Radar interferometer positioning system phase optimization method

Abstract

The invention relates to a radar interferometer positioning system phase optimization method, which comprises the following steps of: in a satellite research and development stage, performing phase consistency optimization, receiving channel phase consistency optimization, radio frequency cable phase consistency optimization and antenna installation error optimization on an antenna; after a satellite enters an orbit, a calibration station is built on the ground, and error optimization is carried out through establishment of an error model and on-orbit calibration. According to the method, phase errors of all links in the positioning calculation process under an interferometer system can be optimized, and it is ensured that the target positioning precision of a satellite meets the requirement.

Description

Technical Field

[0001] The invention relates to the technical field of satellite positioning, and in particular to a phase optimization method for a radar interferometer positioning system. Background Art

[0002] The principle of interferometer direction finding and positioning technology is to use the phase difference formed by radio waves on the direction finding baseline to determine the direction of the incoming wave. For the interferometer direction finding system, common array forms include: uniform circular array; non-uniform linear array; "L-shaped, T-shaped, cross-shaped" orthogonal array, irregular array, etc. Compared with the linear array, the circular array has the advantages of no mirror ambiguity, independent angular resolution, and omnidirectional direction finding. The non-uniform linear array and the "L-shaped, T-shaped, cross-shaped" orthogonal array can further achieve full-band and omnidirectional direction finding by optimizing the baseline selection of the antenna array.

[0003] In order to achieve high-precision positioning functions in multiple frequency bands and improve system capabilities, a combination of long and short baselines can be used: although the long baseline has multiple phase values, that is, "phase ambiguity", the actual phase can be solved using the short baseline. The longer the long baseline, the more antenna elements are required for deambiguation, and the higher the direction-finding accuracy of the system. By combining different formations, long and short baselines are established on the satellite structure, and an extension mechanism is added to extend the baseline length when necessary, deambiguation and direction-finding can be achieved to meet positioning needs.

[0004] In the process of positioning and solving, the fixed multi-baseline interferometer direction-finding positioning system measures the arrival time and frequency of the target signal and the phase difference between the interferometer antenna and the target signal. The target position is estimated based on time and combined with orbital position information and interferometer antenna installation information. The above observation information will affect the positioning accuracy due to various errors such as system error, algorithm error and mechanical error, and must be corrected.

[0005] Therefore, designing a phase optimization method for radar interferometer positioning system is a technical problem that needs to be solved urgently. Summary of the invention

[0006] In order to solve the technical problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a phase optimization method for a radar interferometer positioning system, which can optimize the phase error of the antenna, the phase error of the radio frequency cable, the phase error introduced by the local oscillator noise, the phase error between the receiving phase comparison channels, the phase error of the digital phase detection, the phase error caused by the antenna installation position, etc., so as to improve the system direction finding accuracy.

[0007] To achieve the above-mentioned object of the invention, the present invention provides a radar interferometer positioning system phase optimization method, comprising:

[0008] During the satellite development phase, the antenna phase consistency, receiving channel phase consistency, RF cable phase consistency, and antenna installation error are optimized.

[0009] After the satellite enters orbit, a calibration station is built on the ground to optimize the error by establishing an error model and conducting on-orbit calibration.

[0010] According to a technical solution of the present invention, the antenna phase consistency optimization specifically includes:

[0011] According to the positioning accuracy of the satellite, the phase consistency of the unit antenna is optimized from three aspects: antenna processing accuracy optimization, antenna testing accuracy optimization, and antenna screening optimization. At the same time, the phase difference between the antennas after array formation is obtained through the microwave darkroom test method, and it is bound to the direction finding system for use in subsequent processing and solving.

[0012] According to a technical solution of the present invention, the receiving channel phase consistency optimization specifically includes:

[0013] The phase consistency of the receiving channel is determined by the phase consistency of the frequency conversion local oscillator and the microwave channel;

[0014] Aiming at the fixed phase deviation of the receiving channel, two correction methods, non-real-time correction and real-time correction, are designed. The phase difference correction data of the channel is obtained through the ground signal source and the internal self-test source of the equipment respectively, so as to correct the phase error value of the channel.

[0015] According to a technical solution of the present invention, the RF cable phase consistency optimization specifically includes:

[0016] Calculate the fixed errors of the cable related to length, material, temperature, and force, create a data file, bind the errors to the interferometer direction-finding system, and complete the phase consistency optimization of the cable.

[0017] According to a technical solution of the present invention, the antenna installation error optimization specifically includes:

[0018] The antenna installation error is optimized by accurately measuring and adjusting the antenna installation position;

[0019] The position measurement is completed by using a satellite precision measurement system and / or an industrial photogrammetry system. Different precision optimization methods are used for antennas in different positions to optimize the installation error of the antenna on the installation surface, the installation error between the antenna installation surface and the satellite body, the vibration and thermal deformation deviation of the satellite body, and the direction finding error caused by the mechanism control accuracy.

[0020] According to a technical solution of the present invention, after the satellite enters orbit, a calibration station is built on the ground to perform error optimization by establishing an error model and performing on-orbit calibration, which specifically includes:

[0021] Establish an error model. The error factors that affect the positioning accuracy after the satellite enters orbit include phase difference measurement error, baseline length measurement error, interferometer installation angle error, observation platform attitude error, observation platform position error, and frequency measurement error.

[0022] At the current typical system error level of each observation, ignoring the direction-finding deviation caused by frequency measurement error and observation platform system error, the following observation equation is obtained:

[0023]

[0024] Among them, Δ represents the systematic error and δ represents the random error. represents the phase difference, d represents the baseline length, θ represents the baseline installation azimuth, and ε represents the baseline installation elevation angle;

[0025] Establish multiple calibration stations on the ground, use the two prior information of calibration station location and signal frequency, and estimate the systematic error of each observation by measuring the phase difference;

[0026] The ground calibration source system uses a high-power signal generator to simulate radar signals of standard signal styles in each frequency band and transmit them to the satellite. The interferometer array antenna on the payload receives the calibration source signal and measures the signal parameters. By comparing it with the real data of the ground calibration station, the system deviation parameters are obtained.

[0027] According to the design requirements, complete the calibration work of the entire frequency band, and correct the system's positioning results based on the current status and parameters of the satellite.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention is based on the fixed baseline interferometer direction finding and positioning system. Starting from the phase difference that has an important impact on the direction finding performance, the present invention analyzes the possible phase difference errors in the positioning solution process, including: phase error between unit antennas, phase error between RF cables, phase error between phase comparison channels, phase error introduced by local oscillator noise, phase error of digital phase discrimination, and antenna installation error. Before the satellite enters orbit, the above errors are optimized to improve the positioning accuracy of the satellite.

[0030] (2) After the satellite is in orbit, in order to further improve the satellite positioning accuracy and overcome the influence of system errors on positioning accuracy, the error model is established by comprehensively considering the influencing factors such as baseline installation measurement error, inconsistency between antenna phase center and geometric center, inconsistency between antenna amplitude and phase, inconsistency between cable amplitude and phase, satellite attitude error, satellite position error, target signal carrier frequency error, etc. The correction coefficient is obtained through on-orbit calibration to correct the positioning result.

[0031] (3) In the positioning and solving process, the factors that affect the phase error are decomposed, and different optimization methods are adopted for different phase errors. Through the two means of mechanical optimization and algorithm design, the optimization effect of the phase error is improved, the accumulation of phase error in the system processing and solving process is reduced, and the positioning accuracy of the system is guaranteed.

[0032] (4) The phase optimization method in the present invention was first proposed and applied in the fixed multi-baseline interferometer direction finding positioning system. Its positioning effect and positioning accuracy have been verified by satellite in-orbit applications. This method can provide research ideas for subsequent satellites with the same system or in the same field. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 A schematic diagram schematically shows an antenna layout in a radar interferometer positioning system according to an embodiment of the present invention;

[0035] Figure 2 A schematic diagram schematically shows the principle of satellite positioning in a radar interferometer system according to an embodiment of the present invention;

[0036] Figure 3 A schematic diagram of a phase optimization method according to an embodiment of the present invention is schematically shown;

[0037] Figure 4 Schematically showing two phase correction methods according to an embodiment of the present invention;

[0038] Figure 5 The following schematically shows an on-orbit positioning result correction process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] A radar interferometer positioning system phase optimization method of the present invention is suitable for optimizing the system phase error of a fixed multi-baseline interferometer direction-finding positioning system. The method can effectively overcome the phase error of the antenna, the phase error of the radio frequency cable, the phase error introduced by the local oscillator noise, the phase error between the receiving phase comparison channels, the phase error of the digital phase detection, the phase error caused by the antenna installation position, etc., thereby improving the system direction-finding accuracy.

[0041] In order to improve the positioning accuracy of the satellite to the target and meet the full-band and all-round direction finding requirements, different formation combinations are selected in the interferometer formation, such as Figure 1 As shown in the figure. In this formation, the long baseline antenna layout is realized by adding a satellite deployment mechanism, and the short baseline antenna layout is located on the satellite pairing floor. The overall layout constitutes a combination of long and short baselines, which comprehensively guarantees high positioning accuracy and ambiguity resolution capabilities.

[0042] In this formation, the satellite can measure the direction of the target wave through the two-dimensional interferometer it carries, and use the direction line to intersect with the earth's surface to achieve instant positioning of the ground target. The schematic diagram is shown in Figure 2 Assume that the height of the satellite from the ground is h, and the radius of the earth is R. The angles θ1 and θ2 between the two baselines and the target line of sight are measured by a two-dimensional interferometer. A direction line can be determined by these two angles, and the intersection of the direction line and the earth's surface is the target position.

[0043] In the positioning process, the phase error of the direction finding positioning system directly affects the positioning accuracy of the system. Therefore, the error in the solution process can be decomposed and the phase difference error of each link can be optimized, such as Figure 3 As shown in the figure, during the satellite development stage, the phase error is optimized by combining mechanical optimization with algorithm design, including: antenna phase consistency optimization, receiving channel consistency optimization, RF cable phase consistency optimization, antenna installation error optimization, etc.; after the satellite is put into orbit, a calibration station is built on the ground to further reduce the system error by establishing an error model and conducting on-orbit calibration.

[0044] 1. Antenna phase consistency optimization is divided into phase consistency optimization of unit antenna and phase consistency optimization of array antenna. The phase consistency optimization measures of unit antenna mainly include:

[0045] (1) Optimization of antenna processing accuracy: An integrated processing method can be used to reduce the error introduced by parts assembly. In addition, the processed parts are strictly inspected to ensure that the technical status of the parts meets the technical requirements.

[0046] (2) Antenna test accuracy optimization: This is an important guarantee to ensure that the antenna phase consistency test results meet the requirements. The antenna phase consistency index requirements are high, which puts forward higher accuracy requirements for the antenna phase pattern test. The combined error of antenna testing and installation accuracy should be optimized to not exceed the threshold, and the accuracy optimization requirements should be decomposed into each link of the test process, including: test turntable error, test tooling size error, and installation error.

[0047] (3) Antenna screening and optimization: Improve phase consistency by screening and pairing. After the array antenna units are screened, select the antenna with better phase consistency and install it at the antenna position corresponding to the longest baseline according to the installation requirements of the long baseline to ensure positioning accuracy.

[0048] The phase consistency optimization of the antenna after array formation refers to the correction of the phase consistency of the antenna in the array state. The phase difference of the antenna array corresponding to different frequencies and different incident angles is obtained in the microwave darkroom, and the phase difference correction table between the antennas is established according to the fixed frequency step and angle step. During the satellite's in-orbit operation, the established antenna phase difference correction table is read and called to effectively eliminate the influence of fixed errors.

[0049] 2. Optimizing the consistency of the receiving channel is to optimize the phase difference of the receiving channel. According to the principle of interferometer direction finding and positioning, two phase correction methods, non-real-time correction and real-time correction, are designed for the fixed phase deviation of the receiving channel. Figure 4 As shown in the figure, the non-real-time correction uses the signal source input signal to correct the fixed deviation of the subsystem phase difference, and the real-time correction uses the self-checking source input signal to correct the fixed deviation of the subsystem phase difference.

[0050] (1) In the non-real-time correction mode, the signal is input into the interferometer phase comparison channel after power splitting. The system can obtain the channel phase difference of different frequencies and establish a channel phase difference correction table. During the on-orbit operation, the phase difference measurement result is corrected according to the measurement frequency and the center dwell frequency in combination with the correction table.

[0051] (2) In the real-time correction mode, the system switches to the self-check source through the switch selection to obtain the ground self-check source phase difference correction table. During the on-orbit operation, the on-orbit self-check source phase difference correction table can be obtained. According to the measurement frequency and the center dwell frequency, the correction values ​​of the above three types of correction tables are searched and called to correct the phase difference measurement results.

[0052] 3. RF cable phase consistency optimization refers to the process of optimizing the phase of RF cables according to their characteristics and functions. Cable phase stability includes two aspects: temperature and mechanics. Based on this, the phase consistency of RF cables is optimized from the perspectives of cable selection, processing accuracy, installation requirements, and error correction.

[0053] (1) Combined with the design index requirements, comprehensively consider the cable's insertion loss, phase stability characteristics, weight, length, etc., and select a cable that meets the requirements.

[0054] (2) Use a dedicated cable unloading machine to ensure the cable length and meet the requirement of equal length of each segment. Increase the number of cable components to be processed and select them. Retest the absolute phase of the cable before going online.

[0055] (3) The RF cables must be installed in the same mechanical manner, with the bending radius and torsion method meeting the requirements. They should be bundled as much as possible to ensure consistent ambient temperature. The extravehicular RF cables are coated with multiple layers to reduce the temperature variation range of the extravehicular cables.

[0056] (4) The phase of the cable will change due to wiring, bending, dynamic effects, etc. After the final wiring and fixing of the cable on the satellite, the relative phase of the cable is measured, and the resulting system error can be compensated by real-time system correction and ground calibration.

[0057] 4. Antenna installation error optimization is to measure and adjust the installation position of the antenna to ensure that its installation position is within the accuracy range. The position accuracy of the antenna is optimized by combining the satellite precision measurement system, industrial photogrammetry system and antenna coordinate conversion mathematical operation. According to the antenna array layout, the antenna installation state includes two types: on the floor and on the extension rod mechanism: the antenna on the floor is photographed at multiple angles and multi-view by the industrial photogrammetry system. Figure 3 The antenna on the extension mechanism is measured and reconstructed in two dimensions through precise measurement and coordinate conversion of the extension mechanism and the satellite structure. After the measurement and adjustment of all antennas are completed, the correct position coordinates are recorded and the coordinates are formed into a data file and bound to the satellite payload direction finding system for use in subsequent solution processing.

[0058] 5. On-orbit calibration system error optimization is an effective means to further overcome the systematic error and random error of the interferometer direction-finding system. The premise of high-precision positioning of the interferometer direction-finding positioning system is to accurately know the relative positions of each antenna. Due to the influence of manufacturing process, measurement level, ambient temperature and other conditions, there are not only random errors but also systematic errors between the nominal values ​​and actual values ​​of the interferometer direction-finding positioning system, such as: there may be amplitude / phase inconsistency between the receiving channels, deviation between the antenna phase center and the geometric center, and various measurement errors. The specific process of the on-orbit calibration process is as follows:

[0059] (1) Establish an error model. The main error factors that affect the positioning accuracy after the satellite enters orbit include phase difference measurement error, baseline length measurement error, interferometer installation angle error, observation platform attitude error, observation platform position error, frequency measurement error, etc. In actual engineering applications, under the current typical system error level of each observation quantity, the direction finding deviation caused by the frequency measurement error and the observation platform system error is very small and can usually be ignored. Therefore, the following observation equation can be obtained:

[0060]

[0061] Among them, Δ represents the systematic error and δ represents the random error. represents the phase difference, d represents the baseline length, θ represents the baseline installation azimuth, and ε represents the baseline installation elevation angle.

[0062] (2) Multiple calibration stations are established on the ground. Using the two prior information of known calibration station locations and known signal frequencies, the systematic errors of each observed quantity can be estimated by measuring the phase difference.

[0063] (3) The ground calibration source system uses a high-power signal generator to simulate radar signals with standard signal patterns in each frequency band and transmit them to the satellite. The interferometer array antenna on the payload receives the calibration source signal and measures the signal parameters. By comparing it with the real data from the ground calibration station, the system deviation parameters are obtained.

[0064] (4) According to the design requirements, complete the calibration work of the entire frequency band, and correct the positioning results of the system according to the current status and parameters of the satellite, such as Figure 5 shown.

[0065] The present invention relates to a phase optimization method for a radar interferometer positioning system, which optimizes the phase errors of each link in the positioning solution process under the interferometer system to ensure that the target positioning accuracy of the satellite meets the requirements. The phase difference error of the system may come from the phase inconsistency error of the antenna, the phase error between the radio frequency cables, the phase error introduced by the local oscillator noise, the phase error between the receiving phase comparison channels, the phase error of the digital phase detection, etc. In response to the above errors, during the satellite development stage, optimization measures are proposed from the aspects of antenna phase consistency optimization, receiving channel consistency optimization, radio frequency cable phase consistency optimization, antenna installation error optimization, etc.; after the satellite enters orbit, a calibration station is built on the ground, and the system error and random error are further reduced by establishing an error model and on-orbit calibration. The phase difference error is optimized throughout the entire process from satellite development to on-orbit operation to ensure the positioning accuracy of the satellite.

[0066] It should be noted here that the contents not described in detail in this specification can be implemented by technicians through the description in this specification and the existing technology, so they are not described in detail.

[0067] It should be noted that although the embodiments of the present invention described above are illustrative, they are not intended to limit the present invention, and therefore the present invention is not limited to the above specific embodiments. Without departing from the principles of the present invention, any other embodiments obtained by those skilled in the art under the guidance of the present invention are deemed to be within the protection of the present invention.

Claims

1. A radar interferometer positioning system phase optimization method, characterized in that: include: During the satellite development phase, the antenna phase consistency, receiving channel phase consistency, RF cable phase consistency, and antenna installation error are optimized. After the satellite enters orbit, a calibration station is built on the ground to optimize the error by establishing an error model and conducting on-orbit calibration.

2. The radar interferometer positioning system phase optimization method according to claim 1, characterized in that: The antenna phase consistency optimization specifically includes: According to the positioning accuracy of the satellite, the phase consistency of the unit antenna is optimized from three aspects: antenna processing accuracy optimization, antenna testing accuracy optimization, and antenna screening optimization. At the same time, the phase difference between the antennas after array formation is obtained through the microwave darkroom test method, and it is bound to the direction finding system for use in subsequent processing and solving.

3. The radar interferometer positioning system phase optimization method according to claim 1, characterized in that: The receiving channel phase consistency optimization specifically includes: The phase consistency of the receiving channel is determined by the phase consistency of the frequency conversion local oscillator and the microwave channel; Aiming at the fixed phase deviation of the receiving channel, two correction methods, non-real-time correction and real-time correction, are designed. The phase difference correction data of the channel is obtained through the ground signal source and the internal self-test source of the equipment respectively, so as to correct the phase error value of the channel.

4. The radar interferometer positioning system phase optimization method according to claim 1, characterized in that: The RF cable phase consistency optimization specifically includes: Calculate the fixed errors of the cable related to length, material, temperature, and force, create a data file, bind the errors to the interferometer direction-finding system, and complete the phase consistency optimization of the cable.

5. The radar interferometer positioning system phase optimization method according to claim 1, characterized in that: The antenna installation error optimization specifically includes: The antenna installation error is optimized by accurately measuring and adjusting the antenna installation position; The position measurement is completed by using a satellite precision measurement system and / or an industrial photogrammetry system. Different precision optimization methods are used for antennas in different positions to optimize the installation error of the antenna on the installation surface, the installation error between the antenna installation surface and the satellite body, the vibration and thermal deformation deviation of the satellite body, and the direction finding error caused by the mechanism control accuracy.

6. The radar interferometer positioning system phase optimization method according to claim 1, characterized in that: After the satellite is put into orbit, a calibration station is built on the ground to optimize the error by establishing an error model and conducting on-orbit calibration, including: Establish an error model. The error factors that affect the positioning accuracy after the satellite enters orbit include phase difference measurement error, baseline length measurement error, interferometer installation angle error, observation platform attitude error, observation platform position error, and frequency measurement error. At the current typical system error level of each observation, ignoring the direction-finding deviation caused by frequency measurement error and observation platform system error, the following observation equation is obtained: Among them, Δ represents the systematic error and δ represents the random error. represents the phase difference, d represents the baseline length, θ represents the baseline installation azimuth, and ε represents the baseline installation elevation angle; Establish multiple calibration stations on the ground, use the two prior information of calibration station location and signal frequency, and estimate the systematic error of each observation by measuring the phase difference; The ground calibration source system uses a high-power signal generator to simulate radar signals of standard signal styles in each frequency band and transmit them to the satellite. The interferometer array antenna on the payload receives the calibration source signal and measures the signal parameters. By comparing it with the real data of the ground calibration station, the system deviation parameters are obtained. According to the design requirements, complete the calibration work of the entire frequency band, and correct the system's positioning results based on the current status and parameters of the satellite.

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