A weather radar clutter suppression method based on frequency diversity array

Abstract

The application discloses a weather radar clutter suppression method based on a frequency diversity array, and comprises the following steps: configuring each antenna array element and element spacing of a transmitter in a radar system by using a frequency diversity technology, so that linear array elements of the transmitter constitute a frequency diversity array; after the frequency offset and element spacing of each antenna array element of the transmitter are configured, transmitting a signal to a weather target; determining an overall received signal of the weather target based on a received echo signal of a receiver, a received signal of a point clutter and Gaussian noise; constructing an interference covariance matrix based on a point clutter covariance matrix and a Gaussian white noise covariance matrix; obtaining a weight vector by constructing a beamformer and performing full-dimensional optimal processing on the interference covariance matrix; and filtering the overall received signal to suppress the clutter and obtain a final output signal. The application can significantly improve the accurate detection of a target by a weather radar, timely make a warning and avoid danger for different weathers, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of weather radar clutter suppression, and particularly relates to a weather radar clutter suppression method based on frequency diversity array. BACKGROUND

[0002] Meteorological detection is a technical means for observing, recording and analyzing atmospheric movement and meteorological phenomena. As a modern meteorological detection device, high-resolution radar can meet the needs of meteorological detection by emitting microwave beams to scan and detect cloud layers, precipitation, wind fields and other information in the atmosphere with high precision and real-time data.

[0003] Airborne weather radar is an important airborne navigation equipment for aircraft to detect disaster weather in front and ensure flight safety. When the airborne weather radar works in the downward direction, the echo of ground scatterers in the antenna beam irradiation area enters the receiver through the antenna to form ground clutter. Since low-altitude wind shear usually occurs during takeoff and landing stages, weak meteorological targets are usually submerged in very strong ground clutter background, which brings difficulties to wind shear detection. Moreover, the movement of the aircraft platform will cause the spectrum of ground clutter in the echo signal to shift and broaden, making it more difficult to effectively suppress ground clutter. Therefore, under the background of serious and complex airport dynamic and static ground clutter, it is of great practical significance to study ground clutter suppression technology under wind shear mode for effectively detecting low-altitude wind shear signals and improving the performance of airborne weather radar system.

[0004] In order to improve the time and spatial resolution of radar to improve the understanding of atmospheric and various weather system structures, phased array technology is applied to weather radar. Phased array can control the phase of each array element in the radar array individually, quickly point the beam to the direction of interest through electronic scanning, and control the beam shape by phase weighting through the phase change of the signal emitted by each array element. The beam forming of phased array-based weather radar is mainly based on amplitude weighting of each array element in the array, which can control the main lobe width and side lobe level of the beam, and change the beam pointing direction through phase shift. The directional diagram is only related to the angular dimension information, and the radar performance is lost.

[0005] The strip-like clutter caused by the radar system itself or external radiation source is not limited to certain range units in most cases and is non-stationary in the range-angle domain, which makes the traditional clutter suppression method unable to filter out such clutter. In recent years, the frequency diversity array radar can achieve higher degree of freedom of beam control due to the way of introducing frequency difference between array elements. This technology can more flexibly adjust the direction and shape of the beam by adjusting the frequency of each element in the array. The unique array characteristics of the frequency diversity array weather radar provide a new solution to the performance limitations of the traditional electronically scanned system. Due to different ground structures and path attenuation, clutter will be distributed in different range units. The frequency control array radar system can perform more accurate beam forming in the range and angle dimensions, so that the clutter can be detected and suppressed through the different distribution of clutter in the range dimension, further improving the accuracy and efficiency of weather radar observation and enhancing the early warning capability. Moreover, the frequency control array radar has modulation capability in phase and range, which can modulate the element phase and range to realize rapid and agile beam pointing, reduce the Doppler deviation caused by sidelobe coherent echoes, and thus optimize the collection of weather data and improve the performance and efficiency of the radar system. In addition, the frequency diversity array radar has multiple functions such as moving and stationary target detection, tracking and identification, and adding weather function can better avoid bad weather and complete the assigned task. Therefore, the research on frequency diversity array weather radar is of great significance.

[0006] Object of the invention

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

[0008] In order to achieve the above-mentioned task, the present application adopts the following technical solutions:

[0009] A weather radar clutter suppression method based on frequency diversity array, comprising the following steps:

[0010] The frequency diversity technology is used to configure each antenna element and element spacing of the transmitter in the radar system, so that the linear array elements of the transmitter constitute a frequency diversity array;

[0011] After the transmitter configures the frequency offset and element spacing of each antenna element, the signal is transmitted to the weather target; based on the echo signal received by the receiver, the received signal of the point clutter and the Gaussian noise, the overall received signal of the weather target is determined; the interference covariance matrix is constructed based on the point clutter covariance matrix and the Gaussian white noise covariance matrix;

[0012] The beam former is constructed and the weight vector is obtained by using the interference covariance matrix for full-dimensional optimal processing, and then the weight vector is used to filter the overall received signal to suppress the clutter and obtain the final output signal.

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

[0014] f m = f0+ Δf m , m = 0, 1,..., M-1

[0015] wherein f0 is the reference carrier frequency, which is selected as the carrier frequency of the first antenna element of the transmitter; and M is the number of antenna elements of the transmitter.

[0016] Further, the configuration of the antenna elements and the element spacing of the transmitter in the radar system using the frequency diversity technology comprises:

[0017] judging whether the transmitter uses Logd method, Expf method or Expf-Logd method, and calculating Δf according to the corresponding calculation method m configuring the signal frequency f m transmitted by the antenna elements, and setting the element spacing between the mth antenna element and the first antenna element as d m ;

[0018] ① Logd method

[0019]

[0020] wherein m represents the mth antenna element, d is a configurable parameter for controlling the element spacing, and Δf is a configurable parameter for controlling the frequency increment.

[0021] ② Expf method

[0022]

[0023] wherein b is a configurable constant.

[0024] ③ Expf-Logd method

[0025]

[0026] Further, the determination of the overall received signal of the weather target based on the echo signal received by the receiver, the transmit steering vector and the receive steering vector comprises:

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

[0028]

[0029] wherein represents a MNx1-dimensional complex space, N is the number of receiver antenna elements, R0 is the distance of the meteorological target, θ0 is the angle of the meteorological target, is a Kronecker product, is an echo complex coefficient of the meteorological target, wherein t is a time parameter, sinc is a sinc function, f0 is a carrier frequency, c is the speed of light, a(R0, θ0) is a transmit steering vector, and b(θ0) is a receive steering vector;

[0030] It is assumed that there are Q randomly distributed clutter interferences in the environment, and the signal transmitted by the qth clutter to the nth antenna element of the receiver can be represented as:

[0031]

[0032] wherein x c is the received signal of the point clutter, R q is the distance of the point clutter, θ q is the angle of the point clutter, ξ q is an echo complex coefficient of the qth point clutter; a(R q , θ q ) is a transmit steering vector of the clutter, and b(θ q ) is a receive steering vector of the clutter;

[0033] The overall received signal x of the meteorological target can be represented in the following form:

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

[0035] wherein n is a Gaussian noise.

[0036] Further, the expression forms of the transmit steering vector a(R0, θ0) and the receive steering vector b(θ0) are as follows:

[0037]

[0038] wherein the superscript T is a transpose operator, e is a natural constant, and respectively represent a distance steering vector and an angle steering vector, ⊙ is a Hadamard product, λ0 is a wavelength,

[0039] Further, the interference covariance matrix is constructed based on the point clutter covariance matrix and the Gaussian white noise covariance matrix, comprising:

[0040] The point clutter covariance matrix R c is expressed as:

[0041]

[0042] where x c is the received signal of the point clutter, Q is the number of clutters, 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, and is expressed as:

[0044]

[0045] where is the noise power, I MN is an MN×MN unit matrix;

[0046] 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] s.t.w H u(R0, θ0) = 1

[0051] is obtained by the Lagrange multiplier method:

[0052]

[0053] where w represents the weight vector, and the coefficient R c+n is the interference covariance matrix, and u(R0, θ0) represents the virtual steering vector of the weather target, which can be expressed as the Kronecker product of the transmit and receive steering vectors:

[0054]

[0055] where a(R0, θ0) is the transmit steering vector, b(θ0) is the receive steering vector, R0 is the range of the weather target, and θ0 is the azimuth angle of the weather target.

[0056] Further, the total received signal x is multiplied by the weight vector w and accumulated to obtain the output signal y after suppressing the clutter interference, represented as:

[0057] y = w H x

[0058] where the superscript H represents the conjugate transpose.

[0059] A computer readable storage medium, the medium storing a computer program; the computer program is executed by a processor to implement the weather radar clutter suppression method based on the frequency diversity array.

[0060] A terminal device, comprising a processor, a memory and a computer program stored in the memory; the processor executes the computer program to implement the weather radar clutter suppression method based on the frequency diversity array.

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

[0062] The frequency diversity weather radar introduces a transmission frequency difference between the antenna elements of the phased array, which can distinguish weather targets and clutter interference according to the phase, distance and other information in the scattered echo signal. In addition, the frequency diversity array radar system can perform more accurate beamforming in the distance and angle dimensions, so as to effectively filter out the clutter by setting a null at the clutter position. Therefore, the introduction of the frequency diversity array into the weather radar can suppress the clutter by the different distribution of the clutter in the distance dimension, which can significantly improve the accurate detection of the weather radar on the target, timely warning of different weather, avoiding danger, and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

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

[0064] Figure 2 is the transmission and reception array model of the frequency diversity array MIMO radar;

[0065] Figure 3 is the comparison of the beam patterns of the traditional FDA radar and the FDA-MIMO radar, where (a) is the traditional FDA radar (f m = f0 + mΔf, d = λ / 2), (b) is the traditional FDA-MIMO radar (f m = f0 + mΔf, d = λ / 2);

[0066] Figure 4 is the comparison of the beam emitted by FDA radar and FDA-MIMO radar in different configurations, where (a) is FDA logd; (b) is FDA-MIMO logd; (c) is FDA expf-logd; (d) is FDA-MIMO expf-logd; (e) is FDA expf; (f) is FDA-MIMO expf;

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

[0068] Figure 6 is the point clutter suppression result in different positions in the embodiment, where (a) is the comparison of FDA and FDA-MIMO in the logd design; (b) is the comparison of FDA and FDA-MIMO in the expf-logd design; (c) is the comparison of FDA and FDA-MIMO in the expf design;

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

[0070] The present application can generate angle, distance and time related antenna patterns by introducing a frequency diversity array, which can effectively realize distance clutter suppression by using the distance dimension zero point of the transmitting pattern. Thus, the weather radar applying the method can generate beams related to both distance and angle, and can realize distance beam control in addition to angle beam control, can effectively suppress distance related clutter, filter out ground clutter to the greatest extent, reduce the influence of clutter residues on wind shear signals, and improve the detection performance and efficiency of the weather radar. The frequency diversity radar has multiple functions such as dynamic and static target detection, tracking and identification, and adding weather function can make it better avoid bad weather and complete the intended task. Therefore, the system can provide more accurate and efficient technical means for weather detection of high resolution radar.

[0071] Referring to the drawings, the weather radar clutter suppression method based on a frequency diversity array provided by the present application comprises the following steps:

[0072] Step 1, the frequency diversity technology is used to configure each antenna element and element spacing of the transmitter in the radar system, so that the linear array elements of the transmitter constitute a frequency diversity array.

[0073] Unlike the electromagnetic waves emitted by each antenna element of the phased array, the frequency diversity array introduces a small frequency change in the frequency of each element, so that the center frequency of different antenna elements is different, which is equivalent to introducing a frequency difference for each element.

[0074] Suppose the transmitter of the weather radar is composed of M antenna elements, each of which is arranged at a certain interval; a small frequency step, denoted as Δf, is introduced between each of the antenna elements m The frequency step Δf m (kHz order) is much smaller than the reference operating carrier frequency f0(MHz ~ GHz order) of the antenna elements, so the signal frequency f m emitted by the mth antenna element can be expressed as:

[0075] f m = f0+ Δf m , m = 0, 1,..., M-1 (1)

[0076] Where f0is the reference carrier frequency, which is selected as the carrier frequency of the first antenna element of the transmitter; M is the number of antenna elements of the transmitter.

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

[0078]

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

[0080] In order to produce a maximum value at the expected target position (θ0, r0), the complex weight is configured as a H (θ0, r0), so the transmit pattern can be expressed as:

[0081]

[0082] Where the superscript H denotes the conjugate transpose operator, M is the number of antenna elements of the transmitter, Δf m is the frequency step introduced between each antenna element, 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 element, c is the speed of light, θ0is the expected target angle, r0is the expected target distance; a(θ, r) is the transmit steering vector, θ and r represent the angle and distance of any point in space; a(θ, r) can be expressed as:

[0083]

[0084] It can be seen from equation (3) 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 transmitting beam is coupled in distance and angle, the range and angle of the target cannot be directly estimated by the output of the FDA beamformer. But the beam pattern is also related to Δf m and d m , so the desired single-peak beam can be obtained by setting appropriate Δf m and d m .

[0085] The conventional FDA radar uses a uniform change in frequency offset on the antenna elements of the transmitter, which forms a distance-angle coupled beam, and forms a periodic beam with a period of c / (2Δf m ) in the distance dimension, resulting in 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 a loss of system SINR. Therefore, in order to obtain a single-peak beam in the distance-angle dimension, the present application uses three different frequency offset and 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 transmitter of the current radar system:

[0087] When the transmitter uses the Logd method, the signal frequency f m of the antenna element is configured by Δf m in ①, and the element spacing is set to d m in ①; when it uses the Expf method, the signal frequency f m of each antenna element is configured by Δf m in ②, and the element spacing is set to d m in ②; when it uses the Expf-Logd method, the signal frequency f m of the antenna element is configured by Δf m in ③, and the element spacing is set to d m in ③.

[0088] ① Frequency offset and element spacing form under Logd method design

[0089] Set the frequency offset Δf m in equation (1) to be a linear frequency offset, and the element spacing to be a logarithmic form, where the calculation of the frequency offset Δf m and the element spacing d m is as follows:

[0090]

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

[0092] 2. Frequency offset and element spacing form under Expf method design

[0093] For Expf setting, the frequency offset in the system is set to grow exponentially, and the element spacing is set to vary linearly, where the frequency offset Δf m and the element spacing d m are calculated as follows:

[0094]

[0095] where b is a configurable constant; as can be seen from (6), the frequency increment under Expf setting is nonlinearly varied, and the single maximum beam peak value it produces is conducive to decoupling the range and angle, and the parameter b value here is 1.4.

[0096] 3. Frequency offset and element spacing form under Expf-Logd method design

[0097] The frequency offset in the system is set to grow exponentially, and the element spacing is set to vary logarithmically, where the frequency offset Δf m and the element spacing d m under Expf-Logd method are calculated as follows:

[0098]

[0099] where the parameter d in all three settings is 0.021, to avoid producing grating lobe phenomenon. Similarly, the Expf-logd configuration can also produce a single maximum peak beam, thereby helping to suppress the main lobe clutter interference.

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

[0101] Step 2, after the transmitter configures the frequency offset and element spacing of each antenna element, the signal is transmitted to the weather target; based on the echo signal received by the receiver, the received signal of the point clutter and the Gaussian noise, the overall received signal of the weather target is determined; based on the point clutter covariance matrix and the Gaussian white noise covariance matrix, the interference covariance matrix is constructed.

[0102] After the received echo signal is subjected to mixing frequency processing on the reference carrier frequency, digital mixing frequency processing on the step frequency, and matched filtering processing, a received signal in vector form can be obtained, that is, a snapshot signal x composed of the space-time two-dimensional steering vector of the weather target is obtained s :

[0103]

[0104] wherein represents a MNx1-dimensional complex space, N is the number of antenna elements of the receiver, R0 is the distance of the weather target, θ0 is the angle of the weather target, is a Kronecker product, is the echo complex coefficient of the weather target, wherein t is a time parameter, sinc is a sine function, f0 is a carrier frequency, c is the speed of light, a(R0, θ0) is a transmit steering vector, and b(θ0) is a receive steering vector, and the expression form is as follows:

[0105]

[0106] wherein the superscript T is a transpose operator, e is a natural constant, respectively represent the distance steering vector and the angle steering vector, is a Hadamard product, Δf m is the frequency step introduced between each antenna element of the transmit signal, d m is the element spacing setting, R0 is the distance of the weather target, θ0 is the angle of the weather target, and λ0 is the wavelength,

[0107] As shown in equation (10), the transmit steering vector of the frequency diversity array antenna has distance-angle dependence. Unlike traditional phased array radars, the clutter distribution of the FDA radar in the spatial frequency domain will change with the change of the slant range; therefore, the FDA can realize the differentiation of the clutter and the target in the distance area by utilizing the controllable freedom degree in the distance dimension. In addition, the transmit pattern is also closely related to the frequency offset and the element spacing; therefore, in order to filter out the ground clutter to the greatest extent and improve the accuracy of the wind shear signal wind speed estimation, the frequency diversity array is introduced, the non-uniform array is arranged, and the frequency offset is set, and the weather target and the clutter are differentiated in the distance-angle dimension to realize the reservation of the weather target and the filtering of the clutter.

[0108] Suppose that Q random distributed clutter interferences are generated in the environment, the signal of the qth clutter propagating to the nth antenna element of the receiver can be expressed as:

[0109]

[0110] where x c is the received signal of the point clutter, R q is the distance of the point clutter, θ q is the angle of the point clutter, ξ q is the echo complex coefficient of the qth point clutter; a(R q , θ q ) is the transmitting steering vector of the clutter, 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 respectively, Δf m is the frequency step introduced between the antenna elements of the transmitting signal, d m is the distance between the antenna elements, λ0 is the wavelength, c is the speed of light, and f0 is the carrier frequency.

[0114] Considering the existence of the weather target, Q point clutters and noise, the overall received signal x of the weather target can be expressed in the following form:

[0115]

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

[0117] The point clutter covariance matrix R c can be expressed as:

[0118]

[0119] where x c is the received signal of the point clutter, Q is the number of clutters, 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] where is the noise power, I MN is the MN x MN identity matrix.

[0123] The interference covariance matrix is then 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, the weight vector is obtained by constructing the beamformer and using the interference covariance matrix for full-dimensional optimal processing, and then the weight vector is used 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 accumulated to obtain the output signal after suppressing clutter interference, by adjusting the distance and phase of each element in the weight vector, the enhancement of the weather target direction and the suppression of clutter interference can be realized; expressed by the formula as:

[0127] y = w H x (18)

[0128] where w is the MN x 1 weight vector, x is the overall received signal, and the superscript 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, the output total power is minimum while keeping the expected target output power unchanged, so as to maximize the signal-to-interference-and-noise ratio (SINR), the beamformer based on the minimum mean square error distortionless response criterion can be expressed as:

[0130]

[0131] obtained by the Lagrange multiplier method is:

[0132]

[0133] where the coefficient where R c+n is the interference covariance matrix, u(R0, θ0) represents the virtual steering vector of the weather target, which can be expressed as the Kronecker product of the transmit and receive steering vectors:

[0134]

[0135] Wherein a(R0, θ0) is a transmitting steering vector, b(θ0) is a receiving steering vector, R0 is the distance of the meteorological target, and θ0 is the azimuth angle of the meteorological target.

[0136] Supposing 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 the signals received by the array antenna are combined by weighting through constructing a weight vector matrix, so that the signals in the direction of the meteorological target are enhanced, and the clutter interference signals in the non-desired direction are suppressed. That is, through the MVDR adaptive beam forming algorithm, the optimal beam pattern under the condition of the existence of the clutter interference can be obtained, the beam pattern can form a null at the interference distance point of the clutter interference, and an energy beam is generated at the distance-angle position of the meteorological target, so that the purpose of suppressing the clutter interference is achieved.

[0137] Embodiment:

[0138] When the airborne meteorological radar works in the downward direction, the geometric configuration of the FDA meteorological radar is as shown in Figure 1 Supposing that the flight direction of the aircraft is consistent with the normal direction of the array, the array is assumed to be a one-dimensional equidistant linear array after column synthesis, and the array is composed of M equivalent array elements. For any scattering point, the slant distance of the scattering point to the jth array element can be expressed as Here, R represents a reference slant distance, θ is an azimuth angle, and φ is a pitch angle. Due to the motion of the aircraft platform and the difference between the azimuth and the pitch during beam scanning, the clutter characteristics of each element are also different, that is, the clutter and the target are distributed in different distance elements.

[0139] The present application is based on the distribution of the transmitting and receiving arrays of the frequency diversity array meteorological radar, as shown in Figure 2 The meteorological radar adopts the frequency diversity array, and considers the co-sited MIMO radar with the same transmitting and receiving array elements. M arrays work independently, transmit radar waves of specific frequencies, and N receiving array elements receive the echo signals. Since a fixed frequency less than the carrier frequency is introduced for each transmitting array element, the radar system contains M transmitting arrays with different frequencies, and the frequencies are f0, f1, …, f M-1 The meteorological radar receives the echo through multiple narrow beams, forms the steering matrix of the frequency diversity array, and obtains the output result of the array. The inertial navigation parameters and radio altimeter data provided by the inertial navigation system and the radio altimeter and other airborne navigation equipment can be used to obtain accurate information such as the pitch, azimuth and ground speed of the aircraft. The clutter region can be roughly estimated by using this as prior information.

[0140] The distance-angle two-dimensional beam of the traditional FDA radar and the FDA-MIMO radar is as shown in Figure 3 The frequency offsets of the two are linearly changed, and the array element spacing is half of the wavelength. As shown inFigure 3 Results show that the beams of traditional FDA radars and FDA-MIMO radars exhibit periodic variations, with a period of 25 km, determined by c / 2Δf, where c is the speed of light and Δf is the frequency offset. Therefore, when received clutter and true targets are both within this periodic distance, FDA radars and FDA-MIMO radars cannot effectively distinguish between true and false targets, hindering their ability to combat clutter interference. Therefore, designing the frequency offset and element spacing is considered.

[0141] The transmit beam design of FDA and FDA-MIMO radar is carried out using three different frequency offsets and array element spacings. Figure 4 Figure 1 compares the transmit beams of FDA and FDA-MIMO radars in different configurations. It can be seen that both FDA and FDA-MIMO radars can form a single peak beam in the range-angle space under the expf-logd and expf settings. This allows for clutter suppression by nulling at different range bins.

[0142] The clutter suppression process is as follows Figure 5 As 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 it by e -j2πΔf(m-1)t The second step is to perform matched filtering on each transmitted waveform. The sum of the signals from the N receiving elements after matched filtering can be combined into a column vector. The covariance matrix of the received signal is estimated, and then the adaptive optimal weights are calculated through optimization to suppress clutter.

[0143] The clutter suppression method for airborne weather 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 angle 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 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 in the figure, when the frequency offset and array element spacing settings proposed in 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 two-dimensional space of distance and angle. In addition,Figure 7 For the relationship between output SINR and input Delta f, the output SINR increases with the increase of Delta f. Therefore, the effective design of frequency offset is the key to suppress interference, and the frequency offset and array element spacing designed in the present application make the FDA-MIMO radar superior to the FDA radar in suppressing clutter interference; the experimental results fully prove the effectiveness of the method of the present application.

[0144] The weather radar precision detection method based on the frequency diversity array of the present application can effectively distinguish clutter interference and targets through the distance dimension freedom introduced by the frequency diversity array, and can form a single peak value beam at the target position through decoupling of distance and angle by designing different frequency offsets and array element spacings. The frequency control array distance-angle two-dimensional adaptive filtering is used for effective suppression of clutter, which significantly improves the detection precision of the weather radar and has a wide application prospect.

[0145] The above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should 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 offset 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, the received signal of the point clutter and the Gaussian noise received by the receiver; Construct interference covariance matrix based on point clutter covariance matrix and Gaussian white noise covariance matrix; By constructing a beamformer and performing full-dimensional optimal processing using the interference covariance matrix to obtain a weight vector, the overall received signal is filtered using the weight vector 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, wherein: 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 recorded as Δf m , then the signal frequency f transmitted by the mth antenna element m Expressed as: 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 2, wherein: The configuration of antenna array elements and element spacing of a transmitter in a radar system using frequency diversity technology includes: Determine whether the transmitter uses the Logd method, Expf method, or Expf-Logd method, and calculate according to the corresponding calculation method 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, and d is a configurable parameter used to control the spacing between antenna elements. 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 3, wherein: 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 includes: The received echo signal is 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 , express dimensional complex space, N is the number of receiver antenna elements, R0 is the distance to the meteorological target, 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, is the launch steering vector, To receive the steering vector; Note that there are Q pseudo-randomly distributed clutter interferences in the environment, and the signal of the qth clutter propagating to the nth antenna array element of the receiver is expressed as: where x c is the received signal of point clutter, R q is the distance of the point clutter, is the angle of point clutter, is the echo complex coefficient of the clutter at the qth point; is the clutter emission steering vector, is the receiving steering vector of the clutter; The overall received signal x of the meteorological target is expressed as follows: 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: Launch steering vector , receive steering vector The expression is as follows: The superscript T is the transposition operator, and e is a natural constant. and denote the distance steering vector and the angle steering vector respectively, is the Hadamard product, is the wavelength, .

6. The method for suppressing clutter of a weather radar based on a frequency diversity array according to claim 5, 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 Expressed as: where x c is the received signal of point clutter, E{} represents the expected 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, 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: 。 7. The method for suppressing clutter of a weather radar based on a frequency diversity array according to claim 1, wherein: The beamformer is expressed as: By the Lagrange multiplier method, we can get: Where w represents the weight vector, superscript H represents the conjugate transpose operation, the coefficient , is the interference covariance matrix, The virtual guidance vector representing the meteorological target is expressed as the Kronecker product of the transmit and receive guidance vectors: in is the launch steering vector, To receive the steering vector, R0 is the distance to 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, wherein: The overall received signal x is multiplied by the weight vector w and then accumulated to obtain the output signal y after suppressing clutter interference, which is expressed as: The superscript H represents the conjugate transpose.

9. A computer-readable storage medium storing a computer program; wherein: 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 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.

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