Fan diagram
A fan diagram is called the directional diagram or antenna diagram of a directional antenna or antenna group if it has a very small opening angle in one dimension and a large opening angle in the other dimension .
Such a diagram is achieved, for example, by
- a parabolic reflector that is narrow in one dimension or only a segment of a paraboloid is used,
- several antennas can be arranged in a one-dimensional antenna array.
The larger the extension of the reflector or the antenna array, the smaller the radiation angle in this dimension.
Applications
Vertical compartments
Vertically aligned (standing) fan diagrams are used by secondary and primary radar devices in order to be able to record different flight altitudes with the highest horizontal angular resolution.
Horizontal compartments
Horizontal, “lying” fan diagrams have, for example, height finder radar devices. The horizontal angle of their fan charts is a few degrees, while the vertical angle is often less than one degree. Radio transmitters in the VHF, VHF and UHF range also often have a horizontal fan-shaped characteristic in order to bundle the transmission power in the direction of or slightly below the horizon. In this way, unnecessary radiation into space or in the direction of inversion layers causing overreaching is avoided. Antennas of the cellular network also have horizontal fan diagrams. Both these and radio transmitters use vertical antenna arrays for this purpose, the individual elements of which are controlled somewhat out of phase, if necessary, in order to incline the fan slightly towards the surface of the earth despite being installed vertically on a mast.