An Optimization Design Method for Doppler Filters in Cognitive Radar

Abstract

This invention relates to the field of radar signal processing and provides an optimized design method for Doppler filters in cognitive radar. The method includes: determining M transmitted wave azimuth angles; determining the Doppler frequency of the corresponding m-th main clutter wave based on the m-th transmitted wave azimuth angle, where m ranges from 1 to M; determining the corresponding Doppler channel using the Doppler frequency of the m-th main clutter wave; adjusting the frequency range of the Doppler filter based on the Doppler channel of the m-th main clutter wave to obtain an adjusted Doppler filter; receiving multiple sets of echo signals within a preset range threshold, and determining the output signal-to-noise ratio of the Doppler filter based on the multiple sets of echo signals and the adjusted Doppler filter, to determine the maximum detectable target area within the preset range threshold. The improved filter based on the method provided by this invention can provide a larger detectable area and higher detection accuracy, and can adapt well to complex clutter scenarios.

Description

Technical Field

[0001] This invention belongs to the field of radar signal processing technology, specifically relating to an optimization design method for a Doppler filter used in cognitive radar. Background Technology

[0002] Due to the aircraft's motion relative to the ground, airborne radar experiences varying relative velocities between clutter blocks in different directions and the radar, leading to clutter Doppler spectrum broadening and decreased target detection performance. To address this issue, the concept of Space-Time Adaptive Processing (STAP) emerged. STAP methods are commonly used in Doppler filters to utilize two-dimensional space-time degrees of freedom to distinguish targets from clutter in the angle-Doppler plane, adaptively creating notches at clutter locations to effectively improve the signal-to-clutter ratio. However, in practice, traditional Doppler filters or STAP filters struggle to completely suppress clutter, resulting in low target detection performance. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides an optimized design method for a Doppler filter used in cognitive radar. The technical problem to be solved by this invention is achieved through the following technical solution:

[0004] This invention provides an optimized design method for a Doppler filter used in cognitive radar, comprising: determining M transmission wave azimuth angles for transmitting radar detection waves, where M is a positive integer; determining the Doppler frequency of the corresponding m-th main clutter wave based on the m-th transmission wave azimuth angle, where m takes values ​​from 1 to M; determining the Doppler channel of the m-th main clutter wave using the Doppler frequency of the m-th main clutter wave; adjusting the frequency range of the Doppler filter based on the M main clutter wave Doppler channels to obtain an adjusted Doppler filter; receiving multiple sets of echo signals within a preset range gate, and determining multiple output signal-to-noise ratios (SNRs) of the adjusted Doppler filter within the preset range gate based on the multiple sets of echo signals and the adjusted Doppler filter, wherein each output SNR is used to determine the maximum target detectable area within the current range gate, and one range gate corresponds to one output SNR.

[0005] In some embodiments, determining the M transmission wave azimuth angles for transmitting radar detection waves includes: Step S1: obtaining the m-th transmission wave azimuth angle and the beamwidth corresponding to the m-th transmission wave azimuth angle; when m is 1, the first transmission wave azimuth angle is a preset initial transmission wave azimuth angle; Step S2: connecting adjacent beams at a 3dB beamwidth, and using the m-th transmission wave azimuth angle, the beamwidth corresponding to the m-th transmission wave azimuth angle, and the beamwidth corresponding to the (m+1)-th transmission wave azimuth angle, the (m+1)-th transmission wave azimuth angle is calculated by reverse calculation; Step S3: determining whether the (m+1)-th transmission wave azimuth angle is within a preset scanning angle interval; if it is, then setting m = m+1, repeating steps S1 to S3; if it is not, then stopping the calculation, and using the calculated multiple transmission wave azimuth angles within the preset scanning angle interval as the M transmission wave azimuth angles for transmitting radar detection waves.

[0006] In some embodiments, the Doppler frequency of the m-th main clutter includes: the m-th first normalized Doppler frequency and the m-th second normalized Doppler frequency; the Doppler channel of the m-th main clutter includes: the Doppler channel corresponding to the m-th first normalized Doppler frequency and the Doppler channel corresponding to the m-th second normalized Doppler frequency; determining the Doppler channel of the m-th main clutter using the Doppler frequency of the m-th main clutter includes: obtaining the value range of the center frequency of the channel of the Doppler filter, wherein one channel corresponds to one center frequency; obtaining the frequency closest to the m-th first normalized Doppler frequency from the value range as the first center frequency, wherein the first center frequency is greater than the m-th first normalized Doppler frequency; and obtaining the frequency closest to the m-th second normalized Doppler frequency as the second center frequency, wherein the second center frequency is greater than the m-th second normalized Doppler frequency; obtaining the first center frequency... The Doppler channel corresponding to the frequency is obtained, and the Doppler channel corresponding to the third center frequency in the range of values ​​is obtained. Using the Doppler channel corresponding to the first center frequency and the Doppler channel corresponding to the third center frequency, the Doppler channel corresponding to the m-th first normalized Doppler frequency is determined. The third center frequency is less than the m-th first normalized Doppler frequency, and the Doppler channel corresponding to the third center frequency is adjacent to the Doppler channel corresponding to the first center frequency. The Doppler channel corresponding to the second center frequency is obtained, and the Doppler channel corresponding to the fourth center frequency in the range of values ​​is obtained. Using the Doppler channel corresponding to the second center frequency and the Doppler channel corresponding to the fourth center frequency, the Doppler channel corresponding to the m-th second normalized Doppler frequency is determined. The fourth center frequency is less than the m-th second normalized Doppler frequency, and the Doppler channel corresponding to the fourth center frequency is adjacent to the Doppler channel corresponding to the second center frequency.

[0007] In some embodiments, the Doppler frequency of the m-th main clutter includes: the m-th first normalized Doppler frequency and the m-th second normalized Doppler frequency; the m-th first normalized Doppler frequency is less than the m-th second normalized Doppler frequency; the Doppler channel of the m-th main clutter includes: a Doppler channel corresponding to a first center frequency and a Doppler channel corresponding to a second center frequency; the first center frequency is the value of the center frequency of the Doppler filter channel that is greater than and closest to the m-th first normalized Doppler frequency. The frequency of the normalized Doppler frequency, wherein the second center frequency is the frequency in the range that is greater than and closest to the m-th second normalized Doppler frequency; the adjustment of the frequency range of the Doppler filter based on the M main clutter Doppler channels to obtain an adjusted Doppler filter includes: for the m-th main clutter Doppler frequency, using the value of the Doppler channel corresponding to the first center frequency, dividing the frequency interval formed by the lower limit of the range and the m-th first normalized Doppler frequency to obtain a multi-channel Doppler filter. The frequency range is divided into several sub-frequency ranges: a first sub-frequency range is defined; a first difference is used to divide the frequency range formed by the m-th first normalized Doppler frequency and the m-th second normalized Doppler frequency, resulting in multiple second sub-frequency ranges; the first difference is the difference between the value of the Doppler channel corresponding to the first center frequency and the value of the Doppler channel corresponding to the second center frequency; a second difference is used to divide the frequency range formed by the m-th second normalized Doppler frequency and the upper limit of the value range, resulting in multiple third sub-frequency ranges; the second difference is the difference between the value of the Doppler channel corresponding to the second center frequency and the preset number of transmitted pulses; the multiple first sub-frequency ranges, the multiple second sub-frequency ranges, and the multiple third sub-frequency ranges are used as the m-th Doppler frequency range, and the (m+1)-th Doppler frequency range is determined until the M-th Doppler frequency range is obtained; the M-th Doppler frequency range is used as the new frequency range corresponding to the adjusted Doppler filter, thus obtaining the adjusted Doppler filter.

[0008] In some embodiments, the preset distance gate range includes Q distance gates, wherein one distance gate corresponds to M sets of echo signals, and one transmit wave position angle corresponds to one set of echo signals; receiving multiple sets of echo signals within the preset distance gate range, and determining multiple output signal-to-noise ratios of the adjusted Doppler filter within the preset distance gate range based on the multiple sets of echo signals and the adjusted Doppler filter, includes: for the q-th distance gate, acquiring M sets of echo signals in the q-th distance gate, where the value of q ranges from 1 to Q, and Q is a preset positive integer; inputting the M sets of echo signals into the adjusted Doppler filter. In the device, the M sets of echo signals are dimensionality-reduced to obtain M sets of dimensionality-reduced echo signals; the target spacetime steering vector and the total number of range gates within the preset range gate range are obtained, and the M sets of dimensionality-reduced echo signals are combined to solve for M optimal weights; based on the M optimal weights, M signal-to-noise ratios are determined, where each optimal weight corresponds to one signal-to-noise ratio; the maximum value is selected from the M signal-to-noise ratios and used as the output signal-to-noise ratio corresponding to the q-th range gate, and the output signal-to-noise ratio corresponding to the (q+1)-th range gate is determined until the output signal-to-noise ratio corresponding to the Q-th range gate is obtained.

[0009] In some embodiments, the target spacetime steering vector is obtained through the following steps: obtaining a temporal dimension reduction matrix, a spatial dimension reduction matrix, a target temporal steering vector, and a target spatial steering vector; using the temporal dimension reduction matrix and the target temporal steering vector, determining the dimension-reduced target temporal steering vector; using the spatial dimension reduction matrix and the target spatial steering vector, determining the dimension-reduced target spatial steering vector; and performing a Kronecker product on the dimension-reduced target temporal steering vector and the dimension-reduced target spatial steering vector to obtain the target spacetime steering vector.

[0010] In some embodiments, the expression for the (m+1)th emitted wave position angle is:

[0011]

[0012]

[0013]

[0014] in, It is the beamwidth corresponding to the m-th transmitted wave position angle. This refers to the m-th emitted wave position angle, where λ refers to the wavelength, and L... a This refers to the antenna aperture length. This refers to the beamwidth corresponding to the (m+1)th transmitted wave position angle. It refers to the (m+1)th emitted wave position angle.

[0015] In some embodiments, the expressions for each first normalized Doppler frequency and each second normalized Doppler frequency are as follows:

[0016]

[0017]

[0018] Among them, f d0 This refers to the first normalized Doppler frequency, f. d1 This refers to the second normalized Doppler frequency, where v is the aircraft speed and λ is the wavelength. The transmitted wave position angle refers to the preset yaw angle, θ0 refers to the preset main beam elevation angle, and f refers to the preset pulse repetition frequency.

[0019] In some embodiments, the expression for each optimal weight is:

[0020]

[0021]

[0022]

[0023] Among them, w opt This refers to the optimal weight. This refers to the clutter plus noise covariance matrix obtained by maximum likelihood estimation of the echo signal after dimensionality reduction, where l is the range gate number, S0 is the target space-time steering vector, and (·) H This refers to the transpose process, and L refers to the total number of distance gates. This refers to the echo signal after the dimensionality reduction process. This refers to the target time-domain steering vector after dimensionality reduction, where t refers to the time domain. This refers to the target spatial steering vector after dimensionality reduction, where k refers to the spatial domain. This refers to the Kronecker product, F refers to the time-domain dimensionality reduction matrix, T refers to the spatial-domain dimensionality reduction matrix, and S refers to the Kronecker product. t This refers to the target time-domain steering vector, S k This refers to the target airspace steering vector.

[0024] In some embodiments, the expression for each output signal-to-noise ratio is:

[0025]

[0026] Among them, SNR out This refers to the output signal-to-noise ratio, w opt This refers to the optimal weight. This refers to the clutter plus noise covariance matrix obtained by maximum likelihood estimation of the echo signal after dimensionality reduction, where l is the range gate number, r is the spacetime steering vector at any point in space, and (·) H This refers to transpose processing, |·| 2 It refers to the square of the absolute value.

[0027] This invention offers the following beneficial technical effects: Addressing the problem that traditional Doppler or STAP filters struggle to completely suppress clutter, resulting in low target detection performance, this invention provides an optimized design method for a Doppler filter in cognitive radar. This method obtains the Doppler frequency of the main clutter corresponding to each transmitted wave position angle; by using the Doppler frequencies of multiple main clutter waves as the center frequency of the filter, and then adjusting the frequency range of the Doppler filter using the Doppler channel where each main clutter wave is located, a well-adjusted Doppler filter is obtained. The adjusted Doppler filter overcomes the problem of reduced target gain due to the target's Doppler frequency deviating from the filter's center frequency, thus reducing target detection performance. Furthermore, the adjusted Doppler filter has a larger detectable area and higher target detection accuracy, and can adapt well to complex clutter scenarios.

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the optimization design method for a Doppler filter for cognitive radar provided in an embodiment of the present invention.

[0030] Figure 2 This is a schematic diagram of the clutter distribution curve provided in an embodiment of the present invention;

[0031] Figure 3 The embodiment of the present invention provides the use of conventional filters. Figure 2 A schematic diagram of the output signal-to-noise ratio after clutter processing;

[0032] Figure 4 This is a filter pair improved using the technical solution of the present invention, provided in an embodiment of the present invention. Figure 2 A schematic diagram of the output signal-to-noise ratio after clutter processing;

[0033] Figure 5 The embodiment of the present invention provides the use of conventional filters. Figure 2 The detectable area map output after clutter processing;

[0034] Figure 6 This is a filter pair improved using the technical solution of the present invention, provided in an embodiment of the present invention. Figure 2The detectable area map output after clutter processing. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0036] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0037] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0038] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, disclosure, and appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0039] To address the problem that traditional Doppler filters or STAP filters are unable to completely suppress clutter, resulting in low target detection performance, this invention provides an optimized design method for Doppler filters used in cognitive radar. This method can effectively suppress clutter from different directions, greatly improving the accuracy and efficiency of target detection.

[0040] Now combined Figure 1 The technical solution proposed in this invention will be described in detail. Figure 1 This is a flowchart illustrating the optimized design method for a Doppler filter used in cognitive radar, provided in an embodiment of the present invention. Figure 1As shown, the method includes:

[0041] Step 110: Determine M transmission wave azimuth angles for transmitting radar detection waves, where M is a positive integer.

[0042] Here, step 110 includes: Step S1: Obtain the m-th transmitted wave azimuth angle and the beamwidth corresponding to the m-th transmitted wave azimuth angle; when m is 1, the first transmitted wave azimuth angle is the preset initial transmitted wave azimuth angle; Step S2: Connect adjacent beams at a 3dB beamwidth, and use the m-th transmitted wave azimuth angle, the beamwidth corresponding to the m-th transmitted wave azimuth angle, and the beamwidth corresponding to the (m+1)-th transmitted wave azimuth angle to calculate the (m+1)-th transmitted wave azimuth angle; Step S3: Determine whether the (m+1)-th transmitted wave azimuth angle is within the preset scanning angle interval; if it is, let m = m+1, and repeat steps S1 to S3 above; if it is not, stop the calculation, and use the calculated multiple transmitted wave azimuth angles within the preset scanning angle interval as M transmitted wave azimuth angles for transmitting radar detection waves.

[0043] In one possible implementation, a 3dB width beamwidth formula is used to determine the beamwidth corresponding to each transmit beamwidth angle. Given the m-th transmit beamwidth angle, the beamwidth corresponding to the m-th transmit beamwidth angle can be determined using the 3dB width beamwidth formula. By connecting the beams emitted from the m-th transmit beamwidth angle and the beams emitted from the (m+1)-th transmit beamwidth angle at a 3dB beamwidth, the (m+1)-th transmit beamwidth angle can be determined using the m-th transmit beamwidth angle. This process is repeated to determine the (m+2)-th transmit beamwidth angle, until the determined transmit beamwidth angles exceed the range of a preset scanning angle. Here, the first transmit beamwidth angle is preset to 0 degrees.

[0044] Here, the expression for the (m+1)th emitted wave position angle is:

[0045]

[0046]

[0047]

[0048] in, It is the beamwidth corresponding to the m-th transmitted wave position angle. This refers to the position angle of the m-th emitted wave, where λ is the wavelength, and L... a This refers to the antenna aperture length. It refers to the beamwidth corresponding to the (m+1)th transmitted wave position angle. It refers to the (m+1)th emitted wave position angle.

[0049] After determining the emission wave azimuth angles for transmitting dozens or hundreds of pulses, in step 120, multiple emission wave azimuth angles are used for further processing.

[0050] Step 120: Based on the m-th transmitted wave azimuth angle, determine the corresponding m-th main clutter Doppler frequency, where m takes the value from 1 to M.

[0051] Here, the frequencies of the main clutter corresponding to each transmitted wave position angle may be the same or different. Taking the Doppler frequency corresponding to the m-th main clutter as an example, the Doppler frequency of the m-th main clutter includes: the m-th first normalized Doppler frequency and the m-th second normalized Doppler frequency; the Doppler channel of the m-th main clutter includes: the Doppler channel corresponding to the m-th first normalized Doppler frequency and the Doppler channel corresponding to the m-th second normalized Doppler frequency.

[0052] Here, the expressions for each first normalized Doppler frequency and each second normalized Doppler frequency are as follows:

[0053]

[0054]

[0055] Among them, f d0 This refers to the first normalized Doppler frequency, f. d1 This refers to the second normalized Doppler frequency, where v is the aircraft speed and λ is the wavelength. α refers to the transmit wave position angle, θ0 refers to the preset yaw angle, f refers to the preset main beam elevation angle, and f refers to the preset pulse repetition frequency.

[0056] It should be understood that the terms "first normalized Doppler frequency" and "second normalized Doppler frequency" are introduced here only to distinguish between the two. The "first normalized Doppler frequency" can also have other names, such as the anterior lobe normalized Doppler frequency; and the "second normalized Doppler frequency" can also have other names, such as the back lobe normalized Doppler frequency.

[0057] After determining the Doppler frequency corresponding to each main clutter, substitute it into step 130 to determine the Doppler channel corresponding to each main clutter.

[0058] Step 130: Use the Doppler frequency of the m-th main clutter to determine the Doppler channel of the m-th main clutter.

[0059] Specifically, step 130 includes: obtaining the value range of the center frequency of the Doppler filter channel, wherein one channel corresponds to one center frequency; from the value range, obtaining the frequency closest to the m-th first normalized Doppler frequency as the first center frequency, wherein the first center frequency is greater than the m-th first normalized Doppler frequency; and obtaining the frequency closest to the m-th second normalized Doppler frequency as the second center frequency, wherein the second center frequency is greater than the m-th second normalized Doppler frequency; obtaining the Doppler channel corresponding to the first center frequency, and obtaining the Doppler channel corresponding to the third center frequency in the value range, and using the Doppler channel corresponding to the first center frequency and the Doppler channel corresponding to the third center frequency... The system first determines the Doppler channel corresponding to the m-th first normalized Doppler frequency, where the third center frequency is less than the m-th first normalized Doppler frequency, and the Doppler channel corresponding to the third center frequency is adjacent to the Doppler channel corresponding to the first center frequency. It then obtains the Doppler channel corresponding to the second center frequency and the Doppler channel corresponding to the fourth center frequency within the range of values. Using the Doppler channels corresponding to the second and fourth center frequencies, it determines the Doppler channel corresponding to the m-th second normalized Doppler frequency, where the fourth center frequency is less than the m-th second normalized Doppler frequency, and the Doppler channel corresponding to the fourth center frequency is adjacent to the Doppler channel corresponding to the second center frequency.

[0060] Here, assuming the number of transmitted pulses is known, and the center frequency range of the Doppler filter or STAP filter is (-0.5, 0.5), the range of values ​​for the center frequency of the Doppler filter or STAP filter channel can be expressed as:

[0061] f FFT (1:M+1)=linspace(-0.5,0.5,M+1);

[0062] Among them, f FFT This refers to the center frequency of the channel of a Doppler or STAP filter, f. FFT (1:M+1) means uniformly dividing a frequency interval of length 1 using the number of transmitted pulses M, where M is the number of transmitted pulses. linspace(·) means uniformly dividing the frequency interval from -0.5 to 0.5 using the number of transmitted pulses M. For example, linspace(a,b,c) means uniformly dividing the range [a,b] into c points.

[0063] After obtaining the Doppler frequencies of multiple main clutters in step 120, the Doppler channels where the main clutters are located are determined using the Doppler frequencies of each main clutter. Assume that the number of Doppler channels corresponding to the first center frequency is l0, and the number of Doppler channels corresponding to the second center frequency is l1. Then, the Doppler channels corresponding to the m-th first normalized Doppler frequency can be expressed as l0 - 1 to l0, and the Doppler channels corresponding to the m-th second normalized Doppler frequency can be expressed as l1 - 1 to l1, where l0 < l1. For example, assume that there are 8 groups of channels in the Doppler filter, and the values of the center frequencies corresponding to each channel are: -0.5, -0.4, -0.3, - .2, -0.1, 0, 0.1, and 0.2. The first normalized Doppler frequency corresponding to the m-th main clutter is -0.15, and the second normalized Doppler frequency is 0.15. Then, the first center frequency is -0.1, the Doppler channel corresponding to the first center frequency is 5, the third center frequency is -0.2, the Doppler channel corresponding to the third center frequency is 4, and channels 4 and 5 form the m-th first normalized Doppler frequency; the second center frequency is 0.2, the Doppler channel corresponding to the second center frequency is 8, and the fourth center frequency is 0.1, the Doppler channel corresponding to the fourth center frequency is 7, and channels 7 and 8 form the m-th second normalized Doppler frequency.

[0064] Step 140: Based on the Doppler channels of M main clutters, adjust the frequency range of the Doppler filter to obtain an adjusted Doppler filter.

[0065] Here, a slight change in the center frequency of the Doppler filter or STAP filter will significantly affect the clutter suppression effect, and the target gain and signal-to-noise ratio will also change with the filter center frequency. In other words, the number of filters and the center frequency of the filters determine the detection performance of different velocity targets at this wave position . Since the orientations of each transmitted wave position angle are different, the frequencies of the clutters in different azimuths may be the same or different. Therefore, in the present invention, the Doppler frequency of the main clutter is used as one of the center frequencies in the filter bank, and the frequencies of the main clutters in different azimuths are used to adjust the center frequency of the Doppler filter or STAP filter to optimize the clutter suppression effect of the Doppler filter or STAP filter.

[0066] Here, the Doppler frequency of the m-th main clutter includes: the m-th first normalized Doppler frequency and the m-th second normalized Doppler frequency; the m-th first normalized Doppler frequency is less than the m-th second normalized Doppler frequency; the Doppler channel of the m-th main clutter includes: the Doppler channel corresponding to the first center frequency and the Doppler channel corresponding to the second center frequency; the first center frequency is the frequency within the range of the center frequency of the Doppler filter channel that is greater than and closest to the m-th first normalized Doppler frequency, and the second center frequency is the frequency within the range that is greater than and closest to the m-th second normalized Doppler frequency.

[0067] Specifically, step 140 includes: for the m-th main clutter Doppler frequency, using the value of the Doppler channel corresponding to the first center frequency, dividing the frequency interval formed by the lower limit of the value range and the m-th first normalized Doppler frequency to obtain multiple first sub-frequency intervals; using a first difference, dividing the frequency interval formed by the m-th first normalized Doppler frequency and the m-th second normalized Doppler frequency to obtain multiple second sub-frequency intervals, wherein the first difference refers to the difference between the value of the Doppler channel corresponding to the first center frequency and the value of the Doppler channel corresponding to the second center frequency; using a second difference, The frequency interval formed by the m-th second normalized Doppler frequency and the upper limit of the value range is divided to obtain multiple third sub-frequency intervals. Here, the second difference refers to the difference between the value of the Doppler channel corresponding to the second center frequency and the preset number of transmitted pulses. The multiple first sub-frequency intervals, multiple second sub-frequency intervals, and multiple third sub-frequency intervals are taken as the m-th Doppler frequency range. The (m+1)-th Doppler frequency range is then determined until the M-th Doppler frequency range is obtained. The M-th Doppler frequency range is taken as the new frequency range corresponding to the adjusted Doppler filter to obtain the adjusted Doppler filter.

[0068] It should be noted that using M Doppler frequency ranges as the new frequency range corresponding to the adjusted Doppler filter can be understood as the Doppler filter's frequency range encompassing M Doppler frequency ranges. When facing different dominant clutter, the Doppler filter's frequency range will adaptively adjust to the Doppler frequency range corresponding to that dominant clutter, thereby effectively suppressing the dominant clutter. For example, when facing the m-th dominant clutter, the new frequency range corresponding to the adjusted Doppler filter includes the m-th Doppler frequency range; when facing the (m+1)-th dominant clutter, the new frequency range corresponding to the adjusted Doppler filter includes the (m+1)-th Doppler frequency range. The new frequency range corresponding to the adjusted Doppler filter will also differ depending on the type of dominant clutter.

[0069] For example, the number of Doppler channels corresponding to the first center frequency of the m-th main clutter is l0, the number of Doppler channels corresponding to the second center frequency is l1, and the center frequency range of the Doppler filter or STAP filter is (-0.5, 0.5). The specific operation to obtain the new frequency range corresponding to the adjusted Doppler filter can be expressed as:

[0070] (1) Using the Doppler channel number l0 corresponding to the first center frequency to define the range (-0.5, f) of the filter's lower limit and the first normalized Doppler frequency. d0 The multiple first sub-frequency intervals obtained by uniformly dividing the frequency range can be represented as: f FFT (1:l0)=linspace(-0.5,f d0 ,l0).

[0071] (2) The first difference can be expressed as: l1-l0+1, where M refers to the number of transmitted pulses, and the frequency interval to be divided is (f d0 ,f d1 The multiple second sub-frequency intervals obtained can be represented as: f NEW (l0:l1+1)=linspace(f d0 ,f d1 (l1-l0+1).

[0072] (3) The second difference can be expressed as: M+3-l1, where M refers to the number of transmitted pulses, and the frequency interval to be divided is (f d1 The multiple third sub-frequency intervals obtained (f, 0.5) can be represented as: NEW (l1+1:M+3)=linspace(f d1 ,0.5,M+3-l1).

[0073] It should be noted that this is merely an example illustrating the adjustment of the center frequency of a Doppler filter or STAP filter using the Doppler frequency of the m-th dominant clutter. Specifically, the length of the original frequency range remains unchanged; for example, the new frequency range corresponding to the Doppler filter is still -0.5 to 0.5. What changes is the length of the internal sub-frequency intervals. Furthermore, the lengths of the first, second, and third sub-frequency intervals may be the same or completely different. For the sake of simplicity, the process of adjusting the center frequency of the Doppler filter or STAP filter using dominant clutter corresponding to other transmitted wave azimuth angles will not be elaborated here.

[0074] By adjusting the Doppler frequency of the main clutter to the center frequency of the Doppler filter or STAP filter, the problem of the target's Doppler frequency deviating from the filter's center frequency can be avoided, which would lead to a decrease in target gain and consequently a reduction in target detection performance.

[0075] Step 150: Receive multiple sets of echo signals within a preset distance gate range, and based on the multiple sets of echo signals and the adjusted Doppler filter, the adjusted Doppler filter has multiple output signal-to-noise ratios within the preset distance gate range. Each output signal-to-noise ratio is used to determine the maximum target monitorable area in the current distance gate. One distance gate corresponds to one output signal-to-noise ratio.

[0076] Here, when airborne radar detects aerial targets, each wave position typically emits dozens or hundreds of pulses, which are then used by a set of Doppler or STAP filters to distinguish clutter from the target. The target detection performance depends on the signal-to-noise ratio (SNR) of the corresponding filter output. Therefore, the SNR of the filter output reflects the target detection accuracy of the filter.

[0077] Specifically, the preset range gate range includes Q range gates, where each range gate corresponds to M sets of echo signals, and each transmitted wave position angle corresponds to one set of echo signals. Step 150 includes: for the q-th range gate, acquiring M sets of echo signals from the q-th range gate, where q ranges from 1 to Q, and Q is a preset positive integer; inputting the M sets of echo signals into an adjusted Doppler filter to perform dimensionality reduction processing on the M sets of echo signals respectively, obtaining M sets of dimensionality-reduced echo signals; acquiring the target spacetime steering vector and the total number of range gates within the preset range gate range, and combining the M sets of dimensionality-reduced echo signals to solve for M optimal weights; based on the M optimal weights, determining M signal-to-noise ratios, where each optimal weight corresponds to one signal-to-noise ratio; selecting the maximum value from the M signal-to-noise ratios and using the maximum value as the output signal-to-noise ratio corresponding to the q-th range gate, continuing to determine the output signal-to-noise ratio corresponding to the (q+1)-th range gate, until the output signal-to-noise ratio corresponding to the Q-th range gate is obtained.

[0078] The target spacetime steering vector is obtained through the following steps: obtaining the time-domain dimensionality reduction matrix, the spatial-domain dimensionality reduction matrix, the target time-domain steering vector, and the target spatial-domain steering vector; using the time-domain dimensionality reduction matrix and the target time-domain steering vector, determining the dimensionality-reduced target time-domain steering vector; using the spatial-domain dimensionality reduction matrix and the target spatial-domain steering vector, determining the dimensionality-reduced target spatial-domain steering vector; and performing Kronecker product processing on the dimensionality-reduced target time-domain steering vector and the dimensionality-reduced target spatial-domain steering vector to obtain the target spacetime steering vector.

[0079] Here, after determining the adjusted filter bank in step 140, the corresponding time-domain dimensionality reduction matrix and spatial-domain dimensionality reduction matrix can be obtained.

[0080] Here, the echo signal is the snapshot data x when empty. l The spatiotemporal snapshot data x obtained for each transmitted wave position angle is obtained by adjusting the temporal and spatial dimension reduction matrices in the filter bank. l After processing, multiple sets of dimensionality-reduced spatiotemporal snapshot data can be obtained. Each set of space-time snapshot data after dimensionality reduction The expression can be represented as:

[0081] In one possible implementation, the optimal weights for each transmitted wave position angle can be obtained using the Linearly Constrained Minimum Variance (LCMV) criterion. The expression for the LCMV criterion is as follows:

[0082]

[0083] Where S0 refers to the target spacetime steering vector, (·) H This refers to transpose processing, w refers to the weight, and R refers to the weight. l This refers to the covariance matrix of clutter plus noise, where l is the range gate number. Since an ideal clutter plus noise covariance matrix is ​​unavailable, it is usually obtained from dimensionality-reduced spatiotemporal snapshot data. Perform maximum likelihood estimation to obtain the covariance matrix of clutter plus noise. use Replace R l Perform the calculation.

[0084] In one possible implementation, the expression for each optimal weight is:

[0085]

[0086]

[0087]

[0088] Among them, w opt This refers to the optimal weight. This refers to the covariance matrix of clutter plus noise obtained by maximum likelihood estimation of the echo signal after dimensionality reduction, where l is the range gate number, S0 is the target space-time steering vector, and (·) H This refers to transpose processing, where L represents the total number of distance gates. This refers to the echo signal after dimensionality reduction processing. This refers to the target time-domain steering vector after dimensionality reduction, where t refers to the time domain. This refers to the target spatial steering vector after dimensionality reduction, where k refers to the spatial domain. This refers to the Kronecker product, where F is the time-domain dimensionality reduction matrix, T is the spatial-domain dimensionality reduction matrix, and S... t This refers to the target time-domain steering vector, S k It refers to the target airspace steering vector.

[0089] In one possible implementation, the expression for each signal-to-noise ratio is:

[0090]

[0091] Among them, SNR out This refers to the output signal-to-noise ratio, w opt This refers to the optimal weight. This refers to the covariance matrix of clutter plus noise obtained by maximum likelihood estimation of the echo signal after dimensionality reduction, where l is the range gate number, r is the spacetime steering vector at any point in space, and (·) H This refers to transpose processing. 2 It refers to the square of the absolute value.

[0092] To test the target detection performance of the adjusted Doppler filter, embodiments of the present invention provide an appendix. Figure 2 To be continued Figure 6 Comparison and explanation.

[0093] Figure 2 This is a schematic diagram of the clutter distribution curve provided in an embodiment of the present invention. Figure 2 The clutter curves were acquired under the following conditions: aircraft speed of 200 m / s, aircraft altitude of 9000 m, number of array elements of 20, carrier frequency of 900 MHz, array element spacing of half wavelength, bandwidth of 4 MHz, pulse repetition frequency of 600 Hz, number of pulses of 18, yaw angle of 90°, main beam pitch angle of 0°, number of non-uniform subarrays of 4, and range gate number 3000.

[0094] Figure 3 The embodiment of the present invention provides the use of conventional filters. Figure 2 A schematic diagram of the output signal-to-noise ratio after clutter processing. Figure 4 This is a filter pair improved using the technical solution of the present invention, provided in an embodiment of the present invention. Figure 2 A schematic diagram of the output signal-to-noise ratio after clutter processing. (Comparison) Figure 3 and Figure 4 It can be observed that the improved filter based on the technical solution of the present invention has a higher output signal-to-noise ratio near the main clutter compared to the conventional filter, that is, the identified target is clearer and more accurate.

[0095] Figure 5 The embodiment of the present invention provides the use of conventional filters. Figure 2 The detectable area map output after clutter processing. Figure 6 This is a filter pair improved using the technical solution of the present invention, provided in an embodiment of the present invention. Figure 2 The detectable area map output after clutter processing. Compare. Figure 5 and Figure 6 It can be observed that the detectable area of ​​the conventional filter is 0.7215, while the detectable area of ​​the filter improved using the technical solution of this invention is 0.8214. The increase in detectable area means that the filter's information collection capability can be improved, thereby further enhancing target detection performance.

[0096] To address the problem that traditional Doppler or STAP filters struggle to completely suppress clutter, resulting in low target detection performance, this invention provides an optimized design method for a Doppler filter in cognitive radar. The method involves obtaining the Doppler frequency of the main clutter corresponding to each transmitted wave azimuth angle; using the Doppler frequencies of multiple main clutter waves as the center frequency of the filter; and then adjusting the frequency range of the Doppler filter using the Doppler channel of each main clutter wave to obtain an adjusted Doppler filter. This adjusted Doppler filter overcomes the problem of target gain decreasing due to the Doppler frequency of the target deviating from the filter's center frequency, thus reducing target detection performance. Furthermore, the adjusted Doppler filter has a larger detectable area and higher target detection accuracy, and can adapt well to complex clutter scenarios.

[0097] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. An optimization design method for a Doppler filter used in cognitive radar, characterized in that, The method includes: Determine M transmission wave azimuth angles for transmitting radar detection waves, where M is a positive integer; Based on the m-th transmitted wave position angle, determine the corresponding m-th main clutter frequency, where m takes values ​​from 1 to M; The Doppler channel of the m-th main clutter is determined using the Doppler frequency of the m-th main clutter. Based on the M main clutter Doppler channels, the frequency range of the Doppler filter is adjusted to obtain the adjusted Doppler filter; Receive multiple sets of echo signals within a preset distance gate range, and based on the multiple sets of echo signals and the adjusted Doppler filter, determine multiple output signal-to-noise ratios of the adjusted Doppler filter within the preset distance gate range. Each output signal-to-noise ratio is used to determine the maximum target monitorable area in the current distance gate, and one distance gate corresponds to one output signal-to-noise ratio. The Doppler frequency of the m-th main clutter includes: the m-th first normalized Doppler frequency and the m-th second normalized Doppler frequency; the Doppler channel of the m-th main clutter includes: the Doppler channel corresponding to the m-th first normalized Doppler frequency and the Doppler channel corresponding to the m-th second normalized Doppler frequency. The step of determining the Doppler channel of the m-th main clutter using its Doppler frequency includes: Obtain the range of center frequencies of the channels of the Doppler filter, wherein one channel corresponds to one center frequency; From the range of values, the frequency closest to the m-th first normalized Doppler frequency is obtained as the first center frequency, wherein the first center frequency is greater than the m-th first normalized Doppler frequency; and the frequency closest to the m-th second normalized Doppler frequency is obtained as the second center frequency, wherein the second center frequency is greater than the m-th second normalized Doppler frequency. Obtain the Doppler channel corresponding to the first center frequency and the Doppler channel corresponding to the third center frequency in the range of values. Use the Doppler channel corresponding to the first center frequency and the Doppler channel corresponding to the third center frequency to determine the Doppler channel corresponding to the m-th first normalized Doppler frequency. The third center frequency is less than the m-th first normalized Doppler frequency, and the Doppler channel corresponding to the third center frequency is adjacent to the Doppler channel corresponding to the first center frequency. Obtain the Doppler channel corresponding to the second center frequency and the Doppler channel corresponding to the fourth center frequency in the range of values. Use the Doppler channel corresponding to the second center frequency and the Doppler channel corresponding to the fourth center frequency to determine the Doppler channel corresponding to the m-th second normalized Doppler frequency. The fourth center frequency is less than the m-th second normalized Doppler frequency, and the Doppler channel corresponding to the fourth center frequency is adjacent to the Doppler channel corresponding to the second center frequency. The Doppler frequencies of the m-th main clutter include: the m-th first normalized Doppler frequency and the m-th second normalized Doppler frequency; the m-th first normalized Doppler frequency is less than the m-th second normalized Doppler frequency; the Doppler channels of the m-th main clutter include: a Doppler channel corresponding to a first center frequency and a Doppler channel corresponding to a second center frequency; the first center frequency is the frequency within the range of the center frequencies of the channels of the Doppler filter that is greater than and closest to the m-th first normalized Doppler frequency, and the second center frequency is the frequency within the range that is greater than and closest to the m-th second normalized Doppler frequency; The Doppler filter frequency range is adjusted based on M main clutter channels to obtain an adjusted Doppler filter, including: For the Doppler frequency of the m-th main clutter, the lower limit of the value range and the frequency interval formed by the m-th first normalized Doppler frequency are divided using the value of the Doppler channel corresponding to the first center frequency to obtain multiple first sub-frequency intervals. Using the first difference, the frequency interval formed by the m-th first normalized Doppler frequency and the m-th second normalized Doppler frequency is divided to obtain multiple second sub-frequency intervals. The first difference refers to the difference between the value of the Doppler channel corresponding to the first center frequency and the value of the Doppler channel corresponding to the second center frequency. Using the second difference, the frequency interval formed by the m-th second normalized Doppler frequency and the upper limit of the value range is divided to obtain multiple third sub-frequency intervals. The second difference refers to the difference between the value of the Doppler channel corresponding to the second center frequency and the preset number of transmitted pulses. The plurality of first sub-frequency intervals, the plurality of second sub-frequency intervals, and the plurality of third sub-frequency intervals are taken as the m-th Doppler frequency range. The (m+1)-th Doppler frequency range is determined, and so on, until the M-th Doppler frequency range is obtained. The M-th Doppler frequency range is taken as the new frequency range corresponding to the adjusted Doppler filter, and the adjusted Doppler filter is obtained.

2. The optimization design method for a Doppler filter for cognitive radar according to claim 1, characterized in that, Determining the M transmit wave azimuth angles used for transmitting radar detection waves includes: Step S1: Obtain the m-th transmitted wave position angle and the beamwidth corresponding to the m-th transmitted wave position angle; when m is 1, the first transmitted wave position angle is a preset initial transmitted wave position angle; Step S2: Connect adjacent beams at a 3dB beamwidth. Using the mth transmit beam angle, the beamwidth corresponding to the mth transmit beam angle, and the beamwidth corresponding to the (m+1)th transmit beam angle, calculate the (m+1)th transmit beam angle in reverse. Step S3: Determine whether the (m+1)th transmitted wave position angle is within the preset scanning angle interval; if it is, let m=m+1 and repeat steps S1 to S3 above; if it is not, stop the calculation and take the calculated multiple transmitted wave position angles within the preset scanning angle interval as the M transmitted wave position angles used to transmit radar detection waves.

3. The optimization design method for a Doppler filter for cognitive radar according to claim 1, characterized in that, The preset distance gate range includes Q distance gates, where one distance gate corresponds to M sets of echo signals, and one transmit wave position angle corresponds to one set of echo signals; receiving multiple sets of echo signals within the preset distance gate range, and determining multiple output signal-to-noise ratios of the adjusted Doppler filter within the preset distance gate range based on the multiple sets of echo signals and the adjusted Doppler filter, including: For the q-th distance gate, M sets of echo signals are obtained from the q-th distance gate, where the value of q ranges from 1 to Q, and Q is a preset positive integer; The M sets of echo signals are input into the adjusted Doppler filter to perform dimensionality reduction processing on the M sets of echo signals respectively, so as to obtain the M sets of dimensionality-reduced echo signals. Obtain the target spacetime steering vector and the total number of range gates within the preset range gate range, and combine them with the M sets of dimension-reduced echo signals to solve for M optimal weights; Based on the M optimal weights, M signal-to-noise ratios are determined, wherein one optimal weight corresponds to one signal-to-noise ratio; Select the maximum value from the M signal-to-noise ratios and use the maximum value as the output signal-to-noise ratio corresponding to the q-th distance gate. Continue to determine the output signal-to-noise ratio corresponding to the (q+1)-th distance gate until the output signal-to-noise ratio corresponding to the Q-th distance gate is obtained.

4. The optimized design method for a Doppler filter for cognitive radar according to claim 3, characterized in that, The target spacetime steering vector is obtained through the following steps: Obtain the temporal domain dimensionality reduction matrix, the spatial domain dimensionality reduction matrix, the target temporal domain steering vector, and the target spatial domain steering vector; Using the time-domain dimensionality reduction matrix and the target time-domain steering vector, the target time-domain steering vector after dimensionality reduction is determined; Using the spatial domain dimensionality reduction matrix and the target spatial domain steering vector, the target spatial domain steering vector after dimensionality reduction is determined; The target time-domain steering vector and the target spatial-domain steering vector after dimensionality reduction are subjected to Kronecker product to obtain the target space-time steering vector.

5. The optimization design method for a Doppler filter for cognitive radar according to claim 2, characterized in that, The expression for the (m+1)th emitted wave position angle is: ； ； ； in, It is the beamwidth corresponding to the m-th transmitted wave position angle. This refers to the m-th emitted wave position angle. It refers to wavelength. This refers to the antenna aperture length. This refers to the beamwidth corresponding to the (m+1)th transmitted wave position angle. It refers to the (m+1)th emitted wave position angle.

6. The optimization design method for a Doppler filter for cognitive radar according to claim 1, characterized in that, The expressions for each first normalized Doppler frequency and each second normalized Doppler frequency are as follows: ； ； in, This refers to the first normalized Doppler frequency. This refers to the second normalized Doppler frequency. This refers to the speed of the aircraft. It refers to wavelength. This refers to the emitted wave azimuth angle. This refers to the preset yaw angle. This refers to the preset elevation angle of the main beam. This refers to the preset pulse repetition frequency.

7. The optimized design method for a Doppler filter for cognitive radar according to claim 4, characterized in that, The expression for each optimal weight is: ； ； ； in, This refers to the optimal weight. This refers to the covariance matrix of clutter and noise obtained by maximum likelihood estimation of the echo signal after dimensionality reduction. This refers to the gate number. This refers to the target spacetime guidance vector. This refers to transpose processing. This refers to the total number of the distance gates. This refers to the echo signal after the dimensionality reduction process. This refers to the target time-domain steering vector after the dimensionality reduction process. It refers to the time domain. This refers to the target spatial steering vector after the dimensionality reduction process. It refers to the space domain. It refers to the Kronecker product. This refers to the time-domain dimensionality reduction matrix. This refers to the spatial domain dimensionality reduction matrix. This refers to the target time-domain steering vector. This refers to the target airspace steering vector.

8. The optimization design method for a Doppler filter for cognitive radar according to claim 3, characterized in that, The expression for each signal-to-noise ratio is: ； in, This refers to the output signal-to-noise ratio. This refers to the optimal weight. This refers to the covariance matrix of clutter and noise obtained by maximum likelihood estimation of the echo signal after dimensionality reduction. This refers to the gate number. It refers to the spacetime steering vector at any point in space. This refers to transpose processing. It refers to the square of the absolute value.

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