End-on array airborne early warning radar range ambiguity clutter suppression method based on subarray synthesis

Abstract

The application discloses a method for suppressing range ambiguity clutter of an end-on array airborne early warning radar based on subarray synthesis. Firstly, echo signals are subarray synthesized along horizontal rows of an end-on array to form one column of spatial channel data, and then the column of spatial channel data is subarray synthesized along horizontal columns to form one row of spatial channel data, so as to form a cross-shaped horizontal spatial synthesis channel data. Then, the obtained horizontal spatial synthesis channel data is subjected to clutter suppression processing by using a STAP method, so as to effectively filter out the clutter of the end-on array airborne early warning radar. Finally, the data subjected to the STAP processing is subjected to constant false alarm rate (CFAR) detection, so as to realize detection of a moving target. The scheme is suitable for clutter suppression processing of the end-on array airborne early warning radar and has the characteristics of less training sample requirement and low operation complexity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of radar signal processing, and particularly relates to a range ambiguity clutter suppression method for an airborne early warning radar based on subarray synthesis. BACKGROUND

[0002] The basic task of an airborne early warning radar is to detect a moving target at a long distance, and therefore detection power is an important performance index thereof. Under the constraint of the power of existing devices, increasing the antenna aperture is an important means to improve the detection capability thereof. The radiation direction of a conventional side-shooting array antenna is perpendicular to the array plane, and the size of the antenna is often limited by the space for placing the aircraft and the aerodynamic performance. However, the regions such as the wings and the fuselage of an airborne platform can provide more apertures parallel to the radiation direction, and if the aperture resources can be effectively utilized, the detection capability of the airborne early warning radar can be significantly improved. The maximum radiation direction of an end-shooting array is parallel to the array aperture, and is a typical array that meets the above requirements.

[0003] The end-shooting array antenna can be horizontally placed on the top of a back-mounted antenna (such as a wedge tail early warning aircraft), or can be horizontally placed on the wings of a "sensor aircraft" or an unmanned early warning aircraft, so that a super large antenna aperture can be obtained while the requirements for the load and the aerodynamic shape of the aircraft are ensured. Compared with a conventional side-shooting array airborne early warning radar, the elevation pattern of the end-shooting array antenna is significantly widened, and at the same time, the clutter is distributed in the three-dimensional coupling of the horizontal row, the horizontal column and the Doppler domain, so that the clutter characteristics at different ambiguous distances present significant differences, which leads to a serious decline in the performance of the conventional space-time adaptive processing (STAP) method, and greatly increases the range-Doppler blind area of the moving target detection.

[0004] Currently, the existing airborne radar early warning radar range-dependent clutter suppression methods mainly include two categories: one is space-time spectrum correction method. The space-time spectrum correction method mainly includes Doppler compensation method, high-order Doppler compensation method, angle-Doppler compensation method, adaptive angle-Doppler compensation method, non-uniform sampling-based spectrum registration method and space-time interpolation method. The method mainly corrects the space-time spectrum of the training sample clutter to be consistent with the distance unit to be detected, so as to eliminate the adverse effects of the range-dependent clutter on the subsequent clutter suppression. However, in the case of serious range ambiguity, the performance of the algorithm is sharply decreased due to the fact that the clutter spectrum of different ambiguous distances cannot be corrected at the same time. The other is the range ambiguity clutter rejection method based on the array elevation dimension, mainly including the elevation preset notch cascaded azimuth-Doppler processing, elevation adaptive cascaded azimuth-Doppler processing, azimuth-elevation-Doppler three-dimensional STAP, and reduced dimension three-dimensional STAP. The method takes the array elevation dimension into the clutter suppression processing according to the difference of the side-looking array airborne early warning radar clutter of different range ambiguities in the elevation space, so as to realize the suppression of the clutter of different distribution. The method has achieved good results in the range ambiguity clutter suppression of the side-looking array airborne early warning radar. However, since the end-on array is horizontally placed, there is no elevation space dimension, so the above method cannot be directly applied to the clutter suppression processing of the end-on array airborne early warning radar.

[0005] Therefore, to realize the effective suppression of the end-on array airborne early warning radar clutter, a STAP method with low dimensionality and effective range ambiguity clutter suppression is needed. SUMMARY

[0006] The present application is to overcome the deficiencies in the above background art, by synthesizing the horizontal end-on array data into cross-shaped space channel data and combining with the STAP technology to realize the effective suppression of the range ambiguity clutter. The present application is suitable for the clutter environment with range ambiguity, and has the characteristics of strong robustness, good slow-moving target detection performance, simple engineering implementation, etc.

[0007] To achieve the above application purpose, the present application provides an end-on array airborne early warning radar range ambiguity clutter suppression method based on subarray synthesis, including the following steps:

[0008] S1: The space domain receiving channel of the end-on array airborne early warning radar receives the echo signal;

[0009] S2: The echo signal received by the horizontal end-on array is subjected to subarray synthesis. First, the echo data is subjected to subarray synthesis along the horizontal row direction of the end-on array to form a column of space channel data, and then the echo data is subjected to subarray synthesis along the horizontal column direction of the array to form a row of space channel data, and finally the column space channel data and the row space channel data are combined to obtain horizontal space synthesis channel data in a cross-shaped structure;

[0010] S3: using the STAP method to perform clutter suppression processing on the horizontal spatial synthesis channel data after subarray synthesis;

[0011] S4: performing CFAR detection on the data processed by the STAP method.

[0012] Firstly, the echo signal is subarray-synthesized along the horizontal row direction of the end-fire array to form a column of spatial channel data, and then subarray-synthesized along the horizontal column direction to form a row of spatial channel data, thereby forming a cross-shaped horizontal spatial synthesis channel data; then the obtained horizontal spatial synthesis channel data is subjected to clutter suppression processing by using the STAP method, so as to effectively filter out the clutter of the end-fire array airborne early warning radar; finally, the data processed by the STAP method is subjected to constant false alarm (CFAR) detection, thereby realizing detection of the moving target. The scheme is suitable for clutter suppression processing of the end-fire array airborne early warning radar, and has the characteristics of less training sample requirement and low computational complexity.

[0013] Further, the subarray synthesis in step S1 and the analog-to-digital conversion have the following sequence relationship:

[0014] Firstly, the echo signal in step S1 is not directly processed, and then the horizontal spatial synthesis channel data of the cross-shaped structure is synthesized at the microwave level in step S2, and this mode is suitable for the traditional phased array radar;

[0015] Secondly, after the echo signal is synthesized at the microwave level to obtain the horizontal spatial synthesis channel data, the analog-to-digital conversion is performed to obtain the digital horizontal spatial synthesis channel data, and this mode is suitable for the subarray-level digital radar;

[0016] Thirdly, the echo signal in step S1 is subjected to frequency down-conversion processing, and then directly subjected to analog-to-digital conversion to obtain the digitized echo data, and then the horizontal spatial synthesis channel data of the cross-shaped structure is synthesized at the digital level in step S2, and this mode is suitable for the full-digital array radar.

[0017] Further, in step S2, the dimensions of the row spatial channel data and the column spatial channel data after subarray synthesis depend on the included angle between the aircraft motion speed and the horizontal row direction normal;

[0018] When the included angle is 0°, the dimension of the row spatial channel data is 0, and the dimension of the column spatial channel data is 8;

[0019] When the included angle is 90°, the dimension of the row spatial channel data is 8, and the dimension of the column spatial channel data is 0;

[0020] When 0°< included angle ≦ 45°, the dimensions of the row spatial channel data and the column spatial channel data are respectively set to 4 and 8;

[0021] When 45° < the included angle < 90°, the dimension of the row spatial channel data and the dimension of the column spatial channel data are respectively set as 8 and 4.

[0022] Further, in step S2, the subarray synthesis is performed along the horizontal row direction of the array to obtain Q-dimensional column spatial channel data, i.e., Q-dimensional column subarray data, and the formula of the subarray synthesis is as follows:

[0023]

[0024] wherein, represents the qth data of the synthesized column subarray, U q represents the number of rows of array elements in the qth subarray, x u,n represents the data in the u-th row and the n-th column of the qth subarray corresponding to the distance unit to be detected, d is the array element spacing, λ is the wavelength, θ0 and respectively represent the azimuth angle and the elevation angle of the main beam, and N is the horizontal row direction array element of the receive antenna array of the end-on array airborne early warning radar.

[0025] Further, in step S2, the subarray synthesis is performed along the horizontal column direction of the array to obtain P-dimensional row spatial channel data, i.e., P-dimensional row subarray data, and the formula of the subarray synthesis is as follows:

[0026]

[0027] wherein, represents the pth data of the synthesized row subarray, V p represents the number of rows of array elements in the pth subarray, x v,m represents the data in the m-th row and the v-th column of the pth subarray corresponding to the distance unit to be detected, and M is the horizontal column direction array element of the receive antenna array of the end-on array airborne early warning radar.

[0028] Further, in step S2, the specific process of obtaining the horizontal spatial synthesis channel data in the cross structure is as follows:

[0029] After the subarray synthesis, the column subarray data and the row subarray data are respectively denoted as and The specific expressions are as follows:

[0030]

[0031]

[0032] At this time, the horizontal spatial synthesis channel data after the spatial subarray synthesis is denoted as:

[0033]

[0034] wherein, is the horizontal spatial synthesis channel data.

[0035] Further, in step S3, the horizontal space synthesis channel data after the subarray synthesis is subjected to STAP processing according to a linear constraint minimum output power criterion.

[0036] Further, in step S3, the STAP method is subarray-pulse domain processing or subarray-Doppler domain processing, and the adaptive weight of STAP is represented as:

[0037] w=μR z -1 s z

[0038] wherein μ represents a constant coefficient of the weight,

[0039] R z represents a clutter covariance matrix after time domain transformation, R z =T H RT;

[0040] R represents a clutter covariance matrix after space domain subarray synthesis,

[0041] E[·] represents expectation, T is a time domain dimension reduction matrix, (·) H is a matrix conjugate transpose, is horizontal space synthesis channel data;

[0042] s z represents a space-time two-dimensional steering vector after time domain transformation, s z =T H s;

[0043] s represents a space-time two-dimensional steering vector,

[0044] s t is a time domain steering vector, s s is a space domain steering vector after subarray synthesis, is a Kronecker product.

[0045] The application also provides an end-on array airborne early warning radar range ambiguity clutter suppression system based on subarray synthesis, which is used for realizing the end-on array airborne early warning radar range ambiguity clutter suppression method based on subarray synthesis, and comprises a receiving unit, an analog-digital conversion unit, a subarray synthesis unit, a STAP processing unit and a CFAR detection processing unit which are sequentially connected in communication.

[0046] The receiving unit is used for receiving echo signals.

[0047] The analog-digital conversion unit is used for analog-digital conversion of the echo signals, so as to realize digitization of the echo signals.

[0048] The subarray synthesis unit is used for subarray synthesis of echo signals received by the horizontal end-fire array, and first subarray synthesis of echo data along the horizontal row direction of the end-fire array to form a column of spatial channel data, then subarray synthesis along the horizontal column direction of the array to form a row of spatial channel data, and finally combination of the column spatial channel data and the row spatial channel data to obtain horizontal spatial synthesis channel data in a cross structure;

[0049] The STAP processing unit adopts a STAP method to perform clutter suppression processing on the horizontal spatial synthesis channel data after subarray synthesis.

[0050] The CFAR detection processing unit performs CFAR detection on the data after STAP processing.

[0051] The CFAR detection processing unit can select a suitable CFAR detection algorithm according to the clutter suppression result to realize effective detection of moving targets.

[0052] Compared with the prior art, the present application has the following beneficial effects:

[0053] (1) The present application makes full use of the horizontal row-horizontal column-Doppler three-dimensional coupling rule of the range ambiguity clutter of the end-fire array airborne early warning radar, and retains the horizontal row and horizontal column spatial degrees of freedom for subsequent adaptive clutter suppression when synthesizing the spatial channel. Therefore, when the end-fire array airborne early warning radar works at a medium / high pulse repetition frequency, i.e. there is range ambiguity, the present application is beneficial to significantly improving the slow target detection capability.

[0054] (2) In the present application, the end-fire array subarray synthesis is a cross structure spatial channel, and the spatial degrees of freedom are optimally distributed in the subarray synthesis process, i.e. they are maximally distributed in the horizontal row and horizontal column directions under the premise of limited spatial degrees of freedom, so as to ensure that the horizontal row-horizontal column-Doppler three-dimensional coupling range ambiguity clutter can be decoupled in subsequent STAP processing. Compared with a single synthesis horizontal row array or horizontal column array, this subarray structure is beneficial to simultaneous suppression of the range ambiguity clutter. Compared with STAP processing using full-dimensional space, this subarray structure significantly reduces the operation amount and training sample requirement while obtaining good range ambiguity clutter suppression performance, which is beneficial to hardware implementation and real-time detection of moving targets. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 is a flowchart of the end-fire array airborne early warning radar range ambiguity clutter suppression method based on subarray synthesis of the present application. DETAILED DESCRIPTION

[0056] The drawings are only used for illustrative description, and cannot be understood as a limitation to the patent; in order to better illustrate the embodiments, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual product size; it is understandable for those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted. The positional relationship described in the drawings is only used for illustrative description, and cannot be understood as a limitation to the patent.

[0057] Embodiment 1:

[0058] As shown in the figure, the application provides a range cell clutter suppression method for an end-fire array airborne early warning radar based on subarray synthesis, comprising the following steps: Figure 1

[0059] S1: The spatial receiving channel of the end-fire array airborne early warning radar receives the echo signal;

[0060] S2: The echo signal received by the horizontal end-fire array is subjected to subarray synthesis, first, the echo data is subjected to subarray synthesis along the horizontal row direction of the end-fire array to form a column of spatial channel data, then the subarray synthesis is performed along the horizontal column direction of the array to form a row of spatial channel data, and finally the column spatial channel data and the row spatial channel data are combined to obtain horizontal spatial synthesis channel data in a cross-shaped structure;

[0061] S3: The horizontal spatial synthesis channel data after subarray synthesis is subjected to clutter suppression processing by using the STAP method;

[0062] S4: The data after STAP processing is subjected to CFAR detection.

[0063] The application first subjects the echo signal to subarray synthesis along the horizontal row direction of the end-fire array to form a column of spatial channel data, then subjects the echo signal to subarray synthesis along the horizontal column direction to form a row of spatial channel data, thereby forming a horizontal spatial synthesis channel data in a cross-shaped structure; then the obtained horizontal spatial synthesis channel data is subjected to clutter suppression processing by using the STAP method, thereby realizing effective filtering of the clutter of the end-fire array airborne early warning radar; finally, the data after STAP processing is subjected to constant false alarm (CFAR) detection, thereby realizing detection of the moving target. The application scheme is suitable for clutter suppression processing of the end-fire array airborne early warning radar, and has the characteristics of less training sample requirement and low computational complexity.

[0064] Among them, the subarray synthesis in step S1 has the following sequence relationship with the analog-to-digital conversion:

[0065] First, the echo signal in step S1 is not directly processed, and then the horizontal spatial synthesis channel data in a cross-shaped structure is synthesized at a microwave level in step S2, which is suitable for a traditional phased array radar;

[0066] ​Secondly, the echo signal is synthesized into horizontal space domain synthesis channel data at microwave level, and then is converted into digital level, to obtain digital horizontal space domain synthesis channel data, which is suitable for a subarray level digital radar;

[0067] Thirdly, the echo signal in step S1 is down-converted, and then is directly converted into digital data, and then the horizontal space domain synthesis channel data of cross structure is synthesized at digital level in step S2, which is suitable for a full digital array radar.

[0068] In the embodiment, the third method is used in step S1, the collected echo signal is down-converted, and then is converted into digital data.

[0069] In the embodiment, the dimension of the row space domain channel data and the column space domain channel data synthesized by the subarray in step S2 depends on the included angle between the moving speed of the carrier and the horizontal row direction;

[0070] When the included angle is 0°, the dimension of the row space domain channel data is 0, and the dimension of the column space domain channel data is 8.

[0071] When the included angle is 90°, the dimension of the row space domain channel data is 8, and the dimension of the column space domain channel data is 0.

[0072] When 0°< the included angle ≦ 45°, the dimension of the row space domain channel data and the dimension of the column space domain channel data are respectively set to 4 and 8.

[0073] When 45°< the included angle < 90°, the dimension of the row space domain channel data and the dimension of the column space domain channel data are respectively set to 8 and 4.

[0074] In the embodiment, in step S2, the subarray is synthesized along the horizontal row direction of the array to obtain the column space domain channel data of Q dimensions, i.e., the column subarray data of Q dimensions, and the formula of the subarray synthesis is as follows:

[0075]

[0076] wherein, represents the qth data of the synthesized column subarray, U q represents the number of rows of the array elements in the qth subarray, x u,n represents the data of the u row and n column in the qth subarray corresponding to the to-be-detected distance unit, d is the array element spacing, λ is the wavelength, θ0 and are respectively the main beam azimuth angle and the elevation angle, and N is the horizontal row direction array element of the receive antenna array of the end-on array airborne early warning radar.

[0077] In the embodiment, in step S2, the subarray synthesis is performed along the horizontal column direction of the array to obtain P-dimensional row space channel data, i.e., P-dimensional row subarray data, and the subarray synthesis formula is as follows:

[0078]

[0079] wherein, represents the pth data of the synthesized row subarray, V p represents the number of rows of array elements in the pth subarray, x v,m represents the data of the mth row and the vth column in the pth subarray corresponding to the to-be-detected distance unit, and M represents the horizontal column direction array element of the receive antenna array of the monostatic array airborne early warning radar.

[0080] In the embodiment, in step S2, the specific process of obtaining the horizontal space synthesis channel data in the cross structure is as follows:

[0081] After the subarray synthesis, the column subarray data and the row subarray data are respectively denoted as and The specific representation is as follows:

[0082]

[0083]

[0084] At this time, the horizontal space synthesis channel data after the space subarray synthesis is denoted as:

[0085]

[0086] wherein, is the horizontal space synthesis channel data.

[0087] In the embodiment, in step S3, the STAP processing is performed on the horizontal space synthesis channel data after the subarray synthesis according to the linear constraint minimum output power criterion.

[0088] In the embodiment, in step S3, the STAP method is the subarray-pulse domain processing or the subarray-Doppler domain processing, and the adaptive weight of the STAP is denoted as:

[0089] w=μR z -1 s z (6)

[0090] wherein, μ represents a constant coefficient of the weight,

[0091] R z represents the clutter covariance matrix after the time domain transformation, and R z =T H RT.

[0092] R represents the clutter covariance matrix after the synthesis of the spatial subarray,

[0093] E[·] represents taking expectation, T is a time domain dimension reduction matrix, (·) H is the matrix conjugate transpose, is the horizontal spatial synthesis channel data;

[0094] s z represents the space-time two-dimensional steering vector after time domain transformation, s z = T H s;

[0095] s represents the space-time two-dimensional steering vector,

[0096] s t is the time domain steering vector, s s is the spatial steering vector after subarray synthesis, is the Kronecker product.

[0097]

[0098]

[0099] In the formula, v is the speed of the carrier, f r is the pulse repetition frequency, and K is the number of pulses in the coherent processing time.

[0100] The present application fully utilizes the distance ambiguity clutter of the end-fire array airborne early warning radar in the horizontal row-horizontal column-Doppler three-dimensional coupling law, and the horizontal row and horizontal column spatial degrees of freedom are retained at the same time when the spatial channel is synthesized, which is used for subsequent adaptive clutter suppression. Therefore, when the end-fire array airborne early warning radar works at medium / high pulse repetition frequency, that is, there is distance ambiguity, the present application is beneficial to significantly improve the slow target detection capability.

[0101] In the present application, the subarray synthesis of the end-fire array is a cross structure spatial channel, and the spatial degrees of freedom are optimally distributed in the subarray synthesis process, that is, the spatial degrees of freedom are maximally distributed in the horizontal row and horizontal column under the premise of limited spatial degrees of freedom, so that the horizontal row-horizontal column-Doppler three-dimensional coupling distance ambiguity clutter can be decoupled in the subsequent STAP processing. Compared with a single synthesis horizontal row array or horizontal column array, the subarray structure is beneficial to realize the simultaneous suppression of the distance ambiguity clutter; compared with the STAP processing using full-dimensional space, the subarray structure significantly reduces the operation amount and training sample requirement while obtaining better distance ambiguity clutter suppression performance, which is beneficial to hardware implementation and real-time detection of moving targets.

[0102] Embodiment 2:

[0103] This embodiment takes a full digital array end-fire array airborne early warning radar as an example for illustration, assuming that the angle between the aircraft motion speed and the normal line of the horizontal line array is 30°, and the dimension of the column airspace channel data and the dimension of the row airspace channel data are respectively set as 8 and 4;

[0104] The horizontal line array and the horizontal column array elements of the end-fire array airborne early warning radar are respectively N and M, and the number of pulses within the coherent processing time is K, in this embodiment, N = 16, M = 8, and K = 16.

[0105] Then the detailed steps of the end-fire array airborne early warning radar range ambiguity clutter suppression method based on subarray synthesis are as follows:

[0106] 1. The echo signal received by the airspace receiving channel of the end-fire array airborne early warning radar is subjected to down-conversion processing, then subjected to analog-digital conversion, and the digitized echo data is stored;

[0107] 2. The echo data is subjected to subarray synthesis along the horizontal line direction of the end-fire array through formula (1), the horizontal line subarray synthesis of the echo data is column airspace channel data of Q dimensions, that is, column subarray data, at this time the dimension Q is 8;

[0108] 3. The echo data is subjected to subarray synthesis along the horizontal column direction of the end-fire array through formula (2), the horizontal column subarray synthesis of the echo data is row airspace channel data of P dimensions, that is, row subarray data, at this time the dimension P is 4;

[0109] 4. The column subarray data and the row subarray data are expressed as formula (3) and formula (4), and then combined into the form of formula (5), so as to obtain the horizontal airspace synthesis channel data in the form of a cross structure;

[0110] 5. The STAP method is used for clutter suppression processing on the horizontal airspace synthesis channel data, wherein the adaptive weight value of the STAP can be expressed as formula (6);

[0111] 6. The data processed by the STAP method is subjected to CFAR (constant false alarm rate) detection, and the detection and processing of the space-based early warning radar moving target are completed.

[0112] Embodiment 3:

[0113] The application also provides an end-fire array airborne early warning radar range ambiguity clutter suppression system based on subarray synthesis, which is used for realizing the end-fire array airborne early warning radar range ambiguity clutter suppression method based on subarray synthesis in the above-mentioned embodiment 1, and the system comprises a receiving unit, an analog-digital conversion unit, a subarray synthesis unit, a STAP processing unit and a CFAR detection processing unit which are sequentially communicatively connected;

[0114] The receiving unit is used for receiving echo signals;

[0115] The analog-to-digital conversion unit is used for analog-to-digital conversion of the echo signal, so as to realize digitization of the echo signal;

[0116] The subarray synthesis unit is used for subarray synthesis of the echo signal received by the horizontal end-fire array. Firstly, the echo data is subarray-synthesized along the horizontal row direction of the end-fire array to form a column of spatial channel data. Then, the spatial channel data is subarray-synthesized along the horizontal column direction of the array to form a row of spatial channel data. Finally, the column spatial channel data and the row spatial channel data are combined to obtain horizontal spatial synthesis channel data in a cross-shaped structure.

[0117] The STAP processing unit adopts the STAP method to perform clutter suppression processing on the horizontal spatial synthesis channel data after subarray synthesis.

[0118] The CFAR detection processing unit performs CFAR detection on the data processed by the STAP method.

[0119] The CFAR detection processing unit can select a suitable CFAR detection algorithm according to the clutter suppression result, so as to realize effective detection of the moving target.

[0120] In the embodiment, the above-mentioned receiving, analog-to-digital conversion, subarray synthesis, STAP processing and CFAR processing can be programmed and realized on a general programmable signal processing board.

[0121] Obviously, the above-mentioned embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Any modification, equivalent replacement and improvement made on the basis of the above-mentioned description can be made by those skilled in the art. It is unnecessary and impossible to enumerate all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A method for suppressing range ambiguity clutter in end-fire array airborne early warning radar based on subarray synthesis, characterized in that, Includes the following steps: S1: The airspace receiving channel of the end-firing array airborne early warning radar received the echo signal; S2: Subarray synthesis is performed on the echo signal received by the horizontal end-fire array. First, the echo data is subarray synthesized into a column of spatial channel data along the horizontal row direction of the end-fire array. Then, the subarray is synthesized into a row of spatial channel data along the horizontal column direction of the array. Finally, the column spatial channel data and the row spatial channel data are combined to obtain horizontal spatial synthesized channel data with a cross-shaped structure. S3: The STAP method is used to suppress clutter in the horizontal spatial synthesized channel data after subarray synthesis. S4: Perform CFAR detection on the data processed by the STAP method; In step S2, subarrays are synthesized along the horizontal row direction of the array to form Q-dimensional column spatial channel data, which is Q-dimensional column subarray data. The formula for subarray synthesis is as follows: in, This represents the q-th data point in the synthesized column subarray. This represents the row number of the array element in the q-th subarray. This represents the data in the u-th row and n-th column of the q-th subarray corresponding to the distance cell to be detected, where d is the element spacing. For wavelength, and These are the azimuth and elevation angles of the main beam, respectively, and N is the horizontal row element of the end-fire array airborne early warning radar receiving antenna array. Subarrays are synthesized along the horizontal column direction of the array to form P-dimensional row-space channel data, which is P-dimensional row subarray data. The subarray synthesis formula is as follows: in, This represents the p-th data element in the synthesized row subarray. This represents the row number of the array element in the p-th subarray. This represents the data in the m-th row and v-th column of the p-th subarray corresponding to the range cell to be detected, where M is the horizontal array element of the end-fire array airborne early warning radar receiving antenna array. The specific process for obtaining horizontal spatial composite channel data with a cross-shaped structure is as follows: After the subarrays are combined, the column subarray and row subarray data are denoted as follows: and Specifically, it is expressed as follows: At this point, the horizontal spatial composite channel data after spatial subarray synthesis is represented as follows: in, This is composite channel data in the horizontal spatial domain.

2. The method for suppressing range ambiguity clutter in end-fire array airborne early warning radar based on subarray synthesis according to claim 1, characterized in that, The echo signal in step S1 is not processed directly. Then, in step S2, the horizontal spatial composite channel data with a cross-shaped structure is synthesized at the microwave level. After the echo signal is synthesized at the microwave level into horizontal spatial composite channel data, it is then converted from analog to digital to obtain digital horizontal spatial composite channel data.

3. The method for suppressing range ambiguity clutter in end-fire array airborne early warning radar based on subarray synthesis according to claim 1, characterized in that, The echo signal in step S1 is down-converted and then converted from analog to digital to obtain digitized echo data. Then, in step S2, the horizontal spatial domain composite channel data with a cross-shaped structure is synthesized digitally.

4. The method for suppressing range ambiguity clutter in an end-fire array airborne early warning radar based on subarray synthesis according to claim 1, characterized in that, In step S2, the dimensions of the row and column spatial channel data after subarray synthesis depend on the angle between the aircraft's speed and the horizontal row normal. When the included angle is 0°, the dimension of the row spatial channel data is 0, and the dimension of the column spatial channel data is 8. When the included angle is 90°, the dimension of the row spatial channel data is 8, and the dimension of the column spatial channel data is 0. When 0° < included angle ≦45°, the dimensions of row spatial channel data and column spatial channel data are set to 4 and 8 respectively; When 45° < included angle < 90°, the dimensions of the row spatial channel data and the column spatial channel data are set to 8 and 4 respectively.

5. The method for suppressing range ambiguity clutter in an end-fire array airborne early warning radar based on subarray synthesis according to claim 1, characterized in that, In step S3, the horizontal spatial domain synthesized channel data after subarray synthesis is processed using STAP according to the minimum output power criterion of linear constraint.

6. The method for suppressing range ambiguity clutter in an end-fire array airborne early warning radar based on subarray synthesis according to claim 1, characterized in that, In step S3, the STAP method is either subarray-pulse domain processing or subarray-Doppler domain processing. The adaptive weights of STAP are expressed as follows: in, Represents the constant coefficients of the weights. ; This represents the clutter covariance matrix after time-domain transformation. ; This represents the clutter covariance matrix after the spatial subarrays are synthesized. ; Let T represent the expected value, and T be the time-domain dimensionality reduction matrix. This is the conjugate transpose of the matrix. This is composite channel data in the horizontal spatial domain; This represents the space-time two-dimensional steering vector after time-domain transformation. ; Represents a spacetime two-dimensional steering vector. ; For time-domain steering vectors, This is the spatial guiding vector after the subarrays are synthesized. For Kronecker product.

7. A range ambiguity clutter suppression system for end-fire array airborne early warning radar based on subarray synthesis, characterized in that, The method according to any one of claims 1 to 6 includes a receiving unit, an analog-to-digital conversion unit, a subarray synthesis unit, a STAP processing unit, and a CFAR detection processing unit that are sequentially connected in communication. The receiving unit is used to receive echo signals; The analog-to-digital conversion unit is used to convert the echo signal into digital form, thereby digitizing the echo signal. The subarray synthesis unit is used to synthesize the echo signal received by the horizontal end-fire array. First, the echo data is synthesized into a column of spatial channel data along the horizontal row direction of the end-fire array. Then, it is synthesized into a row of spatial channel data along the horizontal column direction of the array. Finally, the column spatial channel data and the row spatial channel data are combined to obtain horizontal spatial synthesized channel data with a cross-shaped structure. The STAP processing unit uses the STAP method to perform clutter suppression processing on the horizontal spatial domain synthesized channel data after subarray synthesis. The CFAR detection processing unit performs CFAR detection on the data processed by the STAP method.

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