Calculations: Downtilt Coverage Radius
The downtilt coverage radius can be calculated by the formula listed below, which takes half of the antenna beamwidth in each direction of the downtilt angle from the height of the antenna. For further information on this formula, please review the figure below.
Note: The final value represents a first order approximation and should only be used as a guide. No guarantees or warranties are implied accordingly.
Downtilt Coverage Example

Notes: Horizon means that the -3dB point on the main lobe shoots off into the horizon and does not touch the earth (assuming flat terrain.)