CN111913161A - Method for improving NLFM waveform radar target angle measurement precision - Google Patents

Abstract

The invention discloses a method for improving NLFM waveform radar target angle measurement accuracy. The method includes: performing a first pulse compression process on a radar target echo signal to obtain a first pulse pressure echo signal; The signal is subjected to beamforming processing to obtain the beamforming result; Doppler frequency shift processing is performed on the beamforming result by the Doppler filter to obtain the Doppler frequency estimate; The second pulse pressure echo signal is obtained by the secondary pulse compression processing; the single pulse angle measurement is performed on the second pulse pressure echo signal by the sum-difference beam phase comparison to obtain the radar target angle measurement. The method for improving the angle measurement accuracy of the NLFM waveform radar target provided by the present invention uses the Doppler frequency estimation of the radar target echo signal to design a completely matched impulse response filter to perform pulse compression processing of the radar target echo signal, which is used in The signal-to-noise ratio loss of the angle estimation data is reduced, so the angle measurement accuracy is improved and the performance is stable.

Description

A method to improve the accuracy of NLFM waveform radar target angle measurement

technical field

The invention belongs to the technical field of radar signal processing, and particularly relates to a method for improving the angle measurement accuracy of an NLFM waveform radar target.

Background technique

Non-Linear Frequency Modulation (NLFM) signals can be directly matched and filtered without windowing, which avoids the main lobe broadening and the loss of signal-to-noise ratio caused by windowing. General attention.

In addition to the influence of the parameters of the system itself, the estimation method and the antenna aperture, the target angle measurement accuracy of the radar is also inseparable from the target signal-to-noise ratio. Therefore, to improve the angle measurement accuracy, it can be done by improving the signal-to-noise ratio. The conventional angle measurement method proposed by Zhao Yongbo et al. The target data after signal processing (including pulse compression, beam forming, Doppler filtering, etc.) of the detection channel is measured by the amplitude (or phase) method, and finally the angle of the target is estimated.

However, this method has a loss of signal-to-noise ratio due to its detection channel signal processing. For example, when the radar transmits NLFM waveform, the impulse response filter used for pulse compression does not consider the Doppler information of the target, and its output has a certain signal. Noise ratio loss, so that the target angle measurement accuracy is affected.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems existing in the prior art, the present invention provides a method for improving the accuracy of NLFM waveform radar target angle measurement, including the following steps:

Step 1. Perform the first pulse compression processing on the radar target echo signal to obtain the first pulse pressure echo signal;

Step 2, performing beam synthesis processing on the first pulse pressure echo signal to obtain a beam synthesis result;

Step 3, using a Doppler filter to perform Doppler processing on the beamforming result to obtain an estimated Doppler frequency;

Step 4, performing a second pulse compression process on the radar target echo signal according to the Doppler estimated value to obtain a second pulse pressure echo signal;

Step 5: Performing the sum-difference beam phase comparison monopulse angle measurement on the second pulse pressure echo signal to obtain the radar target angle measurement.

In an embodiment of the present invention, the step 1 specifically includes:

Step 1.1. Obtain the radar target echo signals received by the N array elements. The radar target echo signals are expressed as:

S=[S ₁ , S ₂ ,...,S _N ] ^T ;

Among them, S represents the radar target echo signal, S _i represents the radar target echo signal received by the i-th array element, i=1, 2, 3,..., N, the radar target echo of each array element Signal Si = [S _qr ] _M×R , where S _qr represents the r-th sampling point of the q- _th pulse in the radar target echo signal _Si , M is the number of received pulses for each array element, and R is the radar The number of sampling points in the pulse width of the transmitted signal, [] ^T represents the vector transposition;

Step 1.2. Obtain the pulse compression weight coefficient according to the NLFM waveform transmitted by the radar, and the pulse compression weight coefficient is expressed as:

Y=[F ₁ , F ₂ , . . . , F _R ] ^H ;

Wherein, Y represents the pulse compression weight coefficient, F _r represents the rth value of the pulse compression weight coefficient, r=1, 2, 3..., R, [] ^H represents the vector conjugate transpose;

Step 1.3. Obtain the first pulse pressure echo signal according to the radar target echo signal and the pulse compression weight coefficient, and the first pulse pressure echo signal is expressed as:

X=[X ₁ , X ₂ , .., X _N ] ^T ;

Wherein, X represents the first pulse pressure echo signal, and X _i =S _i Y represents the first pulse pressure echo signal on the i-th array element.

In an embodiment of the present invention, the beamforming result in step 2 is expressed as:

P=a ^H (θ ₀ )X;

Among them, P represents the beamforming result, a(θ ₀ )=[1, exp(j2πdsinθ ₀ /λ),...,exp(j2πd(N-1)sinθ ₀ /λ)] ^T represents the weight vector, and exp represents Exponential power with the base e, j represents the imaginary unit, d represents the spacing of the array elements, and θ ₀ represents the detection beam direction.

In an embodiment of the present invention, the step 3 specifically includes:

Step 3.1, using a Doppler filter to perform Doppler processing on the beamforming result to obtain several amplitude response results;

Step 3.2: Find the frequency point with the largest corresponding amplitude from the several amplitude response results, and obtain the Doppler estimated value according to the corresponding frequency point.

In an embodiment of the present invention, the step 4 specifically includes:

Step 4.1. Perform pulse accumulation on the radar target echo signal according to the Doppler estimated value to obtain a pulse accumulation result, which is expressed as:

G=[G ₁ , G ₂ ,...,G _N ] ^T ;

Among them, G represents the pulse accumulation result, G _i =b(f' _d )S _i represents the pulse accumulation result of the i-th array element, b(f' _d )=[1,exp(j2πf' _d t _r ),. ..,exp(j2πf′ _d ((M-1)t _r )] represents the pilot vector of the target, f _d ' represents the estimated Doppler frequency, and t _r represents the pulse repetition period;

Step 4.2: Update the pulse compression weight coefficient according to the Doppler estimated value to obtain a new pulse compression coefficient, and the new pulse compression coefficient is expressed as:

Q=Y⊙c(f′ _d );

Among them, Q represents the new pulse compression coefficient, c(f' _d )=[1,exp(-j2πf' _d t _s ),...,exp(-j2πf' _d ((R-1)t _s )] ^T represents the Doppler shift function, _ts represents the time interval between adjacent sampling points, and ⊙ represents the Hadamard product;

Step 4.3. Obtain a second pulse pressure echo signal according to the pulse accumulation result and the new pulse compression coefficient, and the second pulse pressure echo signal is expressed as:

Z=[Z ₁ , Z ₂ ,..., Z _N ] ^T ;

Wherein, Z represents the second pulse pressure echo signal, and Z _i =G _i Q represents the second pulse pressure echo signal on the i-th array element.

In an embodiment of the present invention, the step 5 specifically includes:

Step 5.1. Perform the sum-difference beam phase comparison and single-pulse angle measurement on the second pulse pressure echo signal to obtain measurement data, and the measurement data is expressed as:

Wherein, K represents the measurement data, w ₂ =[1,exp(j2πdsinθ ₀ /λ),...,exp(j2πd(N-1)sinθ ₀ /λ)] ^T represents the weight vector of the sum beam, w ₁ = [w ₂ (1:N/2),-w ₂ (N/2+1:N)] represents the weight vector of the difference beam;

Step 5.2, estimate the radar target angle according to the measurement data, and the radar target angle is expressed as:

表示雷达目标测角，||表示求模，a(θ)＝[1,exp(j2πdsinθ/λ),...,exp(j2πd(N-1)sinθ/λ)]^T表示天线阵元的导向矢量，θ表示测角范围。in,

Represents the radar target angle, || represents the modulus, a(θ)=[1, exp(j2πdsinθ/λ),...,exp(j2πd(N-1)sinθ/λ)] ^T represents the antenna element Steering vector, θ represents the angle measurement range.

Compared with the prior art, the beneficial effects of the present invention:

The method for improving the angle measurement accuracy of the NLFM waveform radar target provided by the present invention uses the Doppler frequency estimation of the radar target echo signal to design a completely matched impulse response filter to perform pulse compression processing of the radar target echo signal, using The loss of signal-to-noise ratio for the angle estimation data is reduced, so the angle measurement accuracy is improved and the performance is stable.

Description of drawings

1 is a schematic flowchart of a method for improving the angular measurement accuracy of an NLFM waveform radar target provided by an embodiment of the present invention;

2 is a schematic diagram of the comparison result of the angle root mean square error of the angle measurement when the target angle changes with the conventional angle measurement method and the method provided by the embodiment of the present invention;

3 is a schematic diagram of a comparison result between conventional pulse pressure results and the pulse pressure results of the method provided in the embodiment of the present invention;

FIG. 4 is a partially enlarged schematic diagram of a comparison result of a conventional pulse pressure result and a pulse pressure result of the method provided by an embodiment of the present invention.

Detailed ways

The present invention will be described in further detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

Example 1

Since the NLFM radar waveform is sensitive to the Doppler frequency, the output of the pulse compression will have a loss of signal-to-noise ratio, which will affect the target detection and angle measurement performance of the radar. Therefore, please refer to FIG. 1. FIG. 1 is a schematic flowchart of a method for improving the accuracy of NLFM waveform radar target angle measurement provided by an embodiment of the present invention. An embodiment of the present invention provides a method for improving NLFM waveform radar target angle measurement accuracy. , the method for improving the target angle measurement accuracy of the NLFM waveform radar includes the following steps:

Step 1. Perform a first pulse compression process on the radar target echo signal to obtain a first pulse pressure echo signal.

Specifically, in this embodiment, a uniform linear array including N array elements is used to receive the radar target echo signal, and pulse compression processing is performed on the radar target echo signal. Step 1 specifically includes Step 1.1, Step 1.2, and Step 1.3:

Step 1.1. Obtain the radar target echo signal S received by the N array elements.

Specifically, this embodiment receives radar target echo signals for N array elements. Specifically, the radar target echo signals are expressed as:

S=[S ₁ , S ₂ ,...,S _N ] ^T ;

Among them, S represents the radar target echo signal, S _i represents the radar target echo signal received by the i-th array element, i=1, 2, 3,..., N, the radar target echo of each array element Signal Si = [S _qr ] _M×R , where S _qr represents the r-th sampling point of the q- _th pulse in the radar target echo signal _Si , M is the number of received pulses for each array element, and R is the radar The number of sampling points within the pulse width of the transmitted signal, [] ^T represents the vector transpose.

Step 1.2, obtain the pulse compression weight coefficient according to the NLFM waveform transmitted by the radar.

Specifically, in this embodiment, considering that the NLFM radar waveform is sensitive to the Doppler frequency, the pulse compression weight coefficient is constructed according to the NLFM waveform transmitted by the radar. Specifically, the pulse compression weight coefficient is expressed as:

Y=[F ₁ , F ₂ , . . . , F _R ] ^H ;

Wherein, Y represents the pulse compression weight coefficient, F _r represents the rth value of the pulse compression weight coefficient, r=1, 2, 3..., R, [] ^H represents the vector conjugate transpose.

It should be noted that the pulse compression weight coefficients set corresponding to different radar transmit waveforms are different. Specifically, according to the actual radar transmit waveform settings, the radar transmit waveform in this embodiment is an NLFM waveform.

Step 1.3, obtaining the first pulse pressure echo signal according to the radar target echo signal and the pulse compression weight coefficient.

Specifically, this embodiment calculates the first pulse pressure echo signal according to the radar target echo signal obtained in step 1.1 and the pulse compression weight coefficient obtained in step 1.2. Specifically, the first pulse pressure echo signal is expressed as:

X=[X ₁ , X ₂ , .., X _N ] ^T ;

Wherein, X represents the first pulse pressure echo signal, X _i =S _i Y represents the first pulse pressure echo signal on the i-th array element, i=1, 2, 3,...,N.

In this embodiment, when calculating the first pulse pressure echo signal in step 1.3, the influence of the Doppler frequency shift is not considered, which is the same as the conventional angle measurement method.

Step 2: Perform beam synthesis processing on the first pulse pressure echo signal to obtain a beam synthesis result.

Specifically, in this embodiment, the first pulse pressure echo signal is subjected to beamforming processing through a preset weight vector, and a beamforming result is obtained. Specifically, the beamforming result is expressed as:

P=a ^H (θ ₀ )X;

Among them, P represents the beamforming result, a(θ ₀ )=[1, exp(j2πdsinθ ₀ /λ),...,exp(j2πd(N-1)sinθ ₀ /λ)] ^T represents the preset weight vector , exp represents the exponential power with the base e, j represents the imaginary unit, d represents the array element spacing, and θ ₀ represents the detection beam direction.

Step 3: Doppler processing is performed on the beamforming result by using a Doppler filter to obtain an estimated Doppler frequency.

Specifically, the conventional angle measurement method has a certain loss of signal-to-noise ratio in its output because the pulse response filter of pulse compression does not consider the Doppler information of the target, which affects the accuracy of target angle measurement. Therefore, this embodiment proposes to further conduct radar target angle measurement on the basis of considering Doppler information. Step 3 specifically includes Step 3.1 and Step 3.2:

Step 3.1, using a Doppler filter to perform Doppler processing on the beamforming result to obtain several amplitude response results.

Specifically, during the Doppler processing of the beam synthesis result in this embodiment, since the Doppler frequency is unknown, several Doppler filters are required, and the frequencies of the Doppler filters corresponding to different Doppler filters are Differently, several Doppler filters are used to perform Doppler processing on the beamforming result to obtain several amplitude response results.

Step 3.2: Find the frequency point with the largest corresponding amplitude from several amplitude response results, and obtain the Doppler estimated value according to the corresponding frequency point.

Specifically, after several amplitude response results are obtained in step 3.1, the larger the amplitude, the more the Doppler filter matches the Doppler frequency. Therefore, in this embodiment, the frequency point corresponding to the largest amplitude is found from several amplitude response results. , and determine the Doppler estimated value according to the frequency point, and the pre-estimated value is the Doppler estimated value that will be used to determine the fully matched impulse response filter in this embodiment.

Step 4: Perform a second pulse compression process on the radar target echo signal according to the Doppler estimated value to obtain a second pulse pressure echo signal.

Specifically, after determining the Doppler estimated value according to step 3, use the Doppler estimated value to generate a completely matched impulse response filter, and step 4 specifically includes step 4.1, step 4.2, and step 4.3:

Step 4.1. Perform pulse accumulation on the radar target echo signal according to the Doppler estimated value to obtain the pulse accumulation result.

Specifically, in this embodiment, pulse accumulation is performed on the radar target echo signal through the Doppler estimation value first to obtain a pulse accumulation result. Specifically, the pulse accumulation result is expressed as:

G=[G ₁ , G ₂ ,...,G _N ] ^T ;

Among them, G represents the pulse accumulation result, G _i =b(f' _d )S _i represents the pulse accumulation result of the i-th array element, b(f' _d )=[1,exp(j2πf' _d t _r ),. .., exp(j2πf' _d ((M-1)t _r )] represents the pilot vector of the target, f _d ' represents the estimated Doppler frequency, and _tr represents the pulse repetition period.

Step 4.2: Update the pulse compression weight coefficient according to the Doppler estimated value to obtain a new pulse compression coefficient.

Specifically, this embodiment updates the pulse compression weight coefficient in step 1.2 to obtain a new pulse compression coefficient according to the Doppler estimated value. Specifically, the new pulse compression coefficient is expressed as:

Q=Y⊙c(f′ _d );

Among them, Q represents the new pulse compression coefficient, c(f' _d )=[1,exp(-j2πf' _d t _s ),...,exp(-j2πf' _d ((R-1)t _s )] ^T represents the Doppler shift function, _ts represents the time interval between adjacent sampling points, and ⊙ represents the Hadamard product.

Step 4.3, obtaining a second pulse pressure echo signal according to the pulse accumulation result and the new pulse compression coefficient.

Specifically, in this embodiment, the radar target echo signal and the pulse compression coefficient are respectively considered by the Doppler frequency to obtain the pulse accumulation result after the Doppler frequency consideration and the new pulse compression coefficient, and then according to the pulse accumulation result and the new pulse compression coefficient The new pulse compression coefficient obtains the second pulse pressure echo signal, specifically the second pulse pressure echo signal is expressed as:

Z=[Z ₁ , Z ₂ ,..., Z _N ] ^T ;

Wherein, Z represents the second pulse pressure echo signal, Z _i =G _i Q represents the second pulse pressure echo signal on the i-th array element, i=1, 2, 3,...,N.

Step 5: Perform the sum-difference beam phase comparison monopulse angle measurement on the second pulse pressure echo signal to obtain the radar target angle measurement.

Specifically, in step 4 of this embodiment, a second pulse pressure echo signal Z is obtained through the second pulse compression, and the sum-difference beam phase comparison single-pulse angle measurement is performed on the second pulse pressure echo signal. Step 5 specifically includes step 5.1 , Step 5.2:

Step 5.1. Perform the sum-difference beam phase comparison and single-pulse angle measurement on the second pulse pressure echo signal to obtain measurement data.

Specifically, the present embodiment adopts the single-pulse angle measurement method for phase comparison of sum-difference beams to obtain measurement data corresponding to the angle measurement. Specifically, the measurement data is expressed as:

Wherein, K represents the measurement data, w ₂ =[1,exp(j2πdsinθ ₀ /λ),...,exp(j2πd(N-1)sinθ ₀ /λ)] ^T represents the weight vector of the sum beam, w ₁ = [w ₂ (1:N/2),-w ₂ (N/2+1:N)] represents the weight vector of the difference beam.

Step 5.2, estimating the radar target angle according to the measurement data.

Specifically, the radar target angle is estimated according to the above measurement data K. Specifically, the radar target angle is expressed as:

表示雷达目标测角，||表示求模，a(θ)＝[1,exp(j2πdsinθ/λ),...,exp(j2πd(N-1)sinθ/λ)]^T表示天线阵元的导向矢量，θ表示测角范围。in,

Represents the radar target angle, || represents the modulus, a(θ)=[1, exp(j2πdsinθ/λ),...,exp(j2πd(N-1)sinθ/λ)] ^T represents the antenna element Steering vector, θ represents the angle measurement range.

The method for improving the angle measurement accuracy of a radar target with an NLFM waveform proposed in this embodiment uses the output results of pulse compression processing (without considering Doppler information) and beamforming processing in sequence to determine the Doppler frequency of the radar target echo signal. The estimated value of Doppler frequency is obtained by estimating, and then the estimated value of Doppler frequency is used to generate a completely matched impulse response filter, which is used to perform pulse compression on the original radar target echo signal. , and finally the radar target angle is measured by comparing the phase and monopulse angle of the pulse compression data with the difference beam.

In order to illustrate the effectiveness of the method for improving the NLFM waveform radar target angle measurement accuracy proposed by the present invention, the following computer simulations are used to verify:

1. Simulation conditions

In the simulation, radar transmit signal bandwidth B=2MHz, transmit pulse time width _Tp =300μs, target Doppler frequency _fd =10kHz, radar antenna array element number N=10, wavelength λ=0.05m, array element spacing d= 0.025m, using sum-difference beam phase-comparison monopulse angle measurement method, sum beam pointing at 0°, single-array element SNR=10dB, sampling frequency f _s = 10MHz, target Doppler frequency estimate f' _d = 10.01kHz, Monte Carlo experiment 1000 times.

2. Simulation content

Simulation 1, please refer to FIG. 2. FIG. 2 is a schematic diagram of the comparison result of the angle root mean square error of the angle measurement when the target angle changes between the conventional angle measurement method and the method provided by the embodiment of the present invention. Using the above conditions, through simulation, the conventional measurement method is obtained. The change curve of the angle measurement accuracy when the target angle changes between the angle method and the method of the present invention is shown in Figure 2, wherein the abscissa is the target angle, and the ordinate is the root mean square error of the angle. It can be seen from FIG. 2 that the root mean square error of the conventional angle measurement method and the angle measurement method of the present invention will vary with the change of the target angle. However, the target angle root mean square error of the present invention is smaller. FIG. 2 can fully illustrate that the method of the present invention has higher angle measurement accuracy and more stable performance, and can indeed improve the NLFM waveform angle measurement accuracy.

Simulation 2, please refer to FIG. 3 and FIG. 4 , FIG. 3 is a schematic diagram of the comparison result between the conventional pulse pressure result and the pulse pressure result of the method provided by the embodiment of the present invention, and FIG. 4 is the comparison between the conventional pulse pressure result and the method provided by the embodiment of the present invention. Schematic diagram showing the partial enlargement of the comparison results of the pulse pressure results. Using the above conditions, the target angle is selected as 0°, and the output results of the NLFM pulse compression of the beam are shown in Figure 3, where the abscissa is the distance unit (unit is units), and the ordinate is is the amplitude value of the output signal (normalized by the maximum value of the pulse pressure output according to the method of the present invention). It can be seen from Fig. 3 that there are 5999 points in the distance unit; Fig. 4 is a partial enlarged view of Fig. 3. It can be seen from Fig. 4 that the pulse compression output of the conventional goniometric method has a spectral shift, and the peak power decreases, while the method of the present invention has a This result does not appear in the pulse compression output; it can be further seen from Fig. 4 that the pulse compression result of the conventional angle measurement method will have a direct impact on the angle estimation result due to the reduction of the signal-to-noise ratio; however, the method of the present invention compensates for this, The matched filter designed considering the Doppler frequency improves the signal-to-noise ratio and further improves the angle measurement accuracy. Therefore, the method of the present invention has obvious advantages.

To sum up, the method for improving the angle measurement accuracy of the NLFM waveform radar target provided in this embodiment uses the Doppler frequency estimation of the radar target echo signal to design a completely matched impulse response filter to measure the radar target echo signal. The pulse compression processing of the method reduces the loss of the signal-to-noise ratio of the angle estimation data, so the angle measurement accuracy is improved and the performance is stable.

The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deductions or substitutions can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (6)

1. a method for improving NLFM waveform radar target angle measurement accuracy, is characterized in that, comprises the steps: Step 1. Perform the first pulse compression processing on the radar target echo signal to obtain the first pulse pressure echo signal; Step 2, performing beam synthesis processing on the first pulse pressure echo signal to obtain a beam synthesis result; Step 3, using a Doppler filter to perform Doppler processing on the beamforming result to obtain an estimated Doppler frequency; Step 4, performing a second pulse compression process on the radar target echo signal according to the Doppler estimated value to obtain a second pulse pressure echo signal; Step 5: Performing the sum-difference beam phase comparison monopulse angle measurement on the second pulse pressure echo signal to obtain the radar target angle measurement. 2. the method for improving NLFM waveform radar target angle measurement accuracy according to claim 1, is characterized in that, described step 1 specifically comprises: Step 1.1. Obtain the radar target echo signals received by the N array elements. The radar target echo signals are expressed as: S=[S ₁ , S ₂ ,...,S _N ] ^T ; Among them, S represents the radar target echo signal, S _i represents the radar target echo signal received by the i-th array element, i=1, 2, 3,..., N, the radar target echo of each array element Signal Si = [S _qr ] _M×R , where S _qr represents the r-th sampling point of the q- _th pulse in the radar target echo signal _Si , M is the number of received pulses for each array element, and R is the radar The number of sampling points in the pulse width of the transmitted signal, [] ^T represents the vector transposition; Step 1.2. Obtain the pulse compression weight coefficient according to the NLFM waveform transmitted by the radar, and the pulse compression weight coefficient is expressed as: Y=[F ₁ , F ₂ , . . . , F _R ] ^H ; Wherein, Y represents the pulse compression weight coefficient, F _r represents the rth value of the pulse compression weight coefficient, r=1, 2, 3..., R, [] ^H represents the vector conjugate transpose; Step 1.3. Obtain the first pulse pressure echo signal according to the radar target echo signal and the pulse compression weight coefficient, and the first pulse pressure echo signal is expressed as: X=[X ₁ , X ₂ , .., X _N ] ^T ; Wherein, X represents the first pulse pressure echo signal, and X _i =S _i Y represents the first pulse pressure echo signal on the i-th array element. 3. the method for improving the NLFM waveform radar target angle measurement accuracy according to claim 2, is characterized in that, in described step 2, beam synthesis result is expressed as: P=a ^H (θ ₀ )X; Among them, P represents the beamforming result, a(θ ₀ )=[1, exp(j2πdsinθ ₀ /λ),...,exp(j2πd(N-1)sinθ ₀ /λ)] ^T represents the weight vector, and exp represents Exponential power with the base e, j represents the imaginary unit, d represents the spacing of the array elements, and θ ₀ represents the detection beam direction. 4. the method for improving NLFM waveform radar target angle measurement accuracy according to claim 3, is characterized in that, described step 3 specifically comprises: Step 3.1, using a Doppler filter to perform Doppler processing on the beamforming result to obtain several amplitude response results; Step 3.2: Find the frequency point with the largest corresponding amplitude from the several amplitude response results, and obtain the Doppler estimated value according to the corresponding frequency point. 5. the method for improving NLFM waveform radar target angle measurement accuracy according to claim 4, is characterized in that, described step 4 specifically comprises: Step 4.1. Perform pulse accumulation on the radar target echo signal according to the Doppler estimated value to obtain a pulse accumulation result, which is expressed as: G=[G ₁ , G ₂ ,...,G _N ] ^T ; Among them, G represents the pulse accumulation result, G _i =b(f' _d )S _i represents the pulse accumulation result of the i-th array element, b(f' _d )=[1,exp(j2πf' _d t _r ),. ..,exp(j2πf′ _d ((M-1)t _r )] represents the pilot vector of the target, f _d ' represents the estimated Doppler frequency, and t _r represents the pulse repetition period; Step 4.2: Update the pulse compression weight coefficient according to the Doppler estimated value to obtain a new pulse compression coefficient, and the new pulse compression coefficient is expressed as: Q=Y⊙c(f′ _d ); Among them, Q represents the new pulse compression coefficient, c(f' _d )=[1,exp(-j2πf' _d t _s ),...,exp(-j2πf' _d ((R-1)t _s )] ^T represents the Doppler shift function, _ts represents the time interval between adjacent sampling points, and ⊙ represents the Hadamard product; Step 4.3. Obtain a second pulse pressure echo signal according to the pulse accumulation result and the new pulse compression coefficient, and the second pulse pressure echo signal is expressed as: Z=[Z ₁ , Z ₂ ,..., Z _N ] ^T ; Wherein, Z represents the second pulse pressure echo signal, and Z _i =G _i Q represents the second pulse pressure echo signal on the i-th array element. 6. the method for improving NLFM waveform radar target angle measurement accuracy according to claim 5, is characterized in that, described step 5 specifically comprises: Step 5.1. Perform the sum-difference beam phase comparison and single-pulse angle measurement on the second pulse pressure echo signal to obtain measurement data, and the measurement data is expressed as:

Wherein, K represents the measurement data, w ₂ =[1,exp(j2πdsinθ ₀ /λ),...,exp(j2πd(N-1)sinθ ₀ /λ)] ^T represents the weight vector of the sum beam, w ₁ = [w ₂ (1:N/2),-w ₂ (N/2+1:N)] represents the weight vector of the difference beam; Step 5.2, estimate the radar target angle according to the measurement data, and the radar target angle is expressed as:

in,

Represents the radar target angle, | | represents the modulus, a(θ)=[1, exp(j2πdsinθ/λ),...,exp(j2πd(N-1)sinθ/λ)] ^T represents the antenna element Steering vector, θ represents the angle measurement range.

Images