| Space solar power satellite(SSPS)is a tremendous green energy system that collects and converts solar power to electric power in the outer space,and then,transmits the electric power to earth with microwave.In the existing gigawatts(GW)SSPS concepts,the immense size,the mass of ten thousand tons and the complex feed network of the phased-array microwave transmitting antenna result in great difficulty in engineering implementation and high cost of launching the assembly,which seriously restricting the engineering implementation of the SSPS.Therefore,this thesis proposes a design scheme for the miniaturization of the SSPS microwave transmitting antenna,which obtains a narrow beam and reduces the quality of the antenna under the premise of ensuring the power collection efficiency by means of a smaller-aperture antenna.Firstly,an SSPS microwave transmission antenna scheme based on the plane reflection array and the plane focusing lens is proposed.In the scheme,the transmitting antenna system consists of a modular-designed planar reflector array-flat lens integrated structure,a horn array feed,and connecting trusses.The microwaves emitted by the feed successively converge through the lens,reflect from the reflection array,and focus by the lens,and eventually form a narrow beam to concentrate the energy in the receiving plane.The scheme has the advantages of convenient manufacture and assembly,simple feed network,light weight,and small diameter.Secondly,taking the lightweight antenna,the simple feed networks and high radiation efficiency as starting points,according to the 800:1 scaling ratio of the SSPS microwave transmitting antenna,a phase-shifting unit that can respond to all phases is designed and an antenna array is formed according to the parabolic phase distribution.Then,a horn feed that meets the requirements of the radiation pattern is designed and a simulation model of the planar reflector array antenna is established.The simulation results show that the plane reflection array has a remarkable effect on the convergence of the microwaves emitted by the feed and the total antenna efficiency reaches 75.2%,which reduces the quality of transmitting antenna and simplify the feed networks.Then,with the aim of not increasing the antenna aperture size to compress the beam width and ensuring the power collection efficiency,a low-loss and lightweight planar focusing lens is designed and combined with a planar reflector array antenna to form a SSPS microwave transmission antenna scale simulation model.The result shows that the half-power beamwidth compression ratio after focusing by the lens reaches 46%.In the case of the same beamwidth of the antenna,the aperture area of the reduced-scale model is only 51%of that of the planar array antenna and hence the area of the receiving antenna will be greatly reduced under the premise of ensuring beam collection efficiency of more than 90%.Moreover,the mass density of the reduced-scale antenna system is only 4.89kg/m~2,which achieves miniaturization and lightweight design.The influence of the distribution of support beams on the structural mode of the integrated planar structure is analyzed.Finally,the focusing field of the SSPS microwave transmitting antenna is calculated based on electromagnetic scalar diffraction theory and the antenna pattern and beam collection efficiency are further calculated.The results show in the case of the same aperture transmitting antenna the beamwidth is greatly compressed after focusing by the lens,and the ground receiving antenna area is accordingly reduced according to the narrowed beamwidth.Simultaneously,the beam collection efficiency is still higher than 90%,which verifies the feasibility of the proposed scheme.The comparison with the international typical SSPS highlights the obvious advantages of the current scheme in lightweight and miniaturization. |
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