RF Frequency Behaviours - Absorption, Reflection, Refraction, Diffraction, Scattering

There are a number of different factors which can affect wireless signal:
Absorption - When a signal passes through an object a portion of the strength is absorbed as heat, so the signal strength will weaker when it comes out the other side (the amplitude is reduced).

Reflection - This is when a signal hits an object and is reflected off at an angle (which depends on the angle it hit the object at). An amount of the energy is absorbed in the process. A possible outcome of reflection is multipath where several different signals reach the receiver each taking a different path, often arriving later, out of phase of the main stream. Degraded signals arriving is referred to as downfade (120 - 170 degrees). It is also possible to nullify the signal if the angle is correct (180 degrees). Finally it is also possible if the signal goes full circle (360 degrees) it arrives back in phase and the signal is boosted, this is upfade.
Multipath will often degrade the signal, however 802.11n can use it to it's advantage. Multipath can also be called fading.

Refraction - This happens when a signal passes through an object and comes out at a different angle that it went in at. The most common reason for this to occur is passing through different mediums, such as from dry air to wet air.

Diffraction - This is essentially the signal bending round an object. Diffraction commonly cause blind spots where the signal has bent around an object, think of light and an objects shadow.

Scattering - This is similar to refraction but it is more unpredictable. It happens when a signal hits and object and is scattered in many unpredictable directions. This is caused by the properties of the object, common object which causes scattering are: dust, humidity, micro-droplets of water, uneven surfaces, density fluctuations.