3 ms·
Power drops off with the square of distance in free space. To get power of an RF wave you S = E x H [1]. Both the E & H fields decrease with distance. If you do
by etimberg 8y ago
Power drops off with the square of distance in free space. To get power of an RF wave you S = E x H [1]. Both the E & H fields decrease with distance. If you double the distance and both E&H decrease by half then |S| decreases by a factor of 4.
Interestingly though, in some environments you can actually get better than free space loss. I remember an off-hand comment from a professor in university that in concrete tunnels you can get R^1.6-1.8 because the tunnel acts as a waveguide
1. https://en.wikipedia.org/wiki/Poynting_vector https://en.wikipedia.org/wiki/Poynting_vector