Method and system for constructing high-precision time-frequency phase synchronous system based on rubidium clock

Abstract

The invention provides a high-precision time-frequency phase synchronous system construction method and system based on a rubidium clock. The method comprises the steps that a second pulse signal and main and auxiliary satellite second pulse relative time difference data are provided for a load system through an inter-satellite measurement system; for satellites with relatively advanced second pulse signals, delaying the second pulse signals according to the time difference and then starting a synthetic aperture radar control clock; for satellites with relatively lagged second pulse signals, the second pulse signals of the satellites are directly used for starting a synthetic aperture radar control clock so as to realize double-satellite time consistency control; and meanwhile, a rubidium clock provides a frequency reference for a load system, and double-star load phase synchronization is realized through an alternating opposite transmission scheme of in-pulse phase synchronization pulses. According to the scheme, the system is high in systematicness, nanosecond-level time synchronization and degree-level phase synchronization can be achieved, an operable test verification method is provided, and the reliability of in-orbit operation of the system is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of satellite technology, and in particular to a method for constructing and testing a high-precision time, frequency, and phase synchronization system for a formation-flying interferometric synthetic aperture radar satellite system. Background Technology

[0002] Dual-satellite formation InSAR satellite systems offer the advantages of all-weather, all-time data acquisition, enabling the acquisition of global digital elevation models (DEMs). They are applicable to various scenarios including land resources, earthquake monitoring, disaster prevention and mitigation, and basic geographic information acquisition, and have become one of the most widely researched and prioritized remote sensing methods worldwide. Interferometric synthetic aperture radar (ISAR) technology, by analyzing the phase information of multiple IAR images of the same area, can acquire high-precision three-dimensional elevation models and deformation information of the Earth's surface, finding wide application in surveying, mapping, and geological disaster monitoring. Formation-flying IAR systems, which utilize two or more satellites in a specific configuration for collaborative observation, are the mainstream technology for acquiring high-quality interferometric data.

[0003] In formation-flying interferometric synthetic aperture radar (SAR) systems, strict synchronization of time, frequency, and phase is essential to ensure the accuracy of interferometric processing. Time synchronization requires that the time and altitude of each satellite be aligned to achieve effective acquisition of echo signals; frequency synchronization requires that each satellite use a highly stable, co-originating frequency reference to avoid phase drift introducing system errors; and phase synchronization requires that the echo signals from each satellite maintain a consistent phase or have a definite phase relationship, as inconsistency is the main source of interferometric measurement errors.

[0004] There are many time-frequency design schemes available for reference both domestically and internationally, but most existing time-frequency consistency control schemes are only applicable to ground communication terminals and not to satellites in orbit. CN107422323B, "Bi-base SAR Uninterrupted Phase Synchronization Method and Device", proposes a scheme that performs two samplings within one pulse repetition period, which solves the problem of phase synchronization interrupting imaging. However, this method only considers the design and engineering implementation of the phase synchronization system itself, and does not consider time synchronization, implementation on satellite, and whole-satellite testing. CN117891154A, "A Time-Frequency Consistency Control Method for Formation Satellites Based on Atomic Clocks," only considers achieving high-precision time-frequency synchronization through the satellite platform, without considering coordination with the payload subsystem. CN116559873A, "A Bi-base SAR Time-Frequency Synchronization System," proposes a method to achieve bi-base SAR time synchronization by constructing a time-frequency link independent of GPS signals, which differs from the atomic clock-based implementation method presented in this paper. CN112817022A, "A Time-Frequency Synchronization Method, System, Electronic Equipment, and Storage Medium for Low-Earth Orbit Satellites," proposes a method using the same time reference for time synchronization, with each satellite independently completing its own time synchronization, which differs from the atomic clock-based dual-satellite time-frequency synchronization scheme presented in this paper. CN112134640A, "A Time-Frequency Synchronization System and Method Based on Pulse Modulation Channel," achieves synchronization by constructing a time-frequency transceiver channel, which differs from the atomic clock-based scheme presented in this paper.

[0005] In summary, existing technologies face numerous challenges in achieving high-precision time and frequency synchronization between satellites. First, the onboard environment is complex, and each device inherently experiences time delays and drift. Second, the high-speed movement of satellites in orbit causes dynamic changes in the inter-satellite links. Finally, existing technologies lack a systematic framework for constructing and verifying a closed loop for effectively testing and verifying nanosecond-level time synchronization accuracy and degree-level phase synchronization accuracy on the ground and in orbit.

[0006] Therefore, there is an urgent need in the market for a complete solution that integrates system construction, control methods, calibration and testing verification to solve the problem of building and verifying high-precision time and frequency synchronization for formation interferometric synthetic aperture radar satellite systems. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the purpose of this invention is to provide a method for constructing a high-precision time-frequency phase synchronization system based on a rubidium clock, so as to solve the technical problems in the prior art where there is no complete high-precision time-frequency phase synchronization construction scheme for formation flight interferometric synthetic aperture radar satellite systems, and the lack of a matching, highly operable whole-satellite test and verification method. A method for constructing a high-precision time-frequency phase synchronization system based on a rubidium clock, provided by the present invention, includes: A time and frequency synchronization system is symmetrically deployed on the primary and secondary satellites. The time and frequency synchronization system includes an inter-satellite measurement system, a payload system, and a satellite platform. The inter-satellite measurement system includes a rubidium clock, a navigation receiver, a navigation antenna, and inter-satellite measurement equipment. The payload system includes a payload, a synchronization transceiver, and a phase synchronization antenna. The inter-satellite measurement system provides the payload system with second pulse signals and relative time difference data of second pulses between the primary and secondary satellites. For satellites whose second pulse signals are relatively ahead, the second pulse signals are delayed according to the time difference before the synthetic aperture radar control clock is started. For satellites whose second pulse signals are relatively lagging, the second pulse signals are directly used to start the synthetic aperture radar control clock, so as to achieve time consistency control between the two satellites. The rubidium clock provides a frequency reference to the payload system, and the phase synchronization of the two satellite payloads is achieved through an alternating transmission scheme of intra-pulse phase synchronization pulses, so as to realize the frequency consistency control of the two satellites.

[0008] Preferably, the method further includes the deployment of phase synchronization antennas, wherein the number and installation layout of phase synchronization antennas are determined based on the beamwidth of a single phase synchronization antenna and the requirement to achieve 360° full coverage of the total antenna field of view.

[0009] Preferably, four phase synchronization antennas are installed on the satellite body of each satellite. The beams of the four phase synchronization antennas are respectively pointed towards the four vertices of a virtual regular tetrahedron, and the included angle between any two antenna beam axes is 109.47°.

[0010] Preferably, in the dual-satellite time consistency control, a delay adjustment threshold is set. When the time difference is less than the threshold, no delay adjustment is performed. For satellites whose second pulse signals are relatively ahead, their second pulse signals are delayed according to the time difference before the synthetic aperture radar control clock is started. For satellites whose second pulse signals are relatively lagging, their second pulse signals are used directly to start the synthetic aperture radar control clock.

[0011] Preferably, it also includes dual-satellite delay calibration. During the ground testing phase, a time synchronization test state is constructed using an echo simulator or a fixed delay line. End-to-end measurements of the test link are performed using a standard linear frequency modulation signal with a fixed delay to calibrate and compensate for the link delay.

[0012] Preferably, it also includes a dual-satellite time synchronization test. During the whole-satellite test, a time synchronization test state is established through an echo simulator. The RF output of the simulator is connected to the RF output ports of the primary and secondary satellites through a power divider. The dual satellites are controlled to image simultaneously through commands. The imaging data is pulse compressed and the time synchronization error of the dual satellites is determined based on the time difference corresponding to the peak position of the pulse-compressed signal.

[0013] Preferably, the test also includes a dual-satellite phase synchronization test. During the whole-satellite test, the phase synchronization antennas of the primary and secondary satellites are interconnected through a high-frequency cable. The radio frequency signal of the primary satellite is connected to the echo simulator after passing through a circulator. The output of the simulator is sent to the receivers of the primary and secondary satellites respectively after passing through a power divider. The phase difference and phase synchronization signal of the primary and secondary satellites are extracted and compared to obtain the phase synchronization error.

[0014] According to the present invention, a high-precision time and frequency synchronization system based on a rubidium clock is applied to a primary satellite and a secondary satellite. The synchronization system of each satellite includes an inter-satellite measurement system, a payload system, and a satellite platform. The inter-satellite measurement system includes a rubidium clock, a navigation receiver, a navigation antenna, and inter-satellite measurement equipment. The payload system includes a payload, a synchronization transceiver, and a phase synchronization antenna. The inter-satellite measurement system is used to provide the payload system with second pulse signals and relative time difference data between the primary and auxiliary satellites, and to provide a frequency reference through a rubidium clock; the payload system is used to achieve time consistency control between the two satellites based on the second pulse signals and relative time difference data, and to achieve frequency consistency control between the two satellites based on the frequency reference and the alternating transmission scheme of intra-pulse phase synchronization pulses.

[0015] Preferably, the payload is responsible for transmitting radar pulses and receiving echoes; The synchronous transceiver is responsible for generating and processing pulse signals for phase synchronization, and alternately transmitting and receiving signals with the synchronous transceiver of another satellite through the phase synchronization antenna to achieve the measurement of phase error between the local oscillator signals of the two satellites.

[0016] The phase synchronization antenna is a microwave antenna specifically designed to establish a phase synchronization link between the primary and secondary satellites.

[0017] Preferably, the payload computer can perform nanosecond-level delay processing on the second pulse signal based on the received time difference data to achieve high-precision time synchronization.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a complete end-to-end solution from system composition and control algorithm to calibration and testing. It has strong systematicity and solves the problem of constructing and verifying high-precision time and frequency synchronization for formation interferometric synthetic aperture radar systems.

[0019] 2. By employing a rubidium clock to provide a highly stable reference, and combining active time difference compensation control with an alternating phase synchronization scheme, this invention can achieve nanosecond-level time synchronization and degree-level phase synchronization, providing a prerequisite for high-quality interferometric imaging.

[0020] 3. This invention proposes a clear and operable ground testing method for the entire satellite constellation, which can accurately measure and verify key indicators such as time synchronization and phase synchronization, ensuring that the performance indicators of the system meet the requirements before on-orbit operation and has high verifiability.

[0021] 4. The time synchronization control of this invention is only executed before power-on. During power-on, it is maintained by a highly stable atomic clock. Combined with the construction of adjustment thresholds, it ensures the stability and reliability of on-orbit operation and avoids unnecessary system disturbances. Attached Figure Description

[0022] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 A block diagram of a high-precision time-frequency synchronization satellite system based on a rubidium clock, provided as an embodiment of the present invention; Figure 2 A schematic diagram illustrating a phase synchronization antenna deployment method provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a binary star time and phase synchronization test provided in an embodiment of the present invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0024] Example 1 This embodiment provides a complete implementation scheme for constructing a high-precision time-frequency phase synchronization system based on a rubidium clock. As a specific application scenario, this scheme is applied to a formation-flying interferometric synthetic aperture radar system consisting of two satellites: a primary satellite and a secondary satellite. Figure 1 Satellites A and B are mentioned. The primary and secondary satellites fly collaboratively in predetermined orbits to conduct interferometric observations of the Earth's surface. To achieve high-quality interferometric imaging, the synthetic aperture radar payloads on the primary and secondary satellites must achieve a certain level of synchronization accuracy in time, frequency, and phase. This invention can also be applied to "wheel-type" or "constellation-type" satellite formations, by installing high-precision time-frequency phase synchronization systems based on rubidium clocks on both the transmitting and receiving satellites to achieve time-frequency synchronization between the transmitting satellite and multiple receiving satellites.

[0025] According to the present invention, a high-precision time-frequency phase synchronization system based on a rubidium clock is provided, such as... Figure 1As shown, the synchronization system is symmetrically deployed on the primary and secondary satellites. On each satellite, the system consists of an inter-satellite measurement system, a payload system, and a satellite platform. These subsystems work together to complete a high-precision time and frequency synchronization task.

[0026] Specifically, the inter-satellite measurement system is the core reference source for the entire synchronization system, comprising a rubidium clock, navigation receiver, navigation antenna, and inter-satellite measurement equipment. The rubidium clock, a high-performance atomic clock, generates a reference signal with extremely high frequency stability and accuracy. In this embodiment, it generates a 10MHz sine wave frequency signal and a second pulse signal with nanosecond-level accuracy. The short-term stability of this 10MHz frequency signal reaches the order of 1E-12, providing a unified frequency reference for the entire satellite payload system, while the second pulse signal serves as the reference pulse for time synchronization. The navigation antenna is responsible for receiving broadcast signals from the Global Navigation Satellite System (GNSS). The navigation receiver demodulates and processes the received navigation signals, not only acquiring the satellite's precise orbit and position information, but more importantly, deciphering the standard time information broadcast by the GNSS, and comparing and tamping the second pulse signal generated by the local rubidium clock with this standard time, thereby ensuring the long-term accuracy of the local time. Inter-satellite measurement equipment is a key component for achieving time synchronization between two satellites. It communicates with corresponding equipment on another satellite via an inter-satellite link (such as a dedicated microwave link or laser link). Its core function is to accurately measure and calculate the relative time difference between the second pulse signals of the primary and secondary satellites and provide this time difference data to the payload system in real time.

[0027] The payload system, acting as the execution unit and end-user of time-frequency synchronization, includes the payload, a synchronization transceiver, and one or more phase-synchronization antennas. The payload, a synthetic aperture radar system, is responsible for transmitting radar pulses and receiving echoes, serving as the final executor of interferometry. The payload computer receives a high-stability frequency reference and second pulse signals from a rubidium clock, while simultaneously receiving relative time difference data for the second pulses from inter-satellite measurement equipment. Based on the received time difference data, the payload computer performs nanosecond-level precise delay processing on the second pulse signals. The synchronization transceiver generates and processes the pulse signals used for phase synchronization and alternates between the phase-synchronization antenna and the synchronization transceiver of another satellite to measure the phase error between the two satellite local oscillator signals. The phase-synchronization antenna is a microwave antenna specifically designed to establish a phase-synchronization link between the primary and secondary satellites.

[0028] The satellite platform provides fundamental support such as structural support, energy supply, thermal control, and attitude control for the normal operation of inter-satellite measurement systems and payload systems.

[0029] In this embodiment, to ensure a stable and reliable phase synchronization link can always be established between the primary and secondary satellites under various relative attitudes and distances during satellite formation flight, a specially designed deployment scheme for the phase synchronization antennas was implemented. For example... Figure 2 As shown in the figure, this is a schematic diagram of the phase-synchronous antenna deployment method. To achieve 360° omnidirectional field-of-view coverage, this embodiment installs four phase-synchronous antennas on the satellite body of each satellite. The installation direction of these four phase-synchronous antennas has been optimized, with their beam pointing towards the four vertices of a virtual tetrahedron. In this layout, the angle between the beam axes of any two antennas is 109.47°. It can be understood that in order to seamlessly stitch together the beam coverage of these four antennas, thereby achieving full coverage of the entire 4π spherical solid angle, the beamwidth of a single phase-synchronous antenna must be at least a cone with a half-cone angle of 72 degrees. This layout scheme ensures that regardless of the relative attitude changes of the primary and secondary satellites, at least one pair of phase-synchronous antennas can always be found to align with each other, thereby establishing an uninterrupted phase-synchronous link.

[0030] Based on the aforementioned system hardware composition and antenna layout, this embodiment employs a dual-satellite time consistency control method. This control process is triggered before each payload power-on preparation for an imaging mission. Its purpose is to precisely align the start times of the synthetic aperture radar control clocks on the primary and secondary satellites, maintained by a high-stability atomic clock during power-on. Specifically, the control process includes the following steps: Step S301: The inter-satellite measurement systems on the primary and secondary satellites provide their respective payload systems with high-precision second pulse signals and the relative time difference data between the primary and secondary satellite second pulses calculated by the inter-satellite measurement equipment. For example, suppose that at a certain moment, the inter-satellite measurement equipment measures that the second pulse signal of the primary satellite is 20 nanoseconds ahead of the second pulse signal of the secondary satellite.

[0031] Step S302: The payload computers on the primary and secondary satellites determine whether the satellite's second pulse signal is relatively leading or relatively lagging based on the received time difference data. In the example above, the payload computer on the primary satellite determines that it is leading, while the payload computer on the secondary satellite determines that it is lagging. For the satellite determined to be leading (i.e., the primary satellite), the digital delay unit inside its payload computer will precisely delay the second pulse signal received from the rubidium clock; the delay amount is the measured relative time difference, i.e., 20 nanoseconds. For the satellite determined to be lagging (i.e., the secondary satellite), its payload computer does not perform any delay operation and directly uses the raw second pulse signal received from its local rubidium clock.

[0032] Step S303: The second pulse signal processed by the primary satellite (delayed by 20ns) and the second pulse signal processed by the secondary satellite (without delay) are used as trigger signals to start the synthetic aperture radar control clock inside the payload on their respective satellites.

[0033] Step S304: Due to precise delay compensation for the leading clock source, the synthetic aperture radar control clocks of the primary and secondary satellites are precisely aligned at startup, eliminating time synchronization errors. Once imaging begins, maintaining time synchronization relies entirely on the high stability of their respective rubidium clocks. During a single imaging session (typically several minutes), the time error introduced by the rubidium clock's own drift is far less than the system requirements.

[0034] As an optional implementation, to further improve the stability and reliability of the system during on-orbit operation, this embodiment also introduces a time delay adjustment threshold. For example, this threshold can be set to 17 nanoseconds. This value is typically related to the reference frequency used for time delay adjustment by the payload. For instance, if the reference frequency for time delay adjustment is 30MHz, the time delay adjustment error is approximately 17ns, meaning the threshold can be set to 17 nanoseconds. During the judgment in step S302, subsequent delay adjustment steps are only executed if the absolute value of the measured relative time difference is greater than this threshold. If the measured time difference is 3 nanoseconds, which is less than the threshold, both satellites directly use their respective second pulse signals to start their clocks without any adjustment. This design effectively filters out the effects of measurement noise and minor system jitter, ensuring the stability of the control system.

[0035] For the frequency and phase consistency control of the two satellites, this embodiment adopts a scheme based on a high-stability frequency source and active phase correction. The rubidium clocks on the primary and secondary satellites provide high-precision, highly stable frequency references to their respective payload systems. All frequency sources within the payload (such as local oscillator signal sources, sampling clocks, etc.) are phase-locked synthesized using this frequency reference signal as a reference, thereby ensuring a high degree of frequency consistency between the two satellite payloads. Correspondingly, to compensate for phase drift caused by factors such as temperature drift of onboard equipment and changes in inter-satellite distance, the payload system achieves local oscillator phase synchronization between the two satellite payloads through an alternating transmission scheme of intra-pulse phase synchronization pulses. Specifically, the primary satellite's synchronization transceiver transmits a synchronization pulse containing phase information to the secondary satellite via a phase synchronization antenna. After receiving the pulse, the secondary satellite measures its phase difference with its local oscillator signal; subsequently, the secondary satellite transmits a synchronization pulse back to the primary satellite, and the primary satellite performs the same operation. This alternating transmission and correction process is carried out continuously at a high frequency (e.g., hundreds of times per second), thereby enabling high-precision measurement of the local oscillator phase deviation of the binary system. After ground compensation, the phase synchronization error can be controlled within the degree level.

[0036] Example 2 This embodiment details the ground testing and calibration methods used to verify the performance indicators of the time-frequency synchronization system constructed in Embodiment 1. It should be noted that these methods are crucial steps in ensuring the system meets the construction requirements before launch and constitute an indispensable part of the technical solution of this invention. This embodiment will respectively illustrate the calibration method for the link delay of the dual-satellite system, the testing method for time synchronization performance, and the testing method for phase synchronization performance.

[0037] First, a dual-satellite time delay calibration is performed to accurately calibrate and deduct the additional delay introduced by the test equipment itself. When using a simulator for time and phase synchronization testing, because the radar echo is coupled to the receiving channel through the internal calibration network, the actual received echo signal delay during testing includes not only the simulated theoretical delay but also additional delays from the internal calibration network, the dual-satellite test cable, and the simulator hardware. This portion of the delay needs to be calibrated and compensated during testing. The calibration method in this embodiment is performed during the satellite's ground integration testing phase. A time synchronization test state is constructed by connecting an external echo simulator or a delay line with a fixed and known delay. Assume the fixed delay is... SAR echoes use a start time of The received imaging echo signal is pulse-compressed, and the post-compressed time delay is... Then the delay needs to be compensated as follows: .

[0038] Secondly, the time synchronization performance of the two satellites was tested. This test was conducted when both satellites were fully assembled and in a complete state, aiming to simulate an on-orbit operating scenario and verify the final time synchronization error of the two-satellite synthetic aperture radar system end-to-end. Figure 3 As shown in the diagram, this is a schematic diagram of a dual-satellite time synchronization test. During the test, an echo simulator is used to generate simulated radar echo radio frequency signals. The radio frequency output port of this simulated signal is connected to a 1:2 power divider via a high-frequency cable. The two output ports of the power divider are then connected to the satellite catalog radio frequency ports of the primary and secondary satellites via two precisely calibrated cables of equal length. The satellite catalog radio frequency ports are functionally equivalent to the receiving ports of a synthetic aperture radar antenna (coupled to the antenna receiving channel via an internal calibration network). This connection method is equivalent to the primary and secondary satellites simultaneously receiving identical radar echoes from the same target point.

[0039] After the test began, ground test personnel simultaneously sent activation and imaging commands to both the primary and secondary satellites via the telemetry and control system. The synchronization system of the two satellites executed the time consistency control method described in Example 1, and then activated the synthetic aperture radar for imaging. After imaging, raw echo data was downloaded from both satellites, and standard pulse compression processing was performed on both sets of data. After pulse compression, the original wide pulse signal becomes a narrow pulse with concentrated energy, and its peak position precisely corresponds to the time of the echo signal. Using data analysis software, the time delay corresponding to the peak position of the pulse-compressed signal in the primary satellite data and the time delay corresponding to the peak position of the pulse-compressed signal in the secondary satellite data can be accurately measured. The absolute value of the difference between these two time delays is the end-to-end time synchronization error of the dual-satellite system.

[0040] Finally, the phase synchronization performance of the two satellites was tested. This test was also conducted with the satellites in full configuration to accurately measure the phase synchronization error of the local oscillator signals of the two satellites. (See also...) Figure 3 This diagram illustrates a dual-satellite phase synchronization test. Since long-distance wireless transmission of phase synchronization signals is impossible in a ground-based testing environment, a direct high-frequency cable connection is used to simulate the inter-satellite link. Specifically, the phase synchronization antennas on both the primary and secondary satellites are disconnected from the high-frequency cable, and the RF ports of the primary and secondary satellite's synchronization transceivers are directly interconnected via a high-frequency cable to establish a phase-synchronized communication link. Simultaneously, to verify the phase measurement function, a closed-loop RF signal link needs to be constructed. The output signal from the primary satellite's RF signal source (e.g., generated by the payload) is passed through a circulator and then fed into an echo simulator. The circulator isolates the signal transmission and reception paths. After appropriate delay and attenuation processing, the echo simulator's output signal is divided into two equally distributed paths by a 1:2 power divider and sent to the receivers on the primary and secondary satellites respectively.

[0041] After the test begins, ground test personnel send command packets to activate the synthetic aperture radar systems of the primary and secondary satellites and initiate the phase synchronization system. The synchronization transceivers of the primary and secondary satellites continuously send and receive phase synchronization pulses from each other, transmitting this data along with the imaging data to the data transmission subsystem and then to the ground recording equipment. Test personnel analyze the phase synchronization data on the ground recording equipment to obtain the phase difference between the local oscillator signals of the primary and secondary satellites. Statistical analysis of the phase difference data over the imaging time (e.g., several minutes) allows for the calculation of its mean and standard deviation, thus yielding the final phase synchronization error.

[0042] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as 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; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0043] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for constructing a high-precision time-frequency phase synchronization system based on a rubidium clock, characterized in that, include: A time and frequency synchronization system is symmetrically deployed on the primary and secondary satellites. The time and frequency synchronization system includes an inter-satellite measurement system, a payload system, and a satellite platform. The inter-satellite measurement system includes a rubidium clock, a navigation receiver, a navigation antenna, and inter-satellite measurement equipment. The payload system includes a payload, a synchronization transceiver, and a phase synchronization antenna. The inter-satellite measurement system provides the payload system with second pulse signals and relative time difference data of second pulses between the primary and secondary satellites. For satellites whose second pulse signals are relatively ahead, the second pulse signals are delayed according to the time difference before the synthetic aperture radar control clock is started. For satellites whose second pulse signals are relatively lagging, the second pulse signals are directly used to start the synthetic aperture radar control clock, so as to achieve time consistency control between the two satellites. The rubidium clock provides a frequency reference to the payload system, and the phase synchronization of the two satellite payloads is achieved through an alternating transmission scheme of intra-pulse phase synchronization pulses, so as to realize the frequency consistency control of the two satellites.

2. The method for constructing a high-precision time-frequency phase synchronization system based on a rubidium clock according to claim 1, characterized in that, The method also includes the deployment of phase-synchronous antennas, which determines the number and installation layout of phase-synchronous antennas based on the beamwidth of a single phase-synchronous antenna and the requirement to achieve 360° full coverage of the total antenna field of view.

3. The method for constructing a high-precision time-frequency phase synchronization system based on a rubidium clock according to claim 1, characterized in that, In the dual-satellite time consistency control, a delay adjustment threshold is set. When the time difference is less than the threshold, no delay adjustment is performed.

4. The method for constructing a high-precision time-frequency phase synchronization system based on a rubidium clock according to claim 1, characterized in that, It also includes dual-satellite delay calibration. During the ground testing phase, a time synchronization test state is constructed using an echo simulator or a fixed delay line. End-to-end measurements of the synchronization link are performed using a standard linear frequency modulation signal with a fixed delay to calibrate and compensate for the link delay.

5. The method for constructing a high-precision time-frequency phase synchronization system based on a rubidium clock according to claim 1, characterized in that, It also includes dual-satellite time synchronization testing. During the whole-satellite test, a time synchronization test state is established through an echo simulator. The RF output of the simulator is connected to the RF ports of the primary and secondary satellites through a power divider. The two satellites are controlled to image simultaneously through commands. The imaging data is pulse compressed and the time synchronization error of the two satellites is determined based on the time difference corresponding to the peak position of the pulse-compressed signal.

6. The method for constructing a high-precision time-frequency phase synchronization system based on a rubidium clock according to claim 1, characterized in that, It also includes dual-satellite phase synchronization testing. During the whole-satellite test, the phase synchronization antennas of the primary and secondary satellites are interconnected through a high-frequency cable. The radio frequency signal of the primary satellite is connected to the echo simulator after passing through a circulator. The output of the simulator is sent to the receivers of the primary and secondary satellites after passing through a power divider. The phase difference and phase synchronization signal of the primary and secondary satellites are extracted and compared to obtain the phase synchronization error.

7. The method for constructing a high-precision time-frequency phase synchronization system based on a rubidium clock according to claim 2, characterized in that, Four phase synchronization antennas are installed on the satellite body of each satellite. The beams of the four phase synchronization antennas are respectively pointed towards the four vertices of a virtual tetrahedron, and the included angle between any two antenna beam axes is 109.47°.

8. A high-precision time and frequency synchronization system based on a rubidium clock, applied to a primary satellite and a secondary satellite, characterized in that, Each satellite's synchronization system includes an inter-satellite measurement system, a payload system, and a satellite platform; the inter-satellite measurement system includes a rubidium clock, a navigation receiver, a navigation antenna, and inter-satellite measurement equipment; the payload system includes a payload, a synchronization transceiver, and a phase synchronization antenna. The inter-satellite measurement system is used to provide the payload system with second pulse signals and relative time difference data between the primary and auxiliary satellites, and to provide a frequency reference through a rubidium clock; the payload system is used to achieve time consistency control between the two satellites based on the second pulse signals and relative time difference data, and to achieve frequency consistency control between the two satellites based on the frequency reference and the alternating transmission scheme of intra-pulse phase synchronization pulses.

9. The high-precision time and frequency synchronization system based on a rubidium clock according to claim 8, characterized in that, The payload is responsible for transmitting radar pulses and receiving echoes; The synchronous transceiver is responsible for generating and processing pulse signals for phase synchronization, and alternately transmitting and receiving signals with the synchronous transceiver of another satellite through the phase synchronization antenna, so as to realize the measurement of phase error between the local oscillator signals of the two satellites. The phase synchronization antenna is a microwave antenna specifically designed to establish a phase synchronization link between the primary and secondary satellites. The payload computer can perform nanosecond-level delay processing on the second pulse signal based on the received time difference data.

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