Refiector Deformation Measurement and Correction Methodology of Large Antenna Based on Phased Array Feed

To solve the problem of time-consuming measurement and correction of large antennas’reflector deformation,a new microwave holography methodology based on a Phased Array Feed(PAF)is proposed.Starting from the known expression of receiving signals in microwave holography,the theory of PAF holography is derived through Geometrical Optics.Reflector deformation,as well as pointing deviation and subreflector offset,can be calculated out by applying the derived equations.A measurement and correction system based on PAF holography is depicted,and two kinds of measurement methods are illustrated.The proposed measurement methodology is verified by numerical simulation,and its measurement error is analyzed.The results indicate that our proposed methodology is feasible,especially for Cassegrain antennas.

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.

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.

Influence and Correction of Wavefront Primary Aberrations for Radio Telescopes using Aberration Theory

Dual-reflector antennas are widely used in astronomical observations and satellite communication.Structural deformations of the reflectors for radio telescopes are inevitable in outside working conditions due to exterior environment loads,which will cause distortion in the surface of the primary reflector and displacement of the subreflector,then lead to gain degradation and misalignment.In this paper,the influence and correction of misalignment in a dual-reflector antenna have been studied.From the perspective of wavefront aberration,a method is proposed to correct the wavefront primary aberration by adjusting the subreflector position.The characteristics of wavefront errors caused by structural deformation of the reflector have been analyzed,and relationships between the position motions of the subreflector and the Seidel wavefront aberrations are derived.The adjustment quantities of the subreflector are also derived.The results show the appropriate positional change of the subreflector in the lateral and axial directions can effectively correct the effects of the tilt and defocus in the primary aberrations caused by antenna structural deformations.

Multimodality-based Wind Speed Forecasting Method for the Wind Resistance Control of Large Radio Telescope

A large,fully steerable radio telescope is susceptible to the wind load,leading to structure deformation andpointing deviation of the telescope.To effectively suppress the influence of dynamic wind load,the wind resistancecontrol of the telescope is carried out based on wind speed forecasting.This study developed a wind speedforecasting model to efficiently forecast the wind speed at the telescope position.The proposed model successfullyeliminates the random noise of the original wind speed,effectively extracts the wind speed features and solves theautomatic optimization of the hyperparameters of the forecasting network.This model significantly improves theaccuracy and reliability of wind speed forecasting.To verify the forecasting performance of the proposed model,the wind data from the Qitai Radio Telescope site is examined as a case study.The wind speed forecasting model’sMAE,RMSE and MAPE are 0.0361,0.0703 and 3.87%,respectively.The performance of the proposed modelmeets the requirements of wind resistance control and can provide data support for the radio telescope.

An approximately analytical solution method for the cable-driven parallel robot in FAST

The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the largest single-dish aperture telescope with a cable-driven parallel robot introduced to achieve the highest sensitivity in the world.However,to realize the high-precision,mechanical equations of such a robot are always complicated,so that it is difficult to achieve real-time control by the traditional iterative method.In this regard,this paper proposes an approximately analytical solution method,which uses the approximately linear relationship between the main parameters of FAST to bypass some iterations.With the coefficients of the relationship extracted,static or quasi-static mechanical equations can be analytically solved.In this paper’s example,this method saves at least 90%of the calculating time and the calculated values are consistent with the experimental data.With such huge efficiency improvements,real-time and high-precision control of the FAST will no longer be difficult work.Besides,all the work in this paper is expected to be used in the FAST.

Panel positioning error and support mechanism for a 30-m THz radio telescope

A 30-m TeraHertz（THz） radio telescope is proposed to operate at 200 μm with an active primary surface.This paper presents sensitivity analysis of active surface panel positioning errors with optical performance in terms of the Strehl ratio.Based on Ruze＇s surface error theory and using a Monte Carlo simulation,the effects of six rigid panel positioning errors,such as piston,tip,tilt,radial,azimuthal and twist displacements,were directly derived.The optical performance of the telescope was then evaluated using the standard Strehl ratio.We graphically illustrated the various panel error effects by presenting simulations of complete ensembles of full reflector surface errors for the six different rigid panel positioning errors.Study of the panel error sensitivity analysis revealed that the piston error and tilt/tip errors are dominant while the other rigid errors are much less important.Furthermore,as indicated by the results,we conceived of an alternative Master-Slave Concept-based（MSC-based） active surface by implementating a special Series-Parallel Concept-based（SPC-based） hexapod as the active panel support mechanism.A new 30-m active reflector based on the two concepts was demonstrated to achieve correction for all the six rigid panel positioning errors in an economically feasible way.