Pronounced "fraynel zone." The pattern of electromagnetic radiation that is created by a transmitting station from its antenna to receiving antennas. It is in the shape of an ellipsoid, or 3D ellipse, which looks like an elongated football.
The area around the visual line-of-sight between transmitter and receiver. Radio waves disperse as they leave the antenna. Obstructions in this zone of dispersion (Fresnel Zone) attenuate the signal. In the 2.4GHz ISM band this is particularly true of objects with a large moisture content such as trees.
The Fresnel (pronounced fray-nell) zone is the area around the visual line-of-sight that radio waves spread out into after they leave the antenna. This area must be clear or else radio signal strength will weaken.