Study On Structural Homologous And Innovation Design For Large Steerable Antennas

Large steerable reflector antennas are typical electronic devices,whose structure designs are governed by the electrical performance.With the development of the reflector antenna marching to high frequency bands,high gain,fast response,high pointing accuracy,etc.,how to design the lightweight structure with excellent performance is extremely challenging.For example,the QTT 110 m antenna is planned to be built in Qitai County,Xinjiang,China,with a diameter of 110 meters and a working frequency up to 115 GHz.In order to meet its electrical performance,the surface accuracy needs to be better than 0.2 mm.To design such a large-diameter and high-precision antenna will inevitably involve lots of technical difficulties.The reflector antenna structure consists of panels,back-up structure,reflector support structure and alidade.The first chapter of this dissertation is the introduction,which summarizes the research status and problems of the structural design of large reflector antennas.Chapters 2 ~ 7 is the main work of this dissertation,including two parts: one is the innovation design based on the traditional mode(equal softness design,mold sharing,etc.),the other is the innovative design mode that can bring greater benefits and design freedom.Chapter 8 summarizes and prospects the work of this dissertation.In Chapters 2 ~ 5,a series of studies are carried out aiming at the shortcomings of traditional structural design methods,including the surface accuracy calculation,equal softness design and the mold sharing design of reflector surface panels.Specifically:In Chapter 2,a novel evaluation method for the surface accuracy of reflector antenna is proposed.As an important part in the optimization design of the antenna structure,the accuracy calculation of the antenna is very important.Under gravity loading,the calculation steps of reflector antenna accuracy include solving for static responses,fitting the deformed surface to a paraboloid,pre-setting the antenna panels and calculating the worst accuracy.The traditional pre-setting strategy is to adjust the accuracy of the reflector to the optimum at a rigging angle.However,in antenna structure design,only the worst surface accuracy is constrained,while the optimal surface accuracy is unrestricted,which means that the traditional pre-setting strategy is not optimal.In order to solve this problem,a pre-setting strategy for minimizing the maximum surface error is proposed.Based on this strategy,a new method for evaluating the accuracy of reflector antenna is presented.In Chapter 3,the deformation characteristics are studied and the design criteria for the highprecision antenna structure are gave.Firstly,the ideal deformation forms of the reflector surface under the gravity loading are deduced from the fitting parameters,and the structural characteristics of the ideal deformation are analyzed.Secondly,the optimal supporting parameters of the reflector are given by studying the deformation characteristics of the simplified reflector model.Finally,the structure of the effelsberg 100 m antenna is analyzed,and its shortcomings are pointed out.Based on the discussion in Chapter 3,Chapter 4 shows a new type of equal softness supporting structure scheme,which has been successfully applied to the 110 m antenna structure.The numerical simulation results show that under the gravity loading,the surface accuracy of the antenna can reach 0.3mm,and the weight of the tipping structure is less than 3000 tons,which is far better than the existing scheme.In Chapter 5,an electronic performance-oriented mold sharing method is proposed to reduce the number of molds required to process antenna panels.Compared with the existing methods,the mold reduction method proposed in this dissertation takes into account the influence of the error of each ring panel on the electrical performance,expands the error tolerance of each ring,and can reduce the number of molds.This method can efficiently give the position of the optimal mold,the corresponding relationship between the mold and the panel,and the optimal effective surface precision for a given number of molds,etc.This method has been successfully applied to the die reduction of 110 m antenna panel.The results show that the gain loss of 23 ring panel is only 0.05 d B when 14 kinds of molds are used.The main work of Chapter 6 ~ 7 is to further reduce the weight of the antenna structure,where the innovative design of the antenna mechanism,including cable-truss combined back-up structure and parallel drive antenna alidade,are presented.Specifically: The introduction of prestressing cables in a particular structure can change the stress distribution of the structure and improve the deformation of the structure.Therefore,the prestressing cable has the potential to reduce the weight of the structure and improve the accuracy of the antenna surface.Chapter 6 presents a method for determining the layout of prestressing cables in trusses.To determine the layout of prestressing cables,a topological optimization problem of cable-truss composite structures is considered.In this problem,the initial defect length is used as a design variable,and the cable and bar elements are unified by interpolation method.A continuous variable topological optimization model is obtained,which can be solved by gradient-based method efficiently.Finally,the method is applied to the design of an 8m antenna,and the effectiveness of the proposed strategy is verified.The parallel mechanism represents the development trend of mechanism nowadays.Compared with the series mechanism,the parallel mechanism has the advantages of high rigidity,strong carrying capacity,high-precision and small motion load.In Chapter 7,a novel two-axis parallel mechanism suitable for large antenna is introduced and its motion mechanism is described in detail.The method for determining the relevant geometric parameters is presented,and the design method of parallel drive reflector antenna is given.This new scheme is applied to a 26-meter-diameter antenna and the reflector adopt the cabletruss structure,which reduced the self-weight of the reflector antenna by 40.5% and the drive power by 63.3%.