The Active Compensation Technique for Large Reflector Antennas Based on Quadratic Curve Fitting

Active reflectors are often used to compensate the surface distortion caused by environmental factors that degrade the electromagnetic performance of large high-frequency reflector antennas.This is crucial for maintaining high gain operation in antennas.A distortion compensation method for the active reflector of a large dual-reflector antenna is proposed.A relationship is established between the surface deformation and the optical path difference for the primary reflector by geometric optics.Subsequently,employing finite element analysis,a polynomial fitting approach is used to describe the impact of adjusting points on the reflector surface based on the coordinates of each node.By standardizing the positions of various panels on the reflector,the fitting ns can be applied to the reflector panels of similar shapes.Then,based on the distribution characteristics of the primary reflector panels,the adjustment equation for the actuators is derived by the influence matrix method.It can be used to determine the adjustment amount of actuators to reduce the rms of the optical path difference.And,the least squares method is employed to resolve the matrix equation.The example of a 110 m aperture dual-reflector antenna is carried out by finite element analysis and the proposed method.The results show that the optical path difference is reduced significantly at various elevation cases,which indicates that the proposed method is effective.

Rapid Deformation Calculation for Large Reflector Antennas:A Surrogate Model Method

The surface accuracy of the large-aperture reflector antenna has a significant influence on the observation efficiency.Recent researchers have focused on using the finite element(FE)simulation to study the effect of gravity and heat on the deformation distribution of the main reflector.However,the temperature distribution of the antenna is challenging to obtain,and it takes a long time for the FE simulation to carry out FE modeling and postprocessing.To address these limitations,this study presents a surrogate model based on Extreme Gradient Boosting(XGBoost)and deep Convolutional Neural Network(CNN)to get the deformation distribution of the main reflector quickly.In the design of the surrogate model,using the XGBoost algorithm and sparse sampling to solve the difficulty of obtaining the entire temperature distribution is first proposed,and then a deep CNN is developed for estimating deformation.Based on the effect of dynamic loads on the antenna structure,a diverse data set is generated to train and test the surrogate model.The results show that the surrogate model reduces the calculating time dramatically and can obtain the indistinguishable deformation compared to the FE simulation.This technique provides a valuable tool for temperature and deformation calculation of large-aperture antennas.

Large Telescope Wind Load Estimation with Gradient Segments Superposition and its Servo Control

Obtaining the wind load distribution on the telescope aperture is very important to estimate its influence and reduce the wind disturbance on the telescope system.The aperture of the radio telescope structure can be as large as 100 m and therefore,the uniform wind load on the aperture assumption is not suitable for the radio telescope with large aperture.In this paper,a gradient segments superposition method for calculating the wind load has been proposed.The proposed method has been constructed by combining two regional divisions.First,reflecting surface has been evenly divided in the altitudinal direction.Second,the reflecting surface has been divided into several uniform rings assuming that the wind load coefficient on different rings are different.For the 110 m aperture radio telescope,the wind load estimation results differ by 28%.After that,a structural dynamics model of telescope has been established and a fuzzy PID controller has been designed to reduce wind disturbance.The Root Mean Square Error of telescope pointing under wind disturbance has been reduced by 67.8%.It is suggested that the proposed wind load estimation method has lay a solid foundation for the design of the large telescope system under wind disturbance.

Performance Analysis and Optimization of a Modified Stewart Platform for the Qitai Radio Telescope

This paper presents a modified Stewart platform that enables precise adjustment of the sub-reflector for the Qitai Radio Telescope(QTT).QTT demands a parallel platform capable of carrying a heavy load(≥4000 kg),and moving in elevation from 5°to 88°together with the primary reflector while precisely adjusting the sub-reflector’s position in five degrees of freedom.To meet these requirements,a modified Stewart platform with two separated actuators is proposed,and the comprehensive performance is analyzed and optimized for practical application.The performance of the modified platform is compared to that of the traditional Stewart platform,and the results demonstrate that the modified platform has superior load-bearing capacity and stiffness over the entire elevation angle with more uniform actuator load and stiffness distributions.These results indicate that the modified Stewart platform is well-suited for practical application in QTT.