A method and electronic device for reducing minimum detectable speed by dense deflection scanning

Abstract

The present invention discloses a method and electronic device for reducing the minimum detectable speed by dense offset scanning, comprising: determining a null beam width based on a corresponding transmission pattern of a radar; performing multiple offset scans on a receiving beam and / or a transmitting beam simultaneously within the null beam width, wherein each offset scan comprises: calculating the power of a target in a mainlobe clutter region; calculating the residual power of the clutter; calculating a signal-to-noise ratio based on the target power and the residual power of the clutter; obtaining the maximum signal-to-noise ratio from all signal-to-noise ratios, determining whether the maximum signal-to-noise ratio is greater than or equal to a target detection threshold, and if the maximum signal-to-noise ratio is greater than or equal to the target detection threshold, calculating the minimum detectable speed after the offset scan based on the null beam width; otherwise, obtaining the minimum value of the currently detectable target speed as the minimum detectable speed. The present invention improves the detection performance of low-speed targets, does not require compensation or correction, has a low system degree of freedom, requires a small number of IID samples, and has strong applicability.

Description

Technical Field

[0001] The invention belongs to the technical field of radar target detection, and in particular relates to a method for reducing a minimum detectable speed by dense deflection scanning and an electronic device. Background Art

[0002] Low-speed target detection is a component of radar moving target detection. There are two main reasons for the low speed of low-speed targets: one is that the target itself is very slow, such as helicopters and rotary-wing drones; the other is that the cosine value of the angle between the velocity direction and the line of sight is very low, resulting in a very low radial velocity. For example, a missile launched vertically upward has a very low initial velocity, and the fact that its flight direction is primarily upward makes the radial velocity even lower.

[0003] Minimum detectable velocity (MDV) is a key metric in target detection. It refers to the minimum radial velocity of a target that a radar can detect. It indicates the radar system's ability to detect slow-moving targets and provides the lower bound of the detectable target velocity range. When the target's radial velocity falls below the MDV, it is lost in the mainlobe clutter, making it undetectable and hindering subsequent angle measurement and tracking. Lowering the MDV reduces the target's radial velocity, allowing it to enter the sidelobe clutter region and become easier to detect. Lowering the MDV involves improving the radar system's output signal-to-clutter and noise ratio (SCNR) for slow-moving targets, within certain system resource constraints. This allows even slower targets to meet detection requirements. This can be achieved by optimizing the system's operating mode and parameters or by employing signal processing techniques that enhance the system's clutter suppression capabilities. Current research on MDV primarily focuses on airborne radars operating in MIMO configurations. For example, the paper "Analysis of Relative Motion Characteristics of Low-Earth Orbit Debris in Pulse Radar Staring Mode" (authored by Zhong Xiaoyu et al.) with DOI 10.7642 / j.issn.1674-5620.2014-06-0535-06 investigates the characteristics of pulse Doppler (PD) radars operating in staring mode, deriving the theory that PD radars operating in staring mode can reduce MDV. Staring mode, also known as dwell mode, offers advantages such as increased pulse count, higher data rates, the ability to simultaneously perform multiple functions, and the ability to perform long-term coherent integration. Long-term coherent integration increases the number of coherently integrated pulses, thereby enhancing the resolution of the Doppler filter. This enhanced resolution of the Doppler filter during PD processing reduces MDV. Similarly, when performing Space-Time Adaptive Processing (STAP), increasing the number of coherent accumulation pulses means increasing the degree of freedom of the system. The higher the degree of freedom of the system, the narrower the clutter notch formed after STAP processing, which correspondingly reduces the MDV.

[0004] However, the PD radar operates in staring mode and reduces MDV through long-term coherent integration. However, the long-term coherent integration process will be affected by phenomena such as cross-range unit movement, cross-Doppler unit movement, and cross-beam movement, which requires compensation correction during coherent integration. At the same time, long-term accumulation will reduce the real-time performance of the algorithm, making it less applicable. In addition, the system has a large degree of freedom, and the number of independent and identically distributed (IID) samples required will also increase, making engineering implementation more difficult. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a method and electronic device for reducing the minimum detectable speed by dense deflection scanning. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] In a first aspect, an embodiment of the present invention provides a method for reducing the minimum detectable velocity by dense deflection scanning, comprising:

[0007] Determine the null beam width based on the corresponding transmission pattern of the radar;

[0008] Within the null beam width, the receiving beam and / or the transmitting beam are simultaneously subjected to multiple offset sweeps, wherein for each offset sweep, the following steps are performed: calculating the power of a target in a main lobe clutter region; calculating the clutter residual power; and calculating a signal-to-noise ratio based on the power of the target and the clutter residual power.

[0009] The maximum signal-to-noise ratio is obtained from all signal-to-noise ratios, and it is determined whether the maximum signal-to-noise ratio is greater than or equal to the target detection threshold. If the maximum signal-to-noise ratio is greater than or equal to the target detection threshold, the minimum detectable speed after the offset scan is calculated based on the zero-point beamwidth. Otherwise, the minimum value of the currently detectable target speed is obtained as the minimum detectable speed.

[0010] In one embodiment of the present invention, the power formula for calculating the target in the main lobe clutter area is expressed as:

[0011]

[0012] Among them, p ti represents the power of the target in the main lobe clutter area calculated by the i-th offset scan, p max represents the peak power of the radar transmitter, G t Indicates the transmission gain, G r Indicates the receiving gain, G i represents the antenna pattern gain of the i-th offset scan, λ represents the wavelength, σ trepresents the RCS of the target, τB represents the time-bandwidth product, τ represents the pulse width, B represents the bandwidth, R represents the distance from the target to the radar, L n Indicates system loss.

[0013] In one embodiment of the present invention, calculating the clutter residual power includes:

[0014] Calculate the Doppler frequency of the target in the main lobe clutter area;

[0015] The PD processing method is used to calculate the clutter residual power according to the Doppler frequency of the target.

[0016] In one embodiment of the present invention, calculating the clutter residual power includes:

[0017] Calculate the Doppler frequency of the target in the main lobe clutter area;

[0018] The STAP processing method is used to calculate the clutter residual power according to the Doppler frequency of the target.

[0019] In one embodiment of the present invention, a formula for calculating the signal-to-noise ratio based on the target power and the clutter residual power is expressed as:

[0020]

[0021] Among them, SCNR oi represents the signal-to-noise ratio corresponding to the i-th offset sweep, p ti Indicates the power of the target corresponding to the i-th offset scan, p ci Indicates the residual power of the clutter corresponding to the i-th offset sweep.

[0022] In one embodiment of the present invention, calculating the minimum detectable velocity after deflection scanning according to the zero-point beam width includes:

[0023] determining an undetectable region within the null beamwidth based on all signal-to-noise ratios;

[0024] The velocities of the upper and lower boundaries of the undetectable area corresponding to the lower limit of the zero-point beam width are determined as the minimum positive velocity and the minimum negative velocity that can be detected.

[0025] In one embodiment of the present invention, determining the minimum detectable positive velocity and the minimum detectable negative velocity based on the null beam width includes:

[0026] Determining the velocity corresponding to the zero-point beam width based on all signal-to-noise ratios;

[0027] The speed corresponding to the lower limit of the zero-point beam width is determined as the minimum detectable positive speed and the minimum detectable negative speed.

[0028] In one embodiment of the present invention, the formula for calculating the minimum detectable speed after deflection scanning based on the minimum positive speed and the minimum negative speed is expressed as:

[0029]

[0030] Wherein, MDV represents the minimum detectable velocity, v h represents the minimum positive velocity, v l Indicates the minimum negative speed.

[0031] In one embodiment of the present invention, the radar is an airborne phased array monostatic radar.

[0032] In a second aspect, an embodiment of the present invention provides an electronic device, comprising a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other via the communication bus;

[0033] The memory is used to store computer programs;

[0034] The processor is configured to implement any of the above-mentioned steps of the method for reducing the minimum detectable speed by dense deflection scanning when executing the program stored in the memory.

[0035] Beneficial effects of the present invention:

[0036] The method of reducing the minimum detectable velocity by dense offset scanning proposed in the present invention is a new idea for reducing the minimum detectable velocity. In the Doppler domain, a target is easily detected when it enters the sidelobe clutter area. Whether the target can be detected is related to the target's azimuth angle in the mainlobe clutter and the target's radial velocity. Since the target angle is unknown, the beam is usually only pointed at a fixed position, which cannot achieve the best detection effect. Therefore, the embodiment of the present invention proposes to perform multiple offset scans on the receiving beam and / or the transmitting beam at the same time to improve the search accuracy of the Doppler filter, change the relative position of the target in the mainlobe of the beam, reduce the radial velocity required for the target to enter the sidelobe clutter area, and accordingly reduce the MDV. Based on Based on the theoretical support and the definition of MDV, under certain false alarm probability conditions, the output signal-to-noise ratio (SNR) obtained after signal processing is greater than or equal to the output SNR required for the detection probability required by the system. The minimum target velocity at this time is called MDV. The method proposed in the embodiment of the present invention calculates the SNR in real time based on the power of the target in the mainlobe clutter area and the clutter residual power calculated in each offset scan. The presence of a target is determined based on the comparison result of the SNR and the target detection threshold. If a target is present, the MDV after the offset scan is calculated in real time based on the zero-point beamwidth. The calculated MDV is smaller in this case, thereby improving the detection performance of low-speed targets. Compared with other existing methods, the embodiment of the present invention has good real-time performance, is not affected by the "three-span" phenomenon, does not require a compensation correction process, and has a low system degree of freedom. The number of required IID samples is reduced, which reduces the computational complexity, resulting in high real-time performance and strong applicability of the algorithm. In actual engineering, a method for reducing MDV with small equipment requirements, low computational complexity, and good real-time performance can be adopted.

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the position of a target in the main lobe of a beam provided by an embodiment of the present invention;

[0039] Figure 2 Schematic diagram of the detection principle of the minimum detectable speed provided by an embodiment of the present invention;

[0040] Figure 3 1 is a flow chart of a method for reducing the minimum detectable speed by dense deflection scanning provided by an embodiment of the present invention;

[0041] Figure 4 1 is a schematic diagram of a transmission pattern when the main beam points in the normal direction when N=64, provided by an embodiment of the present invention;

[0042] Figure 5 (a)~ Figure 5(c) is a schematic diagram of the corresponding output SCNR results of the unbiased scan, the received biased scan, and the transmitted / received biased scan provided by an embodiment of the present invention;

[0043] Figure 6 (a)~ Figure 6 (c) is a schematic diagram of the corresponding detection results of the unbiased scan, the received biased scan after PD processing, and the transmitted and received biased scan provided by an embodiment of the present invention;

[0044] Figure 7 (a)~ Figure 7 (b) is a schematic diagram of the SCNR results and detection results after a single wave position has been left in the PD for a long time according to an embodiment of the present invention;

[0045] Figure 8 This is the transmission pattern when the main beam points in the normal direction when N=32 provided by an embodiment of the present invention;

[0046] Figure 9 (a)~ Figure 9 (c) is a schematic diagram of the corresponding output SCNR results of the unbiased scan, the received biased scan, and the transmitted / received biased scan provided by an embodiment of the present invention;

[0047] Figure 10 (a)~ Figure 10 (c) is a schematic diagram of the corresponding detection results of the unbiased scan, the received biased scan after PD processing, and the transmitted and received biased scan provided by an embodiment of the present invention;

[0048] Figure 11 (a)~ Figure 11 (b) is a schematic diagram of the SCNR results and detection results after a single wave position has been left in the PD for a long time according to an embodiment of the present invention;

[0049] Figure 12 It is a structural diagram of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0051] Due to the movement of the target, there is a difference between the Doppler frequency of the target and the Doppler frequency of its local ground clutter. Whether the Doppler frequency of the target still remains in the main lobe clutter area or has entered the side lobe clutter area is related to the azimuth angle of the target and the radial velocity of the target, and of course it is also related to the direction of the main lobe of the beam. In other words, the azimuth angle of the target determines the position of the target in the main lobe, and also determines whether the target can easily escape from the main lobe clutter area in the Doppler domain. Take the left array as an example: if the target is on the left in the main lobe, it is easy for the target to enter the side lobe clutter area when it has a negative radial velocity; if the target is on the right in the main lobe, it is easy for the target to enter the side lobe clutter area when it has a positive radial velocity. Figure 1 As shown, the thick beam represents beam 1, and the thin beam represents beam 2. The target is located at the center relative to beam 1, and to the left relative to beam 2. When the target is located to the left, a relatively small negative radial velocity is sufficient to enter the sidelobe clutter region. However, when the target is located at the center, a relatively large radial velocity, either negative or positive, is required to enter the sidelobe clutter region. This demonstrates that the mainlobe orientation of the beam is a key factor in determining whether a target enters the sidelobe clutter region.

[0052] Considering that the target angle is unknown, the traditional receiving beam and transmitting beam in the same direction are not enough to achieve better detection performance. Using the above principle, it is necessary to simultaneously and densely scan the receiving beam or the transmitting beam and the receiving beam within a smaller beam width so that the main lobe of the beam changes. Figure 2 As shown, the thick lines represent before deflection scanning, and the thin lines represent after deflection scanning. It can be seen that after deflection scanning, the position of the mainlobe clutter zone changes due to the change in beam pointing. Targets originally located at the edge of the mainlobe clutter zone will directly enter the sidelobe clutter zone, while targets originally located at the center of the mainlobe clutter zone will be located at the edge of the mainlobe clutter zone. This will shift the center frequency of the Doppler filter, improving the Doppler filter's search accuracy, increasing its resolution, and reducing the MDV. At the same time, when the target is not at the center of the beam, the target power will decrease. The clutter residual power in the Doppler channel corresponding to the target will also decrease significantly because the Doppler frequency corresponding to the mainlobe clutter angle is not at the center of the Doppler filter, resulting in an increase in the output SCNR. At this time, even targets with sufficiently low radial velocity will enter the sidelobe clutter zone, and the MDV will also decrease accordingly.

[0053] The theoretical basis of the method proposed in the embodiment of the present invention is given below through the generalized likelihood ratio test (GLRT).

[0054] The problem of radar target detection is usually described using a binary hypothesis testing model. Under the hypothesis condition H0, the target does not exist; under the hypothesis condition H1, the target exists. Under the conditions H0 and H1, the output signal corresponding to the K pulse signals received by the radar receiver can be expressed as:

[0055]

[0056] in, r nK It represents the output signal corresponding to the kth pulse signal of the nth array element, where n ranges from 1 to N, where N represents the number of array elements, and k ranges from 1 to K, where K represents the number of pulses. nk The target complex amplitude under the kth pulse of the nth array element, s represents the target's space-time steering vector, c represents the clutter component, and n represents the noise component.

[0057] Let ξ=[θ,v r ] T is the azimuth and radial velocity of the target. The joint probability density functions of the received signals under H0 and H1 conditions are respectively expressed as:

[0058]

[0059]

[0060] Where R is the clutter plus noise covariance matrix, (·) H represents the conjugate transpose operation, (·) -1 Indicates the inverse operation. At this time, GLRT can be expressed as:

[0061]

[0062] in, Represents the likelihood ratio detection value, ζ represents the target detection threshold, a=[a 11 ,L,a NK ] T , max(·) means selecting the largest joint probability density value from a. Substituting formulas (2) and (3) into formula (4), we get About coefficient a nk Take the derivative and set it to zero, and solve for any sum v r , a nk The maximum likelihood estimate formula under H1 conditions is expressed as:

[0063]

[0064] Substituting formula (5) into the θ formula (4), we can simplify it and get:

[0065]

[0066] In the case of bias scanning, the target space-time steering vector formula is expressed as:

[0067] s'=s+δ (7)

[0068] Where δ represents the amount of deflection. Substitute formula (7) into formula (6) to update the amount to be detected for:

[0069]

[0070] Obviously, |(s+δ) H R -1 r| 2 >|s H R -1 r| 2 , take the minimum value of the denominator of formula (8), and let L(δ)=(s+δ) H R -1 (s+δ), find the minimum value of formula (8) with respect to δ. Derivative formula (8) with respect to δ and set its derivative to zero, and the maximum likelihood estimate of δ is:

[0071]

[0072] Substituting formula (9) into formula (8), the formula for the quantity to be detected after partial scanning can be expressed as:

[0073]

[0074] Where I represents the unit matrix. It can be seen that the formula (10) Compared with formula (6), As the numerator increases, the denominator reaches its minimum value, the fraction value becomes larger, and it is easier to exceed the detection threshold.

[0075] Based on the above analysis, the present invention proposes a new method to reduce the minimum detection speed. Figure 3 The embodiment of the present invention provides a method for reducing the minimum detectable speed by dense deflection scanning, which specifically includes the following steps:

[0076] S10. Determine the null beam width according to the corresponding transmission pattern of the radar.

[0077] The embodiment of the present invention is preferably applied to an airborne phased array monostatic radar. A corresponding transmission pattern can be constructed based on relevant parameters of the airborne phased array monostatic radar, such as the number of array elements, array element spacing, wavelength, and azimuth angle of the main beam. Here, only the azimuth angle is considered without considering the pitch angle. The constructed transmission pattern formula is expressed as follows:

[0078]

[0079] Where N is the number of array elements, d is the element spacing, θ is the azimuth angle of the main beam, θ0 is the initial azimuth angle of the main beam, and λ is the wavelength.

[0080] The existing method is used to determine the null beam width according to the corresponding transmission pattern of the radar. Here, the null beam width is specifically the first null beam width, which is recorded as Δθ.

[0081] Perform multiple deflection scans on the receive beam and / or transmit beam simultaneously to form a dense deflection scan. For each deflection scan, the following are performed:

[0082] S20. Calculate the power of the target in the main lobe clutter area.

[0083] The embodiment of the present invention provides an optional solution. The power formula of the target in the main lobe clutter area under the i-th offset scan is calculated by the radar equation as follows:

[0084]

[0085] Among them, p ti represents the power of the target in the main lobe clutter area calculated by the i-th offset scan, p max represents the peak power of the radar transmitter, G t Indicates the transmission gain, G r Indicates the receiving gain, G i represents the antenna pattern gain of the i-th offset scan, λ represents the wavelength, σ t represents the radar cross section (RCS) of the target, τB represents the time-bandwidth product, τ represents the pulse width, B represents the bandwidth, R represents the distance from the target to the radar, L n Indicates system loss.

[0086] S30: Calculate the residual power of the clutter.

[0087] The embodiment of the present invention provides an optional solution, which calculates the Doppler frequency of the target in the main lobe clutter area and uses the PD processing method to calculate the clutter residual power based on the Doppler frequency of the target. Specifically:

[0088] In each offset scan, the echo data received by the radar receiver can be processed by PD or STAP to obtain the clutter residual power of each range-Doppler unit. Simply put, a range gate and a Doppler channel can determine a clutter residual power. The range gate can be set according to the needs, and the Doppler channel is calculated based on the Doppler frequency of the target. The Doppler channel can be calculated by dividing the Doppler frequency by the Doppler resolution. With the range gate and Doppler channel, the clutter residual power p in the i-th offset scan can be calculated. ci .

[0089] Furthermore, the inventors have discovered that, in the case of offset scanning, PD processing produces better detection results than in the case of no offset scanning. However, because PD processing is not effective in suppressing clutter, the SCNR outputted by the target at some locations is reduced. For example, when the target is at the edge of the main lobe, its target power relative to the main beam direction is reduced, making it undetectable. The effect is worse than that of a short-term dwell at a single wave position, i.e., no offset scanning. To obtain better detection results, an embodiment of the present invention provides another optional solution, which calculates the Doppler frequency of the target in the main lobe clutter area; utilizes the STAP processing method to calculate the clutter residual power based on the target's Doppler frequency. For example, an embodiment of the present invention can use the existing Extended Factor Approach (EFA) method to calculate the clutter residual power. The detailed calculation process is not repeated here.

[0090] S40: Calculate the signal-to-noise ratio according to the target power and the residual power of the clutter.

[0091] The embodiment of the present invention provides an optional solution, according to the target power p ti and the residual power of the clutter p ci Calculate the output signal-to-noise ratio SCNR oi The formula is:

[0092]

[0093] Among them, SCNR oi represents the signal-to-noise ratio corresponding to the i-th offset sweep, p ti Indicates the power of the target corresponding to the i-th offset scan, p ci Indicates the residual power of the clutter corresponding to the i-th offset sweep.

[0094] S50. Obtain the maximum signal-to-noise ratio from all signal-to-noise ratios, expressed as:

[0095] max(SCNR o1 ,SCNR o2 ,...,SCNR oI ) (14)

[0096] Where, I represents the total number of partial sweeps, Δθ represents the null beam width, θ i Indicates the first corresponding deflection scan step size.

[0097] Determine whether the maximum signal-to-noise ratio is greater than or equal to the target detection threshold. If the maximum signal-to-noise ratio is greater than or equal to the target detection threshold, it indicates that a target exists. The target detection threshold can be set as an empirical value or calculated based on the false alarm probability and detection probability. Then:

[0098] S60. Calculate the minimum detectable velocity after deflection scanning according to the zero-point beam width.

[0099] The embodiment of the present invention provides an optional solution for calculating the minimum detectable velocity after deflection scanning based on the zero-point beam width, including: determining the minimum detectable positive velocity and the minimum detectable negative velocity based on the zero-point beam width; and calculating the minimum detectable velocity after deflection scanning based on the minimum positive velocity and the minimum negative velocity. It can be seen that for each signal-to-noise ratio calculation process, there is a corresponding set of [θ,v r ], that is, the speed corresponding to the zero-point beam width can be determined by the signal-to-noise ratio. In the embodiment of the present invention, the undetectable area within the zero-point beam width is preferably determined based on all signal-to-noise ratios; the speeds of the upper and lower boundaries of the undetectable area corresponding to the lower limit of the zero-point beam width are determined as the minimum detectable positive speed and minimum detectable negative speed.

[0100] Correspondingly, the formula for calculating the minimum detectable speed after deflection scanning based on the minimum positive speed and the minimum negative speed is expressed as:

[0101]

[0102] Where MDV represents the minimum detectable velocity, v h Indicates the minimum positive velocity, v l Indicates the minimum negative speed.

[0103] If the maximum signal-to-noise ratio is less than the target detection threshold, indicating that there is no target, then:

[0104] S70: Obtain the minimum value of the currently detectable target speed as the minimum detectable speed.

[0105] The entire process of the method for reducing the minimum detectable speed by dense deflection scanning proposed in an embodiment of the present invention is now completed.

[0106] In order to verify the effectiveness of the method for reducing the minimum detectable velocity by dense deflection scanning provided by an embodiment of the present invention, the following experiment was conducted for verification.

[0107] 1. Experimental simulation parameters

[0108] In this experiment, the radar, mounted on a platform flying at a constant speed at an altitude of 8000m, is an airborne phased array single-element radar. The antenna is a horizontal uniform, equidistant linear array with N = 64 elements. One coherent processing interval contains K = 90 coherent pulses. The system bandwidth B is 2.5MHz, the platform speed is 200m / s, and the radar pulse repetition frequency is 4000Hz. The angle between the main beam pointing direction and the normal to the array is 90°, and the target RCS is 1m. 2 , the detection threshold is 9.95dB, and the detection probability p d=0.8, false alarm probability p fa =10 -3 .

[0109] 2. Simulation results analysis

[0110] See Figure 4 , Figure 4 The antenna transmission pattern when the main beam is 90° is given. From the figure, we can see that the azimuth angle range of the main lobe is [88.2°, 91.8°], the null beam width Δθ is 3.6°, and the deflection angle step θ is taken. i is 0.45°.

[0111] See Figure 5 (a)~ Figure 5 (c) Figure 5 (a) shows the simulation results of the output SCNR in the case of no deflection after PD processing. In the experiment, the target was designed to be within the range gate 143, and the output SCNR was obtained by the ratio of the target power to the residual power of the clutter. The power of the target is only related to the azimuth angle. The target power is the strongest when the azimuth angle is 90°. The farther away from 90°, the smaller the target power. The residual power of the clutter in the Doppler channel corresponding to the target is related to the azimuth angle and the radial velocity of the target. It can be seen that when the target speed is 0m / s and the azimuth angle is 90°, the output SCNR is the smallest. This is because the target has no Doppler frequency shift and is buried in the clutter. When the speed is the same, the closer the azimuth angle is to 90°, the larger the output SCNR; when the azimuth angle is the same, the larger the absolute value of the speed, the larger the output SCNR. Then, according to the two cases of receiving beam deflection and introducing deflection in the transmitting and receiving beams, the simulation is carried out. The deflection angle step size is 0.45°, and the left and right deflections are performed 8 times each. In addition to no deflection, the maximum value of the 9 results is taken: Figure 5 (b) It can be seen that when the receiving beam is deflected, the output SCNR becomes larger than when it is not deflected. This is because deflection improves the search accuracy of the Doppler filter, changes the relative position of the target, and makes it easier for the target to enter the sidelobe clutter area. Moreover, the deviation of the target at a certain position from the normal direction causes the target power to decrease. After deflection, the clutter residual power also decreases, and the clutter residual power decreases much more, so the output SCNR increases. Figure 5 (c) It can be seen that when the transmit beam and the receive beam are simultaneously scanned, the output SCNR becomes larger than the previous two cases.

[0112] After obtaining the output SCNR, take the appropriate target detection threshold to obtain the final binary image and calculate MDV, as follows: Figure 6 (a)~ Figure 6(c) As shown in the figure. The gray areas on both sides of the figure are detectable areas, that is, the output SCNR is greater than or equal to the detection threshold. The black area in the middle of the figure is the undetectable area, that is, the output SCNR is less than the detection threshold. The speed corresponding to each deflection scan within the zero-point beam width can be determined by the upper and lower boundaries of the undetectable area. Here, the speed of the upper and lower boundaries of the undetectable area corresponding to the lower limit of the zero-point beam width is determined as the minimum detectable positive speed and minimum negative speed, for example Figure 6 (a) The velocity at the upper boundary of the undetectable area corresponding to the leftmost azimuth is determined as the minimum detectable positive velocity, and the velocity at the lower boundary of the undetectable area is determined as the minimum detectable negative velocity. The vertical width of the black area in the middle is twice the MDV, and the unevenness at the edge is due to the fluctuation of noise. Figure 6 (a) It can be seen that when the target is located to the left of the main lobe center in the unbiased scan condition, the minimum detectable negative and positive velocities are equal to those when it is located to the right, and the resulting MDV is 20.00 m / s. Figure 6 (b) It can be seen that when the target is located to the left of the main lobe center, the receive deflection increases the output SCNR, which improves the minimum detectable positive velocity. Similarly, when the target is located to the right of the main lobe center, the minimum detectable negative velocity is improved, and the calculated MDV is 17.83 m / s. Similarly, from Figure 6 (c) As can be seen, the MDV for both the transmit and receive beams is 14.56 m / s. Compared to the unbiased case, the MDV for both the receive and transmit beams is smaller.

[0113] In the above simulation, the dwell time of each wave position is relatively short, which is 22.5ms. The following simulation is compared with the case of a single wave position with a long dwell time. Since there are 9 wave positions in total, the dwell time is 202.5ms, which corresponds to 810 pulses. The target power is also increased by 9 times. The results are as follows: Figure 7 (a)~ Figure 7 As shown in (b), it can be seen that at this time, the number of coherent accumulation pulses increases, and the target power increases accordingly, but at the same time there is also a strong accumulation effect on the clutter, and the target power and the clutter residual power become stronger at the same time.

[0114] See Figure 8 , Figure 8 Given the transmission pattern when the number of array elements N=32 and the main beam is 90°, the range of the azimuth angle corresponding to the main lobe is [86.4°, 93.6°], the zero-point beam width Δθ is 7.2°, and the deflection step length θ is taken. i It is 0.9°.

[0115] See Figure 9 (a)~ Figure 9(c) shows the output SCNR results of the STAP process without deflection, the output SCNR results of the receive deflection, and the output SCNR results of the transmit and receive deflection. In the experiment, the target was designed to be within the range gate 367, with a deflection angle step of 0.9° and 8 deflections on each side. Figure 9 It can be seen from (a) that the output SCNR increases with the increase of the absolute value of the velocity at the same azimuth angle; at the same velocity, the further away from 90°, the smaller the output SCNR; Figure 9 As can be seen from (b), after receiving the bias scan, the output SCNR becomes larger than that without bias scan, and because the EFA processing narrows the main lobe clutter, the part where the output SCNR is less than 0 also becomes narrower. Figure 9 As can be seen from (c), after both the transmit and receive are deflected, the output SCNR becomes much larger than in the previous two cases.

[0116] After obtaining the output SCNR, take the appropriate target detection threshold to obtain the final binary image and calculate MDV, as follows: Figure 10 (a)~ Figure 10 (c) Based on image 10(a), the MDV for the unbiased scan condition is calculated to be 15.55 m / s. Similarly, based on image 10(b), the MDV for the receive beam with a biased scan condition is calculated to be 8.89 m / s. Based on image 10(c), the MDV for both the transmit and receive beams with a biased scan condition is calculated to be 6.67 m / s. Compared to the unbiased scan condition, the MDV for both the receive beam with a biased scan condition and the transmit and receive beam with a biased scan condition is smaller.

[0117] Figure 11 (a)~ Figure 11 (b) is a simulation comparison of the case where a single wave position stays for a long time. Figure 7 (a)~ Figure 7 (b), the dwell time is 202.5ms, the corresponding pulse number is 810, and the target power is increased by 9 times. Figure 11 (a)~ Figure 11 (b) As can be seen, in the STAP case, increasing the pulse number also increases the accumulation effect on clutter, but EFA processing achieves better suppression, narrowing the notch and increasing the system's output SCNR. The corresponding MDV is 8.64 m / s. The difference between the results of long-dwell at a single wavelength and short-dwell at multiple wavelengths (i.e., dense offset sweeps) is not significant.

[0118] In summary, the method of reducing the minimum detectable velocity by dense offset scanning proposed in the embodiment of the present invention is a new idea for reducing the minimum detectable velocity. In the Doppler domain, a target is easily detected when it enters the sidelobe clutter area. Whether the target can be detected is related to the azimuth angle of the target in the mainlobe clutter and the radial velocity of the target. Since the angle of the target is unknown, the beam is usually only pointed to a fixed position, which cannot achieve the best detection effect. Therefore, the embodiment of the present invention proposes to perform multiple offset scans on the receiving beam and / or the transmitting beam at the same time to improve the search accuracy of the Doppler filter, change the relative position of the target in the mainlobe of the beam, reduce the radial velocity required for the target to enter the sidelobe clutter area, and accordingly change the MDV. Based on the above theoretical support and the definition of MDV, under certain false alarm probability conditions, the output signal-to-noise ratio (SNR) obtained after signal processing is greater than or equal to the output SNR required for the detection probability required by the system. The minimum target speed at this time is called MDV. The method proposed in the embodiment of the present invention calculates the SNR in real time based on the power of the target in the mainlobe clutter area and the clutter residual power calculated in each offset scan. The presence of a target is determined based on the comparison result of the SNR and the target detection threshold. If a target is present, the MDV after the offset scan is calculated in real time based on the zero-point beamwidth. The calculated MDV is smaller, thereby improving the detection performance of low-speed targets. Compared with other existing methods, the embodiment of the present invention has good real-time performance, is not affected by the "three-span" phenomenon, does not require a compensation correction process, and has a low system degree of freedom. Fewer IID samples are required, which reduces the amount of computation, resulting in high real-time performance and strong applicability of the algorithm. In actual engineering, a method for reducing MDV with small equipment requirements, low computational complexity, and good real-time performance can be adopted.

[0119] See Figure 12 , an embodiment of the present invention provides an electronic device, including a processor 1201, a communication interface 1202, a memory 1203 and a communication bus 1204, wherein the processor 1201, the communication interface 1202, and the memory 1203 communicate with each other via the communication bus 1204;

[0120] Memory 1203, used for storing computer programs;

[0121] The processor 1201 is configured to implement the steps of the method for reducing the minimum detectable speed by dense deflection scanning when executing the program stored in the memory 1203 .

[0122] An embodiment of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the steps of the method for reducing the minimum detectable speed of the dense deflection scanning are implemented.

[0123] As for the electronic device / storage medium embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0124] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0125] Although the present invention is described herein in conjunction with various embodiments, those skilled in the art may understand and implement other variations of the disclosed embodiments by reviewing the specification and accompanying drawings in the process of implementing the claimed invention. In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple components or steps. The fact that certain measures are described in different embodiments does not mean that these measures cannot be combined to produce good results.

[0126] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for reducing the minimum detectable velocity by dense deflection scanning, characterized in that: include: Determine the null beam width based on the corresponding transmission pattern of the radar; Within the null beam width, the receiving beam and / or the transmitting beam are simultaneously subjected to multiple offset sweeps, wherein for each offset sweep, the following steps are performed: calculating the power of a target in a main lobe clutter region; calculating the clutter residual power; and calculating a signal-to-noise ratio based on the power of the target and the clutter residual power. The maximum signal-to-noise ratio is obtained from all signal-to-noise ratios, and it is determined whether the maximum signal-to-noise ratio is greater than or equal to the target detection threshold. If the maximum signal-to-noise ratio is greater than or equal to the target detection threshold, the minimum detectable speed after the offset scan is calculated based on the zero-point beamwidth. Otherwise, the minimum value of the currently detectable target speed is obtained as the minimum detectable speed.

2. The method for reducing the minimum detectable speed by dense deflection scanning according to claim 1, characterized in that: The formula for calculating the power of a target in the main lobe clutter area is: Among them, p ti represents the power of the target in the main lobe clutter area calculated by the i-th offset scan, p max Indicates the peak power of the radar transmitter, G t Indicates the transmission gain, G r Indicates the receiving gain, G i represents the antenna pattern gain of the i-th offset scan, λ represents the wavelength, σ t represents the RCS of the target, τB represents the time-bandwidth product, τ represents the pulse width, B represents the bandwidth, R represents the distance from the target to the radar, L n Indicates system loss.

3. The method for reducing the minimum detectable speed by dense deflection scanning according to claim 1, characterized in that: Calculating the residual power of clutter includes: Calculate the Doppler frequency of the target in the main lobe clutter area; The PD processing method is used to calculate the clutter residual power according to the Doppler frequency of the target.

4. The method for reducing the minimum detectable velocity by dense deflection scanning according to claim 1, characterized in that: Calculating the residual power of clutter includes: Calculate the Doppler frequency of the target in the main lobe clutter area; The STAP processing method is used to calculate the clutter residual power according to the Doppler frequency of the target.

5. The method for reducing the minimum detectable velocity by dense deflection scanning according to claim 1, characterized in that: The signal-to-noise ratio (SNR) is calculated based on the target power and the residual power of the clutter as follows: Among them, SCNR oi represents the signal-to-noise ratio corresponding to the i-th offset sweep, p ti Indicates the power of the target corresponding to the i-th offset scan, p ci Indicates the residual power of the clutter corresponding to the i-th offset sweep.

6. The method for reducing the minimum detectable velocity by dense deflection scanning according to claim 1, characterized in that: Calculating the minimum detectable velocity after deflection scanning based on the zero-point beam width includes: determining a minimum detectable positive velocity and a minimum detectable negative velocity based on the zero-point beamwidth; The minimum detectable speed after deflection scanning is calculated according to the minimum positive speed and the minimum negative speed.

7. The method for reducing the minimum detectable velocity by dense deflection scanning according to claim 6, characterized in that: The minimum positive and negative detectable velocities are determined based on the zero-point beamwidth, including: determining an undetectable region within the null beamwidth based on all signal-to-noise ratios; The velocities of the upper and lower boundaries of the undetectable area corresponding to the lower limit of the zero-point beam width are determined as the minimum positive velocity and the minimum negative velocity that can be detected.

8. The method for reducing the minimum detectable velocity by dense deflection scanning according to claim 7, characterized in that: The formula for calculating the minimum detectable speed after deflection scanning based on the minimum positive speed and the minimum negative speed is expressed as: Wherein, MDV represents the minimum detectable velocity, v h represents the minimum positive velocity, v l Indicates the minimum negative speed.

9. The method for reducing the minimum detectable velocity by dense deflection scanning according to claim 1, characterized in that: The radar is an airborne phased array single-base radar.

10. An electronic device comprising a processor, a communication interface, a memory and a communication bus, wherein: The processor, the communication interface, and the memory communicate with each other via the communication bus; The memory is used to store computer programs; The processor is configured to implement the steps of the method for reducing the minimum detectable speed of dense deflection scanning as described in any one of claims 1 to 9 when executing the program stored in the memory.

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