dual aircraft can still adopt a passive working mode, which can prevent the main lobe of the enemy jammer from interfering with the radar receivers in two different directions at the same time.

[0005] Currently, research on improving low-speed target detection performance through dual-aircraft collaboration mainly focuses on the "other transmits, self receives" bistatic radar mode. However, existing technologies do not utilize the effective apertures of both antennas, nor do they employ targeted methods to reduce MDV (measurable velocity deviation). For example, the paper "Minimum detectable velocity evaluation of bistatic radar and its relevance for ground target tracking" by Michael Mertens et al. studied the changes in MDV under different bistatic configurations and verified through simulation that the MDV differs under different configurations, but it did not conduct an in-depth analysis of these changes.

[0006] Therefore, in view of the above situation, there is an urgent need for a new method of dual-machine collaboration to reduce MDV in order to improve the performance of low-speed target detection. Summary of the Invention

[0007] To address the aforementioned problems in the existing technology, this invention provides a method for reducing MDV through MP-STAP dual-machine collaboration. The technical problem to be solved by this invention is achieved through the following technical solution:

[0008] Given radar system parameters, it is determined that both the first and second airborne platforms in the dual-aircraft radar system operate according to a preset mode. This preset mode includes: each airborne platform operating in a self-transmitting and self-receiving mode; the aircraft corresponding to the two airborne platforms flying in the same direction with the same heading and speed; the height of the second airborne platform being greater than that of the first airborne platform; the antennas of the two airborne platforms arranged along the heading; a first preset value for the heading baseline and a second preset value for the vertical baseline; the first preset value being less than the second preset value; and the heading baseline and the vertical baseline representing the horizontal and vertical spacing of the antennas of the two airborne platforms, respectively.

[0009] Acquire clutter data from two airborne platforms; for the clutter data of the second airborne platform, use interpolation shifting to compensate the range-Doppler cells so as to center-align with the corresponding range-Doppler cells in the clutter data of the first airborne platform, thereby obtaining new clutter data for the second airborne platform;

[0010] Based on the clutter data from the first airborne platform and the new clutter data from the second airborne platform, range clutter signals from the two airborne platforms are obtained; range pre-filtering is performed on the range clutter signals from the two airborne platforms respectively to obtain updated clutter data from the two airborne platforms.

[0011] The updated clutter data from the two airborne platforms are subjected to joint space-time adaptive processing with full array degrees of freedom, and the reduced MDV value is obtained using the processing results.

[0012] In one embodiment of the present invention, the first preset value is determined by comparing and analyzing the number of blind speeds and the size of the curve notch corresponding to the speed response result diagrams under different flight paths;

[0013] The second preset value is determined based on the first preset value and the difference in flight altitude between the two carrier aircraft according to the requirements for safe flight.

[0014] In one embodiment of the present invention, the first preset value is 3 meters; the second preset value is 200 meters.

[0015] In one embodiment of the present invention, the clutter data of the second airborne platform is compensated for using an interpolation shifting method to center-align with the corresponding range-Doppler cells in the clutter data of the first airborne platform, thereby obtaining new clutter data for the second airborne platform, including:

[0016] Determine the distance difference Δr and the Doppler frequency difference Δf between the second airborne platform and the first airborne platform. dc Determine Δr and Δf dc The calculation precision is 1 / Q; where Q is a natural number greater than 0;

[0017] Based on Δr and Δf dc Calculate the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for each range-Doppler cell;

[0018] The clutter data of the second airborne platform is interpolated by Q times in Doppler dimension and range gate dimension, so that the dimension of the clutter data changes from N×K×L to N×100K×100L; where N is the number of antenna array elements of the second airborne platform; K is the number of pulses transmitted by the radar transmitter of the second airborne platform; and L is the maximum unambiguous range gate.

[0019] Based on the calculated range gate compensation and Doppler channel compensation for each range-Doppler unit, the second airborne platform relative to the first airborne platform moves the corresponding range-Doppler unit after clutter data interpolation of the second airborne platform to the corresponding position on the range-Doppler plane to align with the center of the same range-Doppler unit of the first airborne platform.

[0020] The clutter data of the second airborne platform after its relocation is resampled to restore it to its original dimension, resulting in new clutter data of the second airborne platform.

[0021] In one embodiment of the present invention, the distance difference Δr and the Doppler frequency difference Δf between the second airborne platform and the first airborne platform are determined. dc The calculation formulas used in the process include:

[0022]

[0023]

[0024] Where R1 is the distance from the first airborne platform to the scattering point; R2 is the distance from the second airborne platform to the scattering point; x 12 h1 is the distance between the first airborne platform and the second airborne platform, expressed as the length of the baseline; h2 is the height of the first airborne platform; h3 is the height of the second airborne platform; f4 is the distance between the first airborne platform and the second airborne platform. d1 f is the Doppler frequency of the clutter block corresponding to the first airborne platform; d2 θ1 is the Doppler frequency of the clutter block corresponding to the second airborne platform; v is the airborne platform speed; λ is the radar operating wavelength; θ1 is the azimuth angle of the first airborne platform; θ2 is the azimuth angle of the second airborne platform. The pitch angle of the first airborne platform; ψ is the pitch angle of the second airborne platform. v1 ψ is the velocity cone angle of the first airborne platform. v2 The velocity cone angle of the second airborne platform.

[0025] In one embodiment of the present invention, the determination of Δr and Δf dc The calculation precision is 1 / Q, including:

[0026] For the current value of i, perform the expression determination steps, including: setting Δr and Δf dc Consider them as functions of R2 and θ2, respectively: Δr = f1(R2,θ2) and Δf dc =f2(R2,θ2), and using the Taylor formula for bivariate functions, determine the expression for the i-th order Lagrange remainder term of each function at a point (R2+Δh,θ2+Δk) in the neighborhood of (R2,θ2). if1 and O if2 Where i is a natural number greater than 0, and i = 1 when executed for the first time; Δh and Δk are preset minimum values;

[0027] Estimate O if1 and O if2 Order of magnitude;

[0028] Determine if the current value of i satisfies the following condition: the sum of 1 / B and O. if1 The order of magnitude of the numerical value is greater than the preset value, and 1 / Bn The value and O if2 The order of magnitude of the value is greater than a preset value; where B is the signal bandwidth; B n Doppler bandwidth;

[0029] If so, determine Δr and Δf. dc Calculation accuracy If not, increment the current value of i and return to the expression determination step until Δr and Δf are determined. dc The calculation accuracy.

[0030] In one embodiment of the present invention, the basis of Δr and Δf dc Calculate the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for each range-Doppler cell, including:

[0031] Let Δr and Δf dc By converting the difference between the range resolution and Doppler resolution into the difference between the range gate and the Doppler channel, the compensation amount of the range gate and the compensation amount of the Doppler channel of the second airborne platform relative to the first airborne platform for all clutter blocks are obtained.

[0032] The clutter block compensation amount corresponding to the center frequency of the Doppler channel is used as the reference for movement. The center of each range-Doppler unit is aligned with the center of the same range-Doppler unit of the first airborne platform. This yields the range gate compensation amount and Doppler channel compensation amount of the second airborne platform relative to the first airborne platform for each range-Doppler unit.

[0033] In one embodiment of the present invention, the step of moving the corresponding range-Doppler unit of the second airborne platform after clutter data interpolation to a corresponding position on the range-Doppler plane according to the calculated range gate compensation amount and Doppler channel compensation amount of the second airborne platform relative to the first airborne platform for each range-Doppler unit includes:

[0034] For each range-Doppler cell after clutter data interpolation of the second airborne platform, the corresponding movement distance is determined based on the calculated absolute values ​​of the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for that range-Doppler cell.

[0035] For each range-Doppler cell after clutter data interpolation of the second airborne platform, the corresponding movement direction is determined based on the positive and negative values ​​of the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for that range-Doppler cell.

[0036] Each range-Doppler unit, after interpolation of the clutter data from the second airborne platform, is moved to its corresponding position on the range-Doppler plane according to its determined moving distance and direction.

[0037] In one embodiment of the present invention, for each range-Doppler cell after clutter data interpolation for the second airborne platform, determining the corresponding movement distance based on the calculated absolute values ​​of the range gate compensation and Doppler channel compensation for that range-Doppler cell relative to the first airborne platform includes:

[0038] For each range-Doppler unit after clutter data interpolation of the second airborne platform, for either the range gate compensation amount or the Doppler channel compensation amount, the movement distance corresponding to that compensation amount of the range-Doppler unit is determined according to the Q multiple of the absolute value of that compensation amount.

[0039] For each range-Doppler cell after clutter data interpolation for the second airborne platform, the corresponding movement direction is determined based on the calculated sign of the range gate compensation and Doppler channel compensation relative to the first airborne platform for that range-Doppler cell, including:

[0040] For each range-Doppler unit after clutter data interpolation of the second airborne platform, the movement direction corresponding to the compensation amount of the range-Doppler unit is determined according to the positive or negative sign of the compensation amount; wherein, when the range gate compensation amount is positive, the movement direction is downward, and when it is negative, the movement direction is upward; when the Doppler compensation amount is positive, the movement direction is to the right, and when it is negative, the movement direction is to the left.

[0041] In one embodiment of the present invention, the step of performing range-direction pre-filtering on the range clutter signals of the two airborne platforms to obtain updated clutter data for the two airborne platforms includes:

[0042] Calculate the cross-correlation function for the range clutter signals of the two airborne platforms;

[0043] The cross-correlation function is subjected to Fourier transform to obtain its spectrum, and the frequency corresponding to the peak value is determined as Δf based on the spectrum characteristics.

[0044] The range clutter signal of the first airborne platform is subjected to matched filtering and windowing within the range of [-B / 2, B / 2-Δf]; the range clutter signal of the second airborne platform is subjected to matched filtering and windowing within the range of [Δf-B / 2, B / 2] to obtain updated clutter data for the two airborne platforms.

[0045] The beneficial effects of this invention are:

[0046] Compared to existing technologies, the method of this invention is applicable to dual-aircraft radar operating in a "self-transmitting and self-receiving" mode under hybrid baselines. Compared to monopolar radar, the antenna aperture of this invention is longer, which can further reduce MDV. Compared to distributed radar, this invention does not have the problem of space-time synchronization, which can save resources and is easier to implement. Moreover, this invention fills the gap in research on the low-speed target detection performance of dual-aircraft radar in "self-transmitting and self-receiving" mode, effectively utilizes the effective aperture of the antennas of the two airborne platforms, and proposes a targeted method to reduce MDV and improve low-speed target detection performance. Attached Figure Description

[0047] Figure 1 This is a flowchart illustrating a method for reducing MDV through MP-STAP dual-machine collaboration provided in an embodiment of the present invention.

[0048] Figure 2 (a)~ Figure 2 (d) shows the velocity response results under different baselines along the heading in the embodiments of the present invention;

[0049] Figure 3 This is a comparison diagram of the adaptive velocity response under four antenna arrangements in the embodiments of the present invention;

[0050] Figure 4 This is a schematic diagram of the geometric structure of a dual-machine observation scenario in an embodiment of the present invention;

[0051] Figure 5 This is a schematic diagram of the clutter RD unit of two airborne platforms in an embodiment of the present invention;

[0052] Figure 6 (a) and Figure 6 (b) is a diagram of the range gate and Doppler channel compensation for each clutter block in the embodiments of the present invention;

[0053] Figure 7 (a) and Figure 7 (b) is a distance gate and Doppler channel compensation diagram for each RD unit in the embodiment of the present invention;

[0054] Figure 8 This is a schematic diagram showing the positions of adjacent RD units before and after interpolation in an embodiment of the present invention;

[0055] Figure 9 This is a schematic diagram of the RD unit shifting after interpolation in an embodiment of the present invention;

[0056] Figure 10 This is a schematic diagram illustrating the geometric relationship between the first airborne platform and a certain RD unit in an embodiment of the present invention;

[0057] Figure 11 (a)~Figure 11 (d) is a diagram showing the theoretical value of the interference phase in an embodiment of the present invention when there is only a vertical baseline;

[0058] Figure 12 This is a schematic diagram illustrating the relationship between the echo spectrum and spatial spectrum of the two airborne platforms in the pre-filtering process of an embodiment of the present invention.

[0059] Figure 13 This is a schematic diagram illustrating the specific process of the MP-STAP method according to an embodiment of the present invention;

[0060] Figure 14 (a)~ Figure 14 (d) is an interference phase diagram between the same RD unit of two platforms under different vertical baselines in an embodiment of the present invention;

[0061] Figure 15 (a) and Figure 15 (b) is an interference phase diagram between the same RD unit of two airborne platforms before and after pre-filtering in an embodiment of the present invention;

[0062] Figures 16(a) to 16(d) This is a diagram showing the results of combined PD processing, ATI processing, and single-base PD processing in an embodiment of the present invention.

[0063] Figures 17(a) to 17(d) The diagram shows the results of combined EFA processing, ATI+EFA processing, and single-base EFA processing in the embodiments of the present invention. Detailed Implementation

[0064] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] To address the issue that existing research on dual-aircraft cooperative MDV reduction primarily employs a bistatic radar mode of "other transmits, self receives," which does not utilize the effective apertures of both antennas and lacks a targeted MDV reduction method, this invention provides an MP-STAP dual-aircraft cooperative MDV reduction method.

[0066] It should be noted that the execution subject of the MP-STAP dual-machine collaborative MDV reduction method provided in this embodiment of the invention can be an MP-STAP dual-machine collaborative MDV reduction device, which can run in an electronic device. This electronic device can be a server or a terminal device, but is not limited to these.

[0067] likeFigure 1 As shown in the embodiment of the present invention, a method for reducing MDV through MP-STAP dual-machine collaboration may include the following steps S1 to S4:

[0068] S1, Under the given radar system parameters, determine that both the first airborne platform and the second airborne platform in the dual-aircraft radar system operate in a preset manner;

[0069] The preset methods include: each airborne platform adopts a self-transmitting and self-receiving working mode; the carrier aircraft corresponding to the two airborne platforms fly in the same direction and have the same heading and speed direction; the height of the second airborne platform is greater than the height of the first airborne platform; the antennas of the two airborne platforms are arranged along the heading; the baseline along the heading uses a first preset value, and the vertical baseline uses a second preset value; the first preset value is less than the second preset value; the baseline along the heading and the vertical baseline are the horizontal and vertical spacing of the antennas of the two airborne platforms, respectively.

[0070] Specifically, in this embodiment of the invention, given radar system parameters are first obtained, including the coordinates of the first and second airborne platforms, the form and number of antenna array elements, the number of pulses, the signal bandwidth, the airborne platform speed, the radar pulse repetition frequency, and the detection threshold.

[0071] Then, it was determined that both the first and second airborne platforms in the dual-aircraft radar system operated according to a preset mode. This preset mode, representing the operating mode and dual-aircraft configuration, was determined beforehand based on experiments.

[0072] The specific process of determining the preset method in the experiment includes:

[0073] In a dual-aircraft radar system, the two carrier aircraft correspond to the first and second airborne platforms, respectively. In "self-transmitting and self-receiving" mode, the two aircraft fly in the same direction, with the same heading and velocity direction. The antennas on each airborne platform are installed along the heading in a frontally equidistant linear array configuration, with N array elements and d element spacing. Both N and d are real numbers greater than 0. The horizontal spacing between the antennas of the two airborne platforms is called the heading baseline, and the length of the heading baseline is defined as x. / / A longer baseline along the flight path results in a longer overall antenna formed by the receiving antennas of the two airborne platforms, leading to a smaller target detection velocity (MDV). However, research has found that an excessively long baseline along the flight path can result in an excessively small MDV and excessive blind velocities. An excessively small MDV can cause false alarms due to clutter motion, affecting target detection performance. Excessive blind velocities can cause targets to become undetectable at too many radial velocities. The change in target response with velocity can be measured using velocity response.

[0074] The term "blind velocity" refers to a situation where the phase difference between the echo signals of a moving target in adjacent cycles is an integer multiple of 2π, making the target echo identical to a stationary echo and thus undetectable. In this case, the radial velocity of the target satisfies the following formula (1):

[0075]

[0076] in, For phase difference; v r Radial velocity; T is one period; λ is the radar operating wavelength; f dt The target Doppler frequency; k = 0, ±1, ±2K.

[0077] The formula for calculating blind speed is shown in formula (2):

[0078]

[0079] Among them, v rb For blind speed; v is the speed of the airborne platform; x / / Let v be the length along the heading baseline. Without velocity ambiguity, v rmax =λf r / 4 represents the maximum radial velocity, v rb ∈[-v rmax ,v rmax ], f r PRF (pulse repetition frequency). The longer the baseline along the heading, the more values ​​of k there are, and the higher the blind speed.

[0080] Therefore, the target's velocity response can be obtained as follows:

[0081]

[0082] Among them, g v (v r ) represents the target's velocity response; blind velocity is the radial velocity corresponding to a velocity response of 0.

[0083] To determine the optimal length of the along-heading baseline, i.e., the first preset value, theoretical analysis was performed on the speed response under different along-heading baselines. Specifically, the first preset value was determined by comparing and analyzing the number of blind speeds and the size of the curve notch corresponding to the speed response results under different along-heading baselines, and selecting the best value. The principle of selection is to have fewer blind speeds and a smaller curve notch.

[0084] The process is illustrated with a specific example. Under a given radar system parameter, the number of blind speeds under different flight paths can be calculated according to formula (2), and the speed response result diagrams under different flight paths can be obtained. For example, in the initial state, the flight path baselines are set to 1m, 10m, and 30m, etc. The number of blind speeds and the curve notch in the corresponding flight path baseline speed response result diagrams are viewed. If the preset requirements for the number of blind speeds and the curve notch are not met, a flight path baseline as an intermediate value can be added on the basis of the initial state. For example, 3m can be added between 1m and 10m to obtain the modified flight path baselines of 1m, 3m, 10m, and 30m, and then observed and analyzed again.

[0085] Figure 2 Figures (a) to (d) show the speed responses at baselines of 1m, 3m, 10m, and 30m, respectively. It can be seen that when the baseline is 1m, the number of blind speeds is 11; when the baseline is 3m, the number of blind speeds is 31; when the baseline is 10m, the number of blind speeds is 101; and when the baseline is 30m, the number of blind speeds is 301. Figure 2 In the graph, the horizontal axis represents radial velocity in m / s (meters per second), and the vertical axis represents velocity response in volts (V). It can be seen that within the velocity range of interest [-200 m / s, 200 m / s], Figure 2 The radial velocity at which the velocity response is 0 in each graph is the blind velocity. Because the radial velocity is plotted at intervals of 0.5, therefore... Figure 2 There are discrepancies between the number of blind speeds in each diagram and the calculated values. The blind speeds at 1m and 3m are fewer, and the notch at 3m is narrower than that at 1m, indicating stronger detection capability for low-speed targets. Therefore, 3m can be defined as the baseline length along the flight path under the radar system parameters. Since any value from 1m to 5m is used, the experimental results and... Figure 2 Similarly, in one alternative implementation, the first preset value is 3 meters.

[0086] To illustrate the advantages of dual-mode radar over monostatic radar, the antennas can be arranged in four ways: one platform with two sub-apertures, one platform with four sub-apertures, two platforms with four sub-apertures, and two platforms with eight sub-apertures. Their adaptive velocity responses are then compared. Figure 3 As shown, the curves of one platform with two apertures are represented by solid lines and hollow circles; the curves of one platform with four apertures are represented by solid lines and solid squares; the curves of two platforms with four apertures are represented by solid lines and solid triangles; and the curves of two platforms with eight apertures are represented by solid lines and solid vertical lines. The expression for the adaptive velocity response is:

[0087]

[0088] Among them, g av (v r ) represents the adaptive velocity response; w represents the spacetime weight vector; w H s is the transpose of w; st (v r ) represents the spacetime steering vector of the target; s s The spatial guidance vector for the target; s t (v r The time-domain steering vector of the target; To obtain the Kronecker product.

[0089] from Figure 3 As can be seen from this, because β=2v / (df) r =0.5, the normalized Doppler frequency corresponding to the maximum spatial frequency of 0.5 is 0.25. Therefore, when the radial velocity is in the range of [-200m / s, -100m / s)U(100m / s, 200m / s], the target enters the noise zone and no extra notch will appear. When the sidelobe clutter and the target are in the same Doppler channel, the spatial adaptive processing needs to form a notch to suppress the sidelobe clutter, and the target's velocity response is better. However, because the distance between the sub-apertures is greater than or equal to half the wavelength, the synthesized pattern will produce grating lobes. According to the characteristics of grating lobes, the formula for calculating the position and number of grating lobes is:

[0090]

[0091] Where N0 is the number of array elements within the sub-aperture; d is the element spacing; θ d θ is the azimuth angle corresponding to the grating lobe; θ0 is the azimuth angle of the main beam. The grating lobes of the synthesized pattern will generate grating clutter. When the grating clutter and the target are in the same Doppler channel, due to spatial ambiguity, the notch formed at this time will cause a grating notch in the target direction. Therefore, the target is suppressed, and the target response at the radial velocity corresponding to the spatial frequency of the grating lobe will decrease. For example, according to equation (5), when the azimuth angle of the main beam is 90°, the pattern under the two apertures of a platform will generate grating lobes at spatial frequencies of ±0.25 and ±0.5. Since β=0.5, the adaptive velocity response will also generate redundant notches around ±50m / s and ±100m / s. Finally, since the notch width of the dual-aircraft radar at 0m / s is smaller than that of the single-base radar, it is beneficial to extend the length of the receiving antenna along the heading baseline, so that the dual-aircraft radar has better detection capability for low-speed targets than the single-base radar.

[0092] Because the baseline along the flight path is limited, to ensure safe flight, this embodiment of the invention requires the two carrier aircraft to fly at different altitudes, i.e., to increase the vertical baseline. Therefore, the second preset value is determined based on the first preset value and the difference in flight altitude between the two carrier aircraft required for safe flight. For example, if the first preset value is 3m, the second preset value could be 200 meters, and so on.

[0093] Please see Figure 4 The geometric structure of the dual-machine detection model in the present invention is given. Figure 4 In this text, Platform 1 and Platform 2 represent the first and second airborne platforms, respectively, and will be referred to as such in subsequent examples. The direction of the velocity (v) of each airborne platform is parallel to the positive Y-axis; the heights of Platform 1 and Platform 2 are h1 and h2, respectively; the platform height is the height from the platform center to the XOY plane; the distance between Platform 1 and Platform 2 is called the baseline, and the length of the baseline is x. 12 Its satisfaction x ⊥ =h2-h1 represents the length of the vertical baseline. The coordinates of platform 1 are (x1, y1, h1); the coordinates of platform 2 are (x2, y2, h2); the coordinates of the scattering point P are (x0, y0, 0); the distances from platform 1 and platform 2 to the scattering point are R1 and R2 respectively; the azimuth angles of platform 1 and platform 2 are θ1 and θ2 respectively; the elevation angles of platform 1 and platform 2 are respectively... and The velocity cone angles of platform 1 and platform 2 are respectively ψ v1 and ψ v2 The observation angles of platform 1 and platform 2 are φ1 and φ2, respectively. For the specific meanings of the above parameters, please refer to [the documentation / reference]. Figure 4 And related technical understanding, which will not be explained in detail here.

[0094] Through the above preliminary experiments, the working mode and dual-system configuration of the dual-aircraft radar system can be determined. The working mode is self-transmitting and self-receiving. The self-transmitting and self-receiving working mode adopted in this embodiment of the invention can make full use of the arrangement of the antennas of the two carrier platforms along the flight direction to obtain a certain baseline along the flight direction, so that the two antennas are combined into a long antenna, thereby increasing the length of the receiving antenna and reducing MDV.

[0095] The dual-baseline configuration is a hybrid baseline configuration under "self-transmitting and self-receiving" conditions, which combines the forward baseline with the vertical baseline. The forward baseline is shorter, and its function is to increase the antenna receiving aperture and reduce MDV; the vertical baseline is longer, and its function is to ensure safe flight.

[0096] S2, acquire clutter data from two airborne platforms; for the clutter data of the second airborne platform, compensate the range-Doppler cells using an interpolation shifting method to center-align with the corresponding range-Doppler cells in the clutter data of the first airborne platform, and obtain new clutter data for the second airborne platform;

[0097] The following explanation of this step is based on the research concept. For two airborne platforms under a mixed baseline, the different locations of the airborne platforms cause misalignment of the received clutter range-Doppler units (RD units). The same ground clutter block will be located in different RD units, and the distance and Doppler frequency of the same RD unit relative to the two airborne platforms will be different. This makes it impossible to jointly process the echo signals of the two airborne platforms, and thus impossible to use the two airborne platforms to reduce MDV. Therefore, the inventors determined through analysis that a certain method should first be adopted to ensure that the RD units corresponding to the two platforms have the same distance and Doppler frequency.

[0098] Specifically, the inventors studied the equidistant loops, equal Doppler lines, and RD cells of clutter in a dual-machine model; please refer to [link to relevant documentation]. Figure 5 To distinguish them, the curves for platform 1 are shown as bold lines. The equidistant rings appear as circular loops on the ground, while the equal Doppler lines appear as hyperbolas. The area enclosed by the circular ring and the adjacent hyperbola constitutes an RD cell. The clutter signal of an RD cell is the superposition of the clutter scattering signals from all clutter scattering points in that area. The equidistant rings and equal Doppler lines of the two airborne platforms overlap on the ground. Because the clutter scattering point at the center of the RD cell, i.e., the clutter scattering point corresponding to the center frequency of the Doppler channel, determines which range gate and Doppler channel the RD cell represents, compensation can be performed on the RD cells. Compensation involves aligning the RD cells with the center scattering points of the two airborne platforms.

[0099] To align the centers of each RD unit on the two airborne platforms, it is necessary to calculate how many distance gates and Doppler channels the RD units differ from the perspectives of the two airborne platforms. According to... Figure 4 From the geometric relationships in the diagram, we can see that:

[0100]

[0101]

[0102]

[0103]

[0104] For the parameters in formulas (6) to (9) above, please refer to [the relevant documentation]. Figure 4 Related explanations.

[0105] Based on this, the range-Doppler cells in the clutter data of the second airborne platform can be compensated by interpolation shifting, so that the centers of the corresponding range-Doppler cells in the clutter data of the second airborne platform and the clutter data of the first airborne platform are aligned, thereby obtaining new clutter data of the second airborne platform.

[0106] Specifically, for the clutter data of the second airborne platform, the range-Doppler cells are compensated using an interpolation shifting method to center-align with the corresponding range-Doppler cells in the clutter data of the first airborne platform, resulting in new clutter data for the second airborne platform, including:

[0107] S21, determine the distance difference Δr and the Doppler frequency difference Δf between the second airborne platform and the first airborne platform. dc Determine Δr and Δf dc The calculation accuracy is 1 / Q;

[0108] Based on the above description, the distance difference Δr and the Doppler frequency difference Δf between the second airborne platform and the first airborne platform are determined. dc The calculation formulas used in the process include:

[0109]

[0110]

[0111] Where R1 is the distance from the first airborne platform to the scattering point; R2 is the distance from the second airborne platform to the scattering point; x 12 h1 is the distance between the first and second airborne platforms, denoted as the baseline length; h2 is the height of the first airborne platform; h3 is the height of the second airborne platform; f4 is the distance between the first and second airborne platforms. d1 f is the Doppler frequency of the clutter block corresponding to the first airborne platform; d2 θ1 is the Doppler frequency of the clutter block corresponding to the second airborne platform; v is the airborne platform velocity; λ is the radar operating wavelength; θ1 is the azimuth angle of the first airborne platform; θ2 is the azimuth angle of the second airborne platform. The pitch angle of the first airborne platform; ψ is the pitch angle of the second airborne platform. v1 ψ is the velocity cone angle of the first airborne platform. v2 The velocity cone angle of the second airborne platform.

[0112] Calculate Δf dc At this time, the clutter block is fixed on the ground, and its azimuth angle is independent of the platform position. Therefore, θ1 and θ2 can be taken to have the same value, both considered as the azimuth angle of the ground clutter block, i.e., θ1 = θ2. From formulas (10) and (11), it can be seen that Δr and Δf... dcIt is related to θ2 and R2, and according to the properties of a triangle, Δr <x 12 Within the range of long-range clutter, the larger R2 is, the smaller Δr is. Considering practical situations, the values ​​are taken as θ2∈[0,π], R2∈(h2,R). 2max ], R is the furthest radar field of view of the second airborne platform. e This is the equivalent radius of the Earth.

[0113] Δr, Δf dc The accuracy of the calculation determines the accuracy of the compensation; therefore, it is necessary to first determine Δr and Δf. dc The calculation accuracy. In one optional implementation, Δr and Δf are determined. dc The calculation precision is 1 / Q, including:

[0114] 1) For the current value of i, perform the expression determination steps, including: setting Δr and Δf dc Consider them as functions of R2 and θ2, respectively: Δr = f1(R2,θ2) and Δf dc =f2(R2,θ2), and using the Taylor formula for bivariate functions, determine the expression for the i-th order Lagrange remainder term of each function at a point (R2+Δh,θ2+Δk) in the neighborhood of (R2,θ2). if1 and O if2 ;

[0115] Where i is a natural number greater than 0, and i = 1 when executed for the first time; Δh and Δk are preset minimum values.

[0116] Specifically, taking i=2 as an example, according to the Taylor formula for bivariate functions, the expression for the second-order Lagrange remainder term of the two functions at a point (R2+Δh, θ2+Δk) in the neighborhood of (R2, θ2) can be given as follows:

[0117]

[0118]

[0119] 2) Estimate O if1 and O if2 Order of magnitude;

[0120] Based on the example above, for formulas (12) and (13), 0 < κ < 1; and because R2 ∈ (h2, R 2max ], θ2∈[0,π], Δh and Δk are preset local minima, for example, 0.01, which can be used to estimate O 2f1 The order of magnitude is 10 -13 O 2f2 The order of magnitude is 10 -12 .

[0121] 3) Determine if the current value of i satisfies: the sum of 1 / B and O if1 The order of magnitude of the numerical value is greater than the preset value, and 1 / B n The value and O if2 The order of magnitude of the numerical value is greater than the preset value;

[0122] The preset value can be 10000 or 100000. Step 3) actually determines whether the following condition is met: O if1 The order of magnitude is much smaller than 1 / B, and O if2 The order of magnitude is much smaller than 1 / B n .

[0123] Based on the order of magnitude obtained in step 2), O can be determined. 2f1 Order of magnitude 10 -13 Much less than 1 / B; O 2f2 The order of magnitude is 10 -12 Much smaller than 1 / B n .

[0124] Where B is the signal bandwidth; B n This refers to the Doppler bandwidth.

[0125] 4) If so, determine Δr and Δf. dc Calculation accuracy

[0126] Where Q is a natural number greater than 0.

[0127] Continuing with the example above, when the condition is met in step 3), it means that the calculation error is within the allowable range and the calculation accuracy should reach [the required level]. Therefore, determine Δr and Δf dc The calculation accuracy is

[0128] 5) If not, increment the current value of i by one and return to the expression determination step until Δr and Δf are determined. dc The calculation accuracy.

[0129] Understandably, since the calculation starts from i=1, if we use the Taylor formula for bivariate functions, we can give an expression for the first-order Lagrange remainder term of the two functions at a point (R2+Δh, θ2+Δk) in the neighborhood of (R2, θ2) and estimate O. 1f1 and O 1f2 The order of magnitude, determining whether condition O is satisfied. 1f1 The order of magnitude is much smaller than 1 / B and O 1f2 The order of magnitude is much smaller than 1 / B n At that time, Δr and Δf will be determined. dcThe calculation precision is 10. The calculation for i=2 will only proceed if the above conditions are not met. Conversely, if i=2 also fails to meet the above conditions, the calculation for i=3 will continue, and so on.

[0130] S22, based on Δr and Δf dc Calculate the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for each range-Doppler cell;

[0131] S22 includes the following steps:

[0132] S221, Δr and Δf dc By converting the difference between the range resolution and Doppler resolution into the difference between the range gate and the Doppler channel, the compensation amount of the range gate and the compensation amount of the Doppler channel for the second airborne platform relative to the first airborne platform are obtained for all clutter blocks.

[0133] S222, based on the compensation amount of the clutter block corresponding to the center frequency of the Doppler channel, the center of each range-Doppler unit is aligned with the center of the same range-Doppler unit of the first airborne platform, so as to obtain the range gate compensation amount and Doppler channel compensation amount of the second airborne platform relative to the first airborne platform for each range-Doppler unit.

[0134] To facilitate understanding of the two steps above, a specific example will be used to illustrate them below.

[0135] First, the range gate compensation and Doppler channel compensation for each clutter block on the second airborne platform are calculated, without considering range ambiguity and Doppler ambiguity. For example, the coordinates of the first airborne platform are (0m, 3m, 7800m), and the coordinates of the second airborne platform are (0m, 0m, 8000m). The range difference Δr and the Doppler frequency difference Δf are then calculated. dc By converting the range resolution and Doppler resolution into the difference between the range gate and the Doppler channel, the range gate compensation and Doppler channel compensation for the second airborne platform relative to the first airborne platform are obtained for all clutter blocks. Figure 6 As shown in (a) and (b). Among them, Figure 6 (a) represents the range gate compensation for each clutter block, and (b) represents the Doppler channel compensation for each clutter block. The two figures show the effect of the original image after being grayscaled.

[0136] from Figure 6As can be seen from (a) and (b), numbers 1-53 are at a distance of R2 from the gate. 0, Then Δf dc ≤0. The clutter block compensation for azimuth angle θ2>π / 2 is greater than or equal to 0 because cosθ2>0. Then Δf dc ≥0. At the same azimuth angle θ2, the absolute value of the compensation amount decreases or remains constant with increasing range gate. At the same range gate, the absolute value of the compensation amount first decreases and then increases with increasing azimuth angle θ2. This is because when θ2 is π / 2, cosθ2 is 0, and Δf dc It is 0.

[0137] Since the dimension of clutter data is N×K×L, where L is the maximum unambiguous distance gate, and clutter suppression targets each RD cell, it is necessary to calculate the compensation amount for each RD cell and perform compensation on an RD cell basis. To obtain the compensation amount for each RD cell, the center of each RD cell can be aligned by shifting the clutter block corresponding to the center frequency of the Doppler channel.

[0138] Please see the results. Figure 7 , Figure 7 The range gate compensation and Doppler channel compensation for the second airborne platform relative to the first airborne platform are given for each RD unit. Figure 7 (a) represents the distance gate compensation amount for each RD unit; Figure 7 (b) represents the Doppler channel compensation amount for each RD unit. Both figures show the effect after grayscale conversion of the original image.

[0139] from Figure 7It can be seen that range gates 1-53 did not receive clutter signals. Doppler channels 1-18 and 49-64 correspond to the noise region, and their range gate compensation and Doppler channel compensation are both 0. In the clutter region, the range gate compensation value ranges from 0 to 1.32. The compensation value of the RD unit for the same range gate increases with the increase of the Doppler channel. The compensation value of the RD unit for the same Doppler channel decreases with the increase of the range gate. The Doppler channel compensation value ranges from -0.15 to 0.16. The compensation value to the left of Doppler channel 33 is greater than or equal to 0, and the compensation value to the right is less than or equal to 0. The absolute value of the compensation value of the RD unit for the same Doppler channel decreases or remains unchanged with the increase of the range gate. In Doppler channel 33, the compensation value is 0 because the cosine of the azimuth angle θ2 at Doppler channel 33 is 0, and the clutter block falls into the same Doppler channel relative to the two platforms. For RD cells under the same range gate, the absolute value of the compensation amount first decreases and then increases with the increase of Doppler channels. For two Doppler channels with opposite center frequencies, the compensation amounts are approximately opposites. For example, the compensation amount for range gate 100 and Doppler channel 23 is 0.07, and the compensation amount for range gate 100 and Doppler channel 43 is -0.07. This is because the azimuth angles of the two platforms at Doppler channel 23 and the two platforms at Doppler channel 43 are both opposites, so the difference in calculated Doppler frequencies is also approximately negative.

[0140] S23, perform Q-fold interpolation of the Doppler dimension and range gate dimension of the clutter data of the second airborne platform to change the dimension of the clutter data from N×K×L to N×100K×100L;

[0141] Where N is the number of antenna array elements of the second airborne platform; K is the number of pulses transmitted by the radar transmitter of the second airborne platform; and L is the maximum unambiguous range gate.

[0142] Continuing with the example above, since each RD cell consists of multiple random, isotropic scattering points, each RD cell is independent and can be moved separately according to the range gate compensation and the Doppler channel compensation. Before the movement, because the accuracy of the compensation is 1 / Q, it is necessary to perform Q-fold interpolation on the Doppler dimension and range gate dimension of the clutter data from the second airborne platform, transforming the dimension of the clutter data to N×QK×QL. For ease of understanding, the following example uses Q=100.

[0143] like Figure 8The figure shows the position coordinates of adjacent RD cells before and after interpolation on the range-Doppler plane. Before interpolation, the coordinates of the RD cell represented by the top-left square are (k, l), the coordinates of the RD cell represented by the bottom-left square are (k, l+1), and the coordinates of the RD cell represented by the top-right square are (k+1, l). The RD cells represented by the top-left square and the bottom-left square differ by one range gate, and the RD cells represented by the top-left square and the top-right square differ by one Doppler channel. After interpolation, the dimensions of the Doppler dimension and the range gate dimension increase, and the adjacent RD cells before interpolation have 99 additional RD cells in the middle of the Doppler dimension and the range gate dimension. That is, the coordinates of the RD unit represented by the square in the upper left corner become ((k-1)×100+1, (l-1)×100+1), the coordinates of the RD unit represented by the square in the lower left corner become ((k-1)×100+1, 100l+1), and the coordinates of the RD unit represented by the square in the upper right corner become (100k+1, (l-1)×100+1). This makes the RD units more finely divided in the range gate and Doppler channel, which meets the accuracy of the compensation amount and makes the movement more precise, thereby aligning the centers of the corresponding RD units from the perspectives of the two airborne platforms more accurately.

[0144] S24. Based on the calculated range gate compensation and Doppler channel compensation for each range-Doppler cell of the second airborne platform relative to the first airborne platform, the corresponding range-Doppler cell of the clutter data of the second airborne platform after interpolation is moved to the corresponding position on the range-Doppler plane to align with the center of the same range-Doppler cell of the first airborne platform.

[0145] Specifically, based on the calculated range gate compensation and Doppler channel compensation for each range-Doppler cell relative to the first airborne platform, the corresponding range-Doppler cells of the second airborne platform, after clutter data interpolation, are moved to their corresponding positions on the range-Doppler plane, including:

[0146] For each range-Doppler cell after clutter data interpolation of the second airborne platform, the corresponding movement distance is determined based on the calculated absolute values ​​of the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for that range-Doppler cell.

[0147] For each range-Doppler cell after clutter data interpolation of the second airborne platform, the corresponding movement direction is determined based on the positive and negative values ​​of the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for that range-Doppler cell.

[0148] Each range-Doppler cell, after interpolation of the clutter data from the second airborne platform, is moved to its corresponding position on the range-Doppler plane according to its determined moving distance and direction.

[0149] Specifically, for each range-Doppler cell after clutter data interpolation of the second airborne platform, the corresponding movement distance is determined based on the calculated absolute values ​​of the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for that range-Doppler cell, including:

[0150] For each range-Doppler cell after clutter data interpolation of the second airborne platform, for either the range gate compensation or the Doppler channel compensation, the movement distance corresponding to that compensation amount of the range-Doppler cell is determined according to the Q multiple of the absolute value of that compensation amount.

[0151] Accordingly, for each range-Doppler cell after clutter data interpolation of the second airborne platform, the corresponding movement direction is determined based on the positive and negative values ​​of the calculated range gate compensation and Doppler channel compensation for that range-Doppler cell relative to the first airborne platform, including:

[0152] For each range-Doppler cell after clutter data interpolation of the second airborne platform, the movement direction corresponding to the compensation amount of the range-Doppler cell is determined according to the sign of the compensation amount;

[0153] Among them, when the distance gate compensation is positive, the movement direction is downward, and when it is negative, the movement direction is upward; when the Doppler compensation is positive, the movement direction is to the right, and when it is negative, the movement direction is to the left.

[0154] Using the above example as a specific illustration, after interpolation is completed, each range-Doppler cell of the clutter data from the second airborne platform can be moved. During the movement, the interpolated RD cells are moved to their corresponding positions on the range-Doppler plane according to the corresponding compensation amount. The moving distance is the absolute value of 100 times the corresponding compensation amount. The moving direction is determined by the sign of the corresponding compensation amount: when the range gate compensation amount is positive, it moves downwards; when it is negative, it moves upwards; when the Doppler compensation amount is positive, it moves to the right; when it is negative, it moves to the left.

[0155] S25, resample the clutter data after the second airborne platform is moved to restore it to the original dimension, and obtain new clutter data of the second airborne platform.

[0156] Continuing the example above, after all RD cells have been moved, the Doppler dimension and range gate dimension of the clutter data should be resampled every 100 cells to restore the original dimensions. For example, as... Figure 9As shown, the range gate compensation for the RD unit located at range gate 170 and Doppler channel 48 on the second airborne platform is 0.43, and the Doppler channel compensation is -0.04. After interpolation, the RD unit located at range gate 16858 and Doppler channel 4705 is moved down 43 units and left 4 units, to range gate 16901 and Doppler channel 4701. After resampling, it is located at range gate 170 and Doppler channel 48. In this way, a certain RD unit on the first airborne platform is center-aligned with the same RD unit moved on the second airborne platform, and they overlap on the ground; the overlapping area is the clutter-related region.

[0157] In summary, the purpose of S2 is to compensate for the misalignment of clutter RD units received by the two airborne platforms. The same clutter block will be located in different RD units relative to the two platforms, and the distance and Doppler frequency of the same RD unit relative to the two platforms will also differ. This is achieved using an interpolation-based relocation method. First, the range gate compensation and Doppler channel compensation for each RD unit are calculated. Then, the clutter data is interpolated based on the accuracy of the compensation, and the interpolated RD units are moved to their corresponding positions. Finally, the clutter data is resampled to restore the original dimension. Ultimately, the relocated RD units are aligned with the centers of the two platforms, overlapping on the ground.

[0158] S3. Based on the clutter data of the first airborne platform and the new clutter data of the second airborne platform, obtain the range clutter signals of the two airborne platforms; perform range pre-filtering on the range clutter signals of the two airborne platforms respectively to obtain the updated clutter data of the two airborne platforms.

[0159] The difference in observation perspective between the two airborne platforms leads to decorrelation of the received clutter signals, which degrades the signal processing results. The following derives the expressions for the clutter signals received by the RD cells from the two airborne platforms and the expression for the interference phase between the same RD cells.

[0160] Figure 10 The RD element corresponding to the first airborne platform and its geometric relationship are given. Here, platform 1 and platform 2 represent the first airborne platform and the second airborne platform, respectively. Figure 10 In the diagram, Δθ1 represents the angular resolution of a certain RD cell corresponding to the first airborne platform, b1 represents the short side of the RD cell corresponding to the first airborne platform, and a1 represents the long side of the RD cell corresponding to the first airborne platform. An RD cell is composed of several independent clutter scattering points, where the Doppler frequency of the scattering point at the center of the RD cell is the center frequency f of the Doppler channel. d01 Let f be the Doppler frequency on both sides of the Doppler line. d01 -Δfd / 2 and f d01 +Δf d / 2, Δf d =f r / K represents the Doppler resolution. Assume the main lobe of the transmitted beam illuminates the center of the RD cell. Here, the RD cell is approximated as a rectangle, and its area is calculated.

[0161] Relative to the first airborne platform, the shorter side of the RD unit can be considered as the distance resolution multiplied by the secant of the ground angle:

[0162] b1=ΔRsecψ c1 (14)

[0163] Where ΔR=c / (2B) is the distance resolution, c is the speed of light, and ψ c1 For the corner of the floor to be wiped, its sine value satisfies:

[0164]

[0165] The longer side of an RD cell can be considered as the distance from the first airborne platform to the center of the RD cell multiplied by the angular resolution:

[0166] a1=R1Δθ1 (16)

[0167] Δθ1 can be obtained by inverse calculation from the Doppler frequency:

[0168]

[0169] Therefore, the area of ​​a certain RD unit relative to the first airborne platform can be expressed as:

[0170] S RD1 =a1×b1 (18)

[0171] Similarly, relative to the second airborne platform, the area of ​​a certain RD unit can be expressed as:

[0172] S RD2 = a² × b² (19)

[0173] Where a2 and b2 are the long side and short side of a certain RD unit corresponding to the second airborne platform, respectively.

[0174] Consider the central scattering point ρ of the RD unit corresponding to the first airborne platform. 01 Let its coordinates be (x 01 ,y 01 ,0). Relative to the first airborne platform, g(x,y,0) is defined as the platform centered at (x,y,0). 01 ,y 01 The coordinates of the RD cell at (x+x) are (x, 0). 01,y+y 01 The complex amplitude of the scattering point (,0) is expressed as a zero-mean, white complex Gaussian random variable, and its cross-correlation function is:

[0175]

[0176] Where, δ(x) i -x j ,y i -y j ) is a two-dimensional Dirac-delta function.

[0177] Define the time delay from the first airborne platform to the RD unit center as:

[0178]

[0179] The clutter signal spontaneously emitted and received by the first airborne platform at all scattering points of a certain RD cell can then be represented as:

[0180]

[0181] Where E represents the total transmitted energy, and u(t) represents the complex envelope signal. Substituting variables into the above equation, let γ = γ + x 01 β=β+y 01 And by rearranging using narrowband signal conditions, we can obtain:

[0182]

[0183] Among them, f c Let be the carrier frequency. The exponent term in equation (23) is simplified to:

[0184]

[0185] Substituting equation (24) into equation (23) simplifies to:

[0186]

[0187] in,

[0188]

[0189] It satisfies E{a 11} = 0, var{a 11} = 1.

[0190] Similarly, the second airborne platform corresponds to the same RD unit center ρ 02 The coordinates are (x 02 ,y 02 ,0). Relative to the second airborne platform, g(x,y,0) is defined as the axis centered at (x,y,0). 02,y 02 The coordinates of the RD cell at (x+x) are (x, 0). 02 ,y+y 02 The complex amplitude of the scattering point (,0). The time delay from the second airborne platform to the center of the RD unit is defined as:

[0191]

[0192] Then the signals spontaneously emitted and received by all scattering points of the same RD unit corresponding to the second airborne platform are:

[0193]

[0194] After simplification, we get:

[0195]

[0196] in,

[0197]

[0198] It satisfies E{a 22} = 0, var{a 22} = 1.

[0199] Therefore, the interference phase between the clutter signals of each RD unit of the two airborne platforms is:

[0200]

[0201] The range of the interference phase is [-π, π], which is related to the baseline length and the height of the airborne platform.

[0202] Figure 11Figures (a) to (d) show the interference phases when only a vertical baseline exists, and the vertical baseline is 1m, 10m, 30m, and 100m. Each figure is the result of graying out the original image. It can be seen that no clutter signals are received in the noise region and at range gates 1-53. When only a vertical baseline exists between the two airborne platforms, the distance difference is only related to the platform height. In the clutter region, the interference phases are equal at the same range gate. When the vertical baseline is 1m, the interference phases at some range gates are also approximately equal. Interference fringes can be formed at both close and distant clutter distances, and there is interference correlation between the RD units corresponding to the two airborne platforms. When the vertical baseline is 10m or 30m, wider interference fringes can be formed at greater clutter distances, and there is also interference correlation. The shorter the vertical baseline, the wider the interference fringes. When the vertical baseline is long, such as 100m, the interference phases of adjacent range gates are often different, and interference fringes cannot be formed between the range gates. There is no interference correlation between the RD units corresponding to the two airborne platforms. Therefore, it is necessary to improve the clutter interference correlation of the RD units received by two airborne platforms under a long vertical baseline.

[0203] As shown in the preceding analysis of interference correlation, clutter signals do not exhibit interference correlation when the vertical baseline is 200m. To improve the interference correlation between the RD units of the two airborne platforms, this embodiment of the invention employs a range-direction pre-filtering method.

[0204] In one optional implementation, range-direction pre-filtering is performed on the range clutter signals of the two airborne platforms to obtain updated clutter data for the two airborne platforms, including the following steps:

[0205] S31, calculate the cross-correlation function of the range clutter signals of the two airborne platforms;

[0206] It is understandable that the range clutter signals of the two airborne platforms can be obtained from the clutter data of the first airborne platform and the new clutter data of the second airborne platform.

[0207] The range-oriented pre-filtering method in this embodiment of the invention mainly derives the relationship between the spatial spectrum of the complex amplitude of the ground RD unit clutter signal and the spectrum of the clutter signal. Taking the first airborne platform as an example, the radar transmits at [f c -B / 2,f c [+B / 2] represents a constant-amplitude linear frequency modulated (LFM) signal with a bandwidth. When the center frequency f0 of the received clutter signal is at 0, the spatial frequency f on the complex amplitude spatial spectrum is... y1 The time frequencies f of the clutter signal spectrum in the range [-B / 2, B / 2] correspond one-to-one. The expression for the time frequency can be written as:

[0208]

[0209] Because the two airborne platforms observe the ground from different angles, the received clutter signals contain different spectral bands corresponding to complex amplitudes. Figure 12 As shown in the figure. R 11r (f), R 22r (f) represents the clutter range signal r corresponding to the two airborne platforms, respectively. 11r (t), r 22r The Fourier transform of (t), G(f) y ) represents the range-complex amplitude signal g y (f y The Fourier transform of the spatial spectrum of platform 1 and platform 2 is shown. The overlapping portion of the spatial spectrum of platform 1 and platform 2 represents the related portion of the clutter signals received by the two platforms. f1 is the LFM signal transmitted by platform 2 at f c -B / 2 corresponds to the spatial frequency f y1 In the clutter spectrum corresponding to platform 1, f2 is the time frequency of the LFM signal transmitted by platform 1 at f c +B / 2 corresponds to the spatial frequency f y2 The time frequency in the clutter spectrum corresponding to platform 2. The calculation yields:

[0210]

[0211]

[0212] Because the RD unit consists of many scattering points, and each scattering point is statistically independent, the overlapping and non-overlapping portions of the clutter spectrum received by the two airborne platforms are also independent. Therefore, the overlapping portion only contains the relevant parts, while the non-overlapping portion is detrimental to subsequent signal processing. During filtering, the overlapping portion needs to be retained, and the non-overlapping portion needs to be filtered out. When the difference between φ1 and φ2 is not significant (i.e., the baseline length is only a few hundred meters), B / 2-f1 and B / 2+f2 can be replaced by the same value Δf, where Δf can be determined by the carrier frequency f. c The difference in time frequency corresponding to different spatial frequencies on the two platforms is approximated by:

[0213]

[0214] Theoretically, Δf can be calculated using the above formula. However, in practical engineering, since φ1 and φ2 are not significantly different and difficult to distinguish, Δf is usually estimated from the spectrum of the cross-correlation function. The cross-correlation function of the clutter range signals corresponding to the two airborne platforms is:

[0215]

[0216] Among them, c 12r It is a complex constant.

[0217] S32, perform a Fourier transform on the cross-correlation function to obtain its spectrum, and determine the frequency corresponding to the peak value as Δf based on the spectrum characteristics;

[0218] S33, perform matched filtering and windowing on the range clutter signal of the first airborne platform within the range of [-B / 2, B / 2-Δf]; perform matched filtering and windowing on the range clutter signal of the second airborne platform within the range of [Δf-B / 2, B / 2] to obtain updated clutter data for the two airborne platforms.

[0219] Specifically, after calculating Δf, matched filtering can be performed on the range clutter signals of platform 1 and platform 2. The filter for platform 1 needs to cut off the high-frequency components, with a filtering range of [-B / 2, B / 2-Δf]. The filter for platform 2 needs to cut off the low-frequency components, with a filtering range of [Δf-B / 2, B / 2]. Windowing processing is then performed separately to obtain the updated clutter data for the two airborne platforms.

[0220] Among them, windowing processing refers to adding a Hamming window, the purpose of which is to reduce the sidelobe signal in the LFM signal output. This way, the spectrum-correlated part can be retained and the uncorrelated part can be filtered out, thus completing the entire pre-filtering process.

[0221] For information on windowing, please refer to the existing technology documentation; details will not be provided here.

[0222] S4 performs full-array joint space-time adaptive processing on the updated clutter data from the two airborne platforms and uses the processing results to obtain the reduced MDV value.

[0223] S4 is the signal processing process. Generally, signal processing methods can employ interferometer processing and combined processing of the full array degrees of freedom.

[0224] Interferometer processing, or clutter cancellation, is a simple, non-adaptive spatial filtering method for clutter localization. When two platforms fly along their velocity direction, the received clutter signals are first spatially localized using a deeply weighted Doppler filter. Then, numerous zeros are created using spatial degrees of freedom to suppress the clutter. "Spatial localization of clutter signals" means performing an FFT on each platform's signal, then adjusting the outputs of the corresponding Doppler channels of both platforms using weighting coefficients w, and finally canceling the clutter to obtain the final filtered result.

[0225] Therefore, the result of the cancellation of clutter signals received by the two platforms is as follows:

[0226] x ATI =x1-wx2=x1-e jΔφ x2 (37)

[0227] Here, x1 and x2 are the clutter data received by the first airborne platform and the second airborne platform, respectively.

[0228] The drawback of this method is that its effectiveness deteriorates with a smaller number of pulses. This is because when the number of pulses is small, the width of each passband of the Doppler filter is large, and the angle of the main lobe clutter within the passband is large, making it impossible for a single zero point to effectively suppress the main lobe clutter within that passband. Furthermore, due to the limited spatial degrees of freedom, only a cosine-shaped notch response can be formed, resulting in limited detection capability for low-speed targets and poor performance in the sidelobe clutter region. Therefore, this embodiment of the invention considers using the full array degrees of freedom for joint processing.

[0229] The full-array degree-of-freedom joint processing method merges the clutter data from two airborne platforms into a single data set for processing. Here, the updated clutter data from both airborne platforms is processed. The merged clutter data can be represented as follows:

[0230] x un =[x1 x2] T (38)

[0231] After merging, the dimensions of the clutter data become 2N×K×L.

[0232] After merging the clutter data, STAP processing can be performed. Unlike STAP processing for single-base radar, the arrays of the two airborne platforms can be considered as a single long array, and the target's spatial steering vector can be expressed as:

[0233]

[0234] Where, d i Taking the first array element of the second airborne platform as the reference array element, the horizontal distance between each array element and the reference array element is cosψ ati This refers to the antenna cone angle of each array element relative to the target. This method, due to its increased spatial degrees of freedom, offers better clutter suppression than the interferometer method.

[0235] After STAP processing, an output SCNR graph can be obtained. Those skilled in the art will understand that MDV is half the difference between the minimum positive velocity and the minimum negative velocity corresponding to the obtained output SCNR when it is greater than or equal to the detection threshold. The method for obtaining the output SCNR graph is prior art and will not be described here.

[0236] For the specific implementation steps of the embodiments of the present invention, please refer to [link / reference]. Figure 13 understand. Figure 14In the diagram, the four steps corresponding to S1 to S4 are illustrated by modules 1 to 4 respectively. In short, module 1 is used to determine the mode and configuration of the dual-aircraft radar; module 2 is used for interpolation and alignment of clutter RD units for compensation; module 3 is used for range pre-filtering to improve clutter correlation; and module 4 is used for signal processing.

[0237] In summary, to address the issue that the "other transmits, self receives" bistatic radar mode primarily used in dual-aircraft MDV reduction research does not utilize the effective apertures of both antennas and lacks a targeted MDV reduction method, this invention adopts a self-transmitting and self-receiving mode for the dual-aircraft radar system and employs a dual-aircraft configuration with a hybrid baseline consisting of a forward baseline and a vertical baseline. Under this hybrid baseline configuration, to address the issues of clutter RD cell misalignment and clutter signal decorrelation caused by the different positions of the two airborne platforms and differences in observation angles, this invention utilizes interpolation to move and align clutter range-Doppler (RD) cells, then uses range pre-filtering to improve clutter correlation, and finally performs full-array joint space-time adaptive processing (STAP). This dual-aircraft collaborative detection method can be called the Movement Prefiltering-Space-Time Adaptive Processing method, or MP-STAP for short.

[0238] Specifically, for interpolation shifting, the compensation amounts for the range gate and Doppler channel are first calculated. Based on the accuracy of the compensation, the clutter data is interpolated, thereby shifting the RD cells to their centers and restoring the clutter data to its original dimension. For range pre-filtering, based on the relationship between the ground complex amplitude spatial spectrum and the clutter signal spectrum, the overlapping portions of the clutter spectrum in space are retained, while the non-overlapping portions are filtered out to improve correlation. Furthermore, since the alignment of the two airborne platform antennas along the flight path can extend the length of the receiving antenna, full-array joint processing is performed to obtain an improved MDV, thereby enhancing the detection performance of low-speed targets.

[0239] Therefore, compared to existing technologies, the method of this invention is applicable to dual-aircraft radar operating in a "self-transmitting and self-receiving" mode under hybrid baselines. Compared to single-base radar, the antenna aperture of this invention is longer, which can further reduce MDV. Compared to distributed radar, this invention does not have the problem of space-time synchronization, which can save resources and is easier to implement. Moreover, this invention fills the gap in research on the low-speed target detection performance of dual-aircraft radar in "self-transmitting and self-receiving" mode, effectively utilizes the effective aperture of the antennas of the two airborne platforms, and proposes a targeted method to reduce MDV and improve low-speed target detection performance.

[0240] To facilitate understanding of the effects of the methods in the embodiments of the present invention, the following analysis and explanation are based on simulation results.

[0241] In this experiment, the coordinates of platform 1 are (0m, 3m, 7800m), the coordinates of platform 2 are (0m, 0m, 8000m), the antenna is a horizontal uniform front and side equidistant linear array with 8 array elements, one coherent processing interval contains 64 coherent pulses, the system bandwidth is 1MHz, the platform speed is 100m / s, the radar pulse repetition frequency is 2000Hz, and the detection threshold is 9.95dB.

[0242] The performance of the method in the embodiments of the present invention will now be simulated. In order to prevent the echoes received by the two airborne platforms from interfering with each other, the clutter data should be simulated separately under the premise that the ground clutter blocks are the same as those of the two airborne platforms. The following simulation figures have all been grayscaled from the original images. Figure 15 Figures (a) to (d) show the interference phases of echo signals between the same RD unit of two airborne platforms at vertical baselines of 1m, 10m, 30m, and 100m. The simulation method involves performing PD processing on the clutter data and then taking the phase angle of the corresponding RD unit to obtain the interference phase. It can be seen that there are no clutter signals and no interference fringes at range gates 1-53. When the vertical baseline is 1m, there are relatively wide interference fringes, and the interference phases of some RD units are similar, and there are many of them. For example, the interference phases of the RD units in range gates 350-500 are similar. When the vertical baseline is 10m and 30m, the interference fringes become narrower, and the number of RD units with similar interference phases is smaller. The longer the vertical baseline, the fewer the RD units with similar interference phases, and the worse the interference correlation. For example, at 10m, the interference phases of the RD units in range gates 405-415 are similar; at 30m, the interference phases of the RD units in range gates 408-411 are similar. When the vertical baseline is 100m, there is no interference correlation between the RD units. This is consistent with the theoretical analysis above.

[0243] ​ Figures (a) and (b) show the interference phase results of the echo signals between the same RD unit of two airborne platforms before and after pre-filtering, with a 3m baseline along the heading direction and a 200m vertical baseline. It can be seen that before pre-filtering, the interference phase is irregularly distributed, and no interference fringes are formed at different range gates. After pre-filtering, at long-range clutter, more obvious interference fringes appear in the clutter regions of different range gates, and the interference phases in the clutter regions of the same range gate are approximately the same, thus improving the correlation. For example, the interference phase in the clutter region of range gates 410-415 is approximately 35°.

[0244] Figure 16(a) shows the range-Doppler plot after full-array degree-of-freedom joint PD processing; Figure 16(b) shows the range-Doppler plot after ATI processing; Figure 16(c) shows the range-Doppler plot after platform 2 single-base PD processing; and Figure 16(d) shows the clutter residual power results after the three processing methods. In the figures, joint PD represents full-array degree-of-freedom joint PD processing, represented by a solid line with short lines; single-base PD represents single-base PD processing, represented by a solid line with circles; and ATI represents ATI processing, represented by a solid line with squares. It can be seen that the ATI processing has a poorer suppression effect in the sidelobe clutter region, with a residual power approximately 6 dB higher than the joint processing in the sidelobe clutter region. The joint processing effect is more significant, with a residual power approximately 5 dB lower than the single-base processing in the main lobe clutter region. Here, PD represents pulse Doppler, and ATI represents interferometer processing.

[0245] Figure 17(a) shows the range-Doppler plot after full-array degree-of-freedom joint EFA processing, where EFA is the extended factorized space-time adaptive processing method, a type of STAP processing. Figure 17(b) shows the range-Doppler plot after ATI+EFA processing, Figure 17(c) shows the range-Doppler plot after platform 2 single-base EFA processing, and Figure 17(d) shows the output SCNR results after the three processing methods. Joint EFA represents full-array degree-of-freedom joint EFA processing, represented by a solid line with short lines; single-base EFA represents single-base EFA processing, represented by a solid line with circles; and ATI+EFA represents ATI+EFA processing, represented by a solid line with squares. It can be seen that ATI+EFA processing is less effective than joint EFA processing in the sidelobe clutter region, with an output SCNR approximately 12 dB lower. Compared to single-base EFA processing, ATI+EFA processing maintains a roughly the same notch width in the main lobe clutter region, but its output SCNR is approximately 6 dB lower in the sidelobe clutter region. The combined processing results in an output SCNR approximately 6 dB higher in the sidelobe clutter region and a narrower notch in the main lobe clutter region. The MDV under single-base EFA processing is 40.63 m / s, and the MDV under combined EFA processing is 18.75 m / s. Expanding the receiving antenna aperture along the heading baseline of both platforms reduces the MDV. Furthermore, considering the current Doppler resolution, at v... r Within the interval [-200m / s, 200m / s], there exists a radial velocity, i.e., a blind velocity, where the output SCNR is less than the detection threshold.

[0246] With the continuous advancement of science and technology, research on low-speed target detection performance has received increasing attention in recent years. MDV (Mean Distance Detection Value) is one of the important indicators for measuring the ability to detect low-speed targets. Therefore, reducing MDV is beneficial to improving the detection performance of low-speed targets. The aforementioned simulation experiments have demonstrated that the method of this embodiment, under the premise of small equipment size and resource saving, utilizes a dual-aircraft radar operating in a "self-transmitting and self-receiving" mode and reduces MDV through the MP-STAP method. Therefore, the method of this embodiment is very suitable for application in dual-aircraft radar systems, especially in helicopters and rotary-wing UAVs where the target itself has a very low speed.

[0247] In summary, the method of the present invention has broad development prospects and extremely high application value.

[0248] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for reducing MDV through MP-STAP dual-machine collaboration, characterized in that, include: Given radar system parameters, it is determined that both the first and second airborne platforms in the dual-aircraft radar system operate according to a preset mode. This preset mode includes: each airborne platform operating in a self-transmitting and self-receiving mode; the aircraft corresponding to the two airborne platforms flying in the same direction with the same heading and speed; the height of the second airborne platform being greater than that of the first airborne platform; the antennas of the two airborne platforms arranged along the heading; a first preset value for the heading baseline and a second preset value for the vertical baseline; the first preset value being less than the second preset value; and the heading baseline and the vertical baseline representing the horizontal and vertical spacing of the antennas of the two airborne platforms, respectively. Acquire clutter data from two airborne platforms; for the clutter data of the second airborne platform, compensate the range-Doppler cells using an interpolation shifting method to center-align with the corresponding range-Doppler cells in the clutter data of the first airborne platform, thereby obtaining new clutter data for the second airborne platform; Based on the clutter data from the first airborne platform and the new clutter data from the second airborne platform, range clutter signals from the two airborne platforms are obtained; range pre-filtering is performed on the range clutter signals from the two airborne platforms respectively to obtain updated clutter data from the two airborne platforms. The updated clutter data from the two airborne platforms are subjected to joint space-time adaptive processing with full array degrees of freedom, and the reduced MDV value is obtained using the processing results. Specifically, the clutter data of the second airborne platform is compensated for using an interpolation shifting method to center-align with the corresponding range-Doppler cells in the clutter data of the first airborne platform, resulting in new clutter data for the second airborne platform, including: Determine the distance difference between the second airborne platform and the first airborne platform. and Doppler frequency difference ;Sure and Calculation accuracy ;in, It is a natural number greater than 0; based on and Calculate the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for each range-Doppler cell; Doppler and range-gate analysis were performed on the clutter data from the second airborne platform. Multiplication interpolation reduces the dimension of its clutter data from Become ;in, The number of antenna array elements of the second airborne platform; This refers to the number of pulses transmitted by the radar transmitter of the second airborne platform; The maximum number of unambiguous distance gates; Based on the calculated range gate compensation and Doppler channel compensation for each range-Doppler unit, the corresponding range-Doppler unit of the second airborne platform relative to the first airborne platform is moved to the corresponding position on the range-Doppler plane after the clutter data of the second airborne platform is interpolated, so as to align with the center of the same range-Doppler unit of the first airborne platform. The clutter data of the second airborne platform after its relocation is resampled to restore it to its original dimension, resulting in new clutter data of the second airborne platform.

2. The method for reducing MDV through MP-STAP dual-machine collaboration according to claim 1, characterized in that, The first preset value was determined by comparing and analyzing the number of blind speeds and the size of the curve notch corresponding to the speed response results under different along the course baseline and selecting the best value. The second preset value is determined based on the first preset value and the difference in flight altitude between the two carrier aircraft according to the requirements for safe flight.

3. The MP-STAP dual-machine collaborative method for reducing MDV according to claim 2, characterized in that, The first preset value is 3 meters; the second preset value is 200 meters.

4. The MP-STAP dual-machine collaborative method for reducing MDV according to claim 1 or 3, characterized in that, The determination of the distance difference between the second airborne platform and the first airborne platform. and Doppler frequency difference The calculation formulas used in the process include: in, The distance from the first airborne platform to the scattering point; The distance from the second airborne platform to the scattering point; The distance between the first airborne platform and the second airborne platform is represented by the length of the baseline. The height of the first airborne platform; The height of the second airborne platform; The Doppler frequency of the clutter block corresponding to the first airborne platform; This refers to the Doppler frequency of the clutter block corresponding to the second airborne platform; For airborne platform speed; The operating wavelength of the radar; The azimuth angle of the first airborne platform; The azimuth angle of the second airborne platform; The pitch angle of the first airborne platform; The pitch angle of the second airborne platform; The velocity cone angle of the first airborne platform; The velocity cone angle of the second airborne platform.

5. The MP-STAP dual-machine collaborative method for reducing MDV according to claim 4, characterized in that, The determination and Calculation accuracy ,include: In response to the current situation The value, the execution expression determination steps, include: and Considered separately and function and Determine the two functions respectively using the Taylor formula for bivariate functions. a point within the neighborhood of Expression of the remainder term of the first-order Lagrange form and ;in, For natural numbers greater than 0, the first execution ; and This is the preset minimum value; Estimate and Order of magnitude; Determine the current Does the value satisfy: The value and The ratio of the orders of magnitude of the values ​​is greater than the preset value, and The value and The ratio of the orders of magnitude of these values ​​is greater than a preset value; among them, For signal bandwidth; Doppler bandwidth; If so, confirm and Calculation accuracy If not, the current After incrementing the value by one, return to the expression determination steps until a result is determined. and The calculation accuracy.

6. The MP-STAP dual-machine collaborative method for reducing MDV according to claim 5, characterized in that, The basis and Calculate the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for each range-Doppler cell, including: Will and By converting the difference between the range resolution and Doppler resolution into the difference between the range gate and the Doppler channel, the compensation amount of the range gate and the compensation amount of the Doppler channel of the second airborne platform relative to the first airborne platform for all clutter blocks are obtained. The clutter block compensation amount corresponding to the center frequency of the Doppler channel is used as the reference for movement. The center of each range-Doppler unit is aligned with the center of the same range-Doppler unit of the first airborne platform. This yields the range gate compensation amount and Doppler channel compensation amount of the second airborne platform relative to the first airborne platform for each range-Doppler unit.

7. The MP-STAP dual-machine collaborative method for reducing MDV according to claim 6, characterized in that, The step of moving the corresponding range-Doppler unit of the second airborne platform, after clutter data interpolation, to the corresponding position on the range-Doppler plane based on the calculated range gate compensation and Doppler channel compensation for each range-Doppler unit relative to the first airborne platform includes: For each range-Doppler cell after clutter data interpolation of the second airborne platform, the corresponding movement distance is determined based on the calculated absolute values ​​of the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for that range-Doppler cell. For each range-Doppler cell after clutter data interpolation of the second airborne platform, the corresponding movement direction is determined based on the positive and negative values ​​of the range gate compensation and Doppler channel compensation of the second airborne platform relative to the first airborne platform for that range-Doppler cell. Each range-Doppler unit, after interpolation of the clutter data from the second airborne platform, is moved to its corresponding position on the range-Doppler plane according to its determined moving distance and direction.

8. The MP-STAP dual-machine collaborative method for reducing MDV according to claim 7, characterized in that, For each range-Doppler cell after clutter data interpolation for the second airborne platform, the corresponding movement distance is determined based on the calculated absolute values ​​of the range gate compensation and Doppler channel compensation for that range-Doppler cell relative to the first airborne platform, including: For each range-Doppler unit after clutter data interpolation of the second airborne platform, for either the range gate compensation or the Doppler channel compensation, based on the absolute value of that compensation... The multiple determines the movement distance corresponding to this type of compensation amount for the distance-Doppler element; For each range-Doppler cell after clutter data interpolation for the second airborne platform, the corresponding movement direction is determined based on the calculated sign of the range gate compensation and Doppler channel compensation relative to the first airborne platform for that range-Doppler cell, including: For each range-Doppler unit after clutter data interpolation of the second airborne platform, the movement direction corresponding to the compensation amount of the range-Doppler unit is determined according to the positive or negative sign of the compensation amount; wherein, when the range gate compensation amount is positive, the movement direction is downward, and when it is negative, the movement direction is upward; when the Doppler compensation amount is positive, the movement direction is to the right, and when it is negative, the movement direction is to the left.

9. The MP-STAP dual-machine collaborative method for reducing MDV according to claim 8, characterized in that, The process of performing range-direction pre-filtering on the range clutter signals of the two airborne platforms to obtain updated clutter data for the two airborne platforms includes: Calculate the cross-correlation function for the range clutter signals of the two airborne platforms; The cross-correlation function is subjected to a Fourier transform to obtain its spectrum, and the frequency corresponding to the peak value is determined based on the spectral characteristics. ; For the range clutter signal of the first airborne platform Matched filtering and windowing are performed within the range; range clutter signals from the second airborne platform are included. Matched filtering and windowing were performed within the range to obtain updated clutter data for the two airborne platforms.

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