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The track while scan (TWS) is a mode of radar operation in which the radar allocates part of its power to tracking the target or targets while part of its power is allocated to scanning, unlike the straight tracking mode, when the radar directs all its power to tracking the acquired targets. In the TWS mode the radar has a possibility to acquire additional targets as well as providing an overall view of the airspace and helping maintain better situational awareness.〔James Constant (1981) "Fundamentals of Strategic Weapons: Offense and Defense Systems", ISBN 90-247-2545-3, (p. 193 )〕 ==Background== Early airborne radar systems generally operated purely as tracking systems, with a dedicated radar operator manually "tuning" the system to locate targets in a relatively narrow field-of-view in front of the aircraft. The searching area could be moved using a variety of methods, typically phase-shifting or lobe switching on lower frequency systems that required large antennas, or by moving the radar dish on microwave frequency radars. Engagements would start with ground controllers guiding the aircraft into the general area of the target via voice commands to the pilot, and once the aircraft got into range its own radar would pick up the target for the final approach when the radar operator would provide voice commands to the pilot. There was no real distinction between seeking out a target and tracking it. Ground-based radars like the SCR-584 automated this process early in their evolution. In search mode the SCR-584 rotated its antenna through 360 degrees and any returns were plotted on a plan position indicator (PPI). This gave the operators an indication of any targets within its ~25 mile detection range and their direction relative to the radar van. When one of the returns was considered interesting, the radar was flipped to tracking mode and "locked-on". From then on it would automatically keep its antenna pointed at the target, feeding out accurate direction, altitude and range information on a B-Scope display. Operator workload was greatly reduced. Advances in electronics meant it was only a matter of time before automated radars like the SCR-584 could be reduced in size and weight enough to fit into an aircraft. These started appearing in the late 1950s and remained common until the 1980s. The introduction of semi-active radar homing missiles made the lock-on concept especially important. These missiles use the launching aircraft's own radar to "paint" the target with a radar signal, the missile listens for the signal being reflected off the target to home in on. This requires the radar to be locked on in order to provide a steady guidance signal. The drawback is that once the radar is set to tracking a single target, the operator loses information about any other targets. This is the problem that track while scan is meant to address. In traditional radar systems, the display is purely electrical; signals from the radar dish are amplified and sent directly to an oscilloscope for display. There is a one-to-one correspondence between "blips" on the display and a radio signal being received from the antenna. When the antenna is not pointed in a particular direction, the signal from any targets in that direction simply disappear. To improve the operator's ability to read the display, the oscilloscopes typically used a slowly fading phosphor as a crude form of "memory". 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「track while scan」の詳細全文を読む スポンサード リンク
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