A method for reducing range sidelobe clutter using a variety of orthogonal waveforms

Abstract

A short-range clutter suppression method for reducing the number of orthogonal waveforms used, comprising: determining the range of short-range clutter to be suppressed; determining the number of short-range clutter ambiguities M; determining the number of orthogonal waveforms to be used and the corresponding orthogonal waveforms; determining the ambiguity region in which the main clutter region is located; determining the timing of the radar transmitting the orthogonal waveforms and transmitting the orthogonal waveforms; and performing matched filtering on the echo according to the order of the transmitted orthogonal waveforms to obtain the main clutter region signal with short-range ambiguous clutter suppressed. Compared with existing range ambiguity suppression methods, the present application can improve the suppression capability of short-range clutter, and is suitable for cases where there are multiple short-range ambiguities and the main clutter region is outside the multiple ambiguity regions in the short-range region. Especially for cases where the pulse repetition frequency is high, resulting in a large number of observable region ambiguities, the number of orthogonal waveforms is reduced, and the improvement is more obvious.

Description

Technical Field

[0001] This invention relates to a short-range ambiguity clutter suppression method that reduces the types of orthogonal waveforms used, belonging to the field of radar clutter suppression. Background Technology

[0002] In the research of space-based or airborne radar, clutter suppression is one of the most important key technologies. The main method of clutter suppression is space-time adaptive processing (STAP), which requires independent and identically distributed samples to estimate the clutter covariance matrix, thereby further suppressing clutter. When the platform yaws, especially for space-based platforms, the high speed and small yaw angle can cause severe range dependence of short-range clutter. When range ambiguity exists, short-range clutter can fold into the main clutter region of the target being detected, contaminating the clutter samples in the main clutter region, making the clutter covariance matrix estimation inaccurate, and severely reducing clutter suppression performance.

[0003] Therefore, short-range ambiguity clutter suppression has become a major challenge in clutter control. Existing methods for short-range clutter suppression in the presence of range ambiguity mainly fall into two categories. One involves introducing degrees of freedom in the antenna elevation dimension to filter short-range clutter in the spatial domain, reducing its impact. However, this increases antenna size and system complexity, especially for platforms with load height requirements, where increasing the elevation dimension is particularly difficult. The other method involves transmitting orthogonal waveforms to suppress range ambiguity clutter when range ambiguity occurs. However, existing orthogonal waveform pulse transmission methods do not consider the characteristics of short-range clutter; the number of orthogonal waveform types used equals the number of range ambiguities in the entire observation scene, requiring a large variety of orthogonal waveforms. The inherent constraints of orthogonal waveforms and practical results from existing orthogonal waveform generation methods show that fewer orthogonal waveform types make it easier to generate waveforms with good orthogonality, resulting in better short-range clutter suppression. Conversely, more orthogonal waveform types are required, making it harder to obtain waveforms with good orthogonality, leading to poorer short-range clutter suppression.

[0004] In existing technologies, some literature addresses the severe range ambiguity problem faced by space-based radar by proposing a method for range ambiguity clutter suppression using orthogonal transmitted waveforms. This method uses several orthogonal waveforms depending on the number of range ambiguities in the observation area, resulting in a large number of waveform types that are not conducive to generating well-aligned orthogonal waveforms. Furthermore, this method does not fully consider the characteristics of short-range clutter; if directly applied to space-based or airborne radars where multiple ambiguities exist in the short-range clutter region, the suppression effect is not optimal. Other literature addresses multi-hop clutter suppression using sequential orthogonal waveforms for skywave over-the-horizon radars, employing two orthogonal waveforms transmitted alternately. This method is only suitable for retaining a fixed main clutter region (one-hop region) and suppressing the second-hop clutter region. It is not applicable to space-based or airborne radars where multiple ambiguities exist in the short-range clutter region, or when the main clutter region is outside the multiple range ambiguity region. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and solve the problem of short-range clutter suppression.

[0006] The objective of this invention is achieved through the following technical solutions:

[0007] A method for reducing the types of orthogonal waveforms used in short-range ambiguity clutter suppression includes:

[0008] Determine the range of short-range clutter that needs to be suppressed;

[0009] Determine the number M of clutter ambiguity in the near-range region;

[0010] Determine the number of orthogonal waveforms to be used and the corresponding orthogonal waveforms;

[0011] Determine the ambiguity region where the main clutter region of the observation is located;

[0012] Determine the timing sequence for transmitting orthogonal waveforms from the radar, and then transmit the orthogonal waveforms.

[0013] Matched filtering is performed on the echoes according to the sequence of transmitted orthogonal waveforms to obtain the main clutter region signal that suppresses near-range ambiguity clutter.

[0014] In one embodiment of the present invention, the ambiguous range R is determined based on the pulse repetition frequency of the radar system. u This allows us to determine the number of clutter ambiguities in the near-field region.

[0015] In one embodiment of the present invention, based on the fuzzy distance R u Determine the ambiguity region where the main clutter region of the observation is located.

[0016] In one embodiment of the present invention, near-range fuzzy clutter suppression employs M+1 orthogonal waveforms.

[0017] In one embodiment of the present invention, determining the timing of radar-transmitted orthogonal waveforms includes:

[0018] According to the PRF, first emit (nM) S1(t);

[0019] Then emit (nM) more S2(t);

[0020] …

[0021] Launch another (nM) S M+1 (t);

[0022] Then emit (nM) more S1(t);

[0023] Then emit (nM) more S2(t);

[0024] …

[0025] The orthogonal waveform S emitted by the kth pulse m The label m of (t) can be calculated by the following formula:

[0026]

[0027] Where ceil{} represents rounding up; mod[a,b] represents modulo, where a is the dividend, b is the divisor; and n is the fuzzy region ordinal number.

[0028] This process of transmission continues until the pre-set observation time for the main clutter region is reached.

[0029] An electronic device, comprising:

[0030] Processor; and

[0031] Memory is used to store computer program instructions;

[0032] When the computer program instructions are loaded and run by the processor, the processor executes the short-range fuzzy clutter suppression method for reducing the types of orthogonal waveforms used.

[0033] A computer-readable storage medium having stored thereon computer program instructions, which, when loaded and executed by a processor, cause the processor to perform the short-range ambiguity clutter suppression method for reducing the types of orthogonal waveforms used.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] (1) This invention proposes a pulse emission method for reducing the number of orthogonal waveform types in short-range range ambiguity clutter to suppress short-range ambiguity clutter. Compared with existing range ambiguity suppression methods, it can improve the suppression capability of short-range clutter and is applicable to situations where there are multiple range ambiguities in the short range and multiple ambiguity areas outside the short-range area. Especially for situations where the pulse repetition frequency is high and the number of ambiguities in the observable area is large, the number of orthogonal waveforms reduced is greater and the improvement effect is more obvious.

[0036] (2) The method of the present invention can be used for clutter suppression of space-based radar, and can also be used for airborne radar when there is yaw, that is, the azimuth direction of the radar antenna is inconsistent with the direction of platform movement, especially when the antenna is installed as a forward-looking array, that is, the azimuth direction of the antenna is perpendicular to the direction of platform movement, to perform short-range clutter suppression.

[0037] (3) Compared with existing orthogonal waveform fuzzy clutter suppression methods, the present invention uses fewer orthogonal waveforms, making the design of orthogonal waveforms easier and faster;

[0038] (4) Compared with existing orthogonal waveform fuzzy clutter suppression methods, the present invention uses fewer orthogonal waveforms to obtain orthogonal waveforms with better orthogonality, and has a better suppression effect on short-range clutter.

[0039] (5) Compared with existing orthogonal waveform fuzzy clutter suppression methods, the present invention uses fewer orthogonal waveforms, reduces the waveform memory capacity used to store orthogonal waveforms, and reduces waveform memory cost and development difficulty.

[0040] (6) This invention proposes a pulse transmission method for reducing the number of types of orthogonal waveforms in short-range ambiguity clutter. While suppressing short-range clutter, it reduces the types of orthogonal waveforms used, which is beneficial to obtaining orthogonal waveforms with better orthogonality and improving clutter suppression performance.

[0041] (7) The method of the present invention can be used for clutter suppression in space-based radar, and can also be used for short-range clutter suppression in airborne radar when there is yaw, especially when the antenna is installed as a forward-looking array. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the orthogonal waveform transmission and reception of the present invention.

[0043] Figure 2 This is a flowchart of the method of the present invention.

[0044] Figure 3 This is a schematic diagram of the clutter blurring region of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0046] A short-range ambiguity clutter suppression method that reduces the types of orthogonal waveforms used, such as Figure 2 As shown, it includes:

[0047] 1) Determine the range of short-range clutter that needs to be suppressed.

[0048] Based on the radar platform altitude of H km, the maximum distance R of the short-range clutter that needs to be suppressed is determined. n Generally, R is chosen. n =5H, but can be selected according to simulation or actual needs.

[0049] 2) Determine the number of near-range clutter ambiguities, M.

[0050] The fuzzy distance R can be determined based on the PRF. u = c / (2*PRF), where c is the speed of light, approximately taken as 3×10 8 m / s, where PRF is the pulse repetition frequency of the radar system.

[0051] Near-range clutter ambiguity number M = floor(R) n / R u )+1; where floor() is for rounding down.

[0052] 3) Determine the number of orthogonal waveform types to be used and the corresponding orthogonal waveforms;

[0053] To suppress short-range ambiguity clutter, M+1 orthogonal waveforms are required. Let the ideal M+1 orthogonal waveforms be: S m (t), m = 1, 2, ..., M+1;

[0054] Orthogonal signals satisfy the following:

[0055]

[0056] p is an ordinal number;

[0057] Each orthogonal signal satisfies:

[0058]

[0059]

[0060] The value of t ranges from 0 to Tp, where Tp is the length of the transmitted orthogonal waveform pulse and δ is the pulse time difference.

[0061] The M+1 orthogonal waveforms can be selected based on existing orthogonal waveform generation methods.

[0062] 4) Determine which ambiguity region the observed main clutter region is located in.

[0063] The slant range of the nth fuzzy region is (n-1)*Ru to n*Ru; for example Figure 3 As shown.

[0064] Based on the requirements of radar operation, the current search distance is determined to be located in the nth range ambiguity zone.

[0065] 5) Determine the transmission timing of the radar's transmitted orthogonal waveforms.

[0066] According to the PRF, first emit (nM) S1(t);

[0067] Then emit (nM) more S2(t);

[0068] …

[0069] Launch another (nM) S M+1 (t);

[0070] Then emit (nM) more S1(t);

[0071] Then emit (nM) more S2(t);

[0072] …

[0073] The orthogonal waveform S emitted by the kth pulse m The label m of (t) can be calculated by the following formula:

[0074]

[0075] Where ceil{} represents rounding up; mod[a,b] represents modulo, where a is the dividend and b is the divisor;

[0076] This process of transmission continues until the pre-set observation time for the main clutter region is reached.

[0077] 6) The receiving end determines the matching waveform for each received echo and performs matched filtering.

[0078] At the receiving end, the echo is received after the nth transmitted signal, and matched filtering is performed on the echo according to the order of the transmitted orthogonal waveforms to obtain the main clutter region signal that suppresses short-range ambiguity clutter. Assuming the received signal is R(t), and using S... m (t) refers to performing matched filtering. S out (t) represents the output of the matched filter, and τ is the integration variable. Indicates S m (t) Take conjugate.

[0079] Example:

[0080] A short-range ambiguity clutter suppression method for reducing the types of orthogonal waveforms used, flowchart as follows: Figure 2 The specific implementation method is as follows:

[0081] 1) Determine the range of short-range clutter that needs to be suppressed.

[0082] Based on the radar platform's altitude of 10km, the maximum distance R of the short-range clutter that needs to be suppressed is determined. n =50km.

[0083] 2) Determine the number of near-range clutter ambiguities, M.

[0084] The fuzzy distance R can be determined based on the PRF. u = c / (2×PRF), where c is the speed of light, approximately taken as 3×10 8 m / s, where PRF is the pulse repetition frequency of the radar system.

[0085] Near-range clutter ambiguity number M = floor(R) n / R u )+1; where floor() is for rounding down.

[0086] If the PRF is 5000Hz, then R u =30km; near-range clutter ambiguity number M=2.

[0087] 3) Determine the number of orthogonal waveform types and the corresponding orthogonal waveforms to be used;

[0088] To suppress short-range ambiguity clutter, M+1=3 orthogonal waveforms are required. These orthogonal waveforms can be generated using existing orthogonal waveform generation methods.

[0089] 4) Determine which ambiguity region the observed main clutter region is located in.

[0090] The slant range of the nth fuzzy region is (n-1)×Ru~n×Ru; for example Figure 3 As shown.

[0091] Based on the requirements of radar operation, the current search range is determined to be in the fourth range ambiguity zone, namely the slant range of 90km to 120km.

[0092] 5) Determine the timing sequence of the radar's transmitted orthogonal waveforms.

[0093] According to the PRF, the first and second pulses are emitted as S1(t);

[0094] The third and fourth pulses are emitted S2(t);

[0095] Fifth and sixth pulse emission S3(t);

[0096] Seventh and eighth pulse emissions S1(t);

[0097] Ninth and tenth pulse emission S2(t);

[0098] …

[0099] The orthogonal waveform S emitted by the kth pulse m The label m of (t) can be calculated by the following formula:

[0100]

[0101] Where ceil{} represents rounding up; mod[a,b] represents modulo, where a is the dividend and b is the divisor;

[0102] This process of transmission continues until the transmission time reaches the pre-set observation time for the main clutter region.

[0103] The above schematic diagram of the transmitted orthogonal waveforms is shown below. Figure 1 As shown, different shades represent different orthogonal waveforms, with a total of three orthogonal waveforms used. It can be seen that the echo in the fourth blur region is always orthogonal to the echoes in the near-range first and second blur regions that need to be suppressed.

[0104] 6) At the receiving end, the echo is received after the fourth transmitted signal is transmitted, and the echo is matched and filtered according to the order of the transmitted orthogonal waveforms to obtain the main clutter region signal that suppresses the near-range ambiguity clutter. The main clutter region signal includes clutter signal and target signal.

[0105] An electronic device, comprising:

[0106] Processor; and

[0107] Memory is used to store computer program instructions;

[0108] When the computer program instructions are loaded and run by the processor, the processor executes the short-range fuzzy clutter suppression method for reducing the types of orthogonal waveforms used.

[0109] A computer-readable storage medium having stored thereon computer program instructions, which, when loaded and executed by a processor, cause the processor to perform the short-range ambiguity clutter suppression method for reducing the types of orthogonal waveforms used.

[0110] The contents not described in detail in this specification are common knowledge to those skilled in the art.

[0111] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for suppressing short-range ambiguity clutter by reducing the types of orthogonal waveforms used, characterized in that, include: Determine the range of short-range clutter that needs to be suppressed; The ambiguous range R is determined based on the radar system's pulse repetition frequency. u This allows for the determination of the near-range clutter ambiguity number M; R u =c / (2 PRF), where c is the speed of light, PRF is the pulse repetition frequency of the radar system; the number of clutter ambiguities in the near-range region M = floor(R n / R u )+1; where floor() is for flooring down, R n This represents the farthest distance of short-range clutter. Determine the number of orthogonal waveforms to be used and the corresponding orthogonal waveforms; M+1 orthogonal waveforms are used for short-range ambiguity clutter suppression; Determine the ambiguity region where the main clutter region of the observation is located; Determine the timing sequence for transmitting orthogonal waveforms from the radar, and then transmit the orthogonal waveforms. Determine the timing sequence of the radar's transmitted orthogonal waveforms, including: According to the PRF, first emit (nM) S1(t) units; Then emit (nM) more S2(t); … Launch (nM) more S M+1 (t); Then emit (nM) more S1(t); Then emit (nM) more S2(t); … No. k The orthogonal waveform S emitted by each pulse m The label m of (t) is calculated by the following formula: Where ceil{} represents rounding up; mod[a,b] represents modulo, where a is the dividend, b is the divisor; and n is the fuzzy region ordinal number. This process of transmission continues until the pre-set observation time for the main clutter region is reached; Matched filtering is performed on the echoes according to the sequence of transmitted orthogonal waveforms to obtain the main clutter region signal that suppresses near-range ambiguity clutter.

2. The short-range ambiguity clutter suppression method for reducing the types of orthogonal waveforms used according to claim 1, characterized in that, According to the fuzzy distance R u Determine the ambiguity region where the main clutter region of the observation is located.

3. The short-range ambiguity clutter suppression method for reducing the types of orthogonal waveforms used according to claim 1, characterized in that, The M+1 orthogonal waveforms are as follows: m = 1, 2, ..., M+1; Orthogonal signals satisfy the following: ， It is an ordinal number; Each orthogonal signal satisfies: The value range is 0~ , To determine the length of the transmitted orthogonal waveform pulse, For integration variables, This represents the pulse time difference.

4. The short-range ambiguity clutter suppression method for reducing the types of orthogonal waveforms used according to claim 1, characterized in that, The received signal is ,use Matched filtering refers to , For matched filter output, For integration variables, Indicates to Take conjugate.

5. An electronic device, comprising: processor; as well as Memory is used to store computer program instructions; When the computer program instructions are loaded and run by the processor, the processor performs the method as described in any one of claims 1 to 4.

6. A computer-readable storage medium having stored thereon computer program instructions, which, when loaded and executed by a processor, cause the processor to perform the method as described in any one of claims 1 to 4.

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