ng targets and farther for medium to high altitudes. An identification friend or foe subsystem of the radar can look down to detect, identify and track enemy and friendly low-flying aircraft by eliminating ground clutter returns. In this situation, other types of radars may be confused. The unit cost of the E-3 is approximately $270 million, which is greatly effected by the high price eletronic equipment onboard.
E-3机背上的雷达罩是E-3在外观上与其他飞机相比最特别的地方。该雷达罩直径9.1米，厚度1.8米，用两个支柱支撑在离机身3.3米高处。内部安装有雷达天线系统，这一雷达系统使E-3能够提供对大气层、地面、水面的雷达监视能力。对低空飞行目标，其探测距离达320千米以上，对中空、高空目标探测距离更远。雷达系统上的敌我识别分系统具有下视能力，并能抗地面杂波干扰。而其他一些雷达在这种条件下无法去除干扰。E-3的单价高达2.7亿美元，价格受昂贵的电子设备影响很大。
The variations of E-3 include E-3A, E-3B, E-3C and E-3D. The A type is the first production version for US airforce. A type`s inside is quite different from the prototype, the modified fuselage can hold 17 people. They are 4 pilots, 12 operators and 1 onboard officer. The operators will charge the communication, computer, radar and 9 multi-function display plat. The equipment can be devided into six parts which are radar, IFF, data processing, communication, navigation, data display and control. The radar system includes the Northrop Grumman AN/APY-1 radar, the multi function of the radar can seperate the whole 360 degree area into 32 parts and use different function in each part. Scan once, the IFF system can check over 200 targets with IFF receiver installed, no matter the target is in the air, on the ground or sea.
E-3的主要型别有E-3A、B、C，D四种。EC-137D是用波音707-302B改装的试验机，装4台JT3D-9涡扇发动机，共改装两架，其中一架在试飞工作完成后返厂改装成E-3A生产型。
E-3A为美军的首批生产型。机舱内作了 很大的改动，改装后的机舱内可载乘员17名。其中机组4人，系统操纵人员12名，值勤官1名。系统操作人员分别负责操作通信设备、计算机、雷达和9个多用途控制台。机载设备可分成搜索雷达、敌我识别器、数据处理、通信、导航与导引、数据显示与控制等六个部分。雷达系统有诺斯罗普·格鲁曼公司研制的AN/APY-1型S波段脉冲多普勒雷达，可以根据不同的作战条件把360度方位圆划分成32个扇形区，分别在每个扇形区内选用恰当的工作方式组合。敌我识别系统在一次扫描中能询问200个以上装有应答器的空中、海上和陆上目标。
There are some other major subsystems in the E-3, navigation, communications and computers (data processing). The navigation subsystem can off
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