Antenna and propagation

Discussion in 'Homework Help' started by Alfa_ET, Apr 5, 2011.

  1. Alfa_ET

    Thread Starter New Member

    Feb 26, 2011
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    0
    Greetings

    Why is the electric field strength measured by a receiving antenna is inversely proportional to the distance to the transmitting antenna?

    Grateful
     
  2. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    It has to do with the equation of the strength of the electromagnetic field, emitted by a point source. I don't remember it by heart, but it is a function of the distance r and to be precise, r is on the denominator of the fraction in question. Thus, the larger the distance, the more faint is the signal strength.

    You can understand that intuitively: The farther you are away from the emitting antenna, the electromagnetic field gets thinner, and it is more difficult for it to excite the receiving circuit.
     
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  3. Papabravo

    Expert

    Feb 24, 2006
    10,136
    1,786
    So if you have a point source the spherical wave spreads out isotropically in all directions. Now think about the relationship between the volume of a sphere and the surface area of a sphere and you will have an intuitive sense of why the energy density of the radiation depends on the distance.
     
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