An autonomous beam control method for high-resolution SAR system on airship platform

Abstract

A method for autonomous beam control of a high-resolution SAR system on an airship platform includes: determining whether a working state is available; calculating the working parameters and beam control codes required for the system working sequence; the radar control acquisition processor autonomously sends the beam control code data of different sub-band signals corresponding to the current azimuth beam to the antenna beam control machine according to the working sequence, and finally the TR component and other channels execute the data; when the number of resident pulses of an azimuth beam reaches CPI, the radar control processor automatically sends the beam control code data of different sub-band signals corresponding to the current azimuth beam to the antenna beam control machine according to the working sequence, and the radar control processor automatically sends the beam control code data of different sub-band signals corresponding to the current azimuth beam to the antenna beam control machine according to the working sequence, and the radar control processor automatically sends the beam control code data of different sub-band signals to the antenna beam control machine according to the working sequence, and the radar control processor automatically sends the beam control code data of different sub-band signals to the antenna beam control machine according to the working sequence, and the radar control processor automatically sends the beam control code data of different sub-band signals to the antenna beam control machine and the radar control module automatically sends the beam control code data ... p When the radar control acquisition processor sends the beam control code of the multi-subband signal corresponding to the next azimuth beam to the antenna beam control unit, it will continue to switch until all P azimuth beams have been switched, thus achieving rapid autonomous beam control. The method proposed in this paper proposes constraints for the autonomous start of SAR system operation and provides analytical expressions for the calculation of parameters such as the beam control code for high-resolution SAR beams. This method is suitable for practical engineering applications of autonomous high-resolution SAR beam control on unmanned platforms such as airships.

Description

Technical Field

[0001] The present invention relates to an autonomous beam control method for a high-resolution SAR system on an airship platform, belongs to the technical field of radars, and further relates to the field of airship-borne SAR systems. Background Art

[0002] With the rapid development of near-space aerostats and related technologies, as well as test flights of platforms such as airships, near-space airships will achieve long-duration, controlled flight within the next few years. Furthermore, airship platforms offer advantages such as fixed-point flight, persistent airborne presence, wide visual range coverage, strong payload capacity, and high cost-effectiveness. As a new type of remote sensing SAR, airship-based SAR can provide long-term surveillance of key areas, playing a vital role in providing real-time insights into enemy movements and ultimately placing our forces in a favorable position during warfare. High-resolution SAR imaging plays a crucial role in large-scale target surveillance, military reconnaissance, and the precise acquisition of critical target information.

[0003] The range resolution of SAR depends on the radar signal bandwidth. Due to current device limitations, neither DDS chips nor high-speed DA chips can directly generate signals with excessively large bandwidths, which also poses significant challenges for the system's transmission, reception, and acquisition processing. To address the difficulty of directly achieving high-resolution, wide-bandwidth signals, frequency stepping technology can be used to transmit multiple sub-band signals with different carrier frequencies. Sub-band splicing is then used to combine the sub-band echoes into a wideband echo. Airship platforms fly at low altitudes, with echo delays on the order of tens of microseconds. To avoid echo aliasing, only one non-interfering sub-pulse echo is received within a PRI (pulse repetition period). Therefore, coherent splicing of multi-sub-band signals (assuming the number of sub-bands is N) is achieved by transmitting only one sub-pulse within a PRI, receiving the echo of this sub-pulse within that PRI, transmitting a sub-pulse of the next frequency band within the next PRI, and finally transmitting N sub-pulses within N PRIs. Finally, coherent splicing of these N sub-pulses is achieved through post-processing. When transmitting different sub-band signals, each sub-band signal has a different carrier frequency and, therefore, a corresponding antenna beam control code. Therefore, each PRI needs to switch beam control codes to accommodate the different frequencies. Furthermore, the SAR system rotates the antenna beam in azimuth to increase the azimuth accumulation angle and achieve high azimuth resolution. This requires beam switching within each CPI. Consequently, the timing of beam control is very complex.

[0004] The airship platform is an unmanned platform. When the airship-borne SAR payload system is working in a long-duration flight, how to autonomously start the mission and autonomously calculate the working parameters required for the mission, and realize the demand for autonomous beam control under complex time sequences is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to address the problem of beam control under complex working sequence of high-resolution SAR systems of unmanned platforms such as airships, and propose a method for autonomous beam control of high-resolution SAR systems of airship platforms. The method is for unmanned platforms such as airships, and includes: the radar control and acquisition processor of the SAR system receives a working instruction to start up and enter standby mode; receives attitude and position data sent by the combined inertial navigation device and autonomously determines whether it is in working state; autonomously calculates the working parameters and wave control codes required for the working sequence of the system; the radar control and acquisition processor autonomously sends the wave control code data of different sub-band signals corresponding to the current azimuth beam to the antenna wave control machine according to the working sequence, and finally is executed by the TR component channel and the delay compensation unit; when the number of resident pulses of an azimuth beam reaches CPI, the SAR system is automatically controlled. p When the radar control acquisition processor sends the beam control code of the multi-subband signal corresponding to the next azimuth beam to the antenna beam control machine, until P azimuth beams are switched, realizing rapid autonomous control of the beam.

[0006] The technical solution of the present invention is:

[0007] A method for autonomous beam control of a high-resolution SAR system on an airship platform, comprising:

[0008] (1) Using the attitude and position data received from the combined inertial navigation device, determine whether the airship platform has reached a stable working state, and proceed to the next step when the airship has reached a stable working state;

[0009] (2) Select one sub-band signal or N sub-band signals as a transmission signal according to the range resolution, and obtain the center frequency corresponding to the sub-band signal as the transmission signal;

[0010] (3) According to the azimuth resolution, determine the number of azimuth beam scanning angles P and the azimuth beam scanning range {θ p} and the number of pulses CPI per azimuth beam dwell p ;

[0011] (4) According to the azimuth beam scanning range {θ p}, traverse all sub-band signal center frequencies with multiple azimuth beam scanning angles from small to large, and generate the azimuth beam scanning angle θ p , sub-band signal center frequency f j ,f j+1 ,...,f j+N-1 Corresponding wave control code;

[0012] (5) According to the pulse number CPI of the azimuth beam residence p Perform azimuth beam scanning and set the azimuth beam scanning range {θ pThe beam control code of the multi-subband signal corresponding to each azimuth beam scanning angle in} is sent to the antenna beam control machine, traversing the entire azimuth beam scanning range to realize beam switching.

[0013] Preferably, the posture position data includes: platform height H_ft, platform flight speed v_ft;

[0014] Method for judging whether the airship platform has reached a stable working state: the fluctuation of the platform height and platform flight speed data curve within a certain period of time (ΔH _ft , Δv _ft ) does not exceed 10%, as follows:

[0015]

[0016]

[0017]

[0018] Among them, H _ft (s) and v _ft (s) represents the platform height and platform flight speed at the current moment and a certain time before the current moment, s∈1,2,…,S; S is the total number of platform height and platform flight speed measurement data obtained within a certain time, ΔH _ft and Δv _ft They respectively represent the fluctuations of platform height and platform flight speed within a certain period of time.

[0019] Preferably, a method of selecting a sub-band signal or multiple sub-band signals as a transmission signal is specifically as follows:

[0020] 20) Calculate the required transmission signal bandwidth B based on the distance resolution ρ exp ;

[0021] 21) According to the signal bandwidth B of a single sub-band pulse and the required transmit signal bandwidth B calculated in step 20) exp , select one sub-band signal or N sub-band signals as the transmission signal.

[0022] Preferably, the required transmit signal bandwidth B is calculated exp The method is as follows:

[0023]

[0024] Where c is the speed of light, is the initial installation angle of the antenna when the elevation scanning angle is 0°, is the scanning angle of the pitch direction from the normal direction.

[0025] Preferably, a method of selecting a sub-band signal or multiple sub-band signals as a transmission signal is specifically as follows:

[0026] According to the size of the center frequency, the center frequency f i Numbered from small to large, i = 1, 2, ... M; different center frequencies f i Corresponding to different sub-band signals; M is the total number of sub-band signals;

[0027] When the required transmit signal bandwidth B exp Less than or equal to the signal bandwidth B of a single sub-band pulse When , a sub-band signal corresponding to a center frequency is arbitrarily selected from the M center frequencies as the transmission signal;

[0028] On the contrary, N adjacent sub-band signals are selected from the M center frequencies as the transmission signals, and the signals are transmitted using the sub-band splicing method. Within the N pulse repetition frequencies, N sub-pulses are transmitted in sequence from small to large according to the size of the center frequencies of the adjacent sub-band signals.

[0029] Preferably, the N is specifically:

[0030]

[0031] The center frequencies of N adjacent sub-band signals are f j ,f j+1 ,...,f j+N-1 , j∈[1,MN-1].

[0032] Preferably, the number of azimuth beam scanning angles P and the azimuth beam scanning range {θ p} and the number of pulses CPI per azimuth beam dwell p The method is as follows:

[0033]

[0034] in, Indicates rounding up, θ _step is the beam step angle, θ _step =θ BW / k,θ BW is the antenna azimuth beam width, k is the proportional coefficient, k≥10, c is the speed of light; f min is the minimum center frequency of the sub-band signal used as the transmitted signal;

[0035]

[0036] Where, p∈[1, 2, …, P]; θ P is the maximum azimuth beam scanning angle;

[0037]

[0038] Among them, H_ft and v_ft are the platform height and platform flight speed respectively, PRF is the pulse repetition frequency, and ρ is the azimuth resolution; is the initial installation angle of the antenna when the elevation scanning angle is 0°, is the scanning angle of the pitch direction from the normal direction.

[0039] Preferably, the wave control code includes: a delay compensation amount of the delay compensation unit and a phase shift code matched with the phase shifter of the TR component;

[0040] The number of elements in the azimuth and range directions of the antenna array are N respectively. az 、N rg , divided into multiple sub-arrays along the azimuth direction, each sub-array consists of M1 array elements, N az =N1×M1; divided into N1×N rg sub-arrays, called first-level sub-arrays, each of which is divided into two second-level sub-arrays; each sub-array has two second-level delay compensation units and one first-level delay compensation unit, one first-level delay compensation unit is configured in the first-level sub-array, and two second-level delay compensation units are configured in the second-level sub-array.

[0041] Preferably, the delay compensation amount of the delay compensation unit is specifically:

[0042] 51) According to the array aperture length and azimuth beam scanning range {θ p The maximum azimuth beam scanning angle θ in P , calculate the maximum time extension L of the array antenna TTD :

[0043]

[0044] Among them, L az 、L rg are the aperture lengths of the antenna in azimuth and range directions respectively;

[0045] if There is no need to use a delay compensation unit for delay compensation, and the delay compensation amount is 0;

[0046] if Then it is necessary to use a delay compensation unit to perform delay compensation;

[0047] Where k1 is the proportional coefficient, k1=2, and c is the speed of light;

[0048] 52) The delay compensation amount of the two secondary delay compensation units configured in the second-stage sub-array is expressed as L TTD2_1 (t,s) and LTTD2_2 (t, s), the delay compensation amount of the first-level delay compensation unit configured in the first-level sub-array is expressed as L TTD1 (t,s); where t=1,2,...,N1,s=1,2,...,N rg ; respectively determine the delay compensation amount of the first and second delay compensation units;

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055] Among them, λ i is the center frequency f of the current pulse transmission signal i The corresponding wavelength, λ i =c / f i ; Indicates rounding down. is the maximum delay compensation amount of the first-level delay compensation unit, is the maximum delay compensation amount of the second-level delay compensation unit.

[0056] Preferably, the phase shift code determination method is specifically as follows:

[0057] Calculate the phase shift code ψ of each antenna element corresponding to each sub-band signal u,v ;

[0058] when When the phase shift code ψ u,v It can be expressed as:

[0059]

[0060] when When the phase shift code ψ u,v It can be expressed as:

[0061]

[0062] Where u=1,2,...,N az ; v=1,2,3,...,N rg , Indicates rounding down;

[0063] (54) Determine the desired number of bits q of the phase shift code, where the number of bits q of the phase shift code satisfies the following inequality:

[0064]

[0065] where c is the speed of light, d az and d rg are the element spacings in the azimuth and range directions of the antenna respectively, f min is the minimum center frequency of the selected N sub-band signals, f max is the maximum center frequency of the selected N sub-band signals; θ _step is the beam step angle, θ _step = θ BW / k, θ BW is the beam width in the azimuth direction of the antenna, k is a proportionality coefficient, k ≥ 10;

[0066] Quantize the phase shift code ψ u,v into a wave control code that matches the phase shifter of the TR component, specifically:

[0067] When q ≥ l, quantize the phase shift code into a q-bit binary code, and then take the first l bits as the phase shift code in the wave control code;

[0068] When q < l, quantize the phase shift code into q bits, and fill the first l - q bits of the phase shift code in the wave control code with zeros;

[0069] where l is the actual number of bits of the phase shifter of the TR component.

[0070] The beneficial effects of the present invention compared with the prior art are as follows:

[0071] (1) A method for autonomous beam control of a high-resolution SAR system on an airship platform. This method proposes to use the fluctuations of real-time platform flight altitude, speed and other attitude position data provided by a combined inertial navigation device to determine whether the platform reaches a stable working state and whether the SAR system has working conditions, and is applicable to systems of unmanned platforms.

[0072] (2) A method for autonomous beam control of a high-resolution SAR system on an airship platform. This method gives an analytical expression for calculating parameters such as the wave control code of the high-resolution SAR beam, and is applicable to the actual engineering application of autonomous beam control of high-resolution SAR on unmanned platforms such as airships. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 is the processing flow chart of the present invention.

[0074] Figure 2 is the timing schematic diagram of the fast switching of the corresponding beam when multiple sub-band transmitted signals are switched in the present invention.

[0075] Figure 3 It is a schematic diagram of the sub-array division and delay compensation network of the antenna array of the present invention. DETAILED DESCRIPTION

[0076] In order to better understand the above technical solution, the technical solution of the present application is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical solution of the present application, rather than limitations on the technical solution of the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other.

[0077] The following is a further detailed description of the beam autonomous control method of the high-resolution SAR system of the airship platform provided by the embodiment of the present application in conjunction with the accompanying drawings. Figures 1 to 3 As shown) are as follows:

[0078] (1) For unmanned platforms such as airships, the SAR system radar control acquisition processor is turned on and in standby mode after receiving the working instructions from the ground. The working instructions include the following: working mode, range and azimuth resolution are both ρ, the initial installation angle of the antenna (the pitch scanning angle is 0° at this time) is The scanning angle of the pitch direction deviating from the normal direction is The azimuth beamwidth is θ BW , repetition frequency PRF, center frequency f i (i=1,2,..M.) and other initial working parameters;

[0079] (2) The radar control acquisition processor receives the attitude and position data sent by the combined inertial navigation device at a certain frequency (time interval T_gnss), and the attitude and position data include the platform height H_ft, the platform flight speed v_ft, etc. The platform height H_ft and the platform flight speed v_ft are used to determine whether the airship has reached a stable working state. When the airship reaches a stable working state, the radar control acquisition processor is ready for operation and enters step (3);

[0080] The fluctuation of the data curve of platform height and platform flight speed within 5 minutes can be expressed as:

[0081]

[0082]

[0083] Among them, H _ft (s) and v _ft(s) (s=1,2,…,S) represents all the measurement data of the platform height and platform flight speed within 5 minutes from the current moment (inclusive), S is the number of measurement data in 5 minutes, which can be calculated by 300 / T_gnss. E(H _ft (s)) and E(v _ft (s)) is the platform altitude and platform flight speed expected to be achieved by the system mission or the expected value of the measured data within 5 minutes (i.e. ΔH _ft and Δv _ft (s = 1, 2, ..., S) represents the fluctuation of the platform altitude and platform flight speed data curves from the current time (inclusive) for the past 5 minutes. When the platform altitude and flight speed data curves fluctuate by no more than 10% within 5 minutes, the airship is considered to have reached a stable operating state and the radar control acquisition processor is ready for operation.

[0084] (3) The radar control acquisition processor autonomously selects one or more sub-band signals as the transmission signal according to the range resolution ρ and determines the center frequency of the sub-band signal. The instantaneous maximum signal bandwidth that can be achieved by the radar control acquisition processor system hardware is a single sub-band signal B pulse . Different center frequencies f i (i=1, 2, ...M) corresponds to different sub-band signals.

[0085] 30) Calculate the required transmission signal bandwidth based on the distance resolution ρ Where c is the speed of light.

[0086] The method for selecting the transmission signal is as follows:

[0087] 31) When the required transmission signal bandwidth B exp Less than or equal to the signal bandwidth B of a single sub-band pulse When the signal is transmitted, any center frequency is selected from the M center frequencies input from the upper level, and the signal bandwidth of the transmitted signal is B exp , the transmitted signal is an LFM (linear frequency modulation) signal.

[0088] 32) When the required transmission signal bandwidth B exp Greater than the signal bandwidth B of a single sub-band pulse When N adjacent sub-band signals can be selected from all sub-bands, the signal can be transmitted by splicing sub-bands. Within N PRIs, N sub-pulses are transmitted sequentially, from smallest to largest, according to the center frequencies of adjacent sub-band signals. That is, only one sub-band signal pulse is transmitted within one pulse repetition period (PRI), and only the echo of this sub-pulse is received within this PRI. Then, in the next PRI, the sub-pulse of the next sub-band signal is transmitted. The pulse repetition period PRI = 1 / PRF. The center frequencies of N adjacent sub-band signals, arranged from smallest to largest, can be expressed as: f j ,f j+1 ,...f, j+N- (1j=rand(M1,N-), j∈[1,MN-1].

[0089] (4) The radar control acquisition processor autonomously plans the azimuth beam scanning method according to the azimuth resolution ρ requirement, including: the azimuth beam scanning range, the number of azimuth beam scanning angles P, and the number of pulses that reside in each azimuth beam;

[0090] 41) The number of azimuth beam scanning angles is P:

[0091]

[0092] in, represents rounding up, where θ _step is the beam step angle, which can be expressed as θ _step =θ BW / k,θ BW is the antenna azimuth beam width, k is the proportional coefficient, generally k≥10, and c is the speed of light. min is the minimum center frequency of the selected sub-band signal.

[0093] 42) The azimuth beam scanning angle can be expressed as where p∈[1,2,…,P],θ P is the maximum azimuth beam scanning angle.

[0094] 43) The azimuth beam scanning range is a set of P azimuth beam scanning angles {θ p};

[0095] 44) The number of pulses CPI of each azimuth beam residence p :

[0096]

[0097] in, Indicates rounding up, H_ft, v_ft are the platform height and flight speed respectively, c is the speed of light, N is the number of sub-band signals. PRF is the pulse repetition frequency, f min is the minimum center frequency of the selected sub-band signal, ρ is the azimuth resolution, are the initial installation angle of the antenna and the scanning angle of the elevation direction from the normal direction, respectively.

[0098] (5) According to the azimuth beam scanning range {θ p}, traverse the multiple azimuth beam scanning angles in the azimuth beam scanning range from small to large to traverse all sub-band signal center frequencies, and the radar control acquisition processor independently calculates the wave control code to generate all azimuth beam scanning angles θ p , sub-band signal center frequency f j ,f j+1 ,...,f j+M-1 The corresponding wave control code. The wave control code includes the delay compensation amount of the delay compensation unit and the phase shift code of the TR component and the center frequency index number corresponding to the wave control code. The index number of the wave control code is consistent with each sub-band signal (corresponding to the center frequency f j ,f j+1 ,...,f j+M-1 A certain frequency in ) corresponds one to one.

[0099] 51) According to the array aperture length and the maximum azimuth beam scanning angle θ P , L az 、L rg The aperture lengths in the azimuth and range directions of the antenna are calculated to determine the maximum duration L of the array antenna. TTD :

[0100]

[0101] if There is no need to use the delay compensation unit for delay compensation, and the delay compensation amount is 0; if Then it is necessary to use a delay compensation unit to perform delay compensation;

[0102] Among them, k1 is the proportional coefficient, which can generally be taken as k1=2, and c is the speed of light.

[0103] 52) Assume that the antenna array (the number of elements in the azimuth and range directions are N respectively) az 、N rg ) is divided into multiple sub-arrays along the azimuth direction, each sub-array consists of M1 array elements, N az =N1×M1. The total is divided into N1×N rg There are two sub-arrays, called first-level sub-arrays, and each sub-array is divided into two smaller sub-arrays, called second-level sub-arrays. There is a first-level delay compensation unit and two second-level delay compensation units in each sub-array. One first-level delay compensation unit is configured in the first-level sub-array, and two second-level delay compensation units are configured in the second-level sub-array. Figure 3 As shown. The number of delay bits of the second-stage delay compensation unit is A bit, that is, a1λ, a2λ, ..., aA λ, then the maximum delay compensation amount of the first-level delay compensation unit is The delay bit number of the first-stage compensation unit is Bbit, that is, b1λ, b2λ, ..., b B λ, then the maximum delay compensation amount of the second-level delay compensation unit is

[0104] The delay compensation of the second-level delay compensation unit is expressed as L TTD2_1 (t,s) and L TTD2_2 (t,s), the delay compensation of the first-level delay compensation unit is expressed as L TTD1 (t,s), where t=1,2,...,N1, s=1,2,...,N rg According to the structure of the delay compensation network of the array, the delay compensation amounts of the first-level and second-level delay compensation units are determined by the following formulas.

[0105]

[0106]

[0107]

[0108]

[0109]

[0110]

[0111] Among them, λ i is the wavelength corresponding to the center frequency of the current pulse transmission signal, that is, λ i =c / f i .

[0112] 53) Calculate the phase shift code ψ of each antenna element corresponding to each sub-band signal u,v , where u=1,2,...,N az ; v=1,2,3,...,N rg , Indicates rounding down.

[0113] when When the phase shift code ψ u,v It can be expressed as:

[0114]

[0115] when When the phase shift code ψ u,v It can be expressed as:

[0116]

[0117] 54) According to the constraint conditions determine the expected number of bits q of the phase shift code. Where c is the speed of light, d az , d rg are the element spacings in the azimuth and range directions of the antenna respectively, f min is the minimum center frequency of the selected N sub-band signals, f max is the maximum center frequency of the selected N sub-band signals.

[0118] Quantize the phase shift code ψ u,v obtained in step 53) into a wave control code that matches the phase shifter of the TR component. Assume that the actual number of bits of the phase shifter of the TR component is l bits.

[0119] When q ≥ l, quantize the phase shift code into a q-bit binary code, and then take the first l bits as the phase shift code in the wave control code;

[0120] When q < l, quantize the phase shift code into q bits, and fill the first l - q bits of the phase shift code in the wave control code with zeros.

[0121] (6) The radar control acquisition processor independently generates a working timing sequence, and performs azimuth beam scanning according to the number of pulses CPI p for the azimuth beam dwell in step (4), sends the wave control codes of the multi-sub-band signals corresponding to the azimuth beam scanning angles to the antenna wave control machine, traverses the entire azimuth beam scanning range, and uses the wave control codes to achieve beam switching. And within the azimuth beam dwell time of each azimuth scanning angle, fast switching of the wave control of multiple sub-band transmitted signals needs to be achieved.

[0122] Within the dwell time of the azimuth beam scanning angle, the azimuth beam scanning angle remains unchanged. One sub-band signal is transmitted per pulse, and the center frequencies of all N sub-band signals are traversed from small to large, and then looped until the number of azimuth beam dwell pulses CPI p .

[0123] The method for implementing the rapid switching of the wave control of multiple sub-band transmission signals within the azimuth beam dwell time is as follows: first, all the wave control codes with frequency index numbers corresponding to the current azimuth beam scanning angle calculated in real time are distributed to the antenna wave control machine at one time. After the antenna wave control machine verifies that they are correct, they are stored in the RAM at the location specified by the index number; then a pair of beam switching pulse control signals and transmission signal trigger signals with a strict sequence relationship are generated. The function of the beam switching pulse control signal is to send the frequency index number to the antenna wave control machine, and the antenna wave control machine sends the wave control code corresponding to the correct frequency index number to the TR component. The TR component performs phase shifting according to the phase shift code in the wave control code, and the delay compensation unit performs real-time delay compensation according to the delay compensation amount in the wave control code, thereby realizing beam switching. The function of the transmission signal trigger signal is to transmit the RF signal of each sub-band in sequence from small to large according to the sub-band center frequency. The strict timing relationship between the beam switching pulse control signal and the transmission signal trigger signal means that the beam switching pulse control signal is generated earlier than the transmission signal trigger signal, and the time interval is the transmission time of the radar control acquisition processor sending the frequency index number to the antenna wave control machine plus 5us.

[0124] The number of pulses in the current azimuth beam scanning angle reaches the azimuth beam dwell pulse number CPI p When the radar control acquisition processor sends the beam control code of the multi-subband signal corresponding to the next azimuth beam to the antenna beam control machine, the switching of P azimuth beams is completed. The timing diagram of the rapid switching of the corresponding beams when multiple sub-band transmission signals are switched in the present invention is as follows: Figure 2 shown.

[0125] In the solution provided in the embodiment of the present application, the application scenario of the present invention is: the frequency is 14 to 18 GHz, the maximum bandwidth of the single sub-band signal (B pulse ) is 1100MHz, and the center frequencies are f1=14.55G, f2=15.45G, f3=16.45G, and f4=17.45G. The pulse repetition period is 1500Hz, and the electromagnetic wave propagation speed c=3×10 8 m / s, the shortest wavelength λ0 = 0.0167m, and the number of array elements in the array is N az =40, the number of array elements is N rg =8, the azimuth and range spacing of the transmitting array elements are d az =11.9mm, d rg =11.8mm. The delay compensation network of the antenna array adopts a two-stage delay compensation scheme. The first-stage delay compensation network has a delay bit of 3 bits, namely 2λ, 1λ, and 0.5λ. The second-stage compensation network has a delay bit of 3 bits, namely 4λ, 2λ, and 1λ.

[0126] like Figure 1Shown is a processing flow chart of the method of the present invention, which is composed of Figure 1 It can be seen that the present invention provides an airship platform high-resolution SAR system beam autonomous control method, the specific implementation steps are as follows:

[0127] (1) The SAR system radar control acquisition processor is turned on and in standby mode after receiving the working instructions from the ground. The working instructions include the following: the working mode is the beamforming mode, the resolution ρ = 0.08m, the initial installation angle of the antenna (the pitch scanning angle is 0° at this time) is The scanning angle of the pitch direction deviating from the normal direction is Azimuth beamwidth θ BW =2.2°, repetition frequency PRF=1500H, center frequency f i (i=1,2,...4) and other working parameters;

[0128] (2) The radar control acquisition processor receives the attitude and position data sent by the combined inertial navigation device at a certain frequency (time interval T_gnss = 0.05s), the attitude and position data including the platform height H_ft = 3km, the platform flight speed v_ft = 10m / s, etc. When the data curves of the platform height and platform flight speed fluctuate no more than 10% within 5 minutes, that is:

[0129]

[0130]

[0131] If the requirements are met, it is determined that the airship has reached a stable working state and the radar control acquisition processor is ready for working. _ft (s) and v _ft (s) (s = 1, 2, ..., S) respectively represent all measurement data of the platform altitude and platform flight speed calculated within 5 minutes from the current moment (inclusive), S = 300 / T_gnss = 6000.

[0132] (3) The radar control acquisition processor autonomously selects the transmission signal according to the range resolution ρ, including the center frequency and bandwidth selection. The instantaneous maximum signal bandwidth that can be achieved by the radar control acquisition processor system hardware is a single sub-band signal B pulse =1100MHz. Different center frequencies f i (i=1,2,...M) corresponds to different sub-band signals. The required signal bandwidth is calculated based on the resolution. When the required signal bandwidth 2289MHz is greater than the signal bandwidth 1100MHz of a single sub-band, select N=3 adjacent sub-band signals from all sub-bands and transmit the signal in a sub-band splicing manner to meet the requirement. That is, only one subpulse is transmitted within a PRI, and the echo of this subpulse is received within that PRI. A subpulse in the next frequency band is transmitted within the next PRI, and finally all three subpulses are transmitted within three PRIs. The pulse repetition period PRI = 1 / PRF = 1 / 1500s. j is randomly selected from an integer between 1 and 2. Assuming j = 1, the center frequencies of the signals in three adjacent subbands can be expressed as: f1, f2, and f3. That is, f1 = 14.55 GHz, f2 = 15.45 GHz, and f3 = 16.45 GHz.

[0133] (4) The radar control acquisition processor autonomously plans the azimuth beam scanning method according to the azimuth resolution ρ requirement, including the azimuth beam scanning range, the number of azimuth beam scanning angles P, the specific azimuth beam scanning angles, and the number of pulses that reside in each azimuth beam;

[0134] 41) Based on the resolution ρ = 0.08m and the minimum signal center frequency f1 = 14.55G, the required maximum azimuth cumulative angle is calculated as follows: k is the proportional coefficient, which is set to k = 10. The beam step angle is: θ _step =0.2°. The number of azimuth beam scanning angles P is obtained by calculation:

[0135]

[0136] 42) The azimuth beam scanning angle can be expressed as θ p =(p-24)·0.2°, where p∈[1, 2, …, 47], θ P =4.6°.

[0137] 43) The azimuth beam scanning range is the set of P azimuth beam scanning angles {θ p};

[0138] 44) According to H_ft=3km, v_ft=10m / s, c is the speed of light, N=3, PRF=1500, frequency, f min =14.55G is the minimum center frequency of the selected sub-band signal, and the number of pulses CPI of each azimuth beam residence is calculated. p :

[0139]

[0140] (5) According to the azimuth beam scanning range, all sub-band signal center frequencies are traversed from small to large according to multiple azimuth beam scanning angles. The radar control acquisition processor autonomously calculates the wave control code and generates all azimuth beam scanning angles θ p , sub-band signal center frequency f j ,f j+1 ,...,fj+N-1 The corresponding wave control code. The wave control code includes the delay compensation amount of the delay compensation unit and the phase shift code of the TR component and the frequency index number corresponding to the wave control code. The index number of the wave control code is consistent with each sub-band signal (corresponding to the center frequency f j ,f j+1 ,...,f j+N-1 The wave control code includes phase shift code, delay compensation value, etc. The details are as follows:

[0141] 51) According to the array aperture length and the maximum azimuth beam scanning angle θ P =4.6°, the antenna aperture length in azimuth and range is L az =0.5m, L rg =0.12m, Calculate the maximum delay L of the array antenna TTD :

[0142]

[0143]

[0144] because It is determined that a delay compensation unit needs to be used to perform delay compensation.

[0145] 52) Assume that the antenna array (the number of elements in the azimuth and range directions are N respectively) az 、N rg ) is divided into multiple sub-arrays along the azimuth direction, each sub-array consists of M1=8 array elements, and is divided into 5×8 sub-arrays in total. Each sub-array has a first-level delay compensation unit and two second-level delay compensation units, such as Figure 3 As shown. The delay bit number of the second-stage delay compensation network is 3 bits, namely 2λ, 1λ, 0.5λ, which can compensate for a maximum delay of 3.5λ. The delay bit number of the first-stage compensation network is 3 bits, namely 4λ, 2λ, 1λ, which can compensate for a maximum delay of 7λ. The delay compensation of the second-stage delay compensation unit is expressed as L TTD2_1 (t,s) and L TTD2_2 (t,s), the delay compensation of the first-level delay compensation unit is expressed as L TTD1 (t, s), where t = 1, 2, ..., 5, and s = 1, 2, ..., 8. Based on the structure of the array's delay compensation network, the delay compensation amounts for the primary and secondary delay compensation units are determined by the following formulas. Where λ1, λ2, and λ3 are the wavelengths corresponding to the center frequency of the current pulse transmission signal: λ1 = 20.62 mm, λ2 = 19.41 mm, and λ3 = 17.19 mm, respectively.

[0146] 53) Calculate the phase shift code ψ of each antenna element corresponding to each sub-band signalu,v , where u = 1, 2, ..., 40, v = 1, 2, 3, ..., 8,

[0147] when When the phase shift code ψ u,v It can be expressed as:

[0148]

[0149] when When the phase shift code ψ u,v It can be expressed as:

[0150]

[0151] 54) Determine the expected number of phase-shift code bits q=8 according to the following constraints;

[0152]

[0153] Where c = 3 × 10 8 is the speed of light, and the array element spacing in the azimuth and range directions of the antenna is d az =11.9mm, d rg =11.8mm, f1=14.55GHz is the minimum center frequency of the selected sub-band signal, and f3=17.45GHz is the maximum center frequency of the selected sub-band signal.

[0154] The phase shift code calculated above is quantized into a binary code. Assuming that the actual number of bits of the phase shifter of the TR component is l = 6 bits, when q ≥ l, the phase shift code can be quantized to q = 8 bits, and then the first l = 6 bits are taken as the phase shift code in the wave control code.

[0155] (6) The radar control acquisition processor autonomously generates the working sequence, performs azimuth beam scanning according to the number of pulses during the azimuth beam dwell period, and sends the beam control code of the multi-subband signal corresponding to the azimuth beam scan angle to the antenna beam control unit, traversing the entire azimuth beam scan range. During the azimuth beam dwell time at each azimuth scan angle, it is necessary to achieve rapid switching of the beam control of multiple sub-band transmission signals.

[0156] During the dwell time of the azimuth beam scanning angle, the azimuth beam scanning angle remains unchanged, and a sub-band signal is transmitted per pulse, traversing all sub-band signal center frequencies from small to large, and then repeating the cycle until the azimuth beam dwell pulse number CPI is reached. p .

[0157] The method for implementing the rapid switching of the wave control of multiple sub-band transmission signals within the azimuth beam dwell time is as follows: first, all the wave control codes with frequency index numbers corresponding to the current azimuth beam scanning angle calculated in real time are distributed to the antenna wave control machine at one time. After the antenna wave control machine verifies that they are correct, they are stored in the RAM at the location specified by the index number; then a pair of beam switching pulse control signals and transmission signal trigger signals with a strict sequence relationship are generated. The function of the beam switching pulse control signal is to send the frequency index number to the antenna wave control machine, and the antenna wave control machine sends the wave control code corresponding to the correct frequency index number to the TR component. The TR component performs phase shifting according to the phase shift code in the wave control code, and the delay compensation unit performs real-time delay compensation according to the delay compensation amount in the wave control code, thereby realizing beam switching. The function of the transmission signal trigger signal is to transmit the RF signal of each sub-band in sequence from small to large according to the sub-band center frequency. The strict timing relationship between the beam switching pulse control signal and the transmission signal trigger signal means that the beam switching pulse control signal is generated earlier than the transmission signal trigger signal, and the time interval is the transmission time of the radar control acquisition processor sending the frequency index number to the antenna wave control machine plus 5us.

[0158] The number of pulses in the current azimuth beam scanning angle reaches the azimuth beam dwell pulse number CPI p =6615, the radar control acquisition processor sends the beam control code of the multi-subband signal corresponding to the next azimuth beam to the antenna beam control machine until P=47 azimuth beams are switched.

[0159] The specific embodiments of the present invention demonstrate that a method for autonomous beam control of a high-resolution SAR system on an airship platform provides criteria for determining whether the airship has reached a stable operating state and the SAR system is ready for operation. The method also provides analytical expressions for calculating parameters such as the high-resolution SAR beam control code. Based on these calculations, autonomous beam control for azimuth beam scanning that transmits multiple sub-band signals is implemented, completing high-resolution SAR imaging tasks. The method is suitable for practical engineering applications of autonomous high-resolution SAR beam control on unmanned platforms such as airships.

[0160] Although the present invention has been disclosed as above with 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 using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications 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 are within the scope of protection of the technical solutions of the present invention. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other.

[0161] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for autonomous beam control of a high-resolution SAR system on an airship platform, characterized in that: including: (1) Using the attitude and position data sent by the received combined inertial navigation device to determine whether the airship platform has reached a stable working state. After the airship reaches the stable working state, proceed to the next step; (2) Select one sub-band signal or N sub-band signals as the transmitted signal according to the range resolution, and obtain the center frequency corresponding to the sub-band signal used as the transmitted signal; (3) According to the azimuth resolution, determine the number of azimuth beam scanning angles P and the azimuth beam scanning range {θ p } and the number of pulses CPI per azimuth beam dwell p ; (4) According to the azimuth beam scanning range {θ p }, traverse all sub-band signal center frequencies with multiple azimuth beam scanning angles from small to large, and generate the azimuth beam scanning angle θ p , sub-band signal center frequency f j ,f j+1 ,...,f j+N-1 Corresponding wave control code; (5) According to the pulse number CPI of the azimuth beam residence p Perform azimuth beam scanning and set the azimuth beam scanning range {θ p The beam control code of the multi-subband signal corresponding to each azimuth beam scanning angle in the azimuth beam is sent to the antenna beam control machine, traversing the entire azimuth beam scanning range to achieve beam switching; The attitude and position data includes: platform height H_ft, platform flight speed v_ft; Method for judging whether the airship platform has reached a stable working state: the fluctuation of the platform height and platform flight speed data curve within a certain period of time (ΔH _ft , Δv _ft ) does not exceed 10%, as follows: Among them, H _ft (s) and v _ft (s) represents the platform height and platform flight speed at the current moment and a certain time before the current moment, s∈1,2,…,S; S is the total number of platform height and platform flight speed measurement data obtained within a certain time, ΔH _ft and Δv _ft They respectively represent the fluctuations of platform height and platform flight speed within a certain period of time; The wave control code includes: the delay compensation amount of the delay compensation unit and the phase shift code matching the phase shifter of the TR component; The number of elements in the azimuth and range directions of the antenna array are N respectively. az 、N rg , divided into multiple sub-arrays along the azimuth direction, each sub-array consists of M1 array elements, N az =N1×M1; a total of N1×N rg sub-arrays, called first-level sub-arrays, each of which is divided into two second-level sub-arrays; each sub-array has two second-level delay compensation units and one first-level delay compensation unit, one first-level delay compensation unit is configured in the first-level sub-array, and two second-level delay compensation units are configured in the second-level sub-array.

2. The method for autonomous beam control of a high-resolution SAR system on an airship platform according to claim 1, characterized in that: The method for selecting one sub-band signal or multiple sub-band signals as the transmitted signal is specifically as follows: 20) Calculate the required transmission signal bandwidth B based on the distance resolution ρ exp ; 21) According to the signal bandwidth B of a single sub-band pulse and the required transmit signal bandwidth B calculated in step 20) exp , select one sub-band signal or N sub-band signals as the transmission signal.

3. The method for autonomous beam control of a high-resolution SAR system on an airship platform according to claim 2, characterized in that: Calculate the required transmit signal bandwidth B exp The method is as follows: Where c is the speed of light, is the initial installation angle of the antenna when the elevation scanning angle is 0°, is the scanning angle of the pitch direction from the normal direction.

4. The method for autonomous beam control of a high-resolution SAR system on an airship platform according to claim 3, characterized in that: The method for selecting one sub-band signal or multiple sub-band signals as the transmitted signal is specifically as follows: According to the size of the center frequency, the center frequency f i Numbered from small to large, i = 1, 2, ... M; different center frequencies f i Corresponding to different sub-band signals; M is the total number of sub-band signals; When the required transmit signal bandwidth B exp Less than or equal to the signal bandwidth B of a single sub-band pulse When , a sub-band signal corresponding to a center frequency is arbitrarily selected from the M center frequencies as the transmission signal; On the contrary, select N adjacent sub-band signals from the M center frequencies as the transmitted signal, and transmit the signal in the form of sub-band splicing. Transmit N sub-pulses in sequence from small to large according to the magnitudes of the center frequencies of the adjacent sub-band signals within N pulse repetition frequencies.

5. The method for autonomous beam control of a high-resolution SAR system on an airship platform according to claim 4, characterized in that: The specific value of N is: The center frequencies of N adjacent sub-band signals are f j ,f j+1 ,...,f j+N-1 , j∈[1,MN-1].

6. The method for autonomous beam control of a high-resolution SAR system on an airship platform according to claim 1, characterized in that: Determine the number of azimuth beam scanning angles P and the azimuth beam scanning range {θ p } and the number of pulses CPI per azimuth beam dwell p The method is as follows: in, Indicates rounding up, θ _step is the beam step angle, θ _step =θ BW / k,θ BW is the antenna azimuth beam width, k is the proportional coefficient, k≥10, c is the speed of light; f min is the minimum center frequency of the sub-band signal used as the transmitted signal; Where p∈[1, 2, …, P]; θ P is the maximum azimuth beam scanning angle; Among them, H_ft and v_ft are the platform height and platform flight speed respectively, PRF is the pulse repetition frequency, and ρ is the azimuth resolution; is the initial installation angle of the antenna when the elevation scanning angle is 0°, is the scanning angle of the pitch direction from the normal direction.

7. The method for autonomous beam control of a high-resolution SAR system on an airship platform according to any one of claims 1 to 6, characterized in that: The delay compensation amount of the delay compensation unit is specifically: According to the array aperture length and azimuth beam scanning range {θ p The maximum azimuth beam scanning angle θ in P , calculate the maximum time extension L of the array antenna TTD : Among them, L az , L rg are the aperture lengths of the antenna in azimuth and range directions respectively; if There is no need to use a delay compensation unit for delay compensation, and the delay compensation amount is 0; if Then it is necessary to use a delay compensation unit to perform delay compensation; where k1 is a proportionality coefficient, k1 = 2, and c is the speed of light; The delay compensation amount of the two secondary delay compensation units configured in the second-stage sub-array is expressed as L TTD2_1 (t,s) and L TTD2_2 (t, s), the delay compensation amount of the first-stage delay compensation unit configured in the first-stage sub-array is expressed as L TTD1 (t,s); where t=1,2,...,N1,s=1,2,...,N rg ; respectively determine the delay compensation amount of the first and second delay compensation units; Among them, λ i is the center frequency f of the current pulse transmission signal i The corresponding wavelength, λ i =c / f i ; Indicates rounding down. is the maximum delay compensation amount of the first-level delay compensation unit, is the maximum delay compensation amount of the secondary delay compensation unit; d az d rg are the array element spacing in the antenna azimuth and range directions, respectively.

8. The method for autonomous beam control of a high-resolution SAR system on an airship platform according to claim 7, characterized in that: The method for determining the phase shift code is specifically: Calculate the phase shift code ψ of each antenna element corresponding to each sub-band signal u,v ; when When the phase shift code ψ u,v It can be expressed as: when When the phase shift code ψ u,v It can be expressed as: Where u=1,2,...,N az ; v = 1, 2, 3, ..., N rg , Indicates rounding down; (54) Determine the desired number of bits q of the phase shift code. The number of bits q of the phase shift code satisfies the following inequality: Where c is the speed of light, f min is the minimum center frequency of the selected N sub-band signals, f max is the maximum center frequency of the selected N sub-band signals; θ _step is the beam step angle, θ _step =θ BW / k,θ BW is the antenna azimuth beamwidth, k is the proportional coefficient, k≥10; The phase shift code ψ u,v Quantized into a wave control code that matches the phase shifter of the TR component, specifically: When q ≥ l, quantize the phase shift code into a q-bit binary code, and then take the first l bits as the phase shift code in the wave control code; When q < l, quantize the phase shift code into q bits, and fill the first l - q bits of the phase shift code in the wave control code with zeros; where l is the actual number of bits of the phase shifter of the TR component.

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