In optics and radio communications (indeed, in any situation involving the radiation of waves, which includes electrodynamics, acoustics, gravitational radiation and seismology), a Fresnel zone ( /freɪˈnɛl/ fray-NEL), named for physicist Augustin-Jean Fresnel, is one of a (theoretically infinite) number of concentric ellipsoids which define volumes in the radiation pattern of a (usually) circular aperture. Fresnel zones result from diffraction by the circular aperture.
The cross section of the first (innermost) Fresnel zone is circular. Subsequent Fresnel zones are annular (doughnut-shaped) in cross section, and concentric with the first.
To maximize receiver strength, one needs to minimize the effect of the out-of-phase signals by removing obstacles from the radio frequency line of sight (RF LoS). The strongest signals are on the direct line between transmitter and receiver and always lie in the first Fresnel zone.
Read more about Fresnel Zone: Fresnel Zones, Determining Fresnel Zone Clearance
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