Cluster Feed Multi-beam Comunication Satellite Beamforming Technology

Is there a way to make mobile phone signal ubiquitous when it lose its effectiveness in case that fishermen are working out at sea,passengers are flying at a high altitude,and explorers are traveling through deserts or forests,or even a devastating earthquake occurs?The answer is "Yes,that is the space-ground integrated satellite-ground convergence communication network.”The integrated space-ground network includes intersatellite network,ground equipment network and satellite-ground network.The satellite-ground network(A seamless convergence of satellite and ground communication network)provides a truly ubiquitous communication solution that enables communication terminals such as mobile phones to communicate with terrestrial mobile cellular base stations,as well as with satellite networks.The space-ground integrated satellite-ground convergence communication network nests the satellite coverage and the terrestrial base station cellular coverage with multiple frequency multiplexing,which greatly improves the spectrum utilization,thus providing a superior consumption experience for daily use,and an inter-operable communication system for public safety,rapid response and emergency as well.Cluster feed multi-beam communication satellite is the key component of the satellite-ground convergence network,which can realize a high-gain,large-capacity and wide-area dense beam coverage combining with the terrestrial network via multiple technologies such as space and frequency multiplexing.In this dissertation,aiming at the key technologies and difficulties of satellite beamforming in satellite-ground convergence network,combining with the requirement of China's surrounding sea area communication coverage,the problems and solutions of multi-beam communication satellite reflector antenna beamforming are discussed in depth.The work is carried out in the following four aspects.(1)Aiming at the problems of high-gain,large-capacity and wide-area beam coverage required by the satellite-ground convergence network,a satellite-ground convergence network architecture based on terrestrial beamforming is proposed,which is investigated from several aspects as satellite architecture,beam multiplexing mode,multi-beam antenna implementation form and beam synthesis network architecture.Meanwhile,the designing mechanisms of spatial beam multiplexing,multi-beam antenna and beam synthesis network are provided.(2)Based on the beam coverage requirement of the convergence network at China's surrounding sea area,a multi-beam antenna is designed.Aiming at the problems of feed occlusion and lack of beam scanning of axis symmetric reflector antenna,a low coupling design scheme of reflector antenna with cluster feed is proposed,which realizes the beam scanning and area coverage at China's surrounding sea area,and the accuracy test of the reflector prototype and the coupling test of the feed prototype are carried out,and the test results meet the design requirements.(3)For the uncertainty of satellite coverage beams of the convergence network in China's surrounding sea area,the large-scale beamforming problem is transformed into an optimization problem.Due to that traditional optimization algorithms may fail to solve the optimal value,an improved genetic algorithm for the target beam optimization is proposed,which adopts the envelope method to model the target beam optimization problem,thus reducing the control difficulty and computational complexity.The methods of optimal preservation strategy,pseudo-parallel strategy and sharing niche algorithm are introduced to ensure the convergence of the optimization algorithm,increase optimization speed,and enable the algorithm to approximate the Pareto optimal solution.Besides,various errors introduced by the reflector antenna designing are analyzed in this dissertation.The effect of rib periodicity error,surface accuracy error,feed directivity error,feed translation error and feed mutual coupling error on the synthetic beam is evaluated.(4)The forward/backward link channel transmission model,channel calibration and channel amplifier's nonlinear transmission model of the terrestrial beamforming network are provided.Two solutions are given for the amplitude-phase inconsistency of beamforming network channel:Point frequency coherent amplitude-phase detection method and code division coherent amplitude-phase detection method.Due to the poor ability of continuous wave signals to resist wide-band interference,and the insufficient capability of single-frequency continuous wave to solve delay ambiguity,code division coherent detection method is adopted.And a channel amplitude-phase detection method based on composite orthogonal code sequence is proposed,which overcomes the problem of low accuracy of the test result caused by poor cross-correlation performance of small m-sequences,which greatly improves the amplitude and phase detection accuracy of the channel and meets the requirement of beamforming,and the performance of beam synthesis after channel calibration is validated by the prototype.The difference between the gain of beam synthesis and the theoretical value is only 0.2dB.It shows that the detection method of channel amplitude and phase based on composite orthogonal code sequence is effective.