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Question on angular spread

  1. Dec 18, 2012 #1
    1. The problem statement, all variables and given/known data

    I just have a question on finding the area of a receiving antennae. The answer says the area is about 1km. I got an answer close to 1 km.

    λ = 5*10-2 m
    d = 3*103 m

    The angular spread is θ = λ/d

    θ= [itex]\frac{5*10-2}{3*103}[/itex]

    The spatial spread is the diameter of the beam on the target. So that means it is the angular spread times the distance the beam travels. Correct?

    S = r*θ
    S = (5*10^7 m ) * θ
    S ≈ 1 km


    The area of the receiving antennae is them [1km / 2 ]2 * ∏ = 0.78km which is about 1 km.
     
  2. jcsd
  3. Dec 19, 2012 #2

    haruspex

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    The S ≈ 1 km approximation is rather rough. 830m is closer, and that leads to a final answer of about .54 km2 (note: km2, not km). This suggests you have an error somewhere else, but I'm not qualified to say where.
     
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