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Many times in literature I read that Radar is used to detect objects. How does this work? Are reflections from objects with Radar not point reflections? And how does Radar know that all reflections belong to a same object when it is close to another object?

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  • $\begingroup$ If the objects are not points, the reflections are not point reflections. And, radar can only tell that it got reflections back, not whether it is one or two close objects (how close depends on various factors). $\endgroup$ – Jon Custer Nov 15 '17 at 21:04
  • $\begingroup$ @JonCuster On what basis is the clustering of these points to objects done? $\endgroup$ – Poorna Nov 15 '17 at 21:17
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    $\begingroup$ In WW2 with the human eyeball looking at an oscilloscope trace. Nowadays with some computer algorithm. The main thing is to (1) know something is there, (2) how far away it is, and (3) how fast it is moving. $\endgroup$ – Jon Custer Nov 15 '17 at 21:23
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    $\begingroup$ The fact that radar can't easily distinguish between objects is the basis for the effectiveness of chaff - bundles of thin foil strips that burst open midair and flood radar with thousands of useless blips. $\endgroup$ – probably_someone Nov 15 '17 at 21:27
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Mostly by keeping the beam narrow. If the outgoing beam is very thin then it is only likely to hit one object at a time - because only one target fits in the beam. A wider beam might have reflections from many objects.

Another technique is to use the radar to measure the speed of the object. The frequency of the signal reflected from an object moving away/toward the radar is shifted slightly. It is possible to measure the change in the returned radio frequency (compared to the outgoing pulse) and so measure the speed of the target. If you have several returns with different speeds you know each return was from a different target.

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