The Fresnel zones (pronounced frah-nell), named after the French physicist Augustin-Jean Fresnel,
are a theoretically infinite number of ellipsoidal areas around the LOS in an
RF link. Many WLAN administrators refer to the Fresnel zone when it is more
proper to refer to the first Fresnel zone, according to the science of physics.
While it may be the intention of most WLAN administrators to reference the
first Fresnel zone when they speak of only the Fresnel zone, it is important
that you understand the difference. The first Fresnel zone is the zone with the
greatest impact on a WLAN link in most scenarios. The Fresnel zones have been
referenced as an ellipsoid-shaped area, an American football-shaped area.
For more details download the PDF file.