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Wireless & Mobility · Intermediate

Fresnel Zone

The football-shaped area around the visual line of sight between two antennas that must be kept clear.

Definition

The first Fresnel zone is the ellipsoid in which most of the RF energy travels between two antennas. Obstructions within it cause diffraction and reflection losses even when visual line of sight exists. CWNA guidance is to keep blockage below 40 percent, preferably below 20 percent, of the first Fresnel zone.

Example

Trees growing into the midpoint of a 2 km bridge path can degrade the link without blocking the view.

Exam tip

Visual line of sight is not enough; the Fresnel zone must also be mostly clear.

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