1957年10月4日,第一颗人造地球卫星升天。近30年来,卫星在军事、科研、气象、电视广播、资源勘测、导航和通信等诸多方面得到了日益广泛的应用。其中,通信又是各项应用的核心。以卫星作为中继站转发电波的无线电通信进入了一个新的发展阶段,人们提出了“5W”的理想(即无论何人在何时、何地同何人进行何种通信),在实现通 October 4, 1957, the first man-made earth satellite ascended to heaven. In the past 30 years, satellites have been widely used in military, scientific research, meteorology, television broadcasting, resource exploration, navigation and communications. Among them, communication is the core of each application. Radiocommunication, which uses satellites as relay stations to relay radio waves, has entered a new phase of development. People have come up with the ideal of “5W” (that is, no matter when and where they communicate with whom)