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自从发明雷达以来,使用径向圆扫描体制的平面位置显示器(PPI)获得了最为广泛的应用。在这种显示器里,电子束必须与天线同步旋转。某一目标的回波激发了PPI荧光质后,要再等数秒钟(即一个天线旋转周期),才能第二次激发,故PPI的图像随天线的旋转呈亮暗变化。观察PPI图像除了在回波激发的瞬间外,主要依靠萤光质的余辉。由于普通PPI图像亮度较低,为此需在光照度小于101x的半黑的环境里进行观察,当环境亮度稍高时,便需使用观察罩。这对于雷达操作人员是十分不便的。
Since the invention of the radar, the use of a radial circular scanning system for flat position display (PPI) has been the most widely used. In this type of display, the electron beam must rotate in synchronism with the antenna. After a certain target’s echo excites the PPI fluorescent substance, it takes another few seconds (that is, an antenna rotation cycle) to be excited for the second time, so the PPI image changes brightly and darkly with the rotation of the antenna. Observing PPI images, except for the moment of echo excitation, mainly depends on the persistence of luminescent substances. Due to the low brightness of ordinary PPI images, it needs to be observed in the semi-dark environment where the illuminance is less than 101x, and when the ambient brightness is slightly high, the observation mask is needed. This is very inconvenient for radar operators.