The high-gain antenna (HGA) is an antenna with a focused, narrow radiowave beam width. An antenna is a Transducer designed to transmit or Receive electromagnetic waves In other words antennas convert electromagnetic waves into This narrow beam width allows more precise targeting of the radio signal - also known as a directional antenna. A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive 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. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001

Parabolic antenna - the 70m antenna at Goldstone

Helical antenna

A Yagi-Uda antenna. The parabolic antenna is a high-gain reflector antenna used for radio television and data communications and also for radiolocation ( RADAR) on the UHF and The Goldstone Deep Space Communications Complex ( GDSCC) &mdashcommonly called the Goldstone Observatory &mdash is located in California 's Mojave Desert helical antenna is an antenna consisting of a conducting wire wound in the form of a Helix. A Yagi-Uda Antenna, commonly known simply as a Yagi antenna or Yagi, is a Directional antenna system consisting of an array of a dipole From left to right, the elements mounted on the boom are called the reflector, driven element, and director. The reflector is easily identified as being a bit (5%) longer than the driven element, and the director a bit (5%) shorter.

A giant phased-array radar in Alaska

Large Horn Antennain Holmdel, New Jersey. This article is about general theory and electromagnetic phased array The Horn Antenna, at Bell Telephone Laboratories in Holmdel New Jersey, is listed as a National Historic Landmark because of its association with Holmdel Township is a township in Monmouth County, New Jersey, United States. Built to support the Echo satellite communication program^[1], it was later used in experiments that revealed the cosmic background radiation permeating the universe. The Echo satellites were NASA 's first passive Communications satellite experiment ^[2]

Voyager 2 spacecraft. The HGA (a parabolic antenna) is the large bowl-shaped object.

Principle of operation

When transmitting, a high gain antenna allows more of the transmitted power to be sent in the direction of the receiver, increasing the received signal strength. When receiving, a high gain antenna captures more of the signal, again increasing signal strength. Due to reciprocity, these two effects are equal - an antenna that makes a transmitted signal 100 times stronger (compared to an isotropic radiator), will also capture 100 times as much energy as the isotropic antenna when used a receiving antenna. This page is about reciprocity theorems in classical electromagnetism As a consequence of their directivity, directional antennas also send less (and receive less) signal from directions other than the main beam. This property may be used to reduce interference.

There are several ways to make a high-gain antenna - the most common are parabolic antennas, helical antennas, yagi antennas, and phased arrays of smaller antennas of any kind. The parabolic antenna is a high-gain reflector antenna used for radio television and data communications and also for radiolocation ( RADAR) on the UHF and helical antenna is an antenna consisting of a conducting wire wound in the form of a Helix. A Yagi-Uda Antenna, commonly known simply as a Yagi antenna or Yagi, is a Directional antenna system consisting of an array of a dipole This article is about general theory and electromagnetic phased array Horn antennas can also be constructed with high gain, but are less commonly seen. In Telecommunications, the term horn has the following meanings In Radio transmission, an open-ended Waveguide, of increasing Enhancements include a combination of a line feed with a spherical reflector to achieve extremely high gains at specific frequencies.

Antenna gain

Antenna gain is normally measured with respect to a hypothetical antenna that radiates equally in all directions, an isotropic radiator. An isotropic radiator is a theoretical Point source of waves which exhibits the same magnitude or properties when measured in all directions Conservation of energy dictates that high gain antennas must have narrow beams. For example, if a high gain antenna makes a 1 watt transmitter look like a 100 watt transmitter, then the beam can cover at most 1/100 of the sky (otherwise the total amount of energy radiated in all directions would sum to more than the transmitter power, which is not possible). In turn this implies that high-gain antennas must be physically large, since according to the diffraction limit, the narrower the beam desired, the larger the antenna must be (measured in wavelengths). Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle

Applications

High gain antennas are typically the largest component of deep space probes, and the highest gain radio antennas are physically enormous structures, such as the Arecibo Observatory. The Arecibo Observatory is a very sensitive Radio telescope located approximately south-southwest from the town of Arecibo in Puerto Rico. The Deep Space Network uses 35 meter dishes at about 1 cm wavelengths. The Deep Space Network, or DSN, is an international network of communication facilities that supports Interplanetary Spacecraft missions and This combination gives the antenna gain of about 100,000,000 (or 80 db, as normally measured), making the transmitter appear about 100 million times stronger, and a receiver about 100 million times more sensitive, provided the target is within the beam. This beam can cover at most 1/100 millionth of the sky, so very accurate pointing is required.

See also

• Low-gain antenna

References