page_title: Multipath propagation
section_title: Interference
hierarchical_section_title: Multipath propagation / Interference
caption_attribution_description: English: A diagram which I drew to explain some effects seen in TV systems, this for the article on ghosting an effect seen in AN UHF TV systems where a second image is seen displaces horizontally (normally to the right) of the main image.
context_page_description: In radio communication, multipath is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and reflection from water bodies and terrestrial objects such as mountains and buildings.
  Multipath propagation causes multipath interference, including constructive and destructive interference, and phase shifting of the signal; destructive interference causes fading. This may cause a radio signal to become too weak in certain areas to be received adequately, so multipath propagation can be detrimental in radio communication systems. Where the magnitudes of the signals arriving by the various paths have a distribution known as the Rayleigh distribution, this is known as Rayleigh fading. Where one component dominates, a Rician distribution provides a more accurate model, and this is known as Rician fading.
context_section_description: Multipath interference is a phenomenon in the physics of waves whereby a wave from a source travels to a detector via two or more paths and the two (or more) components of the wave interfere constructively or destructively. Multipath interference is a common cause of "ghosting" in analog television broadcasts and of fading of radio waves.
  The condition necessary is that the components of the wave remain coherent throughout the whole extent of their travel.
  The interference will arise owing to the two (or more) components of the wave having, in general, travelled a different length (as measured by optical path length – geometric length and refraction (differing optical speed)), and thus arriving at the detector out of phase with each other.
  The signal due to indirect paths interferes with the required signal in amplitude as well as phase which is called multipath fading.
caption: In this illustration, an object (in this case an aircraft) pollutes the system by adding a second path. The signal arrives at RX by means  of two different paths which have different lengths. The main path is the direct path, while the second is due to a reflection from the plane.
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