CN115267771A - A spaceborne Ka-band SAR system and its on-orbit imaging working method - Google Patents

Abstract

The embodiment of the invention provides a satellite-borne Ka-band SAR system, wherein when the system works in an on-orbit imaging mode, a monitoring timer (3) controls a radar distributor (8) and an antenna power distribution unit (9) to power on each single machine; the monitoring timer (3) is used as a time reference of the satellite-borne Ka-band SAR system and controls the power-on and imaging time sequence of the system; under the control of the frequency synthesizer, a frequency synthesizer part of the frequency synthesizer receiver (4) generates a radio frequency master oscillator signal, and high-power high-orientation pulse wave beams are radiated to a designated area through a pre-power amplifier (6) and an antenna (1) in sequence; the ground object echo sequentially passes through an antenna (1), a pre-amplifier (6), a waveguide switch (7), an analog receiver part of a frequency synthesis receiver (4) and a digital receiver (5) to form formatted data and output the formatted data to a data transmission system, and the data transmission system is used for receiving the output data of the SAR system.

Description

A spaceborne Ka-band SAR system and its on-orbit imaging working method

technical field

The invention belongs to the technical field of synthetic aperture radar, and relates to a spaceborne Ka-band SAR system.

Background technique

Since the atmospheric attenuation in the millimeter-wave band is greater than that in the traditional low-frequency band, the development of spaceborne millimeter-wave SAR in the early stage has been more restricted. In recent years, with the development of a large number of millimeter-wave SAR technology research and the improvement of the corresponding technological level, spaceborne millimeter-wave SAR has entered a stage of rapid development.

Internationally renowned aerospace research institutions such as ESA, Deutscher Aerospace, Netherlands Space Agency, Alenia Space Corporation of Italy, California Institute of Technology, Jet Propulsion Laboratory and other internationally renowned aerospace research institutions have successively proposed several sets of spaceborne Ka-band SAR technical solutions, but most of them remain In the stage of program demonstration, the actual engineering implementation has not yet been carried out.

Among them, the SWOT (the surface water and ocean Topography) satellite developed by the US Jet Propulsion Laboratory and the French National Space Research Center has entered the development stage and is expected to be launched in 2023. The main load of SWOT is Ka-band InSAR, its operating frequency is 35GHz, and it adopts 10m interferometric baseline and 0.4°～3.5° near-bottom observation, which can realize high-precision and wide-swath survey of sea surface, so as to measure the small-scale and medium-sized areas of the ocean. At the same time, it can also measure the height of land water body, and study the spatial and temporal distribution caused by the storage and loss of land water body.

Most of the existing technologies remain at the scheme stage, and the only SWOT system under engineering development uses close-up bottom-sight observation, and the image resolution is poor.

Contents of the invention

The purpose of the present invention is to propose a space-borne Ka-band SAR system for the current situation that there is no on-orbit space-borne SAR system at home and abroad, and to meet the demand for space-borne millimeter-wave fine-grained earth observation.

The system includes: antenna 1, internal scaler 2, monitoring timer 3, frequency synthesis receiver 4, digital receiver 5, pre-amplifier 6, waveguide switch 7, radar distributor 8, antenna power distribution unit 9, waveguide switch connecting plate 10; wherein,

The antenna transmits high-power and high-directional pulse beams to free space, and receives echo signals reflected by ground objects; provides large-angle electronic scanning capabilities in the distance direction; and provides an internal calibration circuit for the spaceborne Ka-band SAR system;

The internal scaler 2 is used to cooperate with the antenna calibration network to realize the calibration of the system amplitude and phase performance, so as to ensure the system performance; measure the relative change of the total gain of the system, measure the change of the amplitude of the transceiver channel of the subsystem, and copy the LFM of the subsystem Signal to provide a reference signal for imaging processing for system error correction;

The monitoring timer 3 is used as the time reference of the spaceborne Ka-band SAR system to ensure the synchronization of the system's receiving and transmitting work, and at the same time perform ground-to-system remote control and telemetry tasks, and control the power-on and imaging timing of the system , detect the working status of the subsystems, and realize the various measurement and control requirements of the ground to the system.

The frequency synthesis receiver 4 includes a frequency synthesis and an analog receiver; wherein, the frequency synthesis adopts an implementation architecture based on FPGA+DA, is compatible with two modes of waveform storage direct reading and waveform real-time calculation, and realizes the system link through pre-distortion processing. Amplitude and phase error compensation, generate radio frequency main vibration signal and send to pre-amplifier 6; analog receiver receives radio frequency echo signal output from waveguide switch, output intermediate frequency echo signal to digital receiver 5 after frequency conversion amplification;

The digital receiver 5 receives the instructions and auxiliary data of the monitoring timer, completes the receiving and collecting of the echo signal; performs down-conversion, digital filtering and BAQ compression on the echo data, and combines and packages the auxiliary data with the system to form a format Format data frame; Output the formatted data after packing to the digital transmission system, and the digital transmission system is used to receive the output data of the SAR system;

The pre-amplifier 6 amplifies the main vibration signal output by the frequency synthesizer to meet the power requirements of the antenna, and outputs it to the antenna;

The waveguide switch 7 is used to switch the calibration signal during system calibration, and is controlled by the monitoring timer to switch to the valid echo input or the valid calibration input in different calibration states;

The radar distributor 8 provides a 30V primary power supply for each stand-alone machine in the cabin, and simultaneously controls the power-on and power-off of each stand-alone machine; each stand-alone machine in the cabin does not include a monitoring timer, and the monitoring timer is directly powered by a satellite platform;

The antenna power distribution unit 9 provides a 60V primary power supply for the secondary power supply of the antenna, and simultaneously controls the power-on and power-off of the secondary power supply of the antenna;

A waveguide connection is adopted between the antenna and the pre-power amplifier, and between the pre-power amplifier and the waveguide switch to reduce transmission loss; the pre-power amplifier and the waveguide switch are uniformly installed on the waveguide adapter board 10; The phased array antenna beam control code is stored and forwarded to control the antenna beam pointing.

Preferably, the frequency synthesizer is composed of a reference frequency source and a frequency modulation signal source, and the reference frequency source provides a reference frequency and a clock signal for the SAR system by a crystal oscillator to ensure system coherence characteristics; various intermediate frequencies are generated according to the reference clock output by the reference frequency source , RF reference.

Preferably, the frequency modulation signal source adopts a digital waveform generation method, and generates a baseband linear frequency modulation signal that meets the needs of the system according to the control signal and timing signal; after quadrature modulation, intermediate frequency gating amplification, frequency up-conversion, filtering and power amplification, the time domain , frequency domain and signal power meet the requirements of radio frequency chirp signal.

Preferably, the analog receiver is composed of a high-frequency amplification and frequency conversion module, an intermediate frequency amplification and an MGC module; the high-frequency amplification and frequency conversion module completes the down-conversion and filtering of the received signal to obtain an intermediate frequency signal; the intermediate frequency amplification and the MGC module perform intermediate frequency echo signals Amplification and gain control to adapt to the dynamic output requirements of the receiver.

Preferably, during the imaging period, the waveguide switch 7 is switched to enable echo input to realize normal reception of ground echo.

Preferably, the antenna adopts a waveguide slot active phased array antenna, capable of large-angle electrical scanning.

Preferably, the internal scaler adopts a non-delay scaling scheme, cooperates with the waveguide switch array to realize high isolation between different circuits, and the isolation between each circuit is ≥70dB.

The present invention also provides a method applicable to the spaceborne Ka-band SAR system, characterized in that it comprises steps:

Step 1: The monitoring timer 3 controls the radar power distribution unit 8 and the antenna power distribution unit 9 to power up each single machine of the system;

Step 2: the monitoring timer 3 controls the frequency-synthesized FM signal source of the frequency-synthesized receiver 4 to generate a broadband linear frequency-modulated (LFM) signal;

Step 3: The LFM signal output by the frequency synthesizer is amplified by the pre-amplifier 6 and then output to the antenna 1 through the circulator;

Step 4: The transmitted signal is output to the GaN TR component for power amplification through power division amplification, and output to the waveguide slot front through the circulator, and the high-power radiation signal is controlled to illuminate different imaging areas;

Step 5: Antenna 1 receives the echo signal reflected by the ground, and returns to the TR component through the same path as the transmission. The echo signal will enter the R channel, and after being synthesized by the power divider for secondary amplification, it will be synthesized and output again;

Step 6: The echo signal enters the pre-amplifier and returns to the waveguide switch 7 through the circulator;

Step 7: In the receiving state of the imaging mode, the waveguide switch is in the on state; the echo signal enters the analog receiver, and is subjected to low noise amplification, down conversion, intermediate frequency filter amplification, and gain control to obtain the intermediate frequency echo signal;

Step 8: After the intermediate frequency signal enters the digital receiver 5, the SAR echo data stream is formed through AD acquisition, quadrature demodulation, filtering, extraction, BAQ compression and packaging and framing;

Step 9: The data stream is transmitted to the ground receiving station through the digital transmission subsystem, and the ground processing system performs BAQ decompression and SAR imaging processing on the echo data to obtain a high-resolution ground scene image.

Description of drawings

Fig. 1 is a block diagram of a spaceborne Ka-band SAR system of the present invention.

Detailed ways

In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

The invention proposes a spaceborne Ka-band SAR system. The system includes: antenna 1, internal scaler 2, monitoring timer 3, frequency synthesis receiver 4, digital receiver 5, pre-amplifier 6, waveguide switch 7, radar distributor 8, antenna power distribution unit 9, waveguide switch connecting plate 10; wherein,

The antenna transmits high-power and high-directional pulse beams to free space, and receives echo signals reflected by ground objects; provides large-angle electronic scanning capabilities in the distance direction; and provides an internal calibration circuit for the spaceborne Ka-band SAR system;

The internal scaler 2 is used to cooperate with the antenna calibration network to realize the calibration of the system amplitude and phase performance, so as to ensure the system performance; measure the relative change of the total gain of the system, measure the change of the amplitude of the transceiver channel of the subsystem, and copy the LFM of the subsystem Signal to provide a reference signal for imaging processing for system error correction;

The monitoring timer 3 is used as the time reference of the spaceborne Ka-band SAR system to ensure the synchronization of the system's receiving and transmitting work, and at the same time perform ground-to-system remote control and telemetry tasks, and control the power-on and imaging timing of the system , detect the working status of the subsystems, and realize the various measurement and control requirements of the ground to the system.

The frequency synthesis receiver 4 includes a frequency synthesis and an analog receiver; wherein, the frequency synthesis adopts an implementation architecture based on FPGA+DA, is compatible with two modes of waveform storage direct reading and waveform real-time calculation, and realizes the system link through pre-distortion processing. Amplitude and phase error compensation, generate radio frequency main vibration signal and send to pre-amplifier 6; analog receiver receives radio frequency echo signal output from waveguide switch, output intermediate frequency echo signal to digital receiver 5 after frequency conversion amplification;

The digital receiver 5 receives the instructions and auxiliary data of the monitoring timer, completes the receiving and collecting of the echo signal; performs down-conversion, digital filtering and BAQ compression on the echo data, and combines and packages the auxiliary data with the system to form a format Format data frame; Output the formatted data after packing to the digital transmission system, and the digital transmission system is used to receive the output data of the SAR system;

The pre-amplifier 6 amplifies the main vibration signal output by the frequency synthesizer to meet the power requirements of the antenna, and outputs it to the antenna;

The waveguide switch 7 is used to switch the calibration signal during system calibration, and is controlled by the monitoring timer to switch to the valid echo input or the valid calibration input in different calibration states;

The radar distributor 8 provides a 30V primary power supply for each stand-alone machine in the cabin, and simultaneously controls the power-on and power-off of each stand-alone machine; each stand-alone machine in the cabin does not include a monitoring timer, and the monitoring timer is directly powered by a satellite platform;

The antenna power distribution unit 9 provides a 60V primary power supply for the secondary power supply of the antenna, and simultaneously controls the power-on and power-off of the secondary power supply of the antenna;

A waveguide connection is adopted between the antenna and the pre-power amplifier, and between the pre-power amplifier and the waveguide switch to reduce transmission loss; the pre-power amplifier and the waveguide switch are uniformly installed on the waveguide adapter board 10; The phased array antenna beam control code is stored and forwarded to control the antenna beam pointing.

According to an embodiment of the present invention, frequency synthesis is made up of reference frequency source and FM signal source, and reference frequency source provides reference frequency and clock signal for SAR system by crystal oscillator, to guarantee system coherent characteristic; According to the reference frequency output of reference frequency source Clock generation for various IF, RF references.

According to an embodiment of the present invention, the FM signal source adopts a digital waveform generation method to generate a baseband linear FM signal that meets the needs of the system according to the control signal and timing signal; The power amplifies to obtain the radio frequency chirp signal whose time domain, frequency domain and signal power meet the requirements.

According to an embodiment of the present invention, the analog receiver is composed of a high-frequency amplification and frequency conversion module, an intermediate frequency amplification and an MGC module; the high-frequency amplification and frequency conversion module completes the down-conversion and filtering of the received signal to obtain an intermediate frequency signal; the intermediate frequency amplification and the MGC module perform Amplification and gain control of intermediate frequency echo signals to meet the dynamic output requirements of the receiver.

According to an embodiment of the present invention, during imaging, the waveguide switch 7 is switched to enable echo input to realize normal reception of ground echo.

According to an embodiment of the present invention, the antenna adopts a waveguide slot active phased array antenna with large-angle electrical scanning capability.

According to an embodiment of the present invention, the internal scaler adopts a non-delayed scaling scheme, cooperates with a waveguide switch array to realize high isolation between different circuits, and the isolation between each circuit is ≥70dB.

The present invention also provides an on-orbit imaging method suitable for a spaceborne Ka-band SAR system, comprising steps:

Step 1: The monitoring timer 3 controls the radar power distribution unit 8 and the antenna power distribution unit 9 to power up each single machine of the system;

Step 2: the monitoring timer 3 controls the frequency-synthesized FM signal source of the frequency-synthesized receiver 4 to generate a broadband linear frequency-modulated (LFM) signal;

Step 3: The LFM signal output by the frequency synthesizer is amplified by the pre-amplifier 6 and then output to the antenna 1 through the circulator;

Step 4: The transmitted signal is output to the GaN TR component for power amplification through power division amplification, and output to the waveguide slot front through the circulator, and the high-power radiation signal is controlled to illuminate different imaging areas;

Step 5: Antenna 1 receives the echo signal reflected by the ground, and returns to the TR component through the same path as the transmission. The echo signal will enter the R channel, and after being synthesized by the power divider for secondary amplification, it will be synthesized and output again;

Step 6: The echo signal enters the pre-amplifier and returns to the waveguide switch 7 through the circulator;

Step 7: In the receiving state of the imaging mode, the waveguide switch is in the on state; the echo signal enters the analog receiver, and is subjected to low noise amplification, down conversion, intermediate frequency filter amplification, and gain control to obtain the intermediate frequency echo signal;

Step 8: After the intermediate frequency signal enters the digital receiver 5, the SAR echo data stream is formed through AD acquisition, quadrature demodulation, filtering, extraction, BAQ compression and packaging and framing;

Step 9: The data stream is transmitted to the ground receiving station through the digital transmission subsystem, and the ground processing system performs BAQ decompression and SAR imaging processing on the echo data to obtain a high-resolution ground scene image.

Obviously, those skilled in the art can make various changes and modifications to the invention without departing from the spirit and scope of the invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies thereof, the present invention also intends to include these modifications and variations.

Claims (8)

1. a kind of space-borne Ka band SAR system is characterized in that, described system comprises: antenna (1), interior scaler (2), monitoring timer (3), frequency synthesis receiver (4), digital receiver (5), pre-amplifier (6), waveguide switch (7), radar distributor (8), antenna power distribution unit (9), waveguide adapter board (10); wherein, The antenna (1) transmits high-power and high-directional pulse beams to free space, and receives echo signals reflected by ground objects; provides large-angle electronic scanning capabilities in the distance direction; and provides an internal calibration circuit for the spaceborne Ka-band SAR system ; The internal scaler (2) is used to cooperate with the antenna calibration network to realize the calibration of the system amplitude and phase performance, so as to ensure the system performance; measure the relative variation of the total gain of the system, measure the change of the amplitude of the transceiver channel of the subsystem, and copy the System LFM signal to provide reference signal for imaging processing for system error correction; The monitoring timer (3) is used as the time reference of the spaceborne Ka-band SAR system to ensure the synchronization of system receiving and transmitting work, and simultaneously perform ground-to-system remote control and telemetry tasks, and control system power-on and Imaging timing, detecting the working status of the subsystems, and realizing the various measurement and control requirements of the ground-to-system. The frequency synthesis receiver (4) includes a frequency synthesis and an analog receiver; wherein, the frequency synthesis adopts an implementation architecture based on FPGA+DA, and is compatible with two modes of waveform storage direct reading and waveform real-time calculation, and the system is realized by pre-distortion processing. Compensation of link amplitude and phase error, generating RF main vibration signal and sending it to pre-amplifier (6); analog receiver receives RF echo signal output from waveguide switch, and outputs intermediate frequency echo signal to digital receiver (5) after frequency conversion and amplification ; The digital receiver (5) receives the instructions and auxiliary data of the monitoring timer, and completes the receiving and collecting of echo signals; performs down-conversion, digital filtering and BAQ compression on the echo data, and combines and packages them with system auxiliary data Form a formatted data frame; output the packaged formatted data to a digital transmission system, and the digital transmission system is used to receive the output data of the SAR system; The pre-amplifier (6) amplifies the main vibration signal output by the frequency synthesizer to meet the power requirements of the antenna, and outputs it to the antenna; The waveguide switch (7) is used to switch the calibration signal during system calibration, and is controlled by the monitoring timer to switch to valid echo input or valid calibration input in different calibration states; The radar distributor (8) provides a 30V primary power supply for each single machine in the cabin, and simultaneously controls the power-on and power-off of each single machine; each single machine in the cabin does not include a monitoring timer, and the monitoring timer is directly powered by the satellite platform; The antenna power distribution unit (9) provides a 60V primary power supply for the secondary power supply of the antenna, and simultaneously controls the power-on and power-off of the secondary power supply of the antenna; Between the antenna and the pre-amplifier, between the pre-amplifier and the waveguide switch, a waveguide connection is used to reduce transmission loss; the pre-amplifier and the waveguide switch are uniformly installed on the waveguide adapter plate (10); the monitoring timer (3 ) through the storage and forwarding of the wave control code of the active phased array antenna to control the antenna beam pointing. 2. The spaceborne Ka-band SAR system as claimed in claim 1, wherein the frequency synthesizer is made up of a reference frequency source and a frequency modulation signal source, and the reference frequency source provides reference frequency and a clock signal for the SAR system by a crystal oscillator, so as to Guarantee system coherence characteristics; generate various intermediate frequency and radio frequency references according to the reference clock output by the reference frequency source. 3. The space-borne Ka-band SAR system as claimed in claim 1, is characterized in that, said FM signal source adopts digital waveform generation mode, produces the baseband chirp signal that meets system needs according to control signal and timing signal; Modulation, intermediate frequency gating amplification, up-conversion, filtering and power amplification to obtain radio frequency chirp signals that meet the requirements in time domain, frequency domain and signal power. 4. The spaceborne Ka-band SAR system as claimed in claim 3, wherein the analog receiver is composed of a high-frequency amplification and frequency conversion module, an intermediate frequency amplification and an MGC module; the high-frequency amplification and frequency conversion module completes the down-conversion of the received signal 1. Filter to obtain the intermediate frequency signal; the intermediate frequency amplifier and the MGC module perform amplification and gain control of the intermediate frequency echo signal to meet the dynamic output requirements of the receiver. 5. The spaceborne Ka-band SAR system according to claim 1, characterized in that, during imaging, the waveguide switch (7) is switched to echo input to enable normal reception of ground echoes. 6. The space-borne Ka-band SAR system according to claim 1, wherein the antenna adopts a waveguide slot active phased array antenna, which has a large-angle electrical scanning capability. 7. The spaceborne Ka-band SAR system as claimed in claim 1, wherein the internal scaler adopts a non-delay calibration scheme, cooperates with the waveguide switch array to realize high isolation between different circuits, and the isolation between each circuit Degree ≥ 70dB. 8. An on-orbit imaging working method applicable to the spaceborne Ka-band SAR system described in any one of claims 1-7, characterized in that it comprises the steps of: Step 1: the monitoring timer (3) controls the radar distribution unit (8) and the antenna power distribution unit (9) to power up each single machine of the system; Step 2: the monitoring timer (3) controls the frequency-synthesis frequency modulation signal source of the frequency synthesis receiver (4) to generate a broadband linear frequency modulation (LFM) signal; Step 3: the LFM signal output by the frequency synthesizer is amplified by the pre-amplifier (6) and then output to the antenna (1) through a circulator; Step 4: The transmitted signal is output to the GaN TR component for power amplification through power division amplification, and output to the waveguide slot front through the circulator, and the high-power radiation signal is controlled to illuminate different imaging areas; Step 5: The antenna (1) receives the echo signal reflected from the ground, and returns to the TR component through the same path as the transmission, and the echo signal will enter the R channel, and then synthesized and output again after being synthesized by a power divider for secondary amplification; Step 6: The echo signal enters the pre-amplifier and returns to the waveguide switch (7) through the circulator; Step 7: In the receiving state of the imaging mode, the waveguide switch is in the on state; the echo signal enters the analog receiver, and is subjected to low noise amplification, down conversion, intermediate frequency filter amplification, and gain control to obtain the intermediate frequency echo signal; Step 8: After the intermediate frequency signal enters the digital receiver (5), the SAR echo data stream is formed through AD acquisition, quadrature demodulation, filtering, extraction, BAQ compression and packaging and framing; Step 9: The data stream is transmitted to the ground receiving station through the digital transmission subsystem, and the ground processing system performs BAQ decompression and SAR imaging processing on the echo data to obtain a high-resolution ground scene image.

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