A spaceborne SAR spotlight working mode adaptive system and observation area determination method

Abstract

The present invention belongs to the field of SAR radar ground reception, and relates to a satellite-borne SAR beamforming working mode adaptive system and observation area determination method. The present invention designs and implements a satellite-borne SAR beamforming working mode adaptive system and observation area determination method, including an antenna, a SAR radar receiver six-degree-of-freedom adaptive platform, a host computer, a slave computer, and a power supply module. Through the operation of this system, the satellite-borne SAR beamforming working state and working mode can be automatically identified on the ground. By comparing the collected parameters with the typical signal characteristics of the satellite-borne SAR beamforming working mode, it can automatically determine whether the satellite-borne SAR is turned on, whether it is in the beamforming working mode, and the corresponding observation area. At the same time, based on the determination method of the above-mentioned adaptive system, the present invention can continuously, dynamically, and in real time determine the working state and observation area under different satellite-borne SAR beamforming working modes.

Description

Technical Field

[0001] The invention belongs to the field of SAR radar ground reception, and relates to a satellite-borne SAR spotlight working mode adaptive system and an observation area determination method. Background Art

[0002] Synthetic Aperture Radar (SAR) boasts all-day, all-weather, high-resolution detection and imaging, strong penetration, and robust anti-interference capabilities, making it widely used in both military and civilian aerospace applications. Spaceborne SAR, with its advantages of high orbital altitude, high flight speed, and freedom from national airspace boundaries, enables long-term, wide-area observation and imaging, as well as highly repeatable, high-resolution imaging. It is particularly well-suited for observing and imaging stationary targets on the ground. To address the conflict between high range resolution and wide mapping bandwidth, spaceborne SAR typically operates in only one mode at a time for Earth observation. Common operating modes include strip, scanning, and spotlight. A spaceborne SAR spotlight mode adaptive system, deployed on the ground, determines whether the SAR is operating by comparing real-time received signals with stored or measured signal characteristics from the SAR's operating state. Based on the received signal characteristics, it rapidly determines whether the SAR is in spotlight mode, adjusts the adaptive system's operating state to adapt to the SAR's operating mode, and further determines the observation area within the spotlight mode.

[0003] SAR is based on different platform carriers, and it needs to consider different influencing factors. Spaceborne SAR and airborne SAR have different platform heights and speeds, and are affected by the earth's rotation and curvature. Therefore, under different platforms, it is necessary to consider the impact of ground clutter spectrum width, range ambiguity, earth rotation, earth curvature, radio wave propagation, etc. on the echo, and build different recognition systems accordingly.

[0004] Currently, SAR radar research focuses primarily on analyzing and processing collected radar signals to determine signal parameters such as frequency, bandwidth, pulse width, arrival time, and arrival angle. However, little research and discussion has been conducted on identifying different SAR radar operating modes and determining observation areas under different carriers. The distinct radar signal characteristics under different SAR radar operating modes determine the signal values collected by adaptive systems for these modes. Therefore, identifying the spotlight operating mode and determining the observation area for spaceborne SAR has important practical significance and application value. Summary of the Invention

[0005] In different operating modes of spaceborne SAR, the characteristic quantities of parameters received by the ground signal receiving system vary. The method for identifying the spotlight operating mode of spaceborne SAR mainly combines the satellite's operating status and the signal parameters and change patterns received by the spaceborne adaptive system to identify the spotlight operating status and mode of the spaceborne SAR. The signal characteristic parameters of the spaceborne SAR in the spotlight operating mode mainly include signal frequency, modulation style, signal amplitude, pulse repetition period, pulse width, signal bandwidth, signal arrival time, signal end time, signal duration, and signal arrival angle. When the signal parameters received by the adaptive system meet the judgment criteria, it can be determined whether the spaceborne SAR is powered on and whether it is in spotlight operating mode. The observation area can be determined based on the above information.

[0006] The present invention solves a technical problem by providing a method and adaptive system for determining the observation area in a spotlight operating mode of a spaceborne SAR. The adaptive system is deployed on the ground and has the capabilities of calculating satellite orbits, collecting radar signals, and determining the operating mode and observation area. First, based on the satellite orbit calculation module, instantaneous situational information between the adaptive system and the satellite is obtained, including the position of the SAR satellite at a certain moment, the satellite sub-satellite point track, the transit time, and the pitch angle parameters θ and azimuth parameters φ of the spaceborne SAR relative to the ground adaptive system. The pitch angle parameters and azimuth parameters are then transmitted to the adaptive system in the spotlight operating mode of the spaceborne SAR. The system converts the angle parameters into electronic control signals, and the control platform adjusts the pitch angle and azimuth angles to direct the antenna toward the transiting spaceborne SAR, completing the initial alignment of the antenna. Second, based on whether a valid spaceborne SAR radar signal is collected, it is determined whether the transiting spaceborne SAR is powered on. If no signal is collected, the transiting spaceborne SAR is deemed not powered on. If a signal is collected and the signal parameters, such as the modulation mode, pulse width τ, and signal bandwidth B, meet the judgment criteria, the transiting spaceborne SAR is deemed powered on. Third, after determining that the spaceborne SAR is turned on, the peak power P of the SAR radar is used to t , antenna main lobe gain G t , the vertical slant distance R between the receiver and the sub-satellite point of the satellite-borne SAR track, the effective area A of the receiver antenna r , judge the instantaneous received signal strength P r With the maximum signal strength P rmax , maximum signal strength P rmax Duration Δt and duration judgment threshold δ Δt The relationship between the received signal bandwidth B and the signal bandwidth judgment threshold δ in the beamforming working mode B2 The relationship between the two is used to determine whether the transiting spaceborne SAR is in the spotlight working mode. Finally, the observation area of the transiting spaceborne SAR is given according to the determined spotlight working mode.

[0007] The technical solution of the present invention is: an adaptive system for determining an observation area in a satellite-borne SAR beamforming working mode, comprising an antenna (1), a SAR radar receiver (2), a six-degree-of-freedom adaptive platform (3), an upper computer (4), and a lower computer (5), characterized in that the antenna (1) comprises a reflecting surface (6), an antenna base (7), a back frame (8), and a feeding system (9); the back frame (8) is fitted with the back of the reflecting surface (6) and is locked and fixed by bolts, and the feeding system (9) is connected to the antenna base (7), characterized in that the antenna base (7) is connected to the six-degree-of-freedom adaptive platform (3), the upper computer (4) controls the six-degree-of-freedom adaptive platform (3) to drive the antenna (1) to adjust the azimuth and / or elevation, and the lower computer (5) calculates the time when the SAR passes over the area according to an orbit calculation module (10), and calculates the initial azimuth angle parameter φ and the elevation angle parameter θ of the receiving antenna of a ground receiver according to the passing time.

[0008] As a further improvement of the present invention, the antenna seat (7) is snap-connected or bolted to the six-degree-of-freedom adaptive platform (3), and the antenna seat (7) can perform follow-up changes in azimuth angle parameters and / or pitch angle parameters under the linkage of the six-degree-of-freedom adaptive platform (3).

[0009] As a further improvement of the present invention, the SAR radar receiver (2) includes a receiver protector (11), a low-noise high-frequency amplifier (12), a mixer (13), a local oscillator (14), an intermediate frequency amplifier (15), a detector (16) and a video amplifier (17). The receiver protector (11) receives the high-frequency signal collected by the antenna (1) through a transceiver switch, and sends the high-frequency signal to the mixer (13) after passing through the low-noise high-frequency amplifier (12). The mixer (13) mixes the high-frequency voltage generated by the local oscillator (14) to reduce the signal frequency to an intermediate frequency (IF). The signal is then sent to the intermediate frequency amplifier (15) to amplify and match filter the intermediate frequency pulse signal to obtain a maximum output signal-to-noise ratio. Finally, the signal is sent to the lower computer (5) after video amplification through the detector (16) and the video amplifier (17).

[0010] As a further improvement of the present invention, the six-degree-of-freedom adaptive platform (3) includes: a base (18), an upper support frame (20) of a mounting seat (19), a lower support frame (21), an electric cylinder (22), and a power supply unit (23); the upper part of the electric cylinder (22) is hinged to the mounting seat (19), and the lower part is hinged to the base (18); the mounting seat (19) is connected to the antenna seat (7).

[0011] As a further improvement of the present invention, the six-degree-of-freedom adaptive platform (3) includes two electronic inclinometers arranged perpendicular to each other, which can detect the error between the six-degree-of-freedom adaptive platform (3) and a preset angle in a steady state and provide a correction control signal.

[0012] As a further improvement of the present invention, the six-degree-of-freedom adaptive platform (3) includes two electronic levels arranged perpendicular to each other, which can detect the horizontal zero-degree angle error of the six-degree-of-freedom adaptive platform (3) when it is initially installed on the antenna base (7) and provide an error compensation control signal.

[0013] As a further improvement of the present invention, the six-degree-of-freedom adaptive platform (3) includes a Beidou module and / or a GNSS module for collecting the longitude and latitude information of the six-degree-of-freedom adaptive platform (3).

[0014] A method for determining the observation area of a spaceborne SAR in a spotlight working mode, which detects the characteristic value of a spaceborne SAR signal received by an adaptive system to determine whether the spaceborne SAR is turned on and in the spotlight working mode, and then determines the observation area, includes the following implementation steps:

[0015] Step 1: Input the longitude and latitude information of the adaptive system into the host computer (4);

[0016] Step 2: Obtain the position h of the SAR satellite at a certain moment, the elevation angle parameter θ and the azimuth angle parameter φ of the SAR satellite relative to the adaptive system, and the maximum observation time window of the SAR satellite [t0,t g ];

[0017] Step 3: Input the satellite's pitch angle parameter θ and azimuth angle parameter φ relative to the adaptive system into the lower computer (5) and convert them into electric control signals and transmit them to the electric cylinder (22) to make the antenna point to the transit satellite-borne SAR;

[0018] Step 4: Determine whether the adaptive system has collected a signal. If not, go to step 2; if collected, go to step 5.

[0019] Step 5: Determine whether the collected signal is a linear frequency modulation signal. If it is not a linear frequency modulation signal, go to step 2; if it is a linear frequency modulation signal, go to step 6;

[0020] Step 6: Set the power-on pulse width judgment threshold δ τ1 , signal bandwidth power-on judgment threshold δ B1 ;

[0021] Step 6.1: Determine whether the collected pulse width τ meets the power-on pulse width judgment threshold δ τ1 Set, that is, satisfy formula (1),

[0022] τ≥δ τ1 (1)

[0023] Step 6.2: Determine the collected signal bandwidth B and the signal bandwidth power-on judgment threshold setting, that is, satisfy formula (2),

[0024] B≥δ B1 (2)

[0025] If both equations (1) and (2) hold, go to step 7, otherwise go to step 2;

[0026] Step 7: The peak power of the spaceborne SAR radar is known to be P t , the antenna main lobe gain is G t , the vertical slant distance between the adaptive system receiver and the spaceborne SAR is R, and the effective area of the adaptive system receiver antenna is A r , the maximum signal strength of spaceborne SAR P max Satisfying formula (3), let P r is the instantaneous signal strength collected, P rmax is the maximum instantaneous signal strength collected;

[0027]

[0028] Step 7.1: If the adaptive system is in the SAR satellite maximum over-the-air observation time window [t0,t g The instantaneous signal strength collected within ] satisfies formula (4):

[0029] P r ≤P rmax -20dbmW (4)

[0030] It is considered that the main lobe of the transiting spaceborne SAR has never reached the ground area where the adaptive system is located, and go to step 2;

[0031] Step 7.2: If the adaptive system is within the maximum SAR satellite observation time window [t0,t g The instantaneous signal strength collected within ] satisfies equations (5) and (6):

[0032] P r >P rmax -20dbmW (5)

[0033] P rmax =P max (6)

[0034] It is considered that the main lobe of the transiting spaceborne SAR has reached the ground area where the adaptive system is located, and go to step 8;

[0035] Step 8: Set the conditions for determining the operating mode of the spaceborne SAR, including the maximum signal strength P rmax Duration judgment threshold δ Δt, the signal bandwidth judgment threshold δ of the beamforming working mode B2 , the pulse width judgment threshold δ of the beamforming working mode τ2 ;

[0036] Step 8.1: Determine the actual maximum signal strength P rmax Whether the duration Δt meets the judgment threshold δ Δt , that is, satisfying formula (7),

[0037] Δt≥δ Δt (7)

[0038] Step 8.2: Determine whether the collected pulse width τ meets the pulse width judgment threshold δ of the beamforming working mode τ2 , which satisfies formula (8):

[0039] τ≥δ τ2 (8)

[0040] Step 8.3: Determine whether the acquisition bandwidth B meets the signal bandwidth δ of the beamforming working mode B2 , which satisfies formula (9):

[0041] B≥δ B2 (9)

[0042] If equations (7)-(9) are all true, it is determined that the system is in the beamforming mode and goes to step 9, otherwise it goes to step 2;

[0043] Step 9: Set the observation area radius r in the beam mode g , then the identified observation area S is: with the adaptive system as the center and a radius of r g The region satisfies formula (10),

[0044]

[0045] Output the observation area S and return to step 2.

[0046] Beneficial effects of the present invention: The present invention designs and implements a method and adaptive system for determining the observation area in the beamforming working mode of a spaceborne SAR, including an antenna, a six-degree-of-freedom adaptive platform for a SAR radar receiving device, a host computer, a slave computer, and a power supply module. Through the operation of this system, the beamforming working state and working mode of the spaceborne SAR can be automatically identified on the ground. By comparing the collected parameters with the typical signal characteristics of the spaceborne SAR beamforming working mode, it is possible to automatically determine whether the spaceborne SAR is turned on, whether it is in the beamforming working mode, and the corresponding observation area. At the same time, based on the determination method of the above-mentioned adaptive system, the present invention can continuously, dynamically, and in real time determine the working state and observation area of different spaceborne SAR beamforming working modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Structure diagram of spaceborne SAR radar antenna and receiver

[0048] Figure 2 Spaceborne SAR radar receiver structure diagram

[0049] Figure 3 Structure diagram of the spaceborne SAR six-degree-of-freedom adaptive platform

[0050] Figure 4 View model diagram of the spaceborne SAR spotlight working mode

[0051] Figure 5 Flowchart of the status of the spaceborne SAR spotlight working mode and the determination of the observation area DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention. Specific implementation method 1

[0054] According to one embodiment of the present invention, Figure 1 The present invention discloses an adaptive system for determining an observation area in a satellite-borne SAR beamforming working mode, comprising an antenna (1), a SAR radar receiver (2), a six-degree-of-freedom adaptive platform (3), an upper computer (4), and a lower computer (5), wherein the antenna (1) comprises a reflecting surface (6), an antenna base (7), a back frame (8), and a feeding system (9); the back frame (8) is fitted to the back of the reflecting surface (6) and is locked and fixed by bolts; the feeding system (9) is connected to the antenna base (7), which is connected to the six-degree-of-freedom adaptive platform (3); the upper computer (4) controls the six-degree-of-freedom adaptive platform (3) to drive the antenna (1) to adjust the azimuth and / or elevation; and the lower computer (5) calculates the time when the SAR passes over the area according to an orbit calculation module (10), and calculates the initial azimuth angle parameter φ and the elevation angle parameter θ of the receiving antenna of a ground receiver according to the passing time. Specific embodiment 2

[0056] According to one embodiment of the present invention, Figure 2The SAR radar receiver (2) comprises a receiver protector (11), a low-noise high-frequency amplifier (12), a mixer (13), a local oscillator (14), an intermediate frequency amplifier (15), a detector (16) and a video amplifier (17). The receiver protector (11) receives the high-frequency signal collected by the antenna (1) through a transceiver switch, and sends the high-frequency signal to the mixer (13) after passing through the low-noise high-frequency amplifier (12). The mixer (13) mixes the high-frequency voltage generated by the local oscillator (14) to reduce the signal frequency to an intermediate frequency (IF). The signal is then sent to the intermediate frequency amplifier (15) to amplify and match filter the intermediate frequency pulse signal to obtain a maximum output signal-to-noise ratio. Finally, the signal is sent to the lower computer (5) after video amplification by the detector (16) and the video amplifier (17). Specific implementation method 3

[0058] According to one embodiment of the present invention, Figure 3 The six-degree-of-freedom adaptive platform (3) comprises: a base (18), an upper support frame (20) of a mounting seat (19), a lower support frame (21), an electric cylinder (22), and a power supply unit (23). The upper portion of the electric cylinder (22) is hinged to the mounting seat (19), and the lower portion is hinged to the base (18). The mounting seat (19) is connected to the antenna seat (7). The upper computer (4) controls the extension and retraction of the electric cylinder (22) of the six-degree-of-freedom adaptive platform (3) to complete the orientation alignment and attitude adjustment of the adaptive system. Specific implementation method 4

[0060] According to one embodiment of the present invention, Figure 4 、 5 A method for determining an observation area in a spaceborne SAR spotlight working mode comprises the following steps:

[0061] Step 1: Input the longitude and latitude information of the adaptive system into the host computer (4);

[0062] Step 2: Obtain the position h of the SAR satellite at a certain moment, the elevation angle parameter θ and the azimuth angle parameter φ of the SAR satellite relative to the adaptive system, and the maximum observation time window of the SAR satellite [t0,t g ];

[0063] Step 3: Input the satellite's pitch angle parameter θ and azimuth angle parameter φ relative to the adaptive system into the lower computer (5) and convert them into electric control signals and transmit them to the electric cylinder (22) to make the antenna point to the transit satellite-borne SAR;

[0064] Step 4: Determine whether the adaptive system has collected a signal. If a frequency modulation signal has been collected, go to step 5.

[0065] Step 5: Determine whether the collected signal is a linear frequency modulation signal. If the collected frequency modulation is a linear frequency modulation signal, go to step 6.

[0066] Step 6: Set the power-on pulse width judgment threshold δ τ1 =5μs, signal bandwidth power-on judgment threshold δ B1 =10MHz;

[0067] Step 6.1: Determine whether the collected pulse width τ meets the power-on pulse width judgment threshold δ τ1 Setting, that is, satisfying formula (11), input simulation data τ=20μs,

[0068] τ≥δ τ1 (11)

[0069] Step 6.2: Determine the collected signal bandwidth B and the signal bandwidth power-on judgment threshold setting, that is, satisfy formula (12), input simulation data B = 200MHz,

[0070] B≥δ B1 (12)

[0071] If both equations (11) and (12) hold, go to step 7;

[0072] Step 7: The peak power of the spaceborne SAR radar is known to be P t =1kW, the antenna main lobe gain is G t =55dB, the vertical slant distance between the adaptive system receiver and the satellite-borne SAR is R = 1000km, and the effective area of the adaptive system receiver antenna is A r =2m 2 , the propagation loss is 5dB, and the maximum signal strength of the satellite-borne SAR is P max Satisfying formula (13), let P r is the instantaneous signal strength collected, P rmax is the maximum instantaneous signal strength collected;

[0073]

[0074] Step 7.2: Input simulation data in the SAR satellite maximum observation time window [t0,t g ] = the instantaneous signal strength P collected within r =60dBmW, P rmax =-51dBmW:

[0075] P r >P rmax -20dBmW (14)

[0076] P rmax =P max(15)

[0077] If equations (14) and (15) are satisfied, it is considered that the main lobe of the transiting spaceborne SAR has reached the ground area where the adaptive system is located, and go to step 8;

[0078] Step 8: Set the conditions for determining the operating mode of the spaceborne SAR, including the maximum signal strength P rmax Duration judgment threshold δ Δt =5s, beamforming mode signal bandwidth judgment threshold δ B2 =150MHz, pulse width judgment threshold δ in beamforming mode τ2 =5μs;

[0079] Step 8.1: Input simulation data to measure the maximum signal strength P rmax Duration Δt=10s, that is,

[0080] Δt≥δ Δt (16)

[0081] Satisfy formula (16);

[0082] Step 8.2: Input the pulse width of simulation data acquisition τ = 20μs, that is,

[0083] τ≥δ τ2 (17)

[0084] Satisfy formula (17);

[0085] Step 8.3: Input simulation data acquisition bandwidth B = 400MHz, that is,

[0086] B≥δ B2 (18)

[0087] That is, if equation (18) is satisfied, it is determined to be in the beamforming working mode and go to step 9;

[0088] Step 9: Set the observation area radius r in the beam mode g =5km, then the identified observation area S is the area with a radius of 5km centered on the adaptive system, satisfying formula (19),

[0089]

[0090] Output the observation area S and return to step 2.

[0091] The above is a preferred embodiment of the present invention. For ordinary technicians in this field, based on the teachings of the present invention, without departing from the principles and spirit of the present invention, changes, modifications, replacements and deformations made to the implementation methods are still within the scope of protection of the present invention.

Claims

1. A method for determining the observation area of a spaceborne SAR in spotlight operating mode, which detects the characteristic value of a spaceborne SAR signal received by an adaptive system to determine whether the spaceborne SAR is turned on and in spotlight operating mode, and then determines the observation area, comprising the following steps: Step 1: Input the longitude and latitude information of the adaptive system into the host computer; Step 2: Obtain the position h of the SAR satellite at a certain moment, the pitch angle parameter θ and azimuth angle parameter φ of the SAR satellite relative to the adaptive system, and the maximum observation time window of the SAR satellite [t0,t g ]; Step 3: Input the satellite's pitch angle parameter θ and azimuth angle parameter φ relative to the adaptive system into the lower computer and convert them into electric control signals and transmit them to the electric cylinder to make the antenna point to the transiting satellite-borne SAR; Step 4: Determine whether the adaptive system has collected a signal. If not, go to step 2; if collected, go to step 5. Step 5: Determine whether the collected signal is a linear frequency modulation signal. If it is not a linear frequency modulation signal, go to step 2; if it is a linear frequency modulation signal, go to step 6; Step 6: Set the power-on pulse width judgment threshold δ τ1 , signal bandwidth power-on judgment threshold δ B1 ; Step 6.1: Determine whether the collected pulse width τ meets the power-on pulse width judgment threshold δ τ1 Set, that is, satisfy formula (1), τ≥δ τ1 (1) Step 6.2: Determine the collected signal bandwidth B and the signal bandwidth power-on judgment threshold setting, that is, satisfy formula (2), B≥δ B1 (2) If both equations (1) and (2) hold, go to step 7, otherwise go to step 2; Step 7: The peak power of the spaceborne SAR radar is known to be P t , the antenna main lobe gain is G t , the vertical slant distance between the adaptive system receiver and the spaceborne SAR is R, and the effective area of the adaptive system receiver antenna is A r , the maximum signal strength of spaceborne SAR P max Satisfying formula (3), let P r is the instantaneous signal strength collected, P rmax is the maximum instantaneous signal strength collected; Step 7.1: If the adaptive system is in the SAR satellite maximum over-the-air observation time window [t0,t g The instantaneous signal strength collected within ] satisfies formula (4): P r ≤P rmax -20dBmW (4) It is considered that the main lobe of the transiting spaceborne SAR has never reached the ground area where the adaptive system is located, and go to step 2; Step 7.2: If the adaptive system is within the maximum SAR satellite observation time window [t0,t g The instantaneous signal strength collected within ] satisfies equations (5) and (6): P r >P rmax -20dBmW (5) P rmax =P max (6) It is considered that the main lobe of the transiting spaceborne SAR has reached the ground area where the adaptive system is located, and go to step 8; Step 8: Set the conditions for determining the operating mode of the spaceborne SAR, including the maximum signal strength P rmax Duration judgment threshold δ Δt , the signal bandwidth judgment threshold δ of the beamforming working mode B2 , the pulse width judgment threshold δ of the beamforming working mode τ2 ; Step 8.1: Determine the actual maximum signal strength P rmax Whether the duration Δt meets the judgment threshold δ Δt , that is, satisfying formula (7), Δt≥δ Δt (7) Step 8.2: Determine whether the acquired pulse width τ meets the pulse width judgment threshold δ of the beamforming working mode τ2 , which satisfies formula (8): τ≥δ τ2 (8) Step 8.3: Determine whether the acquisition bandwidth B meets the signal bandwidth δ of the beamforming working mode B2 , which satisfies formula (9): B≥δ B2 (9) If equations (7)-(9) are all true, it is determined that the system is in the beamforming mode and goes to step 9, otherwise it goes to step 2; Step 9: Set the observation area radius r in strip mode g , then the identified observation area S satisfies formula (10), Output the observation area S and return to step 2.

2. An adaptive system for determining an observation area in a spaceborne SAR spotlight working mode, configured to execute the method for determining an observation area in a spaceborne SAR spotlight working mode according to claim 1, comprising: An antenna, a SAR radar receiver, a six-degree-of-freedom adaptive platform, a host computer, and a slave computer are characterized in that the antenna includes a reflecting surface, an antenna base, a back frame, and a feeding system. The back frame is in contact with the back of the reflecting surface and is fastened and fixed with bolts. The feeding system is connected to the antenna base, and the antenna base is connected to the six-degree-of-freedom adaptive platform. The host computer controls the six-degree-of-freedom adaptive platform to drive the antenna to adjust the azimuth and / or pitch direction. The slave computer calculates the time it takes for the SAR to pass over the area according to the orbit calculation module, and calculates the initial azimuth angle parameter φ and pitch angle parameter θ of the ground receiver's receiving antenna based on the passing time.

3. The adaptive system for determining observation area in a spaceborne SAR spotlight working mode according to claim 2, characterized in that: The antenna base is snap-connected or bolted to the six-degree-of-freedom adaptive platform. The antenna base can make follow-up changes in azimuth angle parameters and / or elevation angle parameters under the linkage of the six-degree-of-freedom adaptive platform.

4. The adaptive system for determining observation area in a spaceborne SAR spotlight working mode according to claim 2, characterized in that: The SAR radar receiver includes a receiver protector, a low-noise high-frequency amplifier, a mixer, a local oscillator, an intermediate frequency amplifier, a detector and a video amplifier. The receiver protector receives the high-frequency signal collected by the antenna through a transceiver switch, and sends it to the mixer after passing through the low-noise high-frequency amplifier. The mixer mixes the equal-amplitude high-frequency voltage generated by the local oscillator to reduce the signal frequency to an intermediate frequency, and transmits it to the intermediate frequency amplifier to amplify and match filter the intermediate frequency pulse signal to obtain the maximum output signal-to-noise ratio. Finally, it is amplified by the detector and video amplifier and sent to the lower computer.

5. The adaptive system for determining observation area in a spaceborne SAR spotlight working mode according to claim 2, characterized in that: The six-degree-of-freedom adaptive platform includes: a base, an upper support frame of the mounting base, a lower support frame, an electric cylinder, and a power supply unit. The upper part of the electric cylinder is hinged to the mounting base, and the lower part is hinged to the base. The mounting base is connected to the antenna base.

6. The adaptive system for determining observation area in a spaceborne SAR spotlight working mode according to claim 2, characterized in that: The six-degree-of-freedom adaptive platform includes two electronic inclinometers arranged perpendicular to each other, which can detect the error between the six-degree-of-freedom adaptive platform and the preset angle in a steady state and provide a correction control signal.

7. The adaptive system for determining observation area in a spaceborne SAR spotlight working mode according to claim 2, characterized in that: The six-degree-of-freedom adaptive platform includes two electronic levels arranged perpendicular to each other, which can detect the horizontal zero-degree angle error of the six-degree-of-freedom adaptive platform when the antenna base is initially installed and provide an error compensation control signal.

8. The adaptive system for determining observation area in a spaceborne SAR spotlight working mode according to claim 2, characterized in that: The six-degree-of-freedom adaptive platform includes a Beidou module and / or a GNSS module for collecting the latitude and longitude information of the six-degree-of-freedom adaptive platform.

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