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到1987年底,全世界共发射各种通信卫星大约700颗,仍使用的卫星转发器约2000台。卫星通信已成为人类通信史上的重要里程碑。但通信卫星的发展目前遇到了两种大的挑战。这就是,卫星固定通信业务地球站一般建在远离城区的空矿地带,并使用几米～几十米口径的大型天线,因此,卫星电波基本上是在地球与36 000公里的地球轨道间上下传播,信号基本不受山、林、高大建筑群的遮挡。显然这种业务无法满足在山、林中移动作业和运动中飞机、船舶、车辆的通信需要,因为这些场合对卫星通信信号存在着遮挡、反射、折射等恶劣地理环境的影响,地面移动情况又不能使用大型天线,因而无
By the end of 1987, a total of about 700 communications satellites were launched worldwide, and about 2,000 satellite transponders were still in use. Satellite communications have become an important milestone in the history of human communications. However, the development of communications satellites currently faces two major challenges. That is, the earth stations of the fixed-satellite service are generally built in open areas far away from urban areas and use large antennas of several meters to tens of meters. Therefore, the satellite waves are basically transmitted up and down between the Earth and 36,000 kilometers of Earth’s orbit , The basic signal from the mountains, forests, tall buildings block. Obviously, this kind of service can not meet the communication needs of aircraft, ships and vehicles in mobile operations and sports in mountains and forests because of the adverse geographical environment such as shading, reflection and refraction of satellite communication signals in these occasions, and the movement of the ground can not Use a large antenna, so no