What is "directional antenna"

Antenna \An*ten"na\, n.; pl. Antenn[ae]. [L. antenna sail-yard; NL., a feeler, horn of an insect.]

1. (Zo["o]l.) A movable, articulated organ of sensation, attached to the heads of insects and Crustacea. There are two in the former, and usually four in the latter. They are used as organs of touch, and in some species of Crustacea the cavity of the ear is situated near the basal joint. In insects, they are popularly called horns, and also feelers. The term in also applied to similar organs on the heads of other arthropods and of annelids.

2. (Electronics) A metallic device, variously shaped, designed for the purpose of either transmitting or receiving radio waves, as for radio or television broadcasting, or for transmitting communication signals. Some types are: whip antenna, antenna tower, horn antenna, dish antenna, directional antenna and rabbit ears. See transmitter, receiver.

n. an antenna that transmits or receives signals only in a narrow angle

A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing for increased performance and reduced interference from unwanted sources. Directional antennas provide increased performance over dipole antennas – or omnidirectional antennas in general – when greater concentration of radiation in a certain direction is desired.

A high-gain antenna (HGA) is a directional antenna with a focused, narrow radiowave beam width. This narrow beam width allows more precise targeting of the radio signals. Most commonly referred to during space missions, these antennas are also in use all over Earth, most successfully in flat, open areas where no mountains lie to disrupt radiowaves. By contrast, a low-gain antenna (LGA) is an omnidirectional antenna with a broad radiowave beam width, that allows for the signal to propagate reasonably well even in mountainous regions and is thus more reliable regardless of terrain. Low gain antennas are often used in spacecraft as a backup to the high-gain antenna, which transmits a much narrower beam and is therefore susceptible to loss of signal.

All practical antennas are at least somewhat directional, although usually only the direction in the plane parallel to the earth is considered, and practical antennas can easily be omnidirectional in one plane. The most common types are the Yagi antenna, the log-periodic antenna, and the corner reflector antenna, which are frequently combined and commercially sold as residential TV antennas. Cellular repeaters often make use of external directional antennas to give a far greater signal than can be obtained on a standard cell phone. Satellite Television receivers usually use parabolic antennas. For long and medium wavelength frequencies, tower arrays are used in most cases as directional antennas.