Compensation method for digital phased array radar receiving beam forming direction change

Abstract

The invention relates to a digital phased array radar receiving beam forming pointing change compensation method, and belongs to the technical field of radar signal processing. Through the two steps of integrated architecture and engineering application operation, real-time calculation and compensation of azimuth angle sine value stepping are carried out in the resident digital beam forming process according to a pulse group, and digital beam forming is carried out on a weighting coefficient of digital beam forming. The pointing precision of a resident receiving beam in a radar in an omnibearing early warning mode to stably point to a target space is effectively improved, the problem that the measurement precision or the measurement effect becomes poor due to receiving beam pointing change caused by radar servo rotation is perfectly solved, and the measurement precision and the measurement effect of the radar in the omnibearing early warning mode are remarkably improved; angle compensation, weighting coefficient calculation and digital beam forming are achieved through one FPGA, the hardware architecture cost and the software and hardware design difficulty are reduced, the real-time requirement for signal processing is met, the radar measurement precision and adaptability are improved, and engineering implementation is facilitated.

Description

Technical Field

[0001] The present invention relates to a compensation method for the change of the receiving beam synthesis direction of a digital phased array radar, belonging to the technical field of radar signal processing. Background Art

[0002] In the all-round early warning mode of modern digital phased array radars, it is required that the spatial direction of the receiving beam be consistent with the spatial direction of the target within the dwell time of the radar. Within one dwell, the azimuth angle and elevation angle of the digital beam direction of the radar are fixed. However, due to the servo uniform rotation process of the radar antenna array surface, the azimuth angle of the radar array surface will change, resulting in the inconsistent spatial direction of the synthesized receiving beam and the actual target spatial direction. The change in spatial direction will cause the accuracy of the azimuth angle measured by the radar for the target to deteriorate or the measured azimuth angle to deviate too much from the actual target space, seriously affecting the measurement accuracy and effect of the digital phased array radar. Summary of the Invention

[0003] The purpose of the present invention is to provide a compensation method for the change of the receiving beam synthesis direction of a digital phased array radar, aiming at the problem that the change of the receiving beam synthesis direction caused by servo rotation within the dwell time in the all-round early warning mode of the digital phased array radar seriously affects the measurement accuracy and effect of the digital phased array radar. This method calculates and compensates the sine value of the azimuth angle step by step in real time according to the pulse group during the digital beam synthesis process within the dwell time, and performs digital beam synthesis on the weighting coefficients of the digital beam synthesis, effectively improving the pointing accuracy of the receiving beam stably pointing to the target space within the dwell time in the all-round early warning mode of the radar, perfectly solving the problem of the deterioration of the measurement accuracy or effect caused by the change of the receiving beam direction caused by radar servo rotation, and significantly improving the measurement accuracy and measurement effect in the all-round early warning mode of the radar; at the same time, this method realizes compensation calculation, beam synthesis weighting coefficient calculation and beam synthesis based on a single FPGA (Field Programmable Gate Array) device. Compared with the traditional DSP+FPGA architecture for realizing corresponding functions, it not only reduces the hardware cost, but also reduces the difficulty of engineering implementation and debugging, and improves the integration degree of the radar system; and within the dwell time of the radar, according to the parameterized control of the number of pulse groups and the parameterized control of the compensation accuracy, the weighting coefficients of the digital beam synthesis after compensation within the dwell time are calculated in real time, realizing compensation adjustment in different terrain environments and for different measurement targets, with strong environmental adaptability.

[0004] The present invention realizes the above purpose through the following technical solutions: A compensation method for the change of the receiving beam synthesis direction of a digital phased array radar, with the hardware platform being an FPGA programmable logic controller and the software being Vivado; its characteristics are: the compensation method for the change of the receiving beam synthesis direction of this digital phased array radar is realized through the following steps: I. Integrated Architecture 1.1) Implement a DSP+FPGA integrated architecture through an FPGA chip. First, calculate the beamforming compensation weighting coefficients, and then perform digital beamforming based on the beamforming compensation weighting coefficients to achieve the purpose of stable beam pointing within a dwell. The calculation formulas for the beamforming compensation weighting coefficients are shown in (3) and (4): where f is the signal frequency, C is the speed of light constant, X and Z are the coordinates of the radar array elements, α is the azimuth angle, β is the elevation angle, n is the number of pulse groups, Δsinα is the sine value compensation step, and sumW win is the sum beam window type and gain control parameter, and diffW win is the difference beam window type and gain control parameter; 1.2) Parametric design: Model the beamforming compensation algorithm and extract the key influencing factors, including: signal frequency f, sine value of azimuth angle sinα, cosine value of elevation angle cosβ, azimuth angle sine compensation step Δsinα, number of pulses per pulse group within a dwell n, window type and gain of sum beam or difference beam sumW win and diffW win ; Dynamically configure these key influencing factors parametrically to enhance the generality and adaptability of the algorithm; 1.3) Azimuth angle α compensation: Perform azimuth angle α compensation within a dwell according to pulse group control and azimuth angle sine compensation step Δsinα control; 1.4) Ping-pong operation: Store the beamforming weighting coefficients in RAM(a) and RAM(b) to solve the problem of mismatch with radar echo data due to delays in compensation calculation and weighting coefficient calculation; 1.5) Trigonometric function operation: Use cordic IP to implement the trigonometric function calculation process of the beam space pointing angle θ in the FPGA to complete the calculation of the final beamforming weighting coefficients.

[0005] II. Engineering application operations: 2.1) Complete azimuth angle α compensation calculation, beamforming weighting coefficient calculation, and digital beamforming within the same FPGA; 2.2) According to the calculation method of the compensation weighting coefficients in Step 1, perform parametric design on f, sinα, cosβ, n, Δsinα, sumW win and diffW win and have the FPGA receive these parameter controls to complete the calculation process in Step 1; 2.3) Use the official CORDIC IP core of Xlinx to implement trigonometric function calculation to complete the trigonometric function calculation process of the beam space pointing angle θ; 2.4) By calculating in advance the compensated azimuth sine value of the next upcoming pulse group and combining pulse group count control, ping-pong writing and reading are performed on two RAMs (a and b) to solve the problem of mismatch between the weighted coefficient calculation delay and the echo data; 2.5) Through the pulse group count control parameter and the azimuth sine value step control parameter, parametric control of the compensation is carried out; 2.6) Two-level ping-pong control to ensure the matching of the compensated weighted coefficient and the radar array sampling echo data; 2.7) Window type and gain control calculation, performing complex multiplication operation on the window type and gain coefficient required by the system and the result of trigonometric function calculation to obtain the weighted coefficient for beam synthesis.

[0006] The beneficial effects of the present invention compared with the prior art are as follows: This compensation method for the change of the receiving beam synthesis pointing of the digital phased array radar combines the receiving beam pointing compensation calculation and the beam synthesis weighted coefficient calculation algorithm. By performing azimuth sine value stepping according to pulse groups within a dwell, it approximately compensates for the change of the receiving beam pointing within the dwell caused by the rotation of the servo, improves the stability and pointing accuracy of the receiving beam, and achieves the purpose of improving the radar measurement accuracy. The hardware development and software design of the traditional FPGA+DSP architecture are both relatively complex, and the method of calculating the weighted coefficient by the CPU and then sending it to the FPGA cannot guarantee the data transmission delay; implementing angle compensation, weighted coefficient calculation, and digital beam synthesis through one FPGA reduces the hardware architecture cost and the design difficulty of software and hardware, while ensuring the real-time requirement of signal processing, effectively compensating for the pointing change of the receiving beam caused by the servo rotation in the all-round early warning mode of the radar, greatly improving the accuracy and adaptability of radar measurement, and facilitating engineering implementation. It solves the problem of deterioration of radar measurement accuracy or effect caused by the change of the receiving beam pointing due to radar servo rotation. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a schematic diagram of the working principle flow of the present invention; Figure 2 It is a schematic diagram of the azimuth compensation principle of the present invention; Figure 3 It is a diagram of the weighted coefficient calculation formula for the uncompensated azimuth; Figure 4 It is a diagram of the weighted coefficient calculation formula after azimuth compensation modeling of the present invention; Figure 5 It is a configuration reference diagram of the CORDIC IP for trigonometric function calculation of the present invention; Figure 6 It is a schematic diagram of the digital beam synthesis principle of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] The following further elaborates on the implementation of the compensation method for the change in the receiving beam synthesis pointing of the digital phased array radar of the present invention in conjunction with the accompanying drawings (see Figures 1 to 6 ): A compensation method for the change in the receiving beam synthesis pointing of a digital phased array radar, with its hardware platform being an FPGA programmable logic controller and its software being Vivado; its characteristics are: the implementation of the compensation method for the change in the receiving beam synthesis pointing of the digital phased array radar includes: Step 1. Implement engineering applications using the hardware architecture 1.1) In the DSP+FPGA architecture implemented through an FPGA chip, the DSP calculates the beam synthesis compensation weighting coefficients, and the FPGA performs digital beam synthesis based on the weighting coefficients calculated by the DSP to achieve the purpose of stable beam pointing within a dwell.

[0009] 1.2) Parametric design, model the compensation algorithm, extract the key influencing factors, and perform parametric dynamic configuration on the key influencing factors to improve the adaptability of the compensation method.

[0010] The key influencing factors, also known as key compensation factors, include: signal frequency f, sine value of azimuth angle sinα, cosine value of elevation angle cosβ, sine compensation step of azimuth angle Δsinα, number of pulses in a pulse group within a dwell n, and window type and gain of sum beam or difference beam; The window type and gain control parameter of the sum beam is sumW win ; The window type and gain control parameter of the difference beam is diffW win .

[0011] 1.3) Azimuth angle α compensation, perform azimuth angle α compensation within a dwell according to pulse group count control and sine compensation step of azimuth angle Δsinα control; Azimuth angle α, elevation angle β.

[0012] 1.4) Ping-pong operation, use two rams (a and b), namely RAM(a) and RAM(b), to store the weighting coefficients of beam synthesis, and solve the problem of mismatch between the compensation calculation and the weighting coefficient calculation delay and the echo data used by the radar.

[0013] 1.5) Trigonometric function operation, use cordic IP to implement trigonometric operations in the FPGA to complete the trigonometric function calculation process of the beam space pointing angle θ; finally, complete the calculation of the beam synthesis weighting coefficients.

[0014] Step 2. The actual application operation of the compensation method for the change in the receiving beam synthesis pointing of the digital phased array radar is as follows: 2.1) Complete the azimuth angle compensation calculation, beam synthesis weighting coefficient calculation, and digital beam synthesis within the same FPGA (see Figure 1 ).

[0015] 2.2) Analyze the beam pointing change and model the compensation method. The final sum-difference beam compensation weighting coefficient formula obtained from the formula derivation after modeling is as shown in (3) and (4) (see Figure 4 ).

[0016] 2.3) According to the calculation method of the sum-difference beam compensation weighting coefficient in step 2.2), parameterize f, sinα, cosβ, n, Δsinα, sumW win and diffW win , and the FPGA receives these parameters to achieve parameterized control (see Figure 1 ).

[0017] 2.4) Use the official CORDIC IP core of Xlinx to implement the trigonometric function calculation and complete the trigonometric function calculation process of the beam space pointing angle θ (see Figure 5 ), Figure 5 is the configuration reference diagram of the CORDIC IP for the trigonometric function calculation of the present invention; where X and Z are the coordinates of the radar array elements, Sinα is the sine value of the azimuth angle, cosβ is the cosine value of the elevation angle, and f is the signal frequency.

[0018] 2.5) By pre-calculating the sine value of the azimuth angle after compensation for the next upcoming pulse group, mainly solve the problem of the delay in calculating the weighting coefficient (see Figure 1 ).

[0019] 2.6) Two-level ping-pong control to ensure the matching of the compensated weighting coefficient and the radar array sampled echo data (see Figure 1 ).

[0020] 2.7) Window type and gain control calculation. Perform complex multiplication on the window type and gain coefficient required by the system and the result of the trigonometric function calculation to obtain the weighting coefficient for beam synthesis (see Figure 1 ).

[0021] 2.8) Digital beam synthesis. After the echo data sampled by the radar array is channel-aligned, perform complex multiplication by channel with the weighting coefficient read from the RAM, and accumulate the results of the complex multiplication to obtain the synthesized beam (see Figure 1 and Figure 6 ). The specific embodiments are as follows

[0022] Complete the azimuth angle compensation calculation, beam synthesis weighting coefficient calculation, and digital beam synthesis within the same FPGA, achieving stable pointing of the received beam during dwell and improving the beam pointing accuracy (see Figure 1 ).

[0023] Modeling of the azimuth angle compensation method. In the all-round early warning mode of the phased array radar, the starting time of the dwell is t0, and the ending time of the dwell is t. At the moment of t0, the digital beam pointing information is sent. At this time, the azimuth angle formed by the normal line of the radar array surface and the position of the target is α. Due to the rotation of the array servo, the actual normal line of the radar array surface is changing, and thus the azimuth angle α formed with the target is also changing.

[0024] At the moment of t when the dwell ends, the actual azimuth angle formed by the normal line of the radar array surface and the target is α t , within the time range from t0 to t, the azimuth angle is constantly changing. In order to make the pointing of the received beam stably point to the target, it is necessary to compensate the azimuth angle α within the dwell.

[0025] Trigonometric function operations are non-linear. In order to make the engineering implementation easier, and the actual azimuth angle α uses the sine value of the azimuth angle sinα when participating in the final coefficient calculation. Therefore, the present invention uses the step of the sine value of the azimuth angle Δsinα to achieve the compensation of the azimuth angle α, effectively improving the spatial pointing accuracy of the received beam.

[0026] Using the step of the sine value of the azimuth angle Δsinα to achieve the compensation of the azimuth angle α, there is the following relationship: within the time range from t0 to t, there are N pulses. Divide the N pulses into n groups, and perform the sine value compensation step of Δsinα according to the pulse groups. Then at n the moment of t, the sine value of the azimuth angle after compensation for the nth pulse group is sinαt = sinα + n * Δsinα, (see Figure 2 ).

[0027] The calculation process and formula of the beam synthesis weighting coefficient are as follows: W sum = (sinθ + i * cosθ) · sumW win The formula for the difference beam weighting coefficient is: W diff = (sinθ + i * cosθ) · diffW win where sumW win is the sum beam window type and gain control parameter, diffW win is the difference beam window type and gain control parameter, θ is the pointing angle of the digital beam synthesis, and · represents complex multiplication calculation.

[0028] The calculation formula for the pointing angle of digital beamforming is as follows: where f is the frequency of the signal, c is the speed of light constant, X and Z are the coordinates of the radar array elements, α is the azimuth angle, and β is the elevation angle. Then, the calculation formula for the beamforming weighting coefficient during step compensation is derived (see Figure 3 ). Figure 3 Formula (1) in Figure 3 is the calculation method for the sum beam weighting coefficient: According to Figure 3 the compensation model of formulas (1) and (2) in Figure 4 , the calculation method for the beamforming weighting coefficient for azimuth angle compensation is obtained (see

[0029] Figure 4 Formula (3) in Figure 4 is the calculation method for the sum beam weighting coefficient after compensation: Extract these key factors such as the signal frequency f, the sine value of the azimuth angle sinα, the cosine value of the elevation angle cosβ, the number of pulses n in the dwell internal pulse group, the window type and gain, and the step of azimuth angle sine compensation Δsinα. By parameterizing these key factors for control, the compensation calculation can achieve dynamic real-time adjustment according to the change of control parameters in different scenarios and different target situations, improving the adaptability of the compensation method (see Figure 1 ).

[0030] Calculate in advance the sine value of the azimuth angle sinα after compensation for the next upcoming pulse group. The pulse group counting module has n pulses for the pulse group controlled by the system. The pulse counting control receives the sampled echo data of the radar array. It generates a trigger signal every time n pulses are received, and at the same time, the pulse group counter is incremented by 1. The azimuth angle compensation calculation performs azimuth angle α compensation calculation based on the trigger signal and the pulse group counter; combined with the pulse group counting control, ping-pong writing and reading are performed on two RAMs (a and b) to solve the problems of calculation delay of the weighting coefficient and coefficient switching delay (see Figure 1 ).

[0031] Two-level ping-pong control RAM (a and b). When performing digital beamforming using the beamforming weighting coefficients stored in RAM (a), the beamforming weighting coefficients required for the next pulse group are calculated in parallel according to the azimuth angle α compensation value of the next pulse group and stored in RAM (b). When performing beamforming using the beamforming weighting coefficients stored in RAM (b) after the next pulse group arrives, the beamforming weighting coefficients required for the pulse group after the next one are calculated in parallel according to the azimuth angle α compensation value of the pulse group after the next one and stored in RAM (a). During one dwell inner loop, the compensated beamforming weighting coefficients in RAM (a) and RAM (b) are updated in a ping-pong manner.

[0032] Write ping-pong control. According to the parity of the pulse group counter, cordic trigonometric operations, window type, and gain calculations are performed, and the calculation results are written into the RAM. When it is odd, the results of CORDIC (b) and window type and gain calculations are written into RAM (b), and when it is even, the results of CORDIC (a) and window type and gain calculations are written into RAM (a).

[0033] Read ping-pong control. According to the parity of the pulse group counter, the RAM reading control is performed. When it is odd, RAM (a) is read, and when it is even, RAM (b) is read (see Figure 1 ).

[0034] Trigonometric function calculation. The beam spatial pointing θ is calculated according to the calculation formula. The original θ value calculated will be greater than [-π, π]. Using the periodicity of trigonometric functions, the beamforming spatial pointing θ is quantized to between [-π, π] without affecting the results of trigonometric function calculations. The quantized angle θ is passed through the CORDIC IP calculation to obtain a complex number: (sinθ + i*cosθ); (see Figure 5 ), Figure 5 which is the configuration reference diagram of the CORDIC IP for trigonometric function calculation of the present invention.

[0035] Window type and gain control calculation. For the convenience of engineering implementation, the sum beam window type and gain coefficient file and the difference beam window type and gain coefficient file are stored in the ROM respectively. According to the window type and gain control, the ROM address is indexed to read the corresponding window type and gain coefficients, and complex multiplication is performed with the results of trigonometric function calculations to finally obtain the compensated beamforming weighting coefficients (see Figure 1 ).

[0036] Digital beamforming. The echo data sampled by the radar array are aligned in channels and then subjected to complex multiplication by channels with the weighting coefficients read from the RAM. Assume the number of channels of the radar array is m, denoted as x m (n), and the number of beams to be synthesized is k, denoted as Yk (n), the beam synthesis is understood as a two-dimensional matrix multiplication operation. The array face channel matrix is [1, m], the weighting coefficient matrix is [m, k], and after the matrix multiplication operation, the matrix [1, k] obtained is the synthesized beam (see Figure 1 and Figure 6 ).

[0037] The compensation method for the change of the receiving beam synthesis pointing of the digital phased array radar is implemented based on the Xilinx FPGA. From the perspective of facilitating engineering implementation, by establishing an azimuth compensation model in the radar dwell according to the step of the sine value of the azimuth angle of the pulse group, extracting key factors through formula derivation for parametric control, calculating the compensation value and the beam synthesis weighting coefficient in advance, and according to the parity of the counter in the pulse group count control, controlling the two-level ping-pong read-write management strategy of the weighting coefficient storage space, combining the window type and the gain control coefficient into a coe file and storing it inside the FPGA, obtaining the required coefficient through address indexing, quantifying the real-time beam space pointing angle θ using the periodicity of the trigonometric function and then performing trigonometric function calculation using the cordic IP, and fully utilizing the parallel processing ability of the FPGA to integrate the compensation calculation, the beam synthesis coefficient calculation and the digital beam synthesis functions onto one FPGA.

[0038] The compensation method for the change of the receiving beam synthesis pointing of the digital phased array radar models from the perspective of engineering implementation, and adopts the step compensation of the sine value of the radar azimuth angle according to the pulse group, effectively compensating the change of the receiving beam pointing caused by the servo rotation during the dwell in the all-round early warning mode of the radar, achieving the effect of stable receiving beam pointing during the dwell and improving the receiving beam pointing accuracy.

[0039] By extracting key factors through formula derivation for parametric control, the adaptability of the compensation method of the present invention to different scenarios is improved. By calculating the azimuth angle α compensation value and the compensated beam synthesis weighting coefficient in advance, the problem that the beam synthesis weighting coefficient cannot be changed between pulses due to calculation delay is solved.

[0040] By controlling the parity of the counter through the pulse group count, performing two-level ping-pong read-write management on the beam synthesis weighting coefficient storage space, the matching problem between the beam synthesis weighting coefficient and the radar array face sampled echo data is solved; by quantifying the beam space pointing to make it adapt to the cordic IP, combining the window type and the gain control into a file for storage, and simplifying the calculation through address indexing, the real-time performance of the calculation is improved. Integrating the azimuth angle α compensation calculation, the beam synthesis weighting coefficient calculation and the digital beam synthesis into one FPGA improves the integration degree of the system, reduces the hardware cost and the design and development difficulty.

[0041] The above are only the preferred embodiments of the present invention. The above examples do not impose any formal restrictions on the essence of the present invention. Any simple modification or variation made by those of ordinary skill in the art in the relevant technical field to the above specific embodiments after reading this specification, and any equivalent embodiments that may be changed or modified by using the disclosed technical content into equivalent variations, still fall within the scope of the technical solution of the present invention without departing from the essence and scope of the present invention.

Claims

1. A method for compensating for changes in the receiving beam synthesis pointing of a digital phased array radar, wherein the hardware platform is an FPGA programmable logic controller and the software is Vivado; the method is characterized in that: the method for compensating for changes in the receiving beam synthesis pointing of a digital phased array radar is implemented by comprising the following steps:

1. Integrated Architecture 1.1) A DSP+FPGA integrated architecture is implemented by using an FPGA chip. The beamforming compensation weighting coefficient is first calculated, and then digital beamforming is performed according to the beamforming compensation weighting coefficient to achieve the purpose of stabilizing the resident internal beam pointing. The beamforming compensation weighting coefficient calculation formula is shown in (3) and (4): in, f is the signal frequency, C is the speed of light constant, X and Z are the coordinates of the radar array unit, α is the azimuth angle, β is the elevation angle, n is the number of pulse groups, Δsinα is the sine value compensation step, sumW win is the beam window type and gain control parameter, diffW win is the difference beam window type and gain control parameter; 1.2) Parameterized design, modeling of the beamforming compensation algorithm, extraction of key influencing factors, including: signal frequency f, azimuth angle sine value sinα, elevation angle cosine value cosβ, azimuth angle sine compensation step Δsinα, number of pulses in the resident pulse group n, window type and gain sumW of the sum beam or difference beam win and diffW win ; These key influencing factors are dynamically configured in a parameterized manner to enhance the versatility and adaptability of the algorithm; 1.3) Azimuth angle α compensation: the azimuth angle α compensation is performed according to the pulse group control and the azimuth angle sine compensation step Δsinα control in the dwell period; 1.4) Ping-Pong operation, using RAM (a) and RAM (b) to store beamforming weighting coefficients, to solve the problem of mismatch with radar echo data due to delays in compensation calculation and weighting coefficient calculation; 1.5) Trigonometric function calculation: Cordic IP is used to implement the trigonometric function calculation process of the beam spatial pointing angle θ in FPGA to complete the calculation of the final beam synthesis weighting coefficients.

2. Engineering application operation: 2.1) Azimuth angle α compensation calculation, beamforming weighting coefficient calculation and digital beamforming are completed in the same FPGA; 2.2) According to the compensation weight coefficient calculation method in step 1, f, sinα, cosβ, n, Δsinα, sumW win and diffW win Perform parameterized design, FPGA receives these parameter controls and completes the calculation process in step 1; 2.3) Use Xlinx's official CORDIC IP core to implement trigonometric function calculations and complete the trigonometric function calculation process of the beam space pointing angle θ; 2.4) By calculating the compensated azimuth sine value sinα of the next upcoming pulse group in advance, combined with the pulse group count control, ping-pong writing and reading are performed on the two RAMs (a and b), solving the problem of mismatch between the weighting coefficient calculation delay and the echo data; 2.5) The compensation is parameterized by the pulse group count control parameter and the azimuth angle sine value step Δsinα control parameter; 2.6) Two-level ping-pong control to ensure that the compensated weighting coefficient matches the radar array sampling echo data; 2.7) Window type and gain control calculation: perform complex multiplication operation on the window type and gain coefficient required by the system and the result of trigonometric function calculation to obtain the weighting coefficient of beam synthesis.

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