Research On Synthesis Of Shaped Reflector And Thermal Analysis Of Antenna In-Orbit

Reflector shaped antennas are widely used for direct broadcast system and communication system between satellites.With the higher frequency transmitted by reflector antenna,the manufacture error and deformation should be less,So thermal deformation of antenna must be analyzed more accurately.Based on extensive referring to relative literatures,research development and application of shaped antenna,prototype of reconfigurable contour beam reflector antenna in orbit and analysis methods of antenna performance influenced by thermal deformation were summed.Shaped antenna can provide a direct coverage over a geographical region and meet its gain distribution.For higher efficiency,single reflector shaped antenna is important for satillate in the future.The radiation fields of perfect conduct reflector were discussed based on geometric optics(GO),physical optical(PO) and geometric theory of diffraction(GTD).A geometric optical design method of single reflector shaped antenna was introduced.A rapid analysis method for radiation field of reflector antenna is desired,So the Fourier-Bessel and Jacobi-Bessel analysis based PO and GB method based on GTD were compared.A 0.6m diameter reflector antenna was shaped to contour China Mainland(CM) in 30 dB gain in 20GHz frequency by GB method.The relation between diameter of reflector and frequency was given for 30dB gain expectation,and these maximum gain covering CM in 20GHz frequency were calculated for each diameter reflectors.Some issues about reconfigurable contour beam reflector antenna were listed after two antennas were introduced and analyzed.Solar radiation heat flux,earth infrared radiation heat flux and reflected solar radiation heat flux by earth are primary causes of non-uniform temperature field which is time-dependent.After calculating satellite orbit parameters,the analysis method for three heat fluxs were given.The formulation of earth infrared radiation factor was presented for parabolic reflector antenna operating in the orbit higher than 3000km.In term of location of sun,earth and satillate,the formulation of satillate orbit angle was deduced when the visual earth region of spacecraft was just radiated partially by sun and entered into earth shadow region. The curves of reflected solar radiation factor by earth with orbit altitude h, location of satillateθ_s and solar light angle i_θ.Shadow effect can not be neglected for thermal analysis of spacecraft,Accroding to the angle between solar light and antenna orbit plane and its orbit location,analytical geometry method was used for accurately calculating solar radiation heat flux distribution of reflector surfaces.To analyze the temperature field under heat flux,the formulations of net radiation flux density between two gray elements and the net flux density of gray surface under external thermal flux were deduced.Based on the characteristic of space environment,the nonlinear temperature distribution in transverse direction of reflector shell self radiation were considered,the finite element formulations were given for orthogonal material layered shell by Galerkin method.A layered element including a inner heat source layer was proposed,and the finite element formulation expressed by DOF of the inner heat source layer were put forward with temperature and heat flux boundarys between adjacent layer.For the higher nonlinear equations induced by radiation,a modified direct iterative method was presented for solution searching.Central difference method and backward difference method were used for transient thermal analyzing,and the result suggested that two methods have same accurate for this problem.The example suggested that the above finite method had higher accurate.To decide the antenna performance influenced by thermal deformation,the deformation was analyzed with a spline function shell element under orthogonal curvilinear coordinate system.In term of relationship between deformation and gain in engineering,root mean square of displacements(RMSD) of reflector shell was looked as index of antenna performance.For a parabolic antenna,RMSD sensitivity to thermal conductivity under steady-state was analyzed,result showed that the sensitivity is dependent on load cases.So orthogonal simulation experiment method was used for MRSD sensitivity testing to thermal conductivity in shell plane k_xy and in transverse direction k_z,specific heat c, modulus of elasticity E and thermal expansion coefficientα,and the MRSD maximum during a period is the design index.The result from one parabolic antenna shows that the influence factor ranges from high to low:α,k_xy,k_z,E and c.These conclusions can provide reference for ply scheme optimization of parabolic antenna next step in order to control the deformation.