Method and system for improving precision of on-orbit SAR antenna pattern of light and small satellite

Abstract

The invention provides a method and a system for improving the precision of an on-orbit SAR antenna pattern of a light and small satellite. The method comprises the following steps: S1, establishing an SAR antenna mechanical flatness field model; s2, establishing a thermal deformation field model of the SAR antenna; s3, establishing an SAR antenna T / R active channel amplitude-phase data field model; s4, SAR antenna machine, thermal and electrical errors are converted into a unified phase coordinate system; s5, establishing a satellite attitude pointing error model, and performing unified physical field conversion; and step S6: respectively carrying out sensitivity analysis on the direction of the antenna pattern aiming at the satellite attitude and the SAR antenna mechanical, thermal and electrical errors. According to the method, ground test and on-orbit data are adopted to compensate for SAR antenna mechanical, electrical and thermal phase errors and satellite platform attitude errors, so that the precision of an SAR antenna pattern model is further improved, and the on-orbit image quality is practically guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of aerospace system technology, and in particular to a method and system for improving the accuracy of on-orbit SAR antenna patterns of lightweight small satellites. Background Art

[0002] Synthetic Aperture Radar (SAR), with its exceptional all-weather, all-day operation, plays an indispensable role in numerous fields. In SAR systems, the accuracy of the antenna pattern model is a key factor influencing the accuracy of SAR images. A precise antenna pattern ensures that the SAR system accurately transmits and receives signals, thereby acquiring high-resolution, high-precision images, providing crucial data support for industries such as geological exploration, ocean monitoring, and disaster assessment.

[0003] In recent years, with the explosive growth in demand for satellite applications across various industries, small satellites have gradually become a focus of research and development in various fields. Compared to traditional large satellites, small satellites offer significant advantages such as low cost, compact size, and light weight, enabling them to more quickly and flexibly meet diverse application needs. Small, lightweight SAR satellites, in particular, demonstrate enormous potential for development in the commercial aerospace sector due to their short development cycles and rapid development pace, enabling rapid response to market demand and operational deployment.

[0004] However, the development of lightweight and small SAR satellites also faces numerous challenges. There is a significant gap in antenna pattern accuracy compared to conventional large satellites. Conventional large satellites have ample time during the ground testing phase, allowing for detailed testing of a large number of different wave positions. This wealth of test data allows for precise acquisition of antenna performance parameters under various conditions, enabling the creation of highly accurate antenna pattern models. However, due to development cycle and cost constraints, the number of wave positions for antenna pattern testing on lightweight and small SAR satellites is extremely limited. To meet deadlines, ground testing had to be simplified. While this simplification increased development speed, it also introduced serious problems. Due to large errors in the input parameters used for antenna pattern modeling, the accuracy of the resulting pattern model was significantly reduced.

[0005] A search of patent documents revealed an invention patent with application number 202310693856.0, which discloses a method and system for analyzing the impact of phased array SAR antenna surface deformation on the radiation pattern. The method includes: obtaining the surface data in the three dimensions of mechanical, electrical, and thermal, and unifying them into a coordinate system with a two-dimensional arrangement of the surface ports; superimposing them with the surface channel amplitude and phase data to obtain the antenna surface single TR amplitude and phase distribution data; thereby obtaining the corresponding radiation pattern; and then evaluating the impact of different factors on the radiation pattern. This patent establishes an antenna radiation pattern model by unifying and superimposing the influencing factors of the three dimensions of antenna mechanical, electrical, and thermal on the TR channel amplitude and phase. However, it does not fully consider the satellite attitude pointing error, and pays insufficient attention to on-orbit application scenarios.

[0006] In summary, in response to the above-mentioned problems of the existing technology, studying a method and system for improving the accuracy of the on-orbit SAR antenna pattern of lightweight and small satellites has become a key task that needs to be solved urgently. Summary of the Invention

[0007] In view of the defects in the prior art, the purpose of the present invention is to provide a method and system for improving the accuracy of the on-orbit SAR antenna pattern of a lightweight small satellite.

[0008] According to the present invention, a method for improving the SAR antenna pattern accuracy of a small and lightweight satellite on-orbit includes the following steps:

[0009] Step S1, obtaining mechanical flatness data of the SAR antenna and establishing a mechanical flatness field model of the SAR antenna;

[0010] Step S2, based on the SAR antenna mechanical flatness field model, obtaining the thermal deformation data of the SAR antenna under different temperature fields, and establishing the SAR antenna thermal deformation field model;

[0011] Step S3, based on the SAR antenna thermal deformation field model, obtaining the T / R active channel amplitude and phase error data of the SAR antenna, and establishing the SAR antenna T / R active channel amplitude and phase data field model;

[0012] Step S4: The mechanical flatness error of the SAR antenna mechanical flatness field model, the electrical error of the SAR antenna T / R active channel amplitude and phase data field model, and the thermal flatness error of the SAR antenna thermal deformation field model are converted into the mechanical flatness error of the SAR antenna mechanical flatness field model.

[0013] Converting to a unified phase coordinate system to obtain phase data in the unified phase coordinate system;

[0014] Step S5, establishing a satellite attitude pointing error model based on the phase data in the unified phase coordinate system, performing unified physical field conversion, and obtaining phase data containing the satellite attitude pointing error;

[0015] Step S6: Based on the phase data including the satellite attitude pointing error, the SAR antenna pattern accuracy is improved by analyzing the sensitivity of the satellite attitude pointing error, mechanical flatness error, thermal flatness error and electrical error to the antenna pattern pointing.

[0016] Preferably, step S1 includes the following sub-steps:

[0017] Step S1.1, attaching targets on the active channels in the azimuth and range directions in the +Z direction of the SAR antenna array;

[0018] Step S1.2: Place a reference ruler next to the SAR antenna, with the reference ruler parallel to the surface of the SAR antenna array;

[0019] Step S1.3: Use a camera to take photos of the targets on the SAR antenna array. Each target should be photographed at least four times at different angles. Each photo should capture at least four target points. After each photo, rotate the camera 90° and take another photo.

[0020] Step S1.4: derive the target's measurement data and perform data processing to obtain the target's three-dimensional coordinate data, and then obtain the mechanical flatness data of the SAR antenna.

[0021] Preferably, step S2 includes the following sub-steps:

[0022] Step S2.1, measuring the mechanical flatness of the SAR antenna and the pointing direction of the star sensor mounting surface at temperature T0;

[0023] Step S2.2, heating the SAR antenna array and measuring the mechanical flatness of the SAR antenna and the pointing direction of the star sensor mounting surface;

[0024] Step S2.3: After returning to temperature, heat the joints of the SAR antenna's deployment mechanism and measure the SAR antenna's mechanical flatness and the star sensor mounting surface pointing direction.

[0025] Step S2.4: After returning to temperature, heat the star sensor bracket of the SAR antenna and measure the mechanical flatness of the SAR antenna and the pointing direction of the star sensor mounting surface;

[0026] Step S2.5: After returning to temperature, heat the star body and joints of the SAR antenna, and measure the mechanical flatness of the SAR antenna and the pointing direction of the star sensor mounting surface;

[0027] Step S2.6: After returning to temperature, heat the SAR antenna's star body, joints, SAR antenna array, and star sensor bracket, and measure the SAR antenna's mechanical flatness and the star sensor mounting surface's pointing direction.

[0028] Step S2.7: Analyze the measurement data under different working conditions in steps S2.1 to S2.6 to obtain thermal deformation data of the SAR antenna under different temperature fields.

[0029] Preferably, the implementation route of the external calibration method in step S3 is: FM signal source → internal calibrator → calibration test cable → horn antenna → antenna waveguide → T / R component → RF link → power splitter combination → radar receiving module, to obtain the T / R active channel amplitude and phase error data of the SAR antenna.

[0030] Preferably, step S3 includes the following sub-steps:

[0031] Step S3.1, establishing a test state of the satellite and the external horn antenna;

[0032] Step S3.2: Power on the entire satellite, power on the SAR subsystem and set it to the master state;

[0033] Step S3.3, compile and upload the integrated service and imaging parameter instruction package;

[0034] Step S3.4: Turn on the SAR payload and record the echo data;

[0035] In step S3.5, the echo data is pulse compressed to obtain the phase of each channel peak point, which is used to establish the amplitude and phase data field model of the SAR antenna T / R active channel.

[0036] Preferably, step S4 includes the following sub-steps:

[0037] Step S4.1, take the SAR antenna + Z plane center geometric point as the reference origin;

[0038] Step S4.2, uniformly converting the mechanical flatness error, electrical error, and thermal flatness error into phase data, and obtaining the phase data of the mechanical, thermal, and electrical errors of the SAR antenna in a unified phase coordinate system.

[0039] Preferably, step S5 includes the following sub-steps:

[0040] Step S5.1, take the SAR antenna + Z plane geometric phase center as the origin O;

[0041] Step S5.2, calculate the distance L{L1, L2...L n}, where n is the number of channels;

[0042] Step S5.3, based on the distance L, calculate the path difference R from each active channel to the origin O = {L1*sinθ, L2*sinθ, ..., L n *sinθ}, where θ is the satellite attitude pointing error. The satellite attitude pointing error includes attitude determination error and attitude control error. The attitude determination error comes from star-sensing measurement error and gyro measurement error, and the attitude control error comes from the control error of the actuator.

[0043] Step S5.4, based on the wave path difference R, calculate the phase difference φ of each active channel n =2π{L1*sinθ,L2*sinθ...L n *sinθ} / λ, where λ is the wavelength;

[0044] Step S5.5: Decompose the satellite attitude pointing error φ of each active channel n , converted to the unified phase coordinate system, and the phase data containing the satellite attitude pointing error is obtained.

[0045] Preferably, in step S6, based on the mechanical flatness error, thermal flatness error, and electrical error of the SAR antenna obtained through ground testing, and the phase change increment of the SAR antenna active channel obtained through on-orbit testing, combined with the satellite attitude pointing error, an internal calibration method is used to solve the amplitude and phase errors of each T / R active channel in the ground and on-orbit states, respectively. The active channel phase error obtained on-orbit is subtracted from the ground test result to obtain the amplitude and phase error change increment of the on-orbit antenna active channel. The results are then unified into the phase coordinate system of the SAR antenna, and the amplitude and phase error change increment of the on-orbit antenna active channel is superimposed on the SAR antenna pattern model to perform error compensation.

[0046] Preferably, step S6 includes the following sub-steps:

[0047] Step S6.1: After compensating for the SAR antenna's base-state error, a SAR antenna pattern model in the all-zero state is established. The all-zero state is the normal state, meaning the antenna beam is not scanned or widened, and all active channels are of equal amplitude and phase, serving as a reference for the SAR antenna pattern's pointing direction.

[0048] Step S6.2: Based on the SAR antenna pattern model in the all-zero state, the satellite attitude pointing error is superimposed to obtain pattern data containing the satellite attitude pointing error, and the sensitivity of the satellite attitude pointing error to the SAR antenna pattern pointing is analyzed;

[0049] Step S6.3, based on the directional pattern data containing the satellite attitude pointing error, the mechanical flatness error of the SAR antenna mechanical flatness field model, the electrical error of the SAR antenna T / R active channel amplitude and phase data field model, and the thermal flatness error of the SAR antenna thermal deformation field model are superimposed in sequence to analyze the sensitivity of the SAR antenna's mechanical error, electrical error, and thermal error to the SAR antenna directional pattern pointing.

[0050] The present invention also provides a system for improving the directional pattern accuracy of a lightweight and small satellite on-orbit SAR antenna, comprising:

[0051] Module M1, obtains the mechanical flatness data of the SAR antenna and establishes the SAR antenna mechanical flatness field model;

[0052] Module M2, based on the SAR antenna mechanical flatness field model, obtains the thermal deformation data of the SAR antenna under different temperature fields and establishes the SAR antenna thermal deformation field model;

[0053] Module M3, based on the SAR antenna thermal deformation field model, obtains the amplitude and phase error data of the T / R active channel of the SAR antenna and establishes the amplitude and phase data field model of the SAR antenna T / R active channel;

[0054] Module M4, the mechanical flatness error of the SAR antenna mechanical flatness field model, the electrical error of the SAR antenna T / R active channel amplitude and phase data field model and the thermal flatness error of the SAR antenna thermal deformation field model are converted into the mechanical flatness error of the SAR antenna mechanical flatness field model.

[0055] Converting to a unified phase coordinate system to obtain phase data in the unified phase coordinate system;

[0056] Module M5, based on the phase data in the unified phase coordinate system, establishes a satellite attitude pointing error model, performs unified physical field conversion, and obtains phase data containing satellite attitude pointing errors;

[0057] Module M6, based on phase data containing satellite attitude pointing error, improves the accuracy of the SAR antenna pattern by analyzing the sensitivity of satellite attitude pointing error, mechanical flatness error, thermal flatness error, and electrical error to the antenna pattern pointing.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] 1. To address the problem of reduced antenna pattern modeling accuracy for small satellites due to the short ground testing cycle and limited number of test wave positions of SAR antenna patterns, the present invention establishes a SAR antenna mechanical flatness field model, a thermal deformation field model, and a T / R active channel amplitude and phase data field model, fully considering the mechanical, electrical, and thermal error data of ground testing, and combining it with in-orbit calibration test data and satellite attitude pointing error data. By establishing multiple error models under different physical fields, the antenna pattern model is subjected to error superposition and sensitivity analysis is completed, effectively improving the SAR antenna pattern modeling accuracy of light and small satellites and ensuring image quality.

[0060] 2. This invention establishes a satellite attitude pointing error model and unifies the satellite attitude pointing error with the mechanical, electrical, and thermal errors of the SAR antenna in the same physical field for analysis. This solves the problem of insufficient modeling accuracy caused by the dispersion of error sources in traditional methods and further improves the accuracy of pattern modeling.

[0061] 3. The method of the present invention is not only applicable to small and light SAR satellites, but can also be extended to the on-orbit pattern model optimization work of medium and large SAR satellites, and has wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0063] Figure 1 1 is a flow chart of a method for improving the SAR antenna pattern accuracy of a lightweight satellite on-orbit according to an embodiment of the present invention;

[0064] Figure 2 is the antenna pattern sensitivity curve in the all-0 state in an embodiment of the present invention;

[0065] Figure 3 is an antenna pattern sensitivity curve to the mechanical flatness error of the antenna in an embodiment of the present invention;

[0066] Figure 4 : is the antenna pattern sensitivity curve to the antenna thermal deformation error in an embodiment of the present invention;

[0067] Figure 5 is an antenna pattern sensitivity curve of the antenna active channel amplitude and phase error in an embodiment of the present invention;

[0068] Figure 6 : This is the antenna pattern sensitivity curve to the satellite attitude pointing error in the embodiment of the present invention. DETAILED DESCRIPTION

[0069] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0070] The present invention proposes a method and system for improving the accuracy of on-orbit SAR antenna patterns for lightweight satellites. The method comprises step S1: establishing a mechanical flatness field model for the SAR antenna; step S2: establishing a thermal deformation field model for the SAR antenna; step S3: establishing an amplitude and phase data field model for the T / R active channel of the SAR antenna; step S4: converting the SAR antenna's mechanical, thermal, and electrical errors to a unified phase coordinate system; step S5: establishing a satellite attitude pointing error model and performing a unified physical field conversion; and step S6: performing sensitivity analysis on the antenna pattern pointing based on the satellite attitude and the SAR antenna's mechanical, thermal, and electrical errors. The present invention uses ground-based testing and on-orbit data to compensate for the SAR antenna's mechanical, electrical, and thermal phase errors, as well as the satellite platform's attitude error, thereby further improving the accuracy of the SAR antenna pattern model and effectively ensuring on-orbit image quality.

[0071] Example 1:

[0072] Figure 1 The present invention is a flowchart of a method for improving the accuracy of an on-orbit SAR antenna pattern of a small and light satellite according to an embodiment of the present invention.

[0073] like Figure 1 As shown, this embodiment provides a method for improving the accuracy of the on-orbit SAR antenna pattern of a lightweight small satellite, including the following steps:

[0074] Step S1, obtaining the mechanical flatness data of the SAR antenna, establishing the SAR antenna mechanical flatness field model, and using a high-precision near-field photogrammetry method on the ground.

[0075] Specifically, step S1 includes the following sub-steps:

[0076] Step S1.1, attaching targets on the active channels in the azimuth and range directions in the +Z direction of the SAR antenna array;

[0077] Step S1.2: Place a reference ruler next to the SAR antenna, with the reference ruler parallel to the surface of the SAR antenna array;

[0078] Step S1.3: Use a camera to take photos of the targets on the SAR antenna array. Each target should be photographed at least four times at different angles. Each photo should capture at least four target points. After each photo, rotate the camera 90° and take another photo.

[0079] Step S1.4: export the target measurement data and process the data to obtain the three-dimensional coordinate data of the target. If enough targets are selected, the mechanical flatness data of the SAR antenna can be obtained.

[0080] Step S2: Based on the SAR antenna mechanical flatness field model, thermal deformation data of the SAR antenna under different temperature fields are obtained, and a SAR antenna thermal deformation field model is established.

[0081] In this embodiment, factors affecting antenna pointing accuracy primarily include antenna thermal deformation and star sensor thermal deformation errors. The key is to establish a SAR antenna thermal deformation field model and the transmission error from the star sensor to the SAR antenna. The entire error transmission path is: star sensor and bracket → star body and joints → deployment mechanism and joints → SAR antenna array.

[0082] Specifically, step S2 includes the following sub-steps:

[0083] Step S2.1, measuring the mechanical flatness of the SAR antenna and the pointing direction of the star sensor mounting surface at temperature T0;

[0084] Step S2.2, heating the SAR antenna array and measuring the mechanical flatness of the SAR antenna and the pointing direction of the star sensor mounting surface;

[0085] Step S2.3: After returning to temperature, heat the joints of the SAR antenna's deployment mechanism and measure the SAR antenna's mechanical flatness and the star sensor mounting surface pointing direction.

[0086] Step S2.4: After returning to temperature, heat the star sensor bracket of the SAR antenna and measure the mechanical flatness of the SAR antenna and the pointing direction of the star sensor mounting surface;

[0087] Step S2.5: After returning to temperature, heat the star body and joints of the SAR antenna, and measure the mechanical flatness of the SAR antenna and the pointing direction of the star sensor mounting surface;

[0088] Step S2.6: After returning to temperature, heat the SAR antenna's star body, joints, SAR antenna array, and star sensor bracket, and measure the SAR antenna's mechanical flatness and the star sensor mounting surface's pointing direction.

[0089] Step S2.7: Analyze the measurement data under different working conditions in steps S2.1 to S2.6 to obtain thermal deformation data of the SAR antenna under different temperature fields.

[0090] Step S3, based on the SAR antenna thermal deformation field model, obtaining the T / R active channel amplitude and phase error data of the SAR antenna, and establishing the SAR antenna T / R active channel amplitude and phase data field model;

[0091] Specifically, after precise measurement and leveling of the SAR antenna, an internal calibration method is used at normal temperature and pressure to calculate the phase error of the active T / R channel. This includes the amplitude and phase errors of the active channel within the T / R assembly, radio frequency link, and calibration link. While the satellite is in orbit, the payload power-on imaging signal passes through the T / R assembly, radio frequency link, and waveguide, but not the calibration link. Conventional internal calibration methods are unable to detect the waveguide phase error. Therefore, the present invention proposes an external calibration method to calculate the phase error of each active T / R channel and the passive waveguide component.

[0092] In this embodiment, the implementation route of step S3 using the external calibration method is: FM signal source → internal calibrator → calibration test cable → horn antenna → antenna waveguide → T / R assembly → RF link → power splitter → radar receiving module, to obtain the amplitude and phase error data of the T / R active channel of the SAR antenna.

[0093] Specifically, step S3 includes the following sub-steps:

[0094] Step S3.1, establishing a test state of the satellite and the external horn antenna;

[0095] Step S3.2: Power on the entire satellite, power on the SAR subsystem and set it to the master state;

[0096] Step S3.3, compile and upload the integrated service and imaging parameter instruction package;

[0097] Step S3.4: Turn on the SAR payload and record the echo data;

[0098] In step S3.5, the echo data is pulse compressed to obtain the phase of each channel peak point, which is used to establish the amplitude and phase data field model of the SAR antenna T / R active channel.

[0099] Step S4: convert the mechanical flatness error of the SAR antenna mechanical flatness field model, the electrical error of the SAR antenna T / R active channel amplitude and phase data field model, and the thermal flatness error of the SAR antenna thermal deformation field model into a unified phase coordinate system to obtain phase data in the unified phase coordinate system.

[0100] Specifically, since the SAR antenna mechanical, electrical, and thermal deformation data are measured and acquired based on different physical fields, the present invention aligns the SAR antenna mechanical, electrical, and thermal three-dimensional deformation data to the phase coordinate system of the SAR antenna to complete the coordinate system one.

[0101] Furthermore, step S4 includes the following sub-steps:

[0102] Step S4.1, take the SAR antenna + Z plane center geometric point as the reference origin;

[0103] Step S4.2, uniformly converting the mechanical flatness error, electrical error, and thermal flatness error into phase data, and obtaining the phase data of the mechanical, thermal, and electrical errors of the SAR antenna in a unified phase coordinate system.

[0104] Step S5: Based on the phase data in the unified phase coordinate system, a satellite attitude pointing error model is established, and a unified physical field conversion is performed to obtain phase data containing the satellite attitude pointing error.

[0105] In this embodiment, the satellite attitude pointing error space is converted into the SAR antenna array physical field.

[0106] Specifically, step S5 includes the following sub-steps:

[0107] Step S5.1, take the SAR antenna + Z plane geometric phase center as the origin O;

[0108] Step S5.2, calculate the distance L{L1, L2...L n}, where n is the number of channels;

[0109] Step S5.3, based on the distance L, calculate the path difference R from each active channel to the origin O = {L1*sinθ, L2*sinθ, ..., L n *sinθ}, where θ is the satellite attitude pointing error. The satellite attitude pointing error includes attitude determination error and attitude control error. The attitude determination error comes from star-sensing measurement error and gyro measurement error, and the attitude control error comes from the control error of the actuator.

[0110] Step S5.4, based on the wave path difference R, calculate the phase difference φ of each active channel n =2π{L1*sinθ,L2*sinθ...L n*sinθ} / λ, where λ is the wavelength;

[0111] Step S5.5: Decompose the satellite attitude pointing error φ of each active channel n , converted to the unified phase coordinate system, and the phase data containing the satellite attitude pointing error is obtained.

[0112] Step S6, based on the phase data containing the satellite attitude pointing error, analyze the sensitivity of the satellite attitude pointing error, mechanical flatness error, thermal flatness error and electrical error to the antenna pattern pointing (sensitivity analysis curves are shown in the attached figure). Figure 6 、 3 ,4,5),complete the improvement of SAR antenna pattern accuracy,.

[0113] In this embodiment, to effectively improve the on-orbit pattern pointing accuracy, the impact of the mechanical flatness error, thermal flatness error, and electrical error of the SAR antenna obtained through ground testing on the antenna pattern accuracy, as well as the phase change increment of the SAR antenna active channel obtained through on-orbit testing, are considered. Combined with the satellite attitude pointing error, an internal calibration method is used to solve the amplitude and phase errors of each T / R active channel in both the ground and on-orbit states. The ground test result is subtracted from the active channel phase error obtained on-orbit to obtain the amplitude and phase error change increment of the on-orbit antenna active channel. This is then unified into the phase coordinate system of the SAR antenna and superimposed on the on-orbit antenna active channel amplitude and phase error change increment to compensate for the error.

[0114] Specifically, step S6 includes the following sub-steps:

[0115] Step S6.1, after compensating the base state error of the SAR antenna, establish the SAR antenna pattern model in the all-0 state. The all-0 state is the normal state, that is, the antenna beam is not scanned or widened, and each active channel has the same amplitude and phase, which serves as the reference for the SAR antenna pattern pointing, as shown in the attached figure. Figure 2 As shown;

[0116] Step S6.2, based on the SAR antenna pattern model in the all-zero state, the satellite attitude pointing error is superimposed to obtain the pattern data containing the satellite attitude pointing error, and the sensitivity of the satellite attitude pointing error to the SAR antenna pattern pointing is analyzed, as shown in the attached figure. Figure 6 As shown;

[0117] Step S6.3, based on the directional pattern data containing the satellite attitude pointing error, the mechanical flatness error of the SAR antenna mechanical flatness field model, the electrical error of the SAR antenna T / R active channel amplitude and phase data field model, and the thermal flatness error of the SAR antenna thermal deformation field model are superimposed in sequence, and the sensitivity of the mechanical error, electrical error, and thermal error of the SAR antenna to the SAR antenna directional pattern pointing are analyzed respectively, corresponding to the attached Figure 3 、 Figure 5 and Figure 4 .

[0118] Example 2:

[0119] The present invention also provides a system for improving the accuracy of on-orbit SAR antenna patterns of light and small satellites. The system for improving the accuracy of on-orbit SAR antenna patterns of light and small satellites can be implemented by executing the process steps of the method for improving the accuracy of on-orbit SAR antenna patterns of light and small satellites. That is, those skilled in the art can understand the method for improving the accuracy of on-orbit SAR antenna patterns of light and small satellites as a preferred implementation of the system for improving the accuracy of on-orbit SAR antenna patterns of light and small satellites.

[0120] Specifically, the lightweight small satellite on-orbit SAR antenna pattern accuracy improvement system includes:

[0121] Module M1 obtains the mechanical flatness data of the SAR antenna and establishes the mechanical flatness field model of the SAR antenna.

[0122] Module M2, based on the SAR antenna mechanical flatness field model, obtains the thermal deformation data of the SAR antenna under different temperature fields and establishes the SAR antenna thermal deformation field model.

[0123] Module M3 obtains the amplitude and phase error data of the T / R active channel of the SAR antenna based on the SAR antenna thermal deformation field model, and establishes the amplitude and phase data field model of the T / R active channel of the SAR antenna.

[0124] Module M4, the mechanical flatness error of the SAR antenna mechanical flatness field model, the electrical error of the SAR antenna T / R active channel amplitude and phase data field model and the thermal flatness error of the SAR antenna thermal deformation field model are converted into the mechanical flatness error of the SAR antenna mechanical flatness field model.

[0125] Convert to a unified phase coordinate system to obtain phase data in the unified phase coordinate system.

[0126] Module M5 establishes a satellite attitude pointing error model based on the phase data in the unified phase coordinate system, performs unified physical field conversion, and obtains phase data containing satellite attitude pointing errors.

[0127] Module M6, based on phase data containing satellite attitude pointing error, improves the accuracy of the SAR antenna pattern by analyzing the sensitivity of satellite attitude pointing error, mechanical flatness error, thermal flatness error, and electrical error to the antenna pattern pointing.

[0128] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0129] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A method for improving the SAR antenna pattern accuracy of a small and light satellite on-orbit, characterized in that: The steps include: Step S1, obtaining mechanical flatness data of the SAR antenna and establishing a mechanical flatness field model of the SAR antenna; Step S2, based on the SAR antenna mechanical flatness field model, obtaining thermal deformation data of the SAR antenna under different temperature fields, and establishing a SAR antenna thermal deformation field model; Step S3, based on the SAR antenna thermal deformation field model, obtaining the T / R active channel amplitude and phase error data of the SAR antenna, and establishing the SAR antenna T / R active channel amplitude and phase data field model; Step S4, converting the mechanical flatness error of the SAR antenna mechanical flatness field model, the electrical error of the SAR antenna T / R active channel amplitude and phase data field model, and the thermal flatness error of the SAR antenna thermal deformation field model into a unified phase coordinate system to obtain phase data in the unified phase coordinate system; Step S5, establishing a satellite attitude pointing error model based on the phase data in the unified phase coordinate system, performing unified physical field conversion, and obtaining phase data containing the satellite attitude pointing error; Step S6: Based on the phase data including the satellite attitude pointing error, the SAR antenna pattern accuracy is improved by analyzing the sensitivity of the satellite attitude pointing error, the mechanical flatness error, the thermal flatness error and the electrical error to the antenna pattern pointing.

2. The method for improving the SAR antenna pattern accuracy of a small satellite on-orbit according to claim 1, characterized in that: The step S1 includes the following sub-steps: Step S1.1, attaching a target on the active channels in the azimuth and range directions in the +Z direction of the SAR antenna array; Step S1.2, placing a reference ruler next to the SAR antenna, wherein the reference ruler is parallel to the surface of the SAR antenna array; Step S1.3: Use a camera to take photos of the targets on the SAR antenna array. Each target should be photographed at least four times at different angles. Each photo should capture at least four target points. After each photo, rotate the camera 90° and take another photo. Step S1.4, deriving the measurement data of the target and performing data processing to obtain the three-dimensional coordinate data of the target point, and then obtaining the mechanical flatness data of the SAR antenna.

3. The method for improving the SAR antenna pattern accuracy of a small satellite on-orbit according to claim 1, characterized in that: The step S2 includes the following sub-steps: Step S2.1, measuring the mechanical flatness and the star-sensing mounting surface pointing direction of the SAR antenna at temperature T0; Step S2.2, heating the SAR antenna array, and measuring the mechanical flatness of the SAR antenna and the pointing direction of the star-sensing mounting surface; Step S2.3: After returning to temperature, heat the deployment mechanism joints of the SAR antenna and measure the mechanical flatness and star sensor mounting surface pointing direction of the SAR antenna; Step S2.4, after returning to temperature, heating the star sensor bracket of the SAR antenna, and measuring the mechanical flatness of the SAR antenna and the pointing direction of the star sensor mounting surface; Step S2.5: After returning to temperature, heat the star body and joints of the SAR antenna, and measure the mechanical flatness of the SAR antenna and the pointing direction of the star-sensing mounting surface; Step S2.6, after returning to temperature, heating the star body, joints, SAR antenna array surface and star sensor bracket of the SAR antenna, and measuring the mechanical flatness of the SAR antenna and the pointing direction of the star sensor mounting surface; Step S2.7: Analyze the measurement data under different working conditions in steps S2.1 to S2.6 to obtain thermal deformation data of the SAR antenna under different temperature fields.

4. The method for improving the SAR antenna pattern accuracy of a small satellite on-orbit according to claim 1, characterized in that: The implementation route of the external calibration method in step S3 is: FM signal source → internal calibrator → calibration test cable → horn antenna → antenna waveguide → T / R component → RF link → power splitter → radar receiving module, to obtain the amplitude and phase error data of the T / R active channel of the SAR antenna.

5. The method for improving the SAR antenna pattern accuracy of a small satellite on-orbit according to claim 1, characterized in that: The step S3 includes the following sub-steps: Step S3.1, establishing a test state of the satellite and the external horn antenna; Step S3.2: Power on the entire satellite, power on the SAR subsystem and set it to the master state; Step S3.3, compile and upload the integrated service and imaging parameter instruction package; Step S3.4: Turn on the SAR payload and record the echo data; Step S3.5: pulse compress the echo data to obtain the phase of each channel peak point, which is used to establish the amplitude and phase data field model of the SAR antenna T / R active channel.

6. The method for improving the SAR antenna pattern accuracy of a small satellite on-orbit according to claim 1, characterized in that: The step S4 includes the following sub-steps: Step S4.1, take the SAR antenna + Z plane center geometric point as the reference origin; Step S4.2: uniformly convert the mechanical flatness error, the electrical error, and the thermal flatness error into phase data to obtain phase data of the mechanical, thermal, and electrical errors of the SAR antenna in a unified phase coordinate system.

7. The method for improving the SAR antenna pattern accuracy of a small satellite on-orbit according to claim 1, characterized in that: The step S5 includes the following sub-steps: Step S5.1, taking the geometric phase center of the SAR antenna + Z plane as the origin O; Step S5.2, calculate the distance L{L1, L2...L n }, where n is the number of channels; Step S5.3, based on the distance L, calculate the path difference R from each active channel to the origin O = {L1*sinθ, L2*sinθ, ..., L n *sinθ}, where θ is the satellite attitude pointing error, which includes attitude determination error and attitude control error. The attitude determination error comes from star-sensing measurement error and gyro measurement error, and the attitude control error comes from the control error of the actuator; Step S5.4, based on the path difference R, calculate the phase difference φ of each active channel n =2π{L1*sinθ,L2*sinθ...L n *sinθ} / λ, where λ is the wavelength; Step S5.5: Decompose the satellite attitude pointing error φ of each active channel n , converted to the unified phase coordinate system, and the phase data containing the satellite attitude pointing error is obtained.

8. The method for improving the SAR antenna pattern accuracy of a small satellite on-orbit according to claim 1, characterized in that: In step S6, based on the mechanical flatness error, thermal flatness error, and electrical error of the SAR antenna obtained through ground testing, and the phase change increment of the SAR antenna active channel obtained through on-orbit testing, combined with the satellite attitude pointing error, an internal calibration method is used to solve the amplitude and phase errors of each T / R active channel in both the ground and on-orbit states. The ground test result is subtracted from the active channel phase error obtained on-orbit to obtain the amplitude and phase error change increment of the on-orbit antenna active channel. The values are then unified into the phase coordinate system of the SAR antenna, and the amplitude and phase error change increment of the on-orbit antenna active channel is superimposed on the SAR antenna pattern model for error compensation.

9. The method for improving the SAR antenna pattern accuracy of a small and light satellite on-orbit according to claim 8, characterized in that: The step S6 includes the following sub-steps: Step S6.1, after compensating for the base state error of the SAR antenna, establish a SAR antenna pattern model in the all-zero state. The all-zero state is the normal state, i.e., the antenna beam is not scanned or widened, and all active channels are of equal amplitude and phase, which serves as a reference for the SAR antenna pattern pointing direction. Step S6.2, based on the SAR antenna pattern model in the all-zero state, superimposing the satellite attitude pointing error to obtain pattern data containing the satellite attitude pointing error, and analyzing the sensitivity of the satellite attitude pointing error to the SAR antenna pattern pointing; Step S6.3, based on the directional pattern data containing the satellite attitude pointing error, the mechanical flatness error of the SAR antenna mechanical flatness field model, the electrical error of the SAR antenna T / R active channel amplitude and phase data field model, and the thermal flatness error of the SAR antenna thermal deformation field model are superimposed in sequence, and the sensitivity of the mechanical error, electrical error, and thermal error of the SAR antenna to the SAR antenna directional pattern pointing are analyzed respectively.

10. A system for improving the SAR antenna pattern accuracy of a small and light satellite on-orbit, characterized in that: include: Module M1, obtaining the mechanical flatness data of the SAR antenna and establishing a mechanical flatness field model of the SAR antenna; Module M2, based on the SAR antenna mechanical flatness field model, obtains thermal deformation data of the SAR antenna under different temperature fields and establishes a SAR antenna thermal deformation field model; Module M3, based on the SAR antenna thermal deformation field model, obtains the T / R active channel amplitude and phase error data of the SAR antenna, and establishes the SAR antenna T / R active channel amplitude and phase data field model; Module M4 converts the mechanical flatness error of the SAR antenna mechanical flatness field model, the electrical error of the SAR antenna T / R active channel amplitude and phase data field model, and the thermal flatness error of the SAR antenna thermal deformation field model into a unified phase coordinate system to obtain phase data in the unified phase coordinate system; Module M5, based on the phase data in the unified phase coordinate system, establishes a satellite attitude pointing error model, performs unified physical field conversion, and obtains phase data containing satellite attitude pointing errors; Module M6 improves the SAR antenna pattern accuracy based on the phase data containing the satellite attitude pointing error by analyzing the sensitivity of the satellite attitude pointing error, the mechanical flatness error, the thermal flatness error, and the electrical error to the antenna pattern pointing.

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