Unit23RadarandARPA..doc

Unit 23 Radar and ARPA Introduction to Radar and ARPA自动雷达标绘仪和雷达的介绍 Today sea Captains can guide their ships safely through a crowded harbor in dense fog,and pilots can take ships through thick fogs to their berths.今天海上船长能在浓雾中指挥他们的船舶安全地通过一个拥挤的海港并且引航员能操船通过厚雾到达他们的泊位。An electronic system called RADAR makes this possible.一个电子叫雷达的系统使这些成为可能。 A radar unit can pierce dardness and weather conditions in which human eyesight is obstructed .一个雷达装置能穿透黑暗和人类视力被阻碍的天气状况。Within its range it can show an observer ships,storm clouds,small islands,coastlines,and prominent landmarks.在它的距离范围之内它能显示一个观测者船舶，风暴云，小岛，海岸线和显著的陆标。It also be used to measure the distance to an object and the speed at which the object is moving toward or away from the observer.它也能被用来测量一个障碍物的距离和这个障碍物移向和远离观测者的速度。 Radar uses eletromagnetic waves usually short-wavelength waves called microwaves.雷达用电磁波一般短波长的波别叫做微波。These waves bounce back from solid objects in their paths and produce an echo.这些波在他恩的路径上反弹回来并且产生一个反射。Scientists learned to use reflected microwaves for detection and measurement.科学家学会利用反射的微波来侦查和测量。The name radar is coined from the first letters of the words “radio detecing and ranging.”这个雷达的名词首次被创造出来表示雷达侦查和测距。 The radar antenna does two jobs.雷达天线做两个工作。First,it receives the high-frequency pulses from the transmitter,focuses them into a beam,and sends them into space.首先，它从发射机接收高频脉冲发射并且将它们送入空中。Second,it picks up reflected pulses coming from objects that have been stuck by the beam .其次它接收从被光波撞击障碍物反射回来的脉冲。The antenna focuses the reflected waves and sends them to the receiver.天线集中反射波并且发射他们到接收机。In operation the antenna rotates continously.运行过程中天线始终保持旋转。Its angle of elevation may also be adjusted.它的角度也可以调整。The field being observed is scanned by the antenna and its signal just as it would be scanned by a light beam for visual searching.这个观测范围是通过天线来观察的并且它的角度也可以通过可见光束来观察。 In a plan-position indictor system(PPI)，the antenna’s movement is tracked by the trace of an oscilloscope tube.在一个计划位置显示器系统中这个天线的移动被通过示波