Editing Path loss (section)

==Causes==
{{Unreferenced section|date=August 2017}}
Path loss normally includes ''propagation losses'' caused by the natural expansion of the [[radio wave]] front in [[free space]] (which usually takes the shape of an ever-increasing sphere), ''absorption losses'' (sometimes called penetration losses), when the signal passes through media not transparent to [[electromagnetic waves]], ''[[diffraction]] losses'' when part of the radiowave front is obstructed by an opaque obstacle, and losses caused by other phenomena.

The signal radiated by a transmitter may also travel along many and different paths to a receiver simultaneously; this effect is called [[Multipath propagation|multipath]]. Multipath waves combine at the receiver antenna, resulting in a received signal that may vary widely, depending on the distribution of the intensity and relative propagation time of the waves and bandwidth of the transmitted signal. The total power of interfering waves in a [[Rayleigh fading]] scenario varies quickly as a function of space (which is known as ''small scale [[fading]]''). Small-scale fading refers to the rapid changes in radio signal amplitude in a short period of time or distance of travel.