What causes attenuation on wireless signals?

Answer 1

Attenuation limits the range of radio signals. Wireless signals are radio waves. Like any type of electromagnetic radiation, they are subject to attenuation. Attenuation 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 radio wavefront is obstructed by an opaque obstacle, and losses caused by other phenomena.

Propagation losses become worse as the distance between the source and receiver increases. Just like a light source becomes less intense to the observer as they move away from the light, the radio signal becomes more faint as the receiver becomes more distant from the signal source. Distance is thus an attenuating factor for all wireless signals.

Absorption losses occur when some of the signal is absorbed by the media between the radio signal source and the receiver. All types of electromagnetic radiation is subject to this kind of attenuation as well: sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light is attenuated while passing through seawater. For radio waves on earth (where wireless computer signals are important), the primary "medium" air and attenuation is an exponential function of the path length through the air. Attenuation is also affected by all the materials a signal must travel through including not only air, but building materials (e.g. wood, concrete, steel, glass, etc.) if the wireless connection is made within a building and weather when the wireless signal is traveling outside the building (e.g. rain, sleet, snow, fog, smog, smoke, etc.). Each medium soaks up different amounts of radio energy. Metals tend to be the worst. It is possible to build what is known as a Faraday Cage that will shield radio signals almost completely by absorbing them and conducting their energy away to "ground".

Some materials block radio signals almost completely even if they are not grounded. Even if they block them, they may still reflect some of the radio waves off in another direction causing interference or simply lengthening the effective path the waves must travel between the source and receiver. If the radio-opaque material has gaps in it, some of the signal may still leak through, but less than the amount that ran into the barrier. A simple analogy would be a screen that lets most of the light through but blocks some of it, lessening the intensity of the light that does make it through. Another analogy would be polarized sunglasses that only pass the light that is vibrating in the direction of the polarization.