Meteorological radar clutter suppression method based on frequency diversity array

Abstract

The invention discloses a meteorological radar clutter suppression method based on a frequency diversity array, and the method comprises the steps: employing a frequency diversity technology to configure the antenna array elements and array element distances of a transmitter in a radar system, and enabling the linear array elements of the transmitter to form the frequency diversity array; after the transmitter configures the frequency offset and the array element spacing of each antenna array element, a signal is transmitted to a meteorological target; determining an overall received signal of the meteorological target based on the echo signal received by the receiver, the received signal of the point clutter and the Gaussian noise; constructing an interference covariance matrix based on the point clutter covariance matrix and the Gaussian white noise covariance matrix; the method comprises the following steps: constructing a beam former, carrying out full-dimensional optimal processing by using an interference covariance matrix to obtain a weight vector, filtering an overall received signal to suppress clutter, and obtaining a final output signal. According to the invention, accurate detection of the meteorological radar on the target can be significantly improved, early warning can be timely made for different meteorology, dangers are avoided, and the method has a wide application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of meteorological radar clutter suppression, and in particular to a meteorological radar clutter suppression method based on a frequency diversity array. Background Art

[0002] Meteorological detection is a technical means to observe, record and analyze atmospheric movement and meteorological phenomena. As a modern meteorological detection equipment, high-resolution radar scans and detects information such as clouds, precipitation, wind field, etc. in the atmosphere through the emission of microwave beams, meeting the needs of meteorological detection with high-precision and real-time data.

[0003] Airborne weather radar is an important airborne navigation device for aircraft to detect hazardous weather ahead and ensure flight safety. When the airborne weather radar is working downward, the echo of the ground scatterer in the antenna beam illumination area enters the receiver through the antenna, forming ground clutter. Since low-altitude wind shear usually occurs during takeoff and landing, weak meteorological targets are usually submerged in a strong ground clutter background, which makes wind shear detection difficult. In addition, the movement of the carrier platform will cause the ground clutter spectrum in the echo signal to shift and broaden, which adds difficulty to more effectively suppress ground clutter. Therefore, in the context of severe and complex dynamic and static ground clutter at the airport, studying ground clutter suppression technology in wind shear mode is of great practical significance for effectively detecting low-altitude wind shear signals and improving the performance of airborne weather radar systems.

[0004] In order to improve the time and space resolution of radar and improve the understanding of the structure of the atmosphere and various weather systems, phased array technology is applied to meteorological radar. The phased array can individually control the phase of each element in the radar array, quickly point the beam to the direction of interest through electronic scanning, and use the phase change of the signal transmitted by each element to control the beam shape through phase weighting. The beam forming of phased array-based meteorological radar is mostly based on the amplitude weighting of each element in the array, which can control the main lobe width and sidelobe level of the beam, and change the beam direction through phase shifting. Its radiation pattern is only related to the angular dimension information, which loses radar performance.

[0005] In most cases, the band clutter caused by the radar system itself or external radiation sources is not limited to certain distance units and is non-stationary in the distance-angle domain, which makes it impossible for traditional clutter suppression methods to filter out such clutter. In recent years, frequency diversity array radar can achieve beam control with higher degrees of freedom due to its way of introducing frequency difference between array elements. This technology can adjust the direction and shape of the beam more flexibly by adjusting the frequency of each element in the array. The unique array characteristics of frequency diversity array meteorological radar provide a new solution to the performance limitations of traditional electronic scanning systems. Due to different ground structures and path attenuation, clutter will be distributed in different distance units. The frequency-controlled array radar system can perform more accurate beam forming in both distance and angle dimensions, so that clutter can be detected and suppressed through different distributions of clutter in the distance dimension, further improving the accuracy and efficiency of meteorological radar observations and enhancing early warning capabilities. In addition, the frequency-controlled array radar has the ability to modulate both phase and distance, and can modulate the phase and distance of the array elements to achieve rapid and agile changes in beam pointing, reduce the Doppler deviation caused by sidelobe coherent echoes, thereby optimizing the collection of meteorological data and improving the performance and efficiency of the radar system. In addition, frequency diversity array radar has multiple functions such as dynamic and static target detection, tracking, and identification. Adding meteorological functions can enable it to better avoid bad weather and complete the given tasks. Therefore, the research on frequency diversity array meteorological radar is of great significance.

[0006] Purpose of the Invention

[0007] The purpose of the present invention is to provide a clutter suppression method for weather radar based on frequency diversity array, so as to provide a more accurate and efficient technical means for high-resolution radar in weather detection.

[0008] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0009] A method for suppressing clutter in a weather radar based on a frequency diversity array comprises the following steps:

[0010] Frequency diversity technology is used to configure the antenna array elements and the spacing between the antenna elements of the transmitter in the radar system so that the linear array elements of the transmitter form a frequency diversity array.

[0011] After the transmitter configures the frequency deviation and element spacing of each antenna array element, it transmits a signal to the meteorological target; based on the echo signal, the received signal of the point clutter and Gaussian noise received by the receiver, the overall received signal of the meteorological target is determined; based on the point clutter covariance matrix and the Gaussian white noise covariance matrix, the interference covariance matrix is ​​constructed;

[0012] By constructing a beamformer and using the interference covariance matrix for full-dimensional optimal processing to obtain a weight vector, the weight vector is then used to filter the overall received signal to suppress clutter and obtain the final output signal.

[0013] Furthermore, the transmitter of the weather radar is composed of M antenna array elements, where the frequency step introduced between the antenna array elements of the transmitter is denoted as Δf m , then the signal frequency f transmitted by the mth antenna element m It can be expressed as:

[0014] f m =f 0 +Δf m ,m=0,1,...,M-1

[0015] where f 0 is the reference carrier frequency, selected as the carrier frequency of the first antenna array element of the transmitter; M is the number of antenna array elements of the transmitter.

[0016] Furthermore, the use of frequency diversity technology to configure antenna array elements and array element spacing of a transmitter in the radar system includes:

[0017] Determine whether the transmitter uses the Logd method, the Expf method, or the Expf-Logd method, and calculate Δf according to the corresponding calculation method m Configure the signal frequency f transmitted by the antenna array element m , and the array element spacing between the mth antenna array element and the first antenna array element is set to d m ;

[0018] ①Logd method

[0019]

[0020] Where m represents the mth antenna element, d is a configurable parameter for controlling the spacing between antenna elements; Δf is a configurable parameter for controlling the frequency increment;

[0021] ②Expf method

[0022]

[0023] Where b is a configurable constant;

[0024] ③Expf-Logd method

[0025]

[0026] Further, the determining of the overall received signal of the meteorological target based on the echo signal received by the receiver, the transmission steering vector, and the reception steering vector includes:

[0027] The received echo signal can be processed by mixing the reference carrier frequency, digital mixing of the step frequency, and matched filtering to obtain a received signal in vector form, that is, a snapshot signal x consisting of a two-dimensional space-time guidance vector of the meteorological target. s :

[0028]

[0029] in represents the MN×1-dimensional complex space, where N is the number of receiver antenna elements, R 0 is the distance of the meteorological target, θ 0 is the angle of the meteorological target, is the Kronecker product, is the echo complex coefficient of the meteorological target, where t is the time parameter, sinc is the Sinker function, and f 0 is the carrier frequency, c is the speed of light, a(R 0 ,θ 0 ) is the launch guidance vector, b(θ 0 ) is the receiving steering vector;

[0030] Note that there are Q pseudo-randomly distributed clutter interferences in the environment, and the signal of the qth clutter propagates to the nth antenna array element of the receiver can be expressed as:

[0031]

[0032] where x c is the received signal of point clutter, R q is the distance of point clutter, θ q is the angle of point clutter, ξ q is the echo complex coefficient of the clutter at the qth point; a(R q ,θ q ) is the clutter transmission steering vector, b(θ q ) is the receiving steering vector of clutter;

[0033] The overall received signal x of the meteorological target can be expressed as follows:

[0034] x=x s +x c +n

[0035] Where n is Gaussian noise.

[0036] Furthermore, the transmission steering vector a(R 0 ,θ 0 ), receiving the steering vector b(θ 0 ) is expressed as follows:

[0037]

[0038] The superscript T is the transposition operator, and e is a natural constant. and denote the distance-oriented vector and the angle-oriented vector, ⊙ is the Hadamard product, λ 0 is the wavelength,

[0039] Furthermore, constructing an interference covariance matrix based on a point clutter covariance matrix and a Gaussian white noise covariance matrix includes:

[0040] Point clutter covariance matrix R c It is expressed as:

[0041]

[0042] where x c is the received signal of point clutter, Q is the number of clutter, ξ q is the echo complex coefficient of the qth point clutter, E{} represents the expectation operation, and the superscript H represents the conjugate transpose operation;

[0043] R n is the Gaussian white noise covariance matrix, expressed as:

[0044]

[0045] in is the noise power, I MN is the identity matrix of MN×MN;

[0046] Then the interference covariance matrix is ​​the sum of the point clutter covariance matrix and the Gaussian white noise covariance matrix:

[0047]

[0048] Further, the beamformer can be expressed as:

[0049]

[0050] swt H u(R 0 ,θ 0 )=1

[0051] By Lagrange multiplier method, we can get:

[0052]

[0053] Where w represents the weight vector, coefficient R c+n is the interference covariance matrix, u(R 0,θ 0 ) represents the virtual guidance vector of the meteorological target, which can be expressed as the Kronecker product of the transmitting and receiving guidance vectors:

[0054]

[0055] Where a(R 0 ,θ 0 ) is the launch guidance vector, b(θ 0 ) is the receiving steering vector, R 0 is the distance of the meteorological target, θ 0 is the azimuth of the meteorological target.

[0056] Furthermore, the overall received signal x is multiplied by the weight vector w and then accumulated to obtain the output signal y after clutter interference is suppressed, which is expressed as:

[0057] y=w H x

[0058] The superscript H represents the conjugate transpose.

[0059] A computer-readable storage medium stores a computer program; when the computer program is executed by a processor, the frequency diversity array-based meteorological radar clutter suppression method is implemented.

[0060] A terminal device comprises a processor, a memory and a computer program stored in the memory; when the processor executes the computer program, the frequency diversity array-based meteorological radar clutter suppression method is implemented.

[0061] Compared with the prior art, the present invention has the following technical features:

[0062] Frequency diversity weather radar introduces transmission frequency differences between antenna elements of a phased array, and can distinguish between weather targets and clutter interference based on information such as phase and distance in the scattered echo signal. In addition, the frequency diversity array radar system can perform more accurate beamforming in both distance and angle dimensions, thereby effectively filtering out clutter by setting nulls at the clutter position. Therefore, introducing frequency diversity arrays into weather radars can suppress clutter through different distributions of clutter in the distance dimension, significantly improving the accuracy of weather radar detection of targets, providing timely warnings for different weather conditions, and avoiding dangers, which has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is the geometric model of the airborne FDA weather radar;

[0064] Figure 2 It is a frequency diversity array MIMO radar transmit and receive array model;

[0065] Figure 3 The beam pattern comparison between the traditional FDA radar and the FDA-MIMO radar, where (a) is the traditional FDA radar (f m =f 0 +mΔf,d=λ / 2), (b) is the traditional FDA-MIMO radar (f m =f 0 +mΔf,d=λ / 2);

[0066] Figure 4 is a comparison of the transmitted beams of FDA radar and FDA-MIMO radar under different configurations, where (a) is FDAlogd; (b) is FDA-MIMO logd; (c) is FDA expf-logd; (d) is FDA-MIMO expf-logd; (e) is FDAexpf; (f) is FDA-MIMO expf;

[0067] Figure 5 It is a diagram of the clutter suppression process;

[0068] Figure 6 1 and 2 are point clutter suppression results at different positions in the embodiment, wherein (a) is a comparison between FDA and FDA-MIMO under logd design; (b) is a comparison between FDA and FDA-MIMO under expf-logd design; (c) is a comparison between FDA and FDA-MIMO under expf design;

[0069] Figure 7 is the relationship between the output SINR and the input Δf in the embodiment. DETAILED DESCRIPTION

[0070] The present invention introduces a frequency diversity array. The frequency diversity array utilizes a small frequency step between array elements to generate an antenna pattern related to angle, distance, and time. The zero point of the distance dimension of its transmission pattern can effectively achieve distance clutter suppression. As a result, the meteorological radar using this method can generate a beam related to both distance and angle. In addition to beam control in the angle dimension, beam control in the distance dimension can also be achieved, which can effectively suppress clutter related to distance. While filtering out ground clutter to the greatest extent, it reduces the impact of clutter residue on wind shear signals, thereby improving the detection performance and efficiency of the meteorological radar. The frequency diversity radar has multiple functions such as dynamic and static target detection, tracking, and identification. Adding meteorological functions can enable it to better avoid bad weather and complete established tasks. Therefore, the system can provide a more accurate and efficient technical means for high-resolution radar in meteorological detection.

[0071] Referring to the accompanying drawings, a method for suppressing clutter in a weather radar based on a frequency diversity array provided by the present invention comprises the following steps:

[0072] Step 1: Use frequency diversity technology to configure the antenna array elements and array element spacing of the transmitter in the radar system so that the linear array elements of the transmitter form a frequency diversity array.

[0073] Different from the phased array where the electromagnetic wave carrier frequency emitted by each antenna element is consistent, the frequency diversity array introduces slight frequency changes in the transmission frequency of each element. Therefore, the center frequencies of different antenna elements are different, which is equivalent to introducing a transmission frequency difference for each element.

[0074] Assume that the transmitter of the weather radar consists of M antenna elements, which are arranged at a certain interval. A small frequency step is introduced between the antenna elements transmitting the signal, denoted as Δf. m , the frequency step Δf m (kHz level) is much smaller than the reference operating carrier frequency f of the antenna array element 0 (MHz~GHz level), then the signal frequency f emitted by the mth antenna element is m It can be expressed as:

[0075] f m =f 0 +Δf m ,m=0,1,...,M1(1)

[0076] where f 0 is the reference carrier frequency, selected as the carrier frequency of the first antenna array element of the transmitter; M is the number of antenna array elements of the transmitter.

[0077] The signal s transmitted by the mth antenna element m (t) can be expressed as:

[0078]

[0079] in is the pulse modulation function, t represents the time within the radar pulse, T p is the pulse duration, represents the waveform transmitted by the mth antenna array element, f m is the signal frequency transmitted by the mth antenna element, and j is an imaginary unit.

[0080] In order to 0 ,r 0 ) produces the maximum value, and the complex weight is configured as a H (θ 0 ,r 0 ), so the transmission pattern can be expressed as:

[0081]

[0082] The superscript H represents the conjugate transpose operator, M is the number of antenna elements in the transmitter, Δf m is the frequency step introduced between antenna elements, d m is the distance between the mth antenna element and the first antenna element, f m is the signal frequency emitted by the mth antenna array element, c is the speed of light, θ 0 is the expected target angle, r 0 is the expected target distance; a(θ,r) is the launch guidance vector, θ and r represent the angle and distance of any point in space; a(θ,r) can be expressed as:

[0083]

[0084] From equation (3), we can see that the beam direction will change with the change of distance and angle, which means that the beam is related to distance and angle. Since the transmit beam is coupled in distance and angle, it is impossible to estimate the range and angle of the target directly from the output of the FDA beamformer. However, the beam pattern is also related to Δf m and d m Therefore, by setting a suitable Δf m and d m To obtain the desired single peak beam.

[0085] The traditional FDA radar uses a uniformly changing frequency offset on the antenna array element of the transmitter, which will form a range-angle coupled beam with a period of c / (2Δf m ) will generate multiple peak beams in the distance dimension. When the interference is located at the maximum direction of any beam, the target will be suppressed as interference, resulting in system SINR loss. Therefore, in order to obtain a single peak beam in the distance-angle dimension, the present invention adopts three different frequency offset and array element spacing design methods.

[0086] Different frequency offset and element spacing designs. Here, three different design principles are used to configure the frequency offset and element spacing of each antenna element in the current radar system transmitter:

[0087] When the transmitter uses the Logd method, the Δf in ① is used. m Configure the signal frequency f transmitted by the antenna array element m , and set the array element spacing to d in ① m form; when the Expp ​​method is used, the Δf in ② is used m Configure the signal frequency f transmitted by each antenna array element m , and set the array element spacing to d in ②m form; when the Expp-Logd method is used, Δf in ③ is used m Configure the signal frequency f transmitted by the antenna array element m , and set the array element spacing to d in ③ m form.

[0088] ① Frequency deviation and array element spacing form designed by Logd method

[0089] Substitute the frequency deviation Δf in formula (1) m The frequency deviation is set to linear, and the array element spacing is set to change in logarithmic form, where the frequency deviation Δf m and the array element spacing d m The calculation of is as follows:

[0090]

[0091] Where d is a configurable parameter for controlling the antenna element spacing; Δf is a configurable parameter for controlling the frequency increment.

[0092] ② Frequency deviation and array element spacing form designed by ExPF method

[0093] For the Expf setting, the frequency deviation in the system is set to increase exponentially and the array element spacing is set to change linearly, where the frequency deviation Δf m and the array element spacing d m The calculation of is as follows:

[0094]

[0095] Where b is a configurable constant. From (6), it can be seen that the frequency increment set by Expf varies nonlinearly. The single maximum beam peak it produces is beneficial to the decoupling of range and angle. The parameter b here is 1.4.

[0096] ③Frequency deviation and array element spacing form designed by Expp-Logd method

[0097] The frequency deviation in the system is set to increase exponentially, and the array element spacing is set to change logarithmically. The frequency deviation Δf under the Expp-Logd method is m and the array element spacing d m The calculation of is as follows:

[0098]

[0099] The parameter d is set to 0.021 in all three settings to avoid grating lobes. Similarly, the ExPF-logd configuration can also produce a single maximum peak beam, which helps to suppress mainlobe clutter interference.

[0100] Frequency diversity array (FDA) can form a range-angle coupled beam pattern by using uniform frequency increments on the transmitting array elements. However, this beam pattern will produce maximum values ​​at multiple distances, and when the clutter interference is at any maximum value, it will cause a loss of signal-to-interference-noise ratio. Therefore, in order to destroy the distance periodicity of the FDA beam, the basic principles of the above three different FDA configurations are designed to decouple the distance and angle, so that the present invention can obtain a single peak beam at the meteorological target position in the distance-angle two-dimensional space by configuring the frequency increment and array element spacing between the array elements.

[0101] Step 2: After the transmitter configures the frequency offset and element spacing of each antenna array element, it transmits a signal to the meteorological target; based on the echo signal, the received signal of the point clutter and the Gaussian noise received by the receiver, the overall received signal of the meteorological target is determined; and the interference covariance matrix is ​​constructed based on the point clutter covariance matrix and the Gaussian white noise covariance matrix.

[0102] The received echo signal can be processed by mixing the reference carrier frequency, digital mixing of the step frequency, and matched filtering to obtain a received signal in vector form, that is, a snapshot signal x consisting of a two-dimensional space-time guidance vector of the meteorological target. s :

[0103]

[0104] in represents the MN×1-dimensional complex space, where N is the number of receiver antenna elements, R 0 is the distance of the meteorological target, θ 0 is the angle of the meteorological target, is the Kronecker product, is the echo complex coefficient of the meteorological target, where t is the time parameter, sinc is the Sinker function, and f 0 is the carrier frequency, c is the speed of light, a(R 0 ,θ 0 ) is the launch guidance vector, b(θ 0 ) is the receiving steering vector, which is expressed as follows:

[0105]

[0106] The superscript T is the transposition operator, and e is a natural constant. denote the distance steering vector and the angle steering vector respectively, ⊙ is the Hadamard product, Δf m is the frequency step introduced between the antenna elements of the transmitted signal, d m is the array element spacing setting, R 0 is the distance of the meteorological target, θ0 is the angle of the meteorological target, λ 0 is the wavelength,

[0107] As shown in equation (10), the transmission steering vector of the frequency diversity array antenna has range angle dependence. Unlike traditional phased array radars, the clutter distribution of FDA radars in the spatial frequency domain changes with the change of slant range; therefore, FDA can distinguish between clutter and targets in the range zone by using its controllable degree of freedom in the range dimension. In addition, the transmission pattern is also closely related to the frequency offset and array element spacing. Therefore, in order to filter out ground clutter to the greatest extent and improve the accuracy of wind speed estimation of wind shear signals, a frequency diversity array is introduced to perform non-uniform array and frequency offset settings, and the characteristic differences between meteorological targets and clutter in the range-angle dimension are used to retain meteorological targets and filter out clutter.

[0108] Assuming that Q pseudo-randomly distributed clutter interferences are generated in the environment, the signal of the qth clutter propagates to the nth antenna element of the receiver and can be expressed as:

[0109]

[0110] where x c is the received signal of point clutter, R q is the distance of point clutter, θ q is the angle of point clutter, ξ q is the echo complex coefficient of the clutter at the qth point; a(R q ,θ q ) is the clutter transmission steering vector, b(θ q ) is the receiving steering vector of the clutter, which can be expressed as:

[0111]

[0112]

[0113] Where R q and θ q are the distance and angle parameters of the qth clutter interference, Δf m is the frequency step introduced between the antenna elements of the transmitted signal, d m is the array element spacing setting, λ 0 is the wavelength, c is the speed of light, f 0 is the carrier frequency.

[0114] Taking into account the existence of meteorological targets, Q point clutter and noise, the overall received signal x of the meteorological target can be expressed as follows:

[0115]

[0116] where x s is the snapshot signal of the meteorological target, x c is the received signal of point clutter, and n is Gaussian noise.

[0117] Point clutter covariance matrix R c It can be expressed as:

[0118]

[0119] where x c is the received signal of point clutter, Q is the number of clutter, ξ q is the echo complex coefficient of the qth point clutter, E{} represents the expectation operation, and the superscript H Represents the conjugate transpose operation.

[0120] R n is the Gaussian white noise covariance matrix, which is:

[0121]

[0122] in is the noise power, I MN is the identity matrix of MN×MN.

[0123] Then the interference covariance matrix is ​​the sum of the point clutter covariance matrix and the Gaussian white noise covariance matrix:

[0124] R c+n =R c +R n (17)

[0125] Step 3, by constructing a beamformer and using the interference covariance matrix to perform full-dimensional optimal processing to obtain a weight vector, and then using the weight vector to filter the overall received signal to suppress clutter and obtain the final output signal.

[0126] The overall received signal x is multiplied by the weight vector w and then accumulated to obtain the output signal y after clutter interference is suppressed. By adjusting the distance and phase of each element in the weight vector, the direction of the meteorological target can be enhanced and clutter interference can be suppressed; it can be expressed as:

[0127] y=w H x (18)

[0128] Where w is the MN×1 weight vector, x is the overall received signal, and H represents the conjugate transpose.

[0129] The process is to construct a beamformer based on the minimum mean square error distortionless response (MVDR), that is, to minimize the total output power while keeping the desired target output power unchanged, so as to maximize the signal to interference plus noise ratio (SINR). The beamformer based on the minimum mean square error distortionless response criterion can be expressed as:

[0130]

[0131] By Lagrange multiplier method, we can get:

[0132]

[0133] The coefficient Where R c+n is the interference covariance matrix, u(R 0 ,θ 0 ) represents the virtual guidance vector of the meteorological target, which can be expressed as the Kronecker product of the transmitting and receiving guidance vectors:

[0134]

[0135] Where a(R 0 ,θ 0 ) is the launch guidance vector, b(θ 0 ) is the receiving steering vector, R 0 is the distance of the meteorological target, θ 0 is the azimuth of the meteorological target.

[0136] Assuming that there are meteorological target signals and interference signals in the receiving array, the optimal weight vector w is calculated according to formula (20), and by constructing a weight vector matrix, the signals received on the array antenna are weighted and combined, so that the signal in the direction of the meteorological target is enhanced, and the clutter interference signal in the undesired direction is suppressed. That is, through the MVDR adaptive beamforming algorithm, the optimal beam pattern in the presence of clutter interference can be obtained. The beam pattern can form a null at the interference distance point of the clutter interference, and generate an energy beam pointing to the meteorological target at the meteorological target distance-angle position, thereby achieving the purpose of suppressing clutter interference.

[0137] Example:

[0138] When the airborne weather radar is working downward, the geometric configuration of the FDA weather radar is as follows: Figure 1 Assume that the aircraft's flight direction is consistent with the array normal direction, and the array is a one-dimensional equidistant linear array after column synthesis. The array consists of M equivalent array elements. For any scattering point, its slant distance to the nth array element can be expressed as Here R represents the reference slant distance, θ is the azimuth, is the pitch angle. Since the movement of the carrier platform and the azimuth and pitch during beam scanning are different, the ground clutter characteristics of each unit are also different, that is, the clutter and the target will be distributed in different distance units.

[0139] The present invention is based on the frequency diversity array weather radar transmission and receiving array distribution as follows Figure 2 As shown. The weather radar uses a frequency diversity array. Considering a co-located MIMO radar with the same transmitting array element and receiving array element, M arrays work independently, transmitting radar waves of a specific frequency, and N receiving array elements receive the echo signal. Since each transmitting array element introduces a fixed frequency less than the carrier frequency, the radar system contains M transmitting arrays with different frequencies, and the frequencies are f 0 ,f 1 ,…,f M-1 The weather radar receives echoes through multiple narrow beams, which can form a frequency diversity array guidance matrix, and then obtain the array output. Using the inertial navigation parameters and radio altitude data provided by airborne navigation equipment such as the inertial navigation system and radio altimeter, accurate aircraft pitch, azimuth and ground speed information can be obtained. Using this as prior information, the clutter area can be roughly estimated.

[0140] The distance-angle two-dimensional beamforms of traditional FDA radar and FDA-MIMO radar are as follows: Figure 3 As shown in , the frequency offset of both devices changes linearly, and the array element spacing is half the wavelength. Figure 3 The results show that the beams of traditional FDA radar and FDA-MIMO radar change periodically, with a period of 25km, depending on c / 2Δf, where c is the speed of light and Δf is the frequency deviation. Therefore, when the received clutter interference and the real target are both at this periodic distance, FDA radar and FDA-MIMO radar cannot effectively distinguish between real and fake targets, which is not conducive to FDA radar and FDA-MIMO radar resisting clutter interference. Therefore, the design of frequency deviation and array element spacing is considered.

[0141] The transmit beam design of FDA and FDA-MIMO radars is carried out using three different frequency offsets and array element spacings. Figure 4 The figure shows the comparison of the transmission beams of FDA and FDA-MIMO under different configurations. It can be seen that FDA and FDA-MIMO radars can form a single peak beam in the range-angle space under the expf-logd and expf settings. Therefore, clutter can be suppressed by zeroing at different range units.

[0142] The clutter suppression process is as follows: Figure 5As shown. Assume that there is a point target in the far field of space. After being received by N array elements, the received signal is mixed first, and then the signal of each receiving channel is processed by M groups of matched filters. The matched filtering includes two steps: the first step is to perform digital mixing related to Δf on each receiving channel, that is, multiplying by e -j2πΔf(m-1)t , the second step is to match filter each transmitted waveform. The sum signal from N receiving array elements after matched filtering can form a column vector, estimate the covariance matrix of the received signal, and then calculate the adaptive optimal weights through optimization problem to suppress clutter.

[0143] The clutter suppression method for airborne meteorological radar using the frequency diversity array space-time adaptive processing algorithm proposed in the present invention is simulated and verified, and the experimental results fully demonstrate the effectiveness of the method of the present invention. The experiment uses M=N=10 array elements, the pitch beam pointing is 0° away from the normal direction of the array, and the horizontal beam pointing is 0° away from the normal direction of the array. Due to the internal motion of the meteorological target, it is assumed that the slant range of the meteorological target is 3km and the azimuth is 3°. The clutter generation distance range is 0km~5km, the spacing is 100m, and the azimuth is -10°~10°. At each range gate, each azimuth range is equally divided into 100 clutter scattering units. FDA radar has the degree of freedom of controllable distance. Combined with MIMO technology, FDA-MIMO radar has greater spatial diversity gain and better distance resolution capability, such as Figure 6 As shown, when the frequency offset and array element spacing settings proposed by the present invention are adopted in the FDA-MIMO radar, all point clutter with distance differences is eliminated, and the matched filter only outputs meteorological targets in the distance-angle two-dimensional space. In addition, Figure 7 The relationship between output SINR and input Δf is shown in Figure 1. The output SINR increases with the increase of Δf. Therefore, the effective design of frequency offset is the key to suppress interference. The frequency offset and array element spacing designed by the present invention make the FDA-MIMO radar better than the FDA radar in suppressing clutter interference. The experimental results fully prove the effectiveness of the method of the present invention.

[0144] The frequency diversity array-based weather radar precision detection method of the present invention can effectively distinguish clutter interference and targets through the distance dimension freedom introduced by the frequency diversity array, and can form a single peak beam at the target position by decoupling the distance and angle by designing different frequency offsets and array element spacings. The frequency-controlled array distance-angle two-dimensional adaptive filtering is used to effectively suppress clutter, and the method significantly improves the detection accuracy of the weather radar and has broad application prospects.

[0145] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for suppressing clutter in a weather radar based on a frequency diversity array, characterized in that: include: Frequency diversity technology is used to configure the antenna array elements and the spacing between the antenna elements of the transmitter in the radar system so that the linear array elements of the transmitter form a frequency diversity array. After the transmitter configures the frequency deviation and element spacing of each antenna array element, it transmits the signal to the meteorological target; Determine the overall received signal of the meteorological target based on the echo signal received by the receiver, the received signal of the point clutter and the Gaussian noise; Construct interference covariance matrix based on point clutter covariance matrix and Gaussian white noise covariance matrix; By constructing a beamformer and using the interference covariance matrix for full-dimensional optimal processing to obtain a weight vector, the weight vector is then used to filter the overall received signal to suppress clutter and obtain the final output signal.

2. The method for suppressing clutter of a weather radar based on a frequency diversity array according to claim 1, characterized in that: The transmitter of the weather radar consists of M antenna array elements, where the frequency step introduced between the antenna array elements of the transmitter is denoted as Δf m , then the signal frequency f transmitted by the mth antenna element m It can be expressed as: f m =f0+Δf m ,m=0,1,...,M-1 Where f0 is the reference carrier frequency, which is selected as the carrier frequency of the first antenna array element of the transmitter; M is the number of antenna array elements of the transmitter.

3. The method for suppressing clutter of a weather radar based on a frequency diversity array according to claim 1, characterized in that: The configuration of each antenna array element and the array element spacing of the transmitter in the radar system by using the frequency diversity technology includes: Determine whether the transmitter uses the Logd method, the Expf method, or the Expf-Logd method, and calculate Δf according to the corresponding calculation method m Configure the signal frequency f transmitted by the antenna array element m , and the array element spacing between the mth antenna array element and the first antenna array element is set to d m ; ①Logd method Where m represents the mth antenna element, d is a configurable parameter for controlling the spacing between antenna elements; Δf is a configurable parameter for controlling the frequency increment; ②Expf method Where b is a configurable constant; ③Expf-Logd method 4. The method for suppressing clutter of a weather radar based on a frequency diversity array according to claim 1, characterized in that: The method of determining the overall received signal of the meteorological target based on the echo signal received by the receiver, the transmission steering vector, and the reception steering vector comprises: The received echo signal can be processed by mixing the reference carrier frequency, digital mixing of the step frequency, and matched filtering to obtain a received signal in vector form, that is, a snapshot signal x consisting of a two-dimensional space-time guidance vector of the meteorological target. s : in represents the MN×1-dimensional complex space, N is the number of receiver antenna array elements, R0 is the distance of the meteorological target, θ0 is the angle of the meteorological target, is the Kronecker product, is the echo complex coefficient of the meteorological target, where t is the time parameter, sinc is the Sinker function, f0 is the carrier frequency, c is the speed of light, a(R0,θ0) is the transmitting steering vector, and b(θ0) is the receiving steering vector; Note that there are Q pseudo-randomly distributed clutter interferences in the environment, and the signal of the qth clutter propagates to the nth antenna array element of the receiver can be expressed as: where x c is the received signal of point clutter, R q is the distance of point clutter, θ q is the angle of point clutter, ξ q is the echo complex coefficient of the clutter at the qth point; a(R q ,θ q ) is the clutter transmission steering vector, b(θ q ) is the receiving steering vector of clutter; The overall received signal x of the meteorological target can be expressed as follows: x=x s +x c n Where n is Gaussian noise.

5. The method for suppressing clutter of a weather radar based on a frequency diversity array according to claim 4, characterized in that: The transmission steering vector a(R0,θ0) and the reception steering vector b(θ0) are expressed as follows: The superscript T is the transposition operator, and e is a natural constant. and They represent the distance steering vector and the angle steering vector respectively, ⊙ is the Hadamard product, λ0 is the wavelength, λ0=c / f0.

6. The method for suppressing clutter of a weather radar based on a frequency diversity array according to claim 1, characterized in that: The construction of the interference covariance matrix based on the point clutter covariance matrix and the Gaussian white noise covariance matrix includes: Point clutter covariance matrix R c It is expressed as: where x c is the received signal of point clutter, Q is the number of clutter, ξ q is the echo complex coefficient of the qth point clutter, E{} represents the expectation operation, and the superscript H represents the conjugate transpose operation; R n is the Gaussian white noise covariance matrix, expressed as: in is the noise power, I MN is the identity matrix of MN×MN; Then the interference covariance matrix is ​​the sum of the point clutter covariance matrix and the Gaussian white noise covariance matrix: R c+n =R c +R n 。 7. The method for suppressing clutter of a weather radar based on a frequency diversity array according to claim 1, characterized in that: The beamformer can be expressed as: s.t.w H u(R0,θ0)=1 By Lagrange multiplier method, we can get: Where w represents the weight vector, coefficient R c+n is the interference covariance matrix, u(R0,θ0) represents the virtual guidance vector of the meteorological target, which can be expressed as the Kronecker product of the transmitting and receiving guidance vectors: Where a(R0,θ0) is the transmitting steering vector, b(θ0) is the receiving steering vector, R0 is the distance of the meteorological target, and θ0 is the azimuth of the meteorological target.

8. The method for suppressing clutter of a weather radar based on a frequency diversity array according to claim 1, characterized in that: The overall received signal x is multiplied by the weight vector w and then accumulated to obtain the output signal y after clutter interference is suppressed, which is expressed as: y=w H x The superscript H represents the conjugate transpose.

9. A computer-readable storage medium, wherein a computer program is stored in the medium; characterized in that: When the computer program is executed by a processor, the method for suppressing clutter of a weather radar based on a frequency diversity array according to any one of claims 1 to 8 is implemented.

10. A terminal device comprising a processor, a memory and a computer program stored in the memory; characterized in that: When the processor executes the computer program, the frequency diversity array-based meteorological radar clutter suppression method according to any one of claims 1 to 8 is implemented.

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