# 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
5,151
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.

Alfa_ET likes this.
3. ### Papabravo Expert

Feb 24, 2006
10,340
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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.