Radar range ambiguity clutter separation method and system

Abstract

The present invention provides a method and system for separating range-ambiguous clutter of a radar, which relates to the technical field of radar clutter processing, and includes: Step S1: According to the actual situation, perform azimuth pulse coding modulation on the transmitted signal of a multi-channel radar; Step S2: Perform azimuth pulse coding modulation with different phase factors on adjacent frames, and the modulation factors are obtained by theoretical calculation; Step S3: By demodulating the azimuth pulse coding at the receiving end, obtain the received echo signals of two adjacent frames; Step S4: Combine the processing results of adjacent frames to compensate for the detection blind area of the azimuth pulse coding. The present invention can effectively separate the range-ambiguous clutter of a multi-channel radar and overcome the deficiency of the existing azimuth pulse coding method that has a repeated detection blind area.

Description

Technical Field

[0001] The present invention relates to the technical field of radar clutter processing, in particular to a radar range ambiguity clutter separation method based on alternating azimuth pulse coding, and in particular to a radar range ambiguity clutter separation method and system. Background Art

[0002] The clutter in the radar detection environment is always non-uniform and non-stationary. In order to prevent Doppler ambiguity, the pulse repetition frequency should not be too low, and the increase in pulse frequency will bring about range ambiguity. Due to the existence of clutter non-uniformity, clutter in different range ambiguity areas has different statistical distribution characteristics. Therefore, the superposition of range ambiguity clutter to the clutter in the current detection area will significantly increase the degree of freedom and non-uniformity of the clutter, destroying its independent and identically distributed (iid) property, thereby sharply deteriorating the radar's multi-channel clutter cancellation capability and target detection performance.

[0003] Azimuth pulse coding (APC) technology modulates each pulse with an appropriate modulation factor when transmitting it, and then demodulates it with the corresponding demodulation factor at the receiving end, so that the fuzzy clutter component and the detection area clutter are separated in the Doppler frequency domain. APC technology can completely eliminate the influence of surface clutter interference signals, and can be adjusted according to the number of times the range ambiguity occurs, so it can handle more range ambiguities. However, after using APC technology, the range fuzzy clutter produces a series of detection blind areas in the Doppler frequency domain. If the target falls into the detection blind area, the radar's detection performance will be greatly reduced.

[0004] The invention patent with publication number CN1517719 discloses a target signal and clutter separation technology in a "stealth" radar, which utilizes 1. clutter such as direct waves and multipath waves and image carrier waves are in a multiplication relationship, while target scattered waves and them are in an addition relationship; 2. the original carrier component does not exist in the self-orthogonal product of the carrier signal; 3. The core of the separation technology is to obtain related carrier waves and direct waves and multipath waves and self-correlation processing to make the clutter approach zero, so as to achieve the purpose of suppressing clutter. Summary of the invention

[0005] In view of the defects in the prior art, the present invention provides a radar range fuzzy clutter separation method and system.

[0006] According to a radar range fuzzy clutter separation method and system provided by the present invention, the scheme is as follows:

[0007] In a first aspect, a radar range fuzzy clutter separation method is provided, the method comprising:

[0008] Step S1: According to the actual situation, perform azimuth pulse coding modulation on the transmission signal of the multi-channel radar;

[0009] Step S2: Perform azimuth pulse coding modulation with different phase factors on adjacent frames, and the modulation factors are obtained through theoretical calculation;

[0010] Step S3: By performing demodulation of the azimuth pulse coding at the receiving end, obtain the received echo signals of two adjacent frames;

[0011] Step S4: Combine the processing results of adjacent frames to compensate for the detection blind area of the azimuth pulse coding.

[0012] Preferably, first perform azimuth pulse coding on the first frame of the radar transmission signal. Assuming that the radar transmits the k-th pulse signal at this time, its azimuth pulse coding modulation term is exp(jω1(k)), where ε1 is the modulation constant, then the modulated radar transmission pulse signal can be expressed as:

[0013]

[0014] where, represents the transmission signal, f1 represents the first frame, t represents the full-time variable, j represents the imaginary unit, K is the total number of pulse accumulations, rect[] represents the rectangular window function, T PRT is the pulse repetition time, T p is the pulse duration, f c is the carrier frequency, μ is the frequency modulation rate; when considering a total of P ambiguous regions, let

[0015] Preferably, according to the modulation constant of the azimuth pulse coding of the first frame, calculate the azimuth pulse coding modulation constant of the adjacent frame through theory where Q is determined by P, then the transmission pulse signal sequence of the second frame can be expressed as:

[0016]

[0017] Preferably, after performing azimuth pulse coding with different modulation factors on adjacent frames, perform demodulation on them respectively during reception. The demodulation factor of the first frame echo data is expressed as exp(jε1k 2 / 2), and the demodulation factor of its adjacent frame echo data is expressed as exp(jε2k 2 / 2); therefore, the superimposed echo data of adjacent frame data for all P ambiguous regions are respectively:

[0018]

[0019]

[0020] Among them, p1 and p2 satisfy p2 - p1 = P, and f a represents the Doppler frequency, and F PRF is the pulse repetition frequency, and r p,n (t, f a ) is the fast time-Doppler domain echo data received by the nth receiving channel in the pth ambiguity region.

[0021] Preferably, in two frames of echo data, for clutter in different range ambiguity regions, their Doppler frequency shift amounts are different;

[0022] Process adjacent two frames of data jointly to eliminate the influence of the detection blind area in the azimuth pulse coding method.

[0023] In a second aspect, a radar range ambiguity clutter separation system is provided, and the system includes:

[0024] Module M1: According to the actual situation, perform azimuth pulse coding modulation on the transmitted signal of a multi-channel radar;

[0025] Module M2: Perform azimuth pulse coding modulation with different phase factors on adjacent frames, and its modulation factor is obtained by theoretical calculation;

[0026] Module M3: Demodulate the azimuth pulse coding at the receiving end to obtain the received echo signals of adjacent two frames;

[0027] Module M4: Compensate the detection blind area of the azimuth pulse coding by combining the processing results of adjacent frames.

[0028] Preferably, first perform azimuth pulse coding on the first frame of the radar transmitted signal. Assuming that the radar transmits the kth pulse signal at this time, its azimuth pulse coding modulation term is exp(jω1(k)), where ε1 is the modulation constant, and the modulated radar transmitted pulse signal can be expressed as:

[0029]

[0030] Among them, represents the transmitted signal, f1 represents the first frame, t represents the full-time variable, j represents the imaginary unit, K is the total number of pulse accumulations, rect[] represents the rectangular window function, and T PRT is the pulse repetition time, and T p is the pulse duration, and f c is the carrier frequency, and μ is the frequency modulation rate; when considering a total of P ambiguity regions, let

[0031] Preferably, based on the modulation constant of the first frame azimuth pulse coding, calculate the azimuth pulse coding modulation constant of the adjacent frame through theoretical calculation Where Q is determined by P, the transmitted pulse signal sequence of the second frame can be expressed as:

[0032]

[0033] Preferably, after azimuth pulse coding with different modulation factors in adjacent frames, they are demodulated separately during reception. The demodulation factor of the first frame echo data is expressed as exp(jε1k 2 / 2), and the demodulation factor of its adjacent frame echo data is expressed as exp(jε2k 2 / 2); Therefore, the superimposed echo data of adjacent frames for all P ambiguous regions are respectively:

[0034]

[0035]

[0036] Where p1 and p2 satisfy p2 - p1 = P, f a represents the Doppler frequency, F PRF is the pulse repetition frequency, r p,n (t, f a ) is the fast time-Doppler domain echo data received by the nth receiving channel in the pth ambiguous region.

[0037] Preferably, for clutter in different range ambiguous regions in the two-frame echo data, their Doppler frequency shift amounts are different;

[0038] Joint processing of adjacent two-frame data is performed to eliminate the influence of the detection blind area in the azimuth pulse coding method.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The present invention can effectively process range ambiguous clutter, and is simple to implement, with low computational complexity and low system cost consumption, overcoming the deficiencies that the positive and negative linear frequency modulation technology cannot process large-area distributed ambiguous clutter and the range digital beamforming technology has high system costs;

[0041] 2. The present invention can eliminate the detection blind area generated after separating range ambiguous clutter and detection area clutter in traditional azimuth pulse coding, thereby more effectively eliminating the influence of range ambiguous clutter. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] By reading the following detailed description of the non-limiting embodiments with reference to the accompanying drawings, other features, objects, and advantages of the present invention will become more apparent:

[0043] Figure 1 It is a schematic diagram of the overall steps of the present invention;

[0044] Figure 2 It is a schematic diagram of the clutter separation process;

[0045] Figure 3 It is a schematic diagram of the range-Doppler spectrum after alternating azimuth pulse coding provided in the embodiment of the present invention;

[0046] Figure 4 It is the range-Doppler spectrum image of range-ambiguous clutter obtained by simulation;

[0047] Figure 5 It is the range-Doppler spectrum image of clutter after range-ambiguous clutter separation obtained by using the method of the present invention in the simulation for the first frame.

[0048] Figure 6 It is the range-Doppler spectrum image of clutter after range-ambiguous clutter separation obtained by using the method of the present invention in the simulation for the second frame. Detailed implementation manners

[0049] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all belong to the protection scope of the present invention.

[0050] The embodiment of the present invention provides a method for separating range-ambiguous clutter of a radar. Referring to Figure 1 and Figure 2 shown, the method specifically includes:

[0051] Step S1: According to the actual situation, perform azimuth pulse coding modulation on the transmitted signal of the multi-channel radar;

[0052] Step S2: Considering the mode of jointly processing multiple frames of data in actual radar, perform azimuth pulse coding modulation with different phase factors on adjacent frames, and the modulation factor is obtained by theoretical calculation;

[0053] Step S3: Demodulate the azimuth pulse coding at the receiving end to obtain the received echo signals of two adjacent frames;

[0054] Step S4: Combine the processing results of adjacent frames to compensate for the detection blind area of the azimuth pulse coding.

[0055] Specifically, first perform azimuth pulse coding on the first frame of the radar transmitted signal. Assume that the radar transmits the kth pulse signal at this time, then its azimuth pulse coding modulation term is exp(jω1(k)), where ε1 is the modulation constant, and the modulated radar transmitted pulse signal can be expressed as:

[0056]

[0057] Among them, represents the transmitted signal, f1 represents the first frame, t represents the full-time variable, j represents the imaginary unit, K is the total number of pulse accumulations, rect[] represents the rectangular window function, T PRT is the pulse repetition time, T p is the pulse duration, f c is the carrier frequency, and μ is the frequency modulation rate; when considering a total of P ambiguous regions, let

[0058] According to the modulation constant of the azimuth pulse coding of the first frame, the modulation constants of the azimuth pulse coding of adjacent frames are calculated theoretically where Q is determined by P, then the transmitted pulse signal sequence of the second frame can be expressed as:

[0059]

[0060] After using different modulation factors for azimuth pulse coding in adjacent frames, they are demodulated separately during reception. The demodulation factor of the first-frame echo data can be expressed as exp(jε1k 2 / 2), and the demodulation factor of its adjacent-frame echo data can be expressed as exp(jε2k 2 / 2); thus, the superimposed echo data of adjacent-frame data for all P ambiguous regions are respectively:

[0061]

[0062]

[0063] where p1 and p2 satisfy p2 - p1 = P, f a represents the Doppler frequency, F PRF is the pulse repetition frequency, r p,n (t, f a ) is the fast-time - Doppler domain echo data received by the nth receiving channel in the pth ambiguous region.

[0064] In the echo data of two frames, for clutter in different range ambiguous regions, their Doppler frequency shift amounts are different; the adjacent two-frame data are jointly processed to eliminate the influence of the detection blind area in the azimuth pulse coding method.

[0065] Next, the present invention will be described in more detail.

[0066] A method for separating radar range ambiguous clutter, the schematic flow diagram thereof is referred to Figure 1 and Figure 2 as shown, specifically as follows:

[0067] Step S1: According to the actual situation, the azimuth pulse code modulation is performed on the transmission signal of the multi-channel radar. Assuming that the radar transmits the kth pulse signal at this time, its azimuth pulse code modulation term is exp(jω1(k)), where ε1 is the modulation constant, then the modulated radar transmit pulse signal can be expressed as:

[0068]

[0069] in, represents the transmitted signal, f1 represents the first frame, t represents the full time variable, j represents the imaginary unit, K is the total number of pulse accumulations, rect[] represents the rectangular window function, T PRT is the pulse repetition time, T p is the pulse duration, f c is the carrier frequency, μ is the modulation frequency; and considering the existence of P fuzzy regions, let

[0070] Step S2: Adopting azimuth pulse code modulation with different phase factors on adjacent frames, the modulation factor exp(-jε2k 2 / 2), where the constant The selection of Q needs to meet the following optimization conditions:

[0071]

[0072] Among them, Q represents the value to be evaluated in the constant ε2; It means optimizing the expression in the brackets to maximize Q. express and The minimum distance after multiple shifts satisfies:

[0073]

[0074] The Q determined in this way can ensure that the distance between the distance ambiguity clutter in the two frames is the farthest, thereby improving the mutual compensation result of the two frames of data.

[0075] Step S3: By demodulating the azimuth pulse code at the receiving end, the received echo signals of two adjacent frames are obtained as follows:

[0076]

[0077]

[0078] Among them, N c Indicates the number of ground clutter blocks, A p,i Indicates the amplitude of the echo signal, tk is the slow time variable, λ is the radar signal wavelength, B is the signal bandwidth, and R p,n,i (t k ) is the instantaneous slant range of the i-th clutter patch in the p-th ambiguity region at slow time t k with respect to the n-th receiving channel of the radar. For a non-nadir-looking radar with a certain yaw angle, when the depression angle and azimuth angle of the scatterer are and θ i respectively, the instantaneous slant range can be expressed as:

[0079]

[0080] where R 0,i +pc·T PRT / 2 represents the initial slant range of the scatterer from the radar platform, ρ c and φ c represent the yaw amplitude and yaw angle respectively; d T and d n represent the distance from the transmitting channel to the first receiving channel of the radar and the distance from the n-th receiving channel to the first receiving channel respectively. After performing Fourier transform on the demodulated received echo signal in the slow time dimension, the signal forms in the Doppler domain are respectively:

[0081]

[0082]

[0083] where r p,n (t,f a ) is the signal in the Doppler domain when the echo received by the n-th receiving channel in the p-th ambiguity region is not azimuth pulse coded, and can be expressed as:

[0084]

[0085] where c represents the speed of light; V p represents the platform motion speed.

[0086] Step S4: Perform azimuth pulse coding with different modulation factors on adjacent frames respectively. The schematic diagrams are as shown in Figure 2 and Figure 3 . In the two-frame echoes, the frequency shift amounts of the range-ambiguous clutter are inconsistent. Therefore, the detection blind area of the original azimuth pulse coding can be compensated by combining the processing results of adjacent frames.

[0087] Perform simulations according to the operation steps of this embodiment. The parameters of the simulation system used are as follows: the platform height is 508 km, the radar carrier frequency is 1.26 GHz, the pulse repetition frequency is 6000 Hz, the signal bandwidth is 3 MHz, and the number of azimuth receiving channels is 16. All the implementation steps of this embodiment are carried out on the MATLAB 2020 simulation platform. Figure 4 is the range-Doppler spectrum with range ambiguity clutter superimposed together, Figure 5 and Figure 6 are the range-Doppler spectrum images of adjacent frames after alternating azimuth pulse coding by the method proposed in the present invention respectively. It can be seen from the results that the method provided by the present invention can achieve a good separation effect on radar range ambiguity clutter.

[0088] The embodiment of the present invention provides a method and system for separating radar range ambiguity clutter, which can effectively separate the range ambiguity clutter of a multi-channel radar and overcome the deficiency of the existing azimuth pulse coding method that there is a repeated detection blind area.

[0089] Those skilled in the art know that in addition to implementing the system and its various devices, modules, and units provided by the present invention in the form of pure computer-readable program code, the method steps can be logically programmed to make the system and its various devices, modules, and units provided by the present invention be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers, etc. to achieve the same function. Therefore, the system and its various devices, modules, and units provided by the present invention can be regarded as a kind of hardware component, and the devices, modules, and units included therein for implementing various functions can also be regarded as the structures within the hardware component; the devices, modules, and units for implementing various functions can also be regarded as both software modules for implementing the method and structures within the hardware component.

[0090] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for separating radar range ambiguity clutter, characterized in that, Including: Step S1: Perform azimuth pulse coding modulation on the transmitted signal of the multi-channel radar; Step S2: Perform azimuth pulse coding modulation with different phase factors for adjacent frames, and the modulation factors are obtained by theoretical calculation; Step S3: Obtain the received echo signals of two adjacent frames by demodulating the azimuth pulse coding at the receiving end; Step S4: Combine the processing results of adjacent frames to compensate for the detection blind area of the azimuth pulse coding; First, perform azimuth pulse coding on the first frame of the radar transmitted signal. Assuming that the radar transmits the k-th pulse signal at this time, its azimuth pulse coding modulation term is exp(jω1(k)), where ε1 is the modulation constant. Then, the modulated radar transmitted pulse signal can be expressed as: Among them, s f1 (t) represents the transmitted signal, f1 represents the first frame, t represents the full-time variable, j represents the imaginary unit, K is the total number of pulse integrations, rect[] represents the rectangular window function, T PRT is the pulse repetition time, T p is the pulse duration, f c is the carrier frequency, and μ is the frequency modulation rate; when considering a total of P ambiguous regions, let According to the modulation constant encoded by the azimuth pulse of the first frame, the modulation constant of the azimuth pulse encoding of adjacent frames is calculated theoretically Where Q is determined by P, the transmitted pulse signal sequence of the second frame can be expressed as: After azimuth pulse coding with different modulation factors in adjacent frames, demodulation is performed separately during reception. The demodulation factor of the echo data of the first frame is expressed as exp(jε1k 2 / 2), and the demodulation factor of the echo data of its adjacent frame is expressed as exp(jε2k 2 / 2); Therefore, the superimposed echo data of adjacent frame data for all P ambiguous regions are respectively: wherein, p1 and p2 satisfy p2 - p1 = P, fa represents the Doppler frequency, F PRF is the pulse repetition frequency, r p,n (t, f a ) is the fast time-Doppler domain echo data received by the nth receiving channel in the pth ambiguity region.

2. The radar range ambiguity clutter separation method according to claim 1, wherein In the echo data of two frames, for the clutter in different range ambiguity regions, the Doppler frequency shift amounts are different; Combine the data of two adjacent frames for processing to eliminate the influence of the detection blind area in the azimuth pulse coding method.

3. A radar range ambiguity clutter separation system, characterized in that, Including: Module M1: Perform azimuth pulse coding modulation on the transmitted signal of the multi-channel radar; Module M2: Perform azimuth pulse coding modulation with different phase factors for adjacent frames, and the modulation factors are obtained by theoretical calculation; Module M3: Obtain the received echo signals of two adjacent frames by demodulating the azimuth pulse coding at the receiving end; Module M4: Combine the processing results of adjacent frames to compensate for the detection blind area of the azimuth pulse coding; First, perform azimuth pulse coding on the first frame of the radar transmitted signal. Assume that the radar transmits the k-th pulse signal at this time, then its azimuth pulse coding modulation term is exp(jω1(k)), where ε1 is the modulation constant. Then the modulated radar transmitted pulse signal can be expressed as: Among them, represents the transmitted signal, f1 represents the first frame, t represents the full-time variable, j represents the imaginary unit, K is the total number of pulse accumulations, rect[] represents the rectangular window function, T PRT is the pulse repetition time, T p is the pulse duration, f c is the carrier frequency, and μ is the frequency modulation rate; when considering a total of P ambiguous regions, let According to the modulation constant encoded by the azimuth pulse of the first frame, the modulation constant of the azimuth pulse encoding of adjacent frames is calculated theoretically Where Q is determined by P, the transmitted pulse signal sequence of the second frame can be expressed as: After azimuth pulse coding with different modulation factors for adjacent frames, they are demodulated separately during reception. The demodulation factor for the echo data of the first frame is expressed as exp(jε1k 2 / 2), and the demodulation factor for the echo data of its adjacent frame is expressed as exp(jε2k 2 / 2); thus, the superimposed echo data for adjacent frame data for all P ambiguous regions are respectively: wherein, p1 and p2 satisfy p2 - p1 = P, fa represents the Doppler frequency, F PRF is the pulse repetition frequency, r p,n (t, f a ) is the fast time-Doppler domain echo data received by the nth receiving channel in the pth ambiguity region.

4. The radar range ambiguity clutter separation system according to claim 3, characterized in that In the echo data of two frames, for the clutter in different range ambiguity regions, the Doppler frequency shift amounts are different; Combine the data of two adjacent frames for processing to eliminate the influence of the detection blind area in the azimuth pulse coding method.

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