Research On Error Characteristics Of Large Aperture Antennas For Space VLBI

Weak signal detection has an increasingly urgent demand for large-aperture and high-capacity spaceborne antennas.Very Long Baseline Interferometry(VLBI),as the current radio observation technology with the highest angular resolution,requires larger-aperture spaceborne antenna to construct the space VLBI to obtain extremely high angular resolution,where the baseline length far exceeds the size of the earth,and realize farther and finer detection and research of cosmic radio sources.However,on the one hand,the existing rocket carrying capacity limits the weight and volume of the satellite,which increases the difficulty of designing and manufacturing the satellite.On the other hand,various factors will affect the stability of the payload and the satellite body,and reduce the performance of the antenna gain and pointing accuracy.Starting from the construction of space VLBI for weak signal detection,this paper aims to conduct systematic research on space radio astronomy design,antenna static error analysis,antenna dynamic problem analysis,and VLBI antenna signal error analysis.The main work and achievements of the paper are as follows:(1)The overall design of the Space radio astronomy observatory is completed.Aiming at the high bandwidth requirements of the space radio astronomy observatory,a folded log-periodic dipole array(Log-periodic Dipole Array,LPDA)array is applied,which can not only obtain a larger observation frequency range,but also reduce the impact of feed phase mismatch,while the folded design can also reduce the overall geometric size.According to the gain requirements of the space radio astronomy observatory,a 30-meter-caliber peripheral truss-type parabolic reflector is applied.The30-meter-caliber can ensure the high gain of the antenna.The structure design of the expandable reflector cable net and truss can reduce the storage size and overall weight,can also further reduce the difficulty of carrying.(2)The influence of the surface error of the reflector on the delay error of VLBI detection is studied.When performing long-term static observation on a known signal source,the reflector error is one of the main factors of the antenna error,and the surface error of the flexible parabolic antenna determines its gain decay.First,the mathematical analysis model of the surface error of the reflector is established,and the optimization solver(Solving Constraint Integer Programs,SCIP)is used to obtain the influence of the surface error on the performance of the antenna under different distributions,especially the peak gain,compared with the conventional method,the solution result difference is more than 1.8d B.Secondly,the transmission link between the antenna performance and the VLBI detection delay error is established,the analysis results of the surface error are converted into the analysis of the delay error,and the influence of different surface error distributions on the VLBI detection delay error is obtained.(3)The influence of feed-related errors on antenna performance and antenna design is analyzed.For large-aperture spaceborne antennas in space,the feed error is another important factor affecting the performance of the antenna.This paper first analyzes the influence of the lateral offset and axial offset of the feed on the performance of the antenna,in which the impact of the axial offset is relatively small,and focuses on the working condition of the lateral offset.Secondly,the influence of aperture distribution and other factors on the antenna performance is studied,and then the antenna performance under the comprehensive various feed-related errors is systematically studied,and the influence on the geometric design of the antenna in actual engineering is also analyzed.(4)The dynamic characteristics of the antenna and the signal error of the VLBI antenna under micro-vibration are studied.In view of the large overall flexibility of the satellite and the greater flexibility of the cable net of the reflector,the satellite’s attitude and orbit control and space factor interference will cause the overall satellite and the reflector antenna to vibrate to varying degrees,affecting the stability of the satellite and the performance of the antenna.First,for the space radio astronomy observatory established in this paper,its dynamic model is established,and the corresponding dynamic response is further given by combining the finite element analysis method.Secondly,the signal error introduced by the slight vibration of the antenna is studied,the corresponding mathematical model is established,the adaptive Kalman filter algorithm is applied to signal processing,and the effectiveness of the algorithm is verified.This paper systematically completes the design of space radio astronomy observatory,antenna error analysis and VLBI signal processing.The study of antennas laid the foundation for the construction of space VLBI.