An airborne SAR (synthetic aperture radar) adaptive system and method for determining an observation area in a beamforming mode

Abstract

The present application belongs to the field of SAR radar ground receiving, and relates to an airborne SAR bunching working mode adaptive system and an observation area determination method. The present application designs and implements an airborne SAR bunching working mode adaptive system and an observation area determination method, which comprises a three-coordinate radar, an antenna, a SAR radar receiver six-degree-of-freedom adaptive platform, an upper computer, a lower computer, and a power supply module. Through the operation of the system, the automatic identification of the airborne SAR bunching working state and working mode on the ground can be completed. Through the comparison of the collected parameters and the typical signal characteristics under the airborne SAR bunching working mode, it can be automatically determined whether the airborne SAR is started, whether it is in the bunching working mode, and the corresponding observation area. At the same time, the present application proposes an observation area determination method based on the above adaptive system, which can continuously, dynamically and in real time determine the working state and observation area under different airborne SAR bunching working modes.

Description

TECHNICAL FIELD

[0001] The work mode adaptive ground receiving system belongs to the field of SAR radar ground receiving, and relates to an airborne SAR spotlight work mode adaptive system and an observation area determination method. BACKGROUND

[0002] Airborne synthetic aperture radar (SAR) has the advantages of all-weather, all-day, high-resolution detection imaging, strong penetration, strong anti-interference ability, etc., and is widely used in military and civilian fields. Generally, airborne SAR has three working modes: strip, scanning and spotlight. The airborne SAR spotlight work mode adaptive system is deployed on the ground, and by comparing the real-time received signals with the stored or calculated signal characteristics under the working state of the airborne SAR, it is determined whether the airborne SAR is working, and then according to the received signal characteristics, it is quickly determined whether the airborne SAR is in the spotlight working mode, the working state of the ground receiving system is adjusted to adapt to the identification of the working mode of the airborne SAR, and further the observation area of the airborne SAR in the spotlight working mode is determined.

[0003] SAR based on different platform carriers needs to consider different influencing factors, airborne SAR and satellite-borne SAR have different platform heights and speeds, and different influences of earth rotation and earth curvature, so under different platforms, the influences of ground clutter spectrum width, range ambiguity, earth rotation, earth curvature, wave propagation, etc. on the echo need to be considered, and different identification systems are constructed accordingly.

[0004] At present, in the field of SAR radar research, the analysis and processing of the collected radar signals are mainly concentrated on, and then the frequency, bandwidth, pulse width, time of arrival, angle of arrival, etc. of the signal are obtained, and the problem of identification and observation area determination of different SAR radar working modes under different carriers is rarely researched and discussed. The radar signal characteristics under different SAR radar working modes are different, which determines that the signal values collected by the ground receiving system for different working modes are different, and the basis for adaptive control signal is also different, so it has important practical significance and application value to identify the airborne SAR spotlight working mode and determine the observation area. SUMMARY

[0005] In different operating modes, airborne SAR receives different characteristic parameters from the ground signal receiving system. The identification method for airborne SAR spotting mode mainly combines the altitude, velocity, and direction information provided by a three-coordinate radar. Based on the signal parameters and their variation patterns received by the airborne ground receiving system, the spotting status and mode of the airborne SAR can be identified. The signal characteristic parameters in airborne SAR spotting mode mainly include signal frequency, modulation pattern, 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 ground receiving system meet the criteria, it can be determined whether the airborne SAR is powered on and in spotting mode, and the observation area can be determined based on this information.

[0006] The technical problem solved by this adaptive ground receiving system for airborne SAR working mode is to provide an adaptive system and observation area determination method for airborne SAR spotting working mode. The adaptive system is deployed on the ground and has the capability to acquire information on the maneuvering status of the SAR airborne platform, acquire radar signals, and determine the working mode and observation area. First, based on three-coordinate radar observations, the altitude, speed, and direction information of the SAR airborne platform are acquired, and the instantaneous situational information between the adaptive system and the airborne platform is determined, including the position of the SAR airborne platform at a certain moment, the airborne platform's ground trajectory, the time of contact, and the elevation angle parameters of the airborne SAR relative to the ground adaptive system. The system first obtains the azimuth and elevation angle parameters φ, and then transmits these parameters to the adaptive ground receiving system in the airborne SAR spotting mode. The system converts these angle parameters into electronically controlled signals, and the control platform adjusts the elevation and azimuth angles to point the antenna towards the airborne SAR, completing the initial antenna alignment. Next, it determines whether the airborne SAR is operational based on whether a valid airborne SAR radar signal has been acquired. If no signal is acquired, the airborne SAR is considered not operational; if a signal is acquired, and the modulation pattern, pulse width τ, and signal bandwidth B all meet the criteria, the airborne SAR is considered operational. Third, after determining that the airborne SAR is operational, the system further analyzes the received instantaneous maximum signal strength P. rmax With receiver sensitivity P rmin The relationship between the maximum signal strength P rmax Duration Δt and duration judgment threshold δ Δt The relationship between the received signal bandwidth B and the threshold δ for judging the signal bandwidth in the beamforming working mode. B2 Based on the relationship, the system determines whether the airborne SAR is in spotlight mode. Finally, based on the determined spotlight mode, the observation area of ​​the airborne SAR is given.

[0007] The technical solution of the adaptive ground receiving system of the working mode is: an adaptive ground receiving system of a SAR airborne working mode, comprising a three-coordinate radar (1), an antenna (2), a SAR radar receiver (3), a six-degree-of-freedom adaptive platform (4), an upper computer (5), and a lower computer (6), characterized in that the antenna (2) comprises a reflector (7), an antenna base (8), a back frame (9), a feeding system, and a power supply unit (10) of the equipment, the back frame (9) is attached to the back of the reflector (7) and is locked and fixed by bolts, the antenna base (8) is connected with the six-degree-of-freedom adaptive platform (4), the lower computer (6) controls the six-degree-of-freedom adaptive platform (4) to drive the antenna (2) to adjust the azimuth and / or the elevation, the upper computer (5) obtains the height information, the speed information, and the direction information of the SAR airborne platform through the three-coordinate radar (1), calculates the time of the SAR over-the-top region, and calculates the initial azimuth angle parameter φ and the elevation angle parameter of the ground receiver receiving antenna and converts into an electric control signal of the six-degree-of-freedom adaptive platform (4).

[0008] As a further improvement of the adaptive ground receiving system of the working mode, the antenna base (8) is clamped or bolted with the six-degree-of-freedom adaptive platform (4), and the antenna base (8) can follow the changes of the azimuth angle parameter and / or the elevation angle parameter under the linkage of the six-degree-of-freedom adaptive platform (4).

[0009] As a further improvement of the adaptive ground receiving system of the working mode, the SAR radar receiver (3) 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 signals collected by the receiving antenna (2) through a transceiver switch, sends the signals to the mixer (13) after the low-noise high-frequency amplifier (12), the mixer (13) mixes with the equal-amplitude high-frequency voltage generated by the local oscillator (14) to reduce the signal frequency to intermediate frequency (IF), and transmits the intermediate frequency pulse signal to the intermediate frequency amplifier (15) for amplification and matched filtering to obtain the maximum output signal-to-noise ratio, and finally sends the video-amplified signals to the lower computer (6) through the detector (16) and the video amplifier (17).

[0010] As a further improvement of the adaptive ground receiving system of the working mode, the six-degree-of-freedom adaptive platform (4) comprises a base (18), a mounting seat (19), an upper support frame (20), 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 with the mounting seat (19), the lower part is hinged with the base (18), and the mounting seat (19) is connected with the antenna base (8).

[0011] As a further improvement of the adaptive ground receiving system of the present working mode, two electronic angle meters arranged perpendicular to each other are included on the six-degree-of-freedom adaptive platform (4), which can detect the error of the six-degree-of-freedom adaptive platform (4) from the preset angle in the steady state and give a correction control signal.

[0012] As a further improvement of the adaptive ground receiving system of the present working mode, two electronic level meters arranged perpendicular to each other are included on the six-degree-of-freedom adaptive platform (4), which can detect the horizontal zero-degree angle error of the six-degree-of-freedom adaptive platform (4) when the antenna pedestal (8) is initially installed, and give an error compensation control signal.

[0013] As a further improvement of the adaptive ground receiving system of the present working mode, a Beidou module and / or a GNSS module are included on the three-coordinate radar (1) and the six-degree-of-freedom adaptive platform (4) to collect the latitude and longitude information of the three-coordinate radar (1) and the six-degree-of-freedom adaptive platform (4).

[0014] An observation area determination method for the above-mentioned airborne SAR adaptive system in the spotlight working mode, which determines whether the airborne SAR is turned on and whether it is in the spotlight working mode by detecting the characteristic value of the airborne SAR signal received by the adaptive ground receiving system, and determines the observation area, including the following implementation steps:

[0015] Step 1: input the latitude and longitude information of the three-coordinate radar (1) and the SAR radar receiver (3) into the upper computer (5);

[0016] Step 2: observe the airspace by the three-coordinate radar (1), and if a platform is found, transmit the collected height information, speed information, and direction information to the upper computer (5);

[0017] Step 3: calculate the position h of the SAR airborne platform at a certain time, the pitch angle parameter and the azimuth angle parameter φ of the SAR airborne platform relative to the adaptive system, and the maximum airborne observation time window [t0, t g ] of the SAR airborne platform relative to the adaptive system by the upper computer (5);

[0018] Step 4: input the pitch angle parameter and the azimuth angle parameter φ of the SAR airborne platform relative to the adaptive system into the lower computer (6) and convert them into electric control signals to be transmitted to the electric cylinder (22) to direct the antenna to the airborne SAR;

[0019] Step 5: determine whether the adaptive system has collected signals, if not, go to step 2; if yes, go to step 6;

[0020] Step 6: judge whether the collected signal is a linear frequency modulation signal, if not, go to Step 2; if yes, go to Step 7;

[0021] Step 7: set the start-up pulse width judgment threshold δ τ1 , and the signal bandwidth start-up judgment threshold δ B1 ;

[0022] Step 7.1: judge whether the collected pulse width τ satisfies the start-up pulse width judgment threshold δ τ1 , i.e. satisfies formula (1),

[0023] τ≥δ τ1 (1)

[0024] Step 7.2: judge whether the collected signal bandwidth B satisfies the signal bandwidth start-up judgment threshold δ

[0025] B≥δ B1 (2)

[0026] If both formula (1) and (2) are satisfied, go to Step 8, otherwise go to Step 2;

[0027] Step 8: set P rmax as the collected instantaneous maximum signal strength, and P rmin as the receiver sensitivity;

[0028] Step 8.1: if the instantaneous maximum signal strength P g collected by the adaptive system within the maximum air-space observation time window [t0, t rmax ] of the SAR airborne platform satisfies formula (3):

[0029] P rmax <P rmin +30(dbmi) (3)

[0030] it is considered that the main lobe of the air-space airborne SAR has not reached the ground area where the adaptive system is located, and go to Step 2;

[0031] Step 8.2: if the instantaneous maximum signal strength P g collected by the adaptive system within the maximum air-space observation time window [t0, t rmax ] of the SAR airborne platform satisfies formula (4):

[0032] P rmax ≥P rmin +30(dbmi) (4)

[0033] it is considered that the main lobe of the air-space airborne SAR has reached the ground area where the adaptive system is located, and go to Step 9;

[0034] Step 9: Set the airborne SAR beamforming mode judgment condition, including the instantaneous signal strength P r Duration judgment threshold δ Δt , beamforming mode signal bandwidth judgment threshold δ B2 , beamforming mode pulse width judgment threshold δ τ2 ;

[0035] Step 9.1: Judge whether the instantaneous signal strength P r and the receiver sensitivity P rmin satisfy equation (5),

[0036] P r ≥ P rmin + 30 (dbmi) (5)

[0037] Step 9.2: Judge whether the instantaneous signal strength P r duration Δt satisfies the judgment threshold δ Δt , that is, equation (6) is satisfied,

[0038] Δt ≥ δ Δt (6)

[0039] Step 9.3: Judge whether the collected pulse width τ satisfies the beamforming mode pulse width judgment threshold δ τ2 , that is, equation (7) is satisfied:

[0040] τ ≥ δ τ1 (7)

[0041] Step 9.4: Judge whether the collected bandwidth B satisfies the beamforming mode signal bandwidth δ B2 , that is, equation (8) is satisfied:

[0042] B ≥ δ B2 (8)

[0043] If equations (5)-(8) are all true, and there is no significant change in signal repetition period, pulse width and signal bandwidth, it is determined that it is in the beamforming mode, and step 10 is entered, otherwise step 2 is entered;

[0044] Step 10, set the observation area radius r g in the beamforming mode, then the identified observation area S is: the area with the adaptive system as the center and the radius r g satisfying equation (9),

[0045] S = πr g 2 (9) output the observation area S, and return to step 2.

[0046] The beneficial effects of the working mode adaptive ground receiving system: the working mode adaptive ground receiving system designed and implemented a kind of airborne SAR bunching working mode adaptive system and observation area determination method, including three coordinate radar, antenna, SAR radar receiver six degrees of freedom adaptive platform, host computer, lower computer and power supply module. Through the operation of the system, the automatic identification of airborne SAR bunching working state and working mode can be completed on the ground, and by comparing the parameters collected and the typical signal characteristics in the airborne SAR bunching working mode, it can be automatically determined whether the airborne SAR is started, whether it is in the bunching working mode, and the corresponding observation area. At the same time, the working mode adaptive ground receiving system based on the determination method of the above adaptive system can continuously, dynamically and real-timely determine the working state and observation area in different airborne SAR bunching working modes. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 Structure diagram of airborne SAR bunching working mode adaptive system

[0048] Figure 2 Structure diagram of airborne SAR radar antenna and receiver

[0049] Figure 3 Structure diagram of airborne SAR radar receiver

[0050] Figure 4 Structure diagram of airborne SAR six degrees of freedom adaptive platform

[0051] Figure 5 View angle model diagram of airborne SAR bunching working mode

[0052] Figure 6 Flow chart of airborne SAR bunching working mode state and observation area determination DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the working mode adaptive ground receiving system embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0054] According to one embodiment of the present application, in combination with Figure 1 , 2An adaptive ground receiving system of a kind of airborne SAR bunching operation mode, comprising a three-coordinate radar (1), an antenna (2), a SAR radar receiver (3), a six-degree-of-freedom adaptive platform (4), an upper computer (5), and a lower computer (6), characterized in that the antenna (2) comprises a reflecting surface (7), an antenna seat (8), a back frame (9), a feeding system, and a power supply unit (10) of the equipment, the back frame (9) is attached to the back of the reflecting surface (7) and is locked and fixed by bolt connection, the antenna seat (8) is connected with the six-degree-of-freedom adaptive platform (4), the lower computer (6) controls the six-degree-of-freedom adaptive platform (4) to drive the antenna (2) to adjust in the azimuth direction and / or the elevation direction, the upper computer (5) acquires height information, speed information, and direction information of the SAR airborne platform according to the three-coordinate radar (1), determines the time of the SAR over-the-top region, determines initial azimuth angle parameters and elevation angle parameters of the antenna according to the over-the-top time, and converts into an electric control signal of the six-degree-of-freedom adaptive platform (4) to control the electric cylinder (22) of the six-degree-of-freedom adaptive platform (4) to extend and retract, so as to complete azimuth alignment and attitude adjustment of the adaptive system.

[0055] According to one embodiment of the present application, in combination Figure 3 The SAR radar receiver (3) 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 high-frequency signals collected by the receiving antenna (2) through a transceiver switch, and sends the signals to the mixer (13) after being amplified by the low-noise high-frequency amplifier (12), the mixer (13) mixes with high-frequency voltage generated by the local oscillator (14) to reduce the signal frequency to intermediate frequency, and transmits the intermediate frequency pulse signal to the intermediate frequency amplifier (15) for amplification and matched filtering to obtain the maximum output signal-to-noise ratio, and finally sends the video-amplified signal to the lower computer (6) through the detector (16) and the video amplifier (17), and the lower computer (6) transmits the collected signal value to the upper computer (5), and the upper computer (5) determines whether the airborne SAR is started and whether it is in the bunching operation mode according to the comparison between the collected signal value and the characteristic signal value in the bunching operation mode.

[0056] According to one embodiment of the present application, in combination Figure 4The six-degree-of-freedom adaptive platform (4) includes: a base (18), a mounting base (19), an upper support frame (20), 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 base (19), and the lower part is hinged to the base (18). The mounting base (19) is connected to the antenna mount (8). After the host computer (5) receives the altitude, speed, and direction information of the SAR airborne platform obtained by the three-coordinate radar (1), it converts the information into the electronic control signal of the six-degree-of-freedom adaptive platform (4) and transmits it to the lower computer (6). The lower computer (6) controls the electric cylinder (22) to extend and retract to adjust the attitude of the SAR radar receiver (3) so that the antenna (2) faces the direction of the airborne SAR platform and completes the adaptive alignment.

[0057] According to one implementation of this working mode adaptive ground receiving system, combined with Figure 5 , 6 A detection method for an adaptive ground receiving system used in the aforementioned airborne SAR spotting mode includes the following steps:

[0058] Step 1: Input the latitude and longitude information of the three-coordinate radar (1) and SAR radar receiver (3) into the host computer (5);

[0059] Step 2: Observe the airspace using a three-coordinate radar (1). If an incoming airborne platform is detected, transmit the collected altitude, speed and direction information to the host computer (5).

[0060] Step 3: The position h of the SAR airborne platform at a certain moment is obtained through calculation by the host computer (5), and the pitch angle parameters of the SAR airborne platform relative to the adaptive system are obtained. And azimuth parameter φ, the maximum observation time window [t0,t] of the SAR airborne platform g ];

[0061] Step 4: Set the pitch angle parameters of the airborne platform relative to the adaptive system. The azimuth angle parameter φ is input into the lower-level machine (6) and converted into an electronic control signal and transmitted to the electric cylinder (22) to make the antenna point to the airborne SAR in the airspace;

[0062] Step 5: Determine whether the adaptive system has acquired a signal. If a frequency modulation signal has been acquired, proceed to step 5.

[0063] Step 6: Determine whether the acquired signal is a linear frequency modulation (LFM) signal. If the acquired LFM signal is a LFM signal, proceed to Step 7.

[0064] Step 7: Set the power-on pulse width judgment threshold δ τ1 =5μs, signal bandwidth power-on judgment threshold δ B1 =10MHz;

[0065] Step 7.1: judging whether the collected pulse width τ satisfies the start-up pulse width judging threshold δ τ1 Setting, i.e. satisfying formula (10), input simulation data τ = 10 μs,

[0066] τ ≥ δ τ1 (10)

[0067] Step 7.2: judging whether the collected signal bandwidth B satisfies the signal bandwidth start-up judging threshold δ

[0068] B ≥ δ B1 (11)

[0069] If both (10) and (11) are established, go to Step 8;

[0070] Step 8: set P rmax as the collected instantaneous maximum signal strength, the receiver sensitivity P rmin = -110 dBmi;

[0071] Step 8.1: if the adaptive system collects the instantaneous maximum signal strength P g = -90 dBmi in the maximum air-space observation time window [t0, t rmax ] of the SAR airborne platform, satisfying formula (12):

[0072] P rmax < P rmin + 30 (dbmi) (12)

[0073] It is considered that the main lobe of the air-space SAR has not reached the ground area where the adaptive system is located, and go to Step 2;

[0074] Step 8.2: if the adaptive system collects the instantaneous maximum signal strength P g = -70 dBmi in the maximum air-space observation time window [t0, t rmax ] of the SAR airborne platform, satisfying formula (13):

[0075] P rmax ≥ P rmin + 30 (dbmi) (13)

[0076] It is considered that the main lobe of the air-space SAR has reached the ground area where the adaptive system is located, and go to Step 9;

[0077] Step 9: setting the airborne SAR working mode judging condition, including the maximum signal strength P rmax and the duration judging threshold δ Δt= 5s, the bundled operation mode signal bandwidth judgment threshold δ B2 = 200MHz, the bundled operation mode pulse width judgment threshold δ τ2 = 15μs;

[0078] Step 9.1: input the simulation data actual measurement maximum signal strength P rmax Duration Δt = 10s, i.e.,

[0079] Δt≥δ Δt (14)

[0080] Satisfy equation (14);

[0081] Step 9.2: input the simulation data pulse width τ = 30μs of the acquisition, i.e.,

[0082] τ≥δ τ1 (15)

[0083] Satisfy equation (15);

[0084] Step 9.3: input the simulation data acquisition bandwidth B = 400MHz, i.e.,

[0085] B≥δ B2 (16)

[0086] Satisfy equation (15), then determine that it is in the bundled operation mode and go to step 10;

[0087] Step 10, set the observation area radius r g = 5km in the bundled mode, then the identified observation area S is: the area with the ground adaptive system as the center and the radius of r g Satisfy equation (17),

[0088] S = πr g 2 = 25π(km 2 ) (17)

[0089] Output the observation area S and go back to step 2.

[0090] The above describes the preferred embodiment of the present operation mode adaptive ground receiving system. According to the teaching of the present operation mode adaptive ground receiving system, the changes, modifications, replacements and deformations made to the embodiment without departing from the principles and spirits of the present operation mode adaptive ground receiving system still fall within the protection scope of the present operation mode adaptive ground receiving system.

Claims

1. A method for determining the observation area in airborne SAR spotting mode, characterized in that, The implementation steps include: Step 1: input the latitude and longitude information of the three-dimensional radar and the SAR radar receiver into the upper computer; Step 2: observe the airspace by the three-dimensional radar, and if a target approaching the airborne platform is found, the height information, speed information and direction information collected are transmitted to the upper computer; Step 3: Obtain the position h of the SAR airborne platform at a certain time, the pitch angle parameter of the SAR airborne platform relative to the adaptive system, and the azimuth angle parameter φ of the SAR airborne platform by calculation of the host computer and the maximum over-the-air observation time window [t0, t g ] of the SAR airborne platform Step 4: Set the pitch angle parameters of the airborne platform relative to the adaptive system. The azimuth parameter φ is input into the lower-level machine and converted into an electronic control signal, which is then transmitted to the electric cylinder to make the antenna point towards the airborne SAR in the airspace. Step 5: determine whether the adaptive system has collected signals, if not, go to step 2; if yes, go to step 6; Step 6: determine whether the collected signals are linear frequency modulation signals, if not, go to step 2; if yes, go to step 7; Step 7.2: determine whether the collected signal bandwidth B meets the signal bandwidth start-up judgment threshold, i.e. formula (2) is met, Step 7: Set the start-up pulse bandwidth judgment threshold δ τ1 , signal bandwidth start-up judgment threshold δ B1 ; Step 7.1: Determine whether the collected pulse width τ satisfies the start-up pulse bandwidth determination threshold δ τ1 Set, i.e. satisfy equation (1), τ≥δ τ1 (1) If both formula (1) and formula (2) are met, go to step 8, otherwise go to step 2; B ≥ δ B1 (2) If formula (5)-(8) are all met, and the signal repetition period, pulse width and signal bandwidth do not change significantly, it is determined that the system is in the spotlight mode, go to step 10, otherwise go to step 2; Step 8: Let P r max P is the instantaneous maximum signal strength collected r min receiver sensitivity; Step 8.1: If the instantaneous maximum signal strength P g collected by the adaptive system within the maximum air-borne observation time window [t0, t r max satisfies equation (3): P r max <P r min +30 (3) Output the observation area S and return to step 2. Step 8.2: If the instantaneous maximum signal strength P g collected by the adaptive system within the maximum air-borne observation time window [t0, t r max satisfies equation (4): P r max ≥P r min +30 (4) The three-dimensional radar, antenna, SAR radar receiver, six-degree-of-freedom adaptive platform, upper computer and lower computer are characterized in that the antenna includes a reflector, an antenna base, a back frame and a feed system; the back frame is attached to the back of the reflector and is locked and fixed by bolts, and the feed system is connected with the antenna base; the antenna base is connected with the six-degree-of-freedom adaptive platform, and the lower computer controls the six-degree-of-freedom adaptive platform to drive the antenna to adjust the azimuth and / or elevation; the upper computer obtains the height information, speed information and direction information of the SAR airborne platform according to the three-dimensional radar, calculates the time of the SAR over-the-top area, and calculates the initial azimuth angle parameter φ and the elevation angle parameter θ of the ground receiver receiving antenna according to the over-the-top time, and converts them into electric control signals for controlling the six-degree-of-freedom adaptive platform. Step 9: Set the airborne SAR working mode judgment condition, including instantaneous signal strength P r Duration judgment threshold δ Δt , the signal bandwidth judgment threshold δ of the bunching working mode B2 , the pulse bandwidth judgment threshold δ of the bunching working mode τ2 ; Step 9.1: Determine instantaneous signal strength P r with receiver sensitivity P r min whether equation (5) is satisfied, P r ≥P r min +30 (5) Step 9.2: judging the instantaneous signal strength P r whether the duration Δt satisfies the judging threshold δ Δt i.e., satisfies Equation (6), Δt > δ Δt (6) Step 9.3: judging whether the collected pulse width τ satisfies the bunched operation mode pulse bandwidth judging threshold value δ τ2 i.e., satisfies equation (7): τ ≥ δ τ1 (7) Step 9.4: Determine whether the acquisition bandwidth B satisfies the signal bandwidth δ of the beamforming operation mode B2 i.e., satisfies equation (8): B ≥ δ B2 (8) The antenna base is clamped or bolted with the six-degree-of-freedom adaptive platform, and the antenna base makes follow-up changes in the azimuth angle parameter and / or the elevation angle parameter under the linkage of the six-degree-of-freedom adaptive platform. Step 10, set the observation region radius r in strip mode g The identified observation region S is then a region centered at the adaptive system with radius r that satisfies equation (9), g ​ S＝πr g 2 (9) 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 signals collected by the receiving antenna through a transceiver switch, and sends them to the mixer after being amplified by the low-noise high-frequency amplifier; the mixer mixes with the equal-amplitude high-frequency voltage generated by the local oscillator to reduce the signal frequency to intermediate frequency, and transmits it to the intermediate frequency amplifier for amplification and matched filtering of the intermediate frequency pulse signal to obtain the maximum output signal-to-noise ratio; finally, it is sent to the lower computer after video amplification by the detector and the video amplifier.

2. An airborne SAR spotlight mode adaptive system for performing the method of claim 1, comprising: ​ 3. The airborne SAR adaptive system of claim 2, wherein, ​ 4. The airborne SAR adaptive system of claim 2, wherein, ​ 5. The airborne SAR spotlight mode adaptive system of claim 2, wherein, The six-degree-of-freedom adaptive platform comprises a base, a mounting seat, an upper support frame, a lower support frame, an electric cylinder, a power supply unit, the upper part of the electric cylinder is hinged to the mounting seat, the lower part is hinged to the base, and the mounting seat is connected to the antenna seat.

6. The airborne SAR spotlight mode adaptive system of claim 2, wherein, The six-degree-of-freedom adaptive platform comprises two electronic angle meters arranged perpendicularly to each other, which detect the error of the six-degree-of-freedom adaptive platform from the preset angle in a steady state and give a correction control signal.

7. The onboard SAR adaptive system of claim 2, wherein, The six-degree-of-freedom adaptive platform comprises two electronic level meters arranged perpendicularly to each other, which detect the horizontal zero-degree angle error of the six-degree-of-freedom adaptive platform in the initial installation of the antenna seat and give an error compensation control signal.

8. The onboard SAR adaptive system of claim 2, wherein, The three-coordinate radar and the six-degree-of-freedom adaptive platform comprise a Beidou module and / or a GNSS module, which are used to collect the longitude and latitude information of the three-coordinate radar and the six-degree-of-freedom adaptive platform.

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