Propagation of wave energy to distance d, 2d, 3d showing how the size of the surface that the energy spreads over increases in proportion to d², (2d)², and (3d)² |
This is counterintuitive, because if one solves the wave equation, the solution is independent of frequency. The physics of the problem is that intensity just falls with distance squared according to how the surface of a sphere increases with the radius as shown in the figure.
The Friis formula used in link budgets says something else. It gives received power, Pr, as a function of transmitter power, Pt, receiver and transmitter antenna gains, Gr and Gt; wavelength, lambda, and distance, d: