Darkroom phase calibration method and device for synthetic aperture radiometer

Abstract

The invention discloses a synthetic aperture radiometer darkroom phase calibration method and device. The method comprises the following steps: installing a synthetic aperture radiometer and a point target emission source in a microwave anechoic chamber; in the first-stage test, unit antenna output ports are connected with equal-length test cables and connected to a microwave test instrument, a synthetic aperture radiometer is set to be in an antenna observation mode, and a point target observation unit antenna phase difference test is carried out; in the second-stage test, the output end of the unit antenna is connected with each receiving channel of the synthetic aperture radiometer, the synthetic aperture radiometer is set to be in an antenna observation mode, and a point target observation full-system phase difference test is carried out; in the third stage of testing, the synthetic aperture radiometer is set to be in a common noise injection calibration mode, and common noise injection calibration is carried out; and calculating and counteracting a near field effect phase difference, a unit antenna phase difference and a receiver channel phase difference to obtain an accurate noise distribution network phase difference parameter. Darkroom phase calibration is achieved under the near-field condition, the result is accurate, and the method is simple, convenient and practical.

Description

Technical Field

[0001] This invention relates to the field of calibration technology for spaceborne microwave radiometers, and in particular to a method and apparatus for phase calibration of an anechoic chamber for a synthetic aperture radiometer. Background Technology

[0002] Aperture synthesizers (AS / RS) are a novel type of radiometer with advantages such as high spatial resolution, and are currently a research hotspot in the field of passive microwave remote sensing. An AS / RS comprises multiple unit antennas, receiver channels, digital correlators, and other equipment. These unit antennas form a sparse array, creating a baseline covering the spatial frequency domain. Images are synthesized through interferometry measurements of these baselines; therefore, the accuracy of the phase of each baseline interferometric measurement is a key factor affecting imaging.

[0003] Because there are phase differences between the unit antennas and receiver channels of each baseline that make up the synthetic aperture radiometer, these phase differences will be superimposed on the phase of each baseline interferometric measurement. Furthermore, there is a phase drift phenomenon during long-term operation in orbit, which will introduce phase errors into the radiometer measurement data and deteriorate the accuracy and stability of the radiometer measurement.

[0004] To eliminate phase differences between receiver channels from the phases of each baseline interferometry, a synthetic aperture radiometer is typically designed with a common noise source for phase calibration. During on-orbit operation, phase calibration is performed at regular intervals. The common noise source injects common noise into each receiver channel through a noise distribution network. At this point, the phase of the correlation coefficient of each baseline interferometry of the radiometer is the sum of the phase differences between each receiver channel and the phase differences between each path of the noise distribution network. If the phase difference of the noise distribution network is known, the phase difference between each receiver channel can be calculated, thereby eliminating the phase difference between receiver channels in the observation data and obtaining accurate observation data.

[0005] The principle of on-orbit phase calibration of a synthetic aperture radiometer is as follows: Figure 1 As shown. During on-orbit observation, when observing any far-field target, for a baseline composed of any two element antennas, the phase of the output correlation coefficient can be expressed as: ; ( The phase difference introduced by the target position For antenna pattern phase difference, (This refers to the receiver channel phase difference). To obtain the required correct target position phase difference, it is necessary to eliminate the antenna pattern phase difference and receiver channel phase difference through on-orbit phase calibration. During phase calibration, a common noise source injects common noise into each channel. At this time, the relevant output phase can be expressed as: ( (The phase difference of the noise distribution network). We can obtain: In the formula, Obtained through in-orbit phase calibration, This can be obtained through ground antenna pattern testing, and the phase difference of the noise distribution network also needs to be measured in ground tests. Only then can the receiver channel phase difference be eliminated in the observation data, and the correct target response be obtained.

[0006] Therefore, ground-based phase calibration tests are necessary before the launch of the synthetic aperture radiometer payload to measure the phase difference of the noise distribution network in advance. This measurement is used for on-orbit phase calibration to eliminate phase differences in the receiver channel. Typically, the phase difference of the noise distribution network can be calibrated by setting up a point target transmitter and measuring the system's point target response. To ensure the accuracy of the phase calibration test, the point target test needs to be conducted in a microwave anechoic chamber to shield against interference. However, many synthetic aperture microwave radiometers currently have very large apertures, and microwave anechoic chambers often cannot meet the far-field conditions. Conducting tests in the near field introduces near-field phase errors, affecting the accuracy of the noise distribution network phase difference measurement.

[0007] Existing technologies, such as patent document CN105548973B which discloses a phase self-calibration method for a synthetic aperture radiometer based on rotating time-division sampling; patent document CN105738851B which discloses a joint calibration method for a synthetic aperture microwave radiometer; and patent document CN109541325B which discloses a spaceborne one-dimensional synthetic aperture microwave radiation measurement system and method, do not address the aforementioned technical problem. Summary of the Invention

[0008] The purpose of this invention is to propose a phase calibration test method for a synthetic aperture radiometer in an anechoic chamber, which solves the difficulty of phase calibration test for a synthetic aperture radiometer caused by the inability of the anechoic chamber to meet the far-field conditions, and realizes phase calibration in an anechoic chamber under near-field conditions, so as to obtain accurate phase difference parameters of the noise distribution network.

[0009] To achieve the above objectives, the present invention provides a phase calibration method for an anechoic chamber of a synthetic aperture radiometer, comprising the following steps: A synthetic aperture radiometer and a point target emission source are installed in a microwave anechoic chamber. Phase 1 testing: Connect the output port of the unit antenna to an equal-length test cable, connect it to the microwave test instrument, set the synthetic aperture radiometer to antenna observation mode, and perform point target observation unit antenna phase difference testing. Second phase test: Connect the output of the unit antenna to each receiving channel of the synthetic aperture radiometer, set the synthetic aperture radiometer to antenna observation mode, and perform a phase difference test of the entire system for point target observation. Phase 3 testing: The integrated aperture radiometer was set to common noise injection calibration mode and common noise injection calibration was performed. Accurate noise distribution network phase difference parameters are obtained by calculating the phase difference to cancel near-field effects, the phase difference of unit antennas, and the phase difference of receiver channels.

[0010] In one possible design, the first phase of testing specifically includes the following steps: Step 1-1: Install the point target transmitter and align the transmitting antenna probe of the point target transmitter with the center of the field of view of the synthetic aperture radiometer. Steps 1-2: Provide two coaxial test cables of equal length, use a vector network analyzer to test their S-parameters, and calculate the phase difference between the two coaxial test cables using the S-parameters. ; Steps 1-3: Set the vector network analyzer to receiver mode and calibrate the phase difference between the two channels of the vector network analyzer. Steps 1-4: Connect the clock signal output port of the vector network analyzer and the clock signal input port of the microwave signal source to synchronize the clocks of the two instruments; use a coaxial cable to connect the output port of the microwave signal source to the amplifier input port of the point target transmitter; adjust the power of the microwave signal source so that the output power of the unit antenna is suitable for the vector network analyzer test. Steps 1-5: Disconnect the radio frequency cables connecting each unit antenna of the synthetic aperture radiometer to each receiver channel; Steps 1-6: Connect two coaxial test cables of equal length to the output ports of the first and second set of unit antennas, and connect the other end of the test cables to the two test ports of the vector network analyzer. Steps 1-7: Use the receiver operating mode of the vector network analyzer to measure the phase difference of the output signals of the two antenna elements and record the test results; Steps 1-8: Replace the second coaxial test cable with the next set of unit antennas in sequence, and repeat steps 1-6 and 1-7 to test the phase difference between each unit antenna and the first set of unit antennas. Steps 1-9: Based on the test results of steps 1-7 and 1-8, the phase difference between any two antenna elements during point target observation is calculated. ; in, Near-field effect phase difference Phase difference of unit antenna, : Test cable phase difference; i and j represent the numbers of any two sets of unit antennas.

[0011] In one possible design, the second phase of testing specifically includes the following steps: Step 2-1: Disconnect the coaxial test cable from the output port of the unit antenna and reconnect the RF cables between each unit antenna of the synthetic aperture radiometer and each receiver channel. Step 2-2: Keep the positions of the synthetic aperture radiometer and the point target transmitter unchanged, and use a coaxial cable to connect the output port of the noise signal source to the amplifier input port of the point target transmitter; adjust the power of the noise signal source so that the output power of the unit antenna is suitable for the synthetic aperture radiometer test.

[0012] Steps 2-3: The synthetic aperture radiometer is set to observation antenna mode. The digital correlator of the synthetic aperture radiometer outputs the correlation results between each receiver channel. The phase of this correlation is the phase difference of the entire system output during the point target transmitter test. ; in, : Receiver channel phase difference; i and j represent the numbers of any two receiver channels.

[0013] In one possible design, the third-phase test specifically includes the following steps: The synthetic aperture radiometer is set to common noise injection calibration mode. A common noise source injects common noise into each receiver channel through a noise distribution network. The digital correlator of the synthetic aperture radiometer outputs the correlation results between each receiver channel, and its phase is the sum of the phase difference between each receiver channel and the phase difference of the noise distribution network. .

[0014] In one possible design, the phase difference of the noise distribution network is calculated as follows: .

[0015] In addition, to achieve the above objectives, the present invention also provides a phase calibration device for an anechoic chamber of a synthetic aperture radiometer, used to implement the method described in any of the above claims, the device comprising: A microwave anechoic chamber, in which various calibration equipment are arranged and calibration operations are performed; Point target emission source, used to provide point target signals required for calibration tests; A microwave signal source is used to provide a single-frequency input signal to a point target transmitter. A noise signal source is used to provide noise input signals to point target emission sources; Microwave testing instruments are used to test the phase difference between two input single-frequency signals of the same frequency. The ground testing equipment and host computer are used to receive and store data collected during the calibration process of the integrated aperture radiometer. Process the calibration data and output the results; The microwave signal source is used to provide a single-frequency input signal to the point target transmitter to achieve the phase difference test of the antenna of the point target observation unit.

[0016] The noise signal source is used to provide noise input signals to the point target emission source in order to realize the phase difference test of the entire point target observation system.

[0017] In one possible design, the point target transmitter includes a transmitting antenna and an amplifier; the amplifier's input port is connected to a noise signal source or a microwave signal source, and its output port is connected to the transmitting antenna, for providing a single-frequency point target signal or a noise point target signal required for calibration testing.

[0018] In one possible design, the microwave test instrument includes a vector network analyzer with a receiver operating mode, capable of testing the phase difference between two single-frequency input radio frequency signals of the same frequency.

[0019] In one possible design, the device also includes multiple coaxial test cables of equal length.

[0020] In one possible design, the device also includes a support for mounting a point target launcher.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: By subtracting the phase difference of the entire system from the phase difference of the antenna of the point target observation unit, the near-field phase error of the anechoic chamber can be offset. This solves the difficulty of phase calibration test of the integrated aperture radiometer caused by the inability of the anechoic chamber to meet the far-field conditions. The anechoic chamber phase calibration can be achieved under near-field conditions, and the accurate phase difference parameters of the noise distribution network can be obtained. The method is simple and practical. Attached Figure Description

[0022] Figure 1 A schematic diagram illustrating the principle of on-orbit phase calibration for a synthetic aperture radiometer; Figure 2 A flowchart of a phase calibration method for an anechoic chamber of a synthetic aperture radiometer provided in an embodiment of the present invention; Figure 3 A schematic diagram of the point target observation unit antenna phase difference test principle for a phase calibration method for an anechoic chamber of a synthetic aperture radiometer provided in an embodiment of the present invention; Figure 4 A schematic diagram of the phase difference test principle of the point target observation system of a phase calibration method for an anechoic chamber of a comprehensive aperture radiometer provided in an embodiment of the present invention; Figure 5 A schematic diagram of the point target observation unit antenna phase difference test for a phase calibration method for an anechoic chamber of a synthetic aperture radiometer provided in an embodiment of the present invention; Figure 6This is a schematic diagram of the phase difference test of the entire point target observation system for a phase calibration method of an integrated aperture radiometer in an anechoic chamber, provided as an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] Aperture synthesized radiometers require ground-based phase calibration tests before launch to measure the phase difference of the noise distribution network in advance. This is used for on-orbit phase calibration in space to eliminate phase differences in the receiver channels. The phase difference of the noise distribution network can usually be calibrated in a microwave anechoic chamber through point target response tests. However, many aperture synthesized microwave radiometers have large apertures, and microwave anechoic chambers cannot meet the far-field conditions. Calibration tests performed in the near field introduce near-field phase errors, affecting the accuracy of the noise distribution network phase difference measurement.

[0025] Based on this, a specific embodiment of the present invention provides a phase calibration method for a synthetic aperture radiometer in an anechoic chamber, which solves the difficulty of phase calibration of a synthetic aperture radiometer caused by the inability of the anechoic chamber to meet the far-field conditions, and achieves phase calibration of the anechoic chamber under near-field conditions, and obtains accurate phase difference parameters of the noise distribution network by testing.

[0026] The calibration method in this embodiment uses a synthetic aperture radiometer as the experimental equipment, which mainly includes: Antenna Array: The antenna array of a synthetic aperture radiometer consists of multiple sets of unit antennas sparsely arranged to receive radiation signals from ground objects; Multi-channel receiver: The receiver of the integrated aperture radiometer includes multiple receiver channels to amplify, frequency convert, and filter the radiation signals from ground objects. The output ports of each unit antenna are connected to the input ports of each receiver channel via cables. Each receiver channel has a calibration switch at the front end, which allows the input of the receiver channel to be switched between antenna signals and common noise signals. Common noise source and noise distribution network: The common noise source generates common noise for on-orbit phase calibration, and the common noise is distributed to the input ports of each receiver channel through the noise distribution network; Digital correlator: Receives signals output from each receiver channel, correlates them pairwise to obtain correlation coefficients, and uses them for imaging with a synthetic aperture radiometer; The aforementioned integrated aperture radiometer can be switched via calibration switches at the front end of each receiver channel to achieve two modes: antenna observation mode and common noise injection calibration mode. In antenna observation mode, the calibration switch is switched to antenna input, and the radiometer receives the antenna signal; in common noise injection calibration mode, the calibration switch is switched to common noise input, and the radiometer receives the common noise injection signal for phase calibration. The calibration method in this embodiment requires the following integrated aperture radiometer anechoic chamber phase calibration device: A microwave anechoic chamber, in which various calibration equipment are arranged and calibration operations are performed; Point target emission source, used to provide point target signals required for calibration tests; A microwave signal source is used to provide a single-frequency input signal to a point target transmitter. A noise signal source is used to provide noise input signals to point target emission sources; A microwave test instrument is used to test the phase difference between two input single-frequency signals of the same frequency; for example, a vector network analyzer is used for this microwave test instrument. The ground testing equipment and host computer are used to receive and store data collected during the calibration process of the integrated aperture radiometer. Process the calibration data and output the results; The microwave anechoic chamber is the test site and environment for phase calibration of the integrated aperture radiometer anechoic chamber. It is used to shield against external interference and ensure the accuracy of the phase calibration test.

[0027] The point target transmitter includes components such as a transmitting antenna and an amplifier. The amplifier's input port is connected to a noise signal source or a microwave signal source, and its output port is connected to the transmitting antenna, used to provide the single-frequency point target signal or noise point target signal required for calibration testing.

[0028] The vector network analyzer is used to test the phase difference of the single-frequency response signals of the point target output by the two antenna units during the phase difference testing phase of the point target observation unit antenna. It is required to have a receiver operating mode capable of testing the phase difference of two single-frequency input RF signals of the same frequency.

[0029] The microwave signal source is used to provide a single-frequency input signal to the point target transmitter to achieve the phase difference test of the antenna of the point target observation unit.

[0030] The noise signal source is used to provide noise input signals to the point target emission source in order to realize the phase difference test of the entire point target observation system.

[0031] Furthermore, the device also includes multiple coaxial test cables of equal length, used to connect the output ports of each unit antenna to the test ports of a microwave test instrument (e.g., a vector network analyzer) during the phase difference test of the point target observation unit antenna.

[0032] Furthermore, the device also includes a bracket for mounting a point target emission source.

[0033] like Figure 2 As shown, this embodiment of the invention provides a phase calibration method for an anechoic chamber of a synthetic aperture radiometer, comprising: A synthetic aperture radiometer and a point target emission source are installed in a microwave anechoic chamber. Phase 1 testing: Connect the output port of the unit antenna to an equal-length test cable, connect it to the microwave test instrument, set the synthetic aperture radiometer to antenna observation mode, and perform point target observation unit antenna phase difference testing. Second phase test: Connect the output of the unit antenna to each receiving channel of the synthetic aperture radiometer, set the synthetic aperture radiometer to antenna observation mode, and perform a phase difference test of the entire system for point target observation. Phase 3 testing: The integrated aperture radiometer was set to common noise injection calibration mode, and common noise injection calibration phase difference test was performed. Accurate noise distribution network phase difference parameters are obtained by calculating the phase difference to cancel near-field effects, the phase difference of unit antennas, and the phase difference of receiver channels.

[0034] Phase difference testing was performed in all three stages of the test. The first stage test used a vector network analyzer to measure the phase difference, while the second and third stages test obtained the phase based on the radiometer output data, which will be further explained later.

[0035] like Figure 3 and Figure 4 As shown, the principle of the above three-stage test in this embodiment is as follows: Under the near-field conditions of the microwave anechoic chamber, the positional relationship between the integrated aperture radiometer and the point target source remains unchanged. In the first stage, the radiometer's operating mode is set to antenna observation mode. By testing the phase difference of the antennas in the point target observation unit, the phase difference between each unit antenna under the condition of observing the point source can be obtained. ; in, Near-field effect phase difference Phase difference of unit antenna, : Test cable phase difference; i and j represent the numbers of any two sets of unit antennas.

[0036] In the second stage, the radiometer was set to antenna observation mode, and the phase difference between each channel of the entire system was obtained by observing the phase difference of the whole system through point target observation. ; in, : Receiver channel phase difference; i and j represent the numbers of any two receiver channels.

[0037] In the third stage, the radiometer's operating mode is set to common noise injection calibration mode. Through common noise injection, the phase difference is tested to obtain the sum of the phase difference of each receiver channel and the phase difference of the noise distribution network. ; in : Phase difference of the noise distribution network; i and j represent the numbers of any two receiver channels.

[0038] Since the positional relationship between the synthetic aperture radiometer and the point target source remained unchanged in both the first and second phases of testing, the near-field effect phase difference between the two tests was... Phase difference with unit antenna The receiver channel phase difference remains unchanged in both the second and third phases of testing. It remains unchanged, thus canceling out the phase difference caused by the near-field effect. Phase difference of unit antenna and receiver channel phase difference The phase difference of the noise distribution network is calculated as follows: .

[0039] Test cable phase difference The S-parameters of the test cable can be obtained through vector network analysis. The phase difference of the noise distribution network obtained from this anechoic chamber calibration... This can be used in the on-orbit phase calibration of the integrated aperture radiometer payload to eliminate the phase difference of the receiver channel.

[0040] Reference Figure 5 In this embodiment, the first stage involves testing the phase difference of the point target observation unit antenna. The specific test steps include: Step 1-1: In a microwave anechoic chamber, place a support opposite the antenna of the synthetic aperture radiometer, install a point target transmitter on the support, and align the transmitting antenna probe of the point target transmitter with the center of the synthetic aperture radiometer's field of view.

[0041] Steps 1-2: Prepare two coaxial test cables of equal length, use a vector network analyzer to test their S-parameters, and calculate the phase difference between the two test cables using the S-parameters. .

[0042] S-parameters refer to scattering parameters, which are used to describe the transmission and reflection of signals in electronic circuits.

[0043] Steps 1-3: The vector network analyzer is set to receiver mode and the phase difference between the two channels of the vector network analyzer is calibrated.

[0044] Steps 1-4: Connect the clock signal output port of the vector network analyzer and the clock signal input port of the microwave signal source using a coaxial cable to synchronize the clocks of the two instruments. Connect the output port of the microwave signal source to the amplifier input port of the point target transmitter using a coaxial cable; adjust the power of the microwave signal source so that the output power of the unit antenna is suitable for vector network analysis testing.

[0045] Steps 1-5: Disconnect the radio frequency cables connecting each unit antenna of the integrated aperture radiometer to each receiver channel.

[0046] Steps 1-6: Connect the two coaxial test cables of equal length to the output ports of the first and second set of unit antennas, and connect the other end of the test cables to the two test ports of the vector network analyzer.

[0047] Steps 1-7: Measure the phase difference of the output signals of the two antenna elements using the receiver operating mode of vector network analysis, and record the test results.

[0048] Steps 1-8: Replace the second coaxial test cable with the next set of unit antennas in sequence, repeat steps 1-6 and 1-7, test the phase difference between each unit antenna and the first set of unit antennas, and record the test results.

[0049] Steps 1-9: Based on the test results of steps 1-7 and 1-8, obtain the phase difference between the first set of element antennas and all other element antennas during point target observation. This is determined by the phase difference between the tested i-th set of element antennas and the first set of antenna elements. The phase difference between the j-th antenna unit and the 1st antenna unit The phase difference between the j-th antenna unit and the i-th antenna unit can be calculated. Using this method, the phase difference between any two sets of unit antennas during point target observation can be calculated. .

[0050] Reference Figure 6 In the second stage of this embodiment, the phase difference test of the entire point target observation system includes the following steps: Step 2-1: Disconnect the coaxial test cable from the output port of the unit antenna and reconnect the RF cables between each unit antenna of the synthetic aperture radiometer and each receiver channel.

[0051] Step 2-2: Keep the positions of the synthetic aperture radiometer and the point target transmitter unchanged, and use a coaxial cable to connect the output port of the noise signal source to the amplifier input port of the point target transmitter; adjust the power of the noise signal source so that the output power of the unit antenna is suitable for the synthetic aperture radiometer test.

[0052] Steps 2-3: Set the synthetic aperture radiometer to observation antenna mode. The digital correlator of the synthetic aperture radiometer outputs the correlation results between each receiver channel. The phase of this correlation is the phase difference of the entire system output during the point target emission source test. ; Store data. In this field, the correlation result is usually obtained by a digital correlator sampling the output voltage of each receiver channel, performing correlation accumulation on the sampled data of each pair of receiver channels, and obtaining the complex correlation coefficient between each pair of receiver channels. The phase of this complex correlation coefficient is the phase difference between the two channels.

[0053] In the third stage of this embodiment, the common noise injection calibration specifically includes the following steps: the synthetic aperture radiometer is set to common noise injection calibration mode, and the common noise source injects common noise into each receiver channel through the noise distribution network. At this time, the digital correlator of the synthetic aperture radiometer outputs the correlation results between each receiver channel, and its phase is the sum of the phase difference between each receiver channel and the phase difference of the noise distribution network. ; Store data.

[0054] After the three-stage test is completed, the near-field effect of the microwave anechoic chamber can be canceled by subtracting the phase difference of the entire system from the phase difference of the antenna of the point target observation unit. Then, the phase difference of the receiver channel can be canceled by subtracting the result from the common noise injection calibration test. Finally, the phase difference of the noise distribution network can be calculated. Then, by analyzing the S-parameters of the test cable using vector network analysis, the phase difference of the test cable can be calculated. The phase difference of the noise distribution network can then be calculated. .

[0055] Phase difference of noise distribution network obtained by anechoic chamber calibration This can be used in the on-orbit phase calibration of the integrated aperture radiometer payload to eliminate phase errors caused by phase drift of the receiver channel while on-orbit.

[0056] As can be seen from the above detailed description of the present invention, the present invention cancels the near-field phase error of the anechoic chamber by subtracting the phase difference of the entire system of the point target test from the phase difference of the antenna of the point target observation unit. This can solve the difficulty of phase calibration test of the integrated aperture radiometer caused by the inability of the anechoic chamber to meet the far-field conditions, realize the phase calibration of the anechoic chamber under the near-field conditions, and obtain accurate phase difference parameters of the noise distribution network. The method is simple and practical.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A phase calibration method for an anechoic chamber of a synthetic aperture radiometer, characterized in that, Including the following steps: A synthetic aperture radiometer and a point target emission source are installed in a microwave anechoic chamber. Phase 1 testing: Connect the output port of the unit antenna to an equal-length test cable, connect it to the microwave test instrument, set the synthetic aperture radiometer to antenna observation mode, and perform point target observation unit antenna phase difference testing. Second phase test: Connect the output of the unit antenna to each receiving channel of the synthetic aperture radiometer, set the synthetic aperture radiometer to antenna observation mode, and perform a phase difference test of the entire system for point target observation. Phase 3 testing: The integrated aperture radiometer was set to common noise injection calibration mode and common noise injection calibration was performed. Accurate noise distribution network phase difference parameters are obtained by calculating the phase difference to cancel near-field effects, the phase difference of unit antennas, and the phase difference of receiver channels.

2. The anechoic chamber phase calibration method for a synthetic aperture radiometer as described in claim 1, characterized in that, The first phase of testing specifically includes the following steps: Step 1-1: Install the point target transmitter and align the transmitting antenna probe of the point target transmitter with the center of the field of view of the synthetic aperture radiometer. Steps 1-2: Provide two coaxial test cables of equal length, use a vector network analyzer to test their S-parameters, and calculate the phase difference between the two coaxial test cables using the S-parameters. ; Steps 1-3: Set the vector network analyzer to receiver mode and calibrate the phase difference between the two channels of the vector network analyzer. Steps 1-4: Connect the clock signal output port of the vector network analyzer and the clock signal input port of the microwave signal source to achieve clock synchronization between the two instruments; Connect the output port of the microwave signal source to the amplifier input port of the point target transmitter using a coaxial cable; Adjust the microwave signal source power to make the unit antenna output power suitable for vector network analyzer testing; Steps 1-5: Disconnect the radio frequency cables connecting each unit antenna of the synthetic aperture radiometer to each receiver channel; Steps 1-6: Connect two coaxial test cables of equal length to the output ports of the first and second set of unit antennas, and connect the other end of the test cables to the two test ports of the vector network analyzer. Steps 1-7: Use the receiver operating mode of the vector network analyzer to measure the phase difference of the output signals of the two antenna elements and record the test results; Steps 1-8: Replace the second coaxial test cable with the next set of unit antennas in sequence, and repeat steps 1-6 and 1-7 to test the phase difference between each unit antenna and the first set of unit antennas. Steps 1-9: Based on the test results of steps 1-7 and 1-8, the phase difference between any two antenna elements during point target observation is calculated. ； in, Near-field effect phase difference Phase difference of unit antenna, Test cable phase difference; i and j represent the numbers of any two sets of unit antennas.

3. The anechoic chamber phase calibration method for a synthetic aperture radiometer as described in claim 2, characterized in that, The second phase of testing specifically includes the following steps: Step 2-1: Disconnect the coaxial test cable from the output port of the unit antenna and reconnect the RF cables between each unit antenna of the synthetic aperture radiometer and each receiver channel. Step 2-2: Keeping the positions of the integrated aperture radiometer and the point target emitter unchanged, use a coaxial cable to connect the output port of the noise signal source to the amplifier input port of the point target emitter. Adjust the power of the noise signal source to make the output power of the unit antenna suitable for the integrated aperture radiometer test. Steps 2-3: The synthetic aperture radiometer is set to observation antenna mode. The digital correlator of the synthetic aperture radiometer outputs the correlation results between each receiver channel. The phase of this correlation is the phase difference of the entire system output during the point target transmitter test. ； in, : Receiver channel phase difference; i and j represent the numbers of any two receiver channels.

4. The anechoic chamber phase calibration method for a synthetic aperture radiometer as described in claim 3, characterized in that, The third phase of testing specifically includes the following steps: The synthetic aperture radiometer is set to common noise injection calibration mode. A common noise source injects common noise into each receiver channel through a noise distribution network. The digital correlator of the synthetic aperture radiometer outputs the correlation results between each receiver channel, and its phase is the sum of the phase difference between each receiver channel and the phase difference of the noise distribution network. .

5. The anechoic chamber phase calibration method for a synthetic aperture radiometer as described in claim 4, characterized in that, The calculated phase difference of the noise distribution network is: 。 6. A phase calibration device for an anechoic chamber of a synthetic aperture radiometer, used to implement the method described in any one of claims 1-5, the device comprising: A microwave anechoic chamber, in which various calibration equipment are arranged and calibration operations are performed; Point target emission source, used to provide point target signals required for calibration tests; A microwave signal source is used to provide a single-frequency input signal to a point target transmitter. A noise signal source is used to provide noise input signals to point target emission sources; Microwave testing instruments are used to test the phase difference between two input single-frequency signals of the same frequency. The ground testing equipment and host computer are used to receive and store data collected during the calibration process of the integrated aperture radiometer. Process the calibration data and output the results; The microwave signal source is used to provide a single-frequency input signal to the point target transmitter to achieve the phase difference test of the antenna of the point target observation unit. The noise signal source is used to provide noise input signals to the point target emission source in order to realize the phase difference test of the entire point target observation system.

7. The phase calibration device for an anechoic chamber of a synthetic aperture radiometer as described in claim 6, characterized in that, The point target transmitter includes a transmitting antenna and an amplifier; the amplifier's input port is connected to a noise signal source or a microwave signal source, and its output port is connected to the transmitting antenna, used to provide the single-frequency point target signal or noise point target signal required for calibration testing.

8. The phase calibration device for an anechoic chamber of a synthetic aperture radiometer as described in claim 6, characterized in that, The microwave testing instrument includes a vector network analyzer with a receiver operating mode, which can test the phase difference between two single-frequency input radio frequency signals of the same frequency.

9. The phase calibration device for an anechoic chamber of a synthetic aperture radiometer as described in claim 6, characterized in that, It also includes multiple coaxial test cables of equal length.

10. The phase calibration device for a synthetic aperture radiometer anechoic chamber as described in claim 6, characterized in that, It also includes a bracket for mounting the point target launcher.

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