Directional antenna

This can increase the power transmitted to receivers in that direction, or reduce interference from unwanted sources.

[1] Most commonly referred to during space missions,[2] these antennas are also in use all over Earth, most successfully in flat, open areas where there are no mountains to disrupt radiowaves.

Cellular repeaters often make use of external directional antennas to give a far greater signal than can be obtained on a standard cell phone.

For long and medium wavelength frequencies, tower arrays are used in most cases as directional antennas.

This property may avoid interference from other out-of-beam transmitters, and always reduces antenna noise.

Still other configurations are possible—the Arecibo Observatory used a combination of a line feed with an enormous spherical reflector (as opposed to a more usual parabolic reflector), to achieve extremely high gains at specific frequencies.

Conservation of energy dictates that high gain antennas must have narrow beams.

This beam can cover at most one hundred millionth (10−8) of the sky, so very accurate pointing is required.