A directional antenna or beam antenna is an antenna which radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only. This can increase the power transmitted to receivers in that direction, or reduce interference from unwanted sources. This contrasts with omnidirectional antennas such as dipole antennas which radiate radio waves over a wide angle, or receive from a wide angle.
The extent to which an antenna's angular distribution of radiated power, its radiation pattern, is concentrated in one direction is measured by a parameter called antenna gain. A high-gain antenna (HGA) is a directional antenna with a focused, narrow beam width, permitting more precise targeting of the radio signals.[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.[citation needed] By contrast, a low-gain antenna (LGA) is an omnidirectional antenna with a broad radiowave beam width, that allows 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.[3]
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 as a receiving antenna. 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 many 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. Horn antennas can also be constructed with high gain, but are less commonly seen. 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.
Antenna gain
Antenna gain is often quoted with respect to a hypothetical antenna that radiates equally in all directions, an isotropic radiator. This gain, when measured in decibels, is called dBi. 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).
Antenna gain can also be measured in dBd, which is gain in Decibels compared to the maximum intensity direction of a half wave dipole. In the case of Yagi type aerials this more or less equates to the gain one would expect from the aerial under test minus all its directors and reflector. It is important not to confuse dBi and dBd; the two differ by 2.15 dB, with the dBi figure being higher, since a dipole has 2.15 db of gain with respect to an isotropic antenna.
Gain is also dependent on the number of elements and the tuning of those elements. Antennas can be tuned to be resonant over a wider spread of frequencies but, all other things being equal, this will mean the gain of the aerial is lower than one tuned for a single frequency or a group of frequencies. For example, in the case of wideband TV antennas the fall off in gain is particularly large at the bottom of the TV transmitting band. In the UK this bottom third of the TV band is known as group A; see gain graph comparing grouped aerials to a wideband aerial of the same size/model.
Other factors may also affect gain such as aperture (the area the antenna collects signal from, almost entirely related to the size of the antenna but for small antennas can be increased by adding a ferrite rod), and efficiency (again, affected by size, but also resistivity of the materials used and impedance matching). These factors are easy to improve without adjusting other features of the antennas or coincidentally improved by the same factors that increase directivity, and so are typically not emphasized.
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 Deep Space Network uses 35 m dishes at about 1 cm wavelengths. 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 one hundred millionth (10−8) of the sky, so very accurate pointing is required.
Use of high gain and Millimeter-wave communication in WPAN gaining increases the probability of concurrent scheduling of non‐interfering transmissions in a localized area, which results in an immense increase in network throughput. However, the optimum scheduling of concurrent transmission is an NP-Hard problem.[4]
Gallery
An early example (1922) of a directional AM radio transmitter using a long wire antenna, built for WOR, then in New Jersey and targeting both New York City and Philadelphia.
Karl Jansky and his rotating directional radio antenna (1932) in Holmdel, New Jersey, which was the world's first radio telescope, discovering radio emissions from the Milky Way.
A Yagi-Uda antenna. 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 longer (5% or more) than all the other elements, and the director(s) a bit shorter (5% or more).
^Zainah Md Zain; Hamzah Ahmad; Dwi Pebrianti; Mahfuzah Mustafa; Nor Rul Hasma Abdullah; Rosdiyana Samad; Maziyah Mat Noh (2020). Proceedings of the 11th National Technical Seminar on Unmanned System Technology 2019: NUSYS'19. Springer Nature. p. 535. ISBN978-981-15-5281-6. Extract of page 535
^Joseph A. Angelo (2014). Encyclopedia of Space and Astronomy. Infobase Publishing. p. 364. ISBN978-1-4381-1018-9. Extract of page 364
^Bilal, Muhammad; et al. (2014). "Time‐Slotted Scheduling Schemes for Multi‐hop Concurrent Transmission in WPANs with Directional Antenna". ETRI Journal. 36 (3): 374–384. arXiv:1801.06018. doi:10.4218/etrij.14.0113.0703. S2CID 2285688.
^Crawford, A.B. , D.C. Hogg and L.E. Hunt (July 1961). "Project Echo: A Horn-Reflector Antenna for Space Communication". The Bell System Technical Journal: 1095–1099. doi:10.1002/j.1538-7305.1961.tb01639.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^. 2001-11-05. Archived from the original on 2008-05-12. Retrieved 2008-05-23.
External links
What are high and low gain?
January 20, 2023
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A directional antenna or beam antenna is an antenna which radiates or receives greater radio wave power in specific directions Directional antennas can radiate radio waves in beams when greater concentration of radiation in a certain direction is desired or in receiving antennas receive radio waves from one specific direction only This can increase the power transmitted to receivers in that direction or reduce interference from unwanted sources This contrasts with omnidirectional antennas such as dipole antennas which radiate radio waves over a wide angle or receive from a wide angle A multi element log periodic dipole arrayA 70 meter Cassegrain radio antenna at GDSCC California Patch antenna gain pattern The extent to which an antenna s angular distribution of radiated power its radiation pattern is concentrated in one direction is measured by a parameter called antenna gain A high gain antenna HGA is a directional antenna with a focused narrow beam width permitting more precise targeting of the radio signals 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 citation needed By contrast a low gain antenna LGA is an omnidirectional antenna with a broad radiowave beam width that allows 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 3 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 citation needed 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 Contents 1 Principle of operation 2 Antenna gain 3 Applications 4 Gallery 5 See also 6 References 7 External linksPrinciple of operation EditWhen 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 as a receiving antenna 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 many 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 Horn antennas can also be constructed with high gain but are less commonly seen 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 Antenna gain EditAntenna gain is often quoted with respect to a hypothetical antenna that radiates equally in all directions an isotropic radiator This gain when measured in decibels is called dBi 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 Antenna gain can also be measured in dBd which is gain in Decibels compared to the maximum intensity direction of a half wave dipole In the case of Yagi type aerials this more or less equates to the gain one would expect from the aerial under test minus all its directors and reflector It is important not to confuse dBi and dBd the two differ by 2 15 dB with the dBi figure being higher since a dipole has 2 15 db of gain with respect to an isotropic antenna Gain is also dependent on the number of elements and the tuning of those elements Antennas can be tuned to be resonant over a wider spread of frequencies but all other things being equal this will mean the gain of the aerial is lower than one tuned for a single frequency or a group of frequencies For example in the case of wideband TV antennas the fall off in gain is particularly large at the bottom of the TV transmitting band In the UK this bottom third of the TV band is known as group A see gain graph comparing grouped aerials to a wideband aerial of the same size model Other factors may also affect gain such as aperture the area the antenna collects signal from almost entirely related to the size of the antenna but for small antennas can be increased by adding a ferrite rod and efficiency again affected by size but also resistivity of the materials used and impedance matching These factors are easy to improve without adjusting other features of the antennas or coincidentally improved by the same factors that increase directivity and so are typically not emphasized Applications EditHigh 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 Deep Space Network uses 35 m dishes at about 1 cm wavelengths 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 one hundred millionth 10 8 of the sky so very accurate pointing is required Use of high gain and Millimeter wave communication in WPAN gaining increases the probability of concurrent scheduling of non interfering transmissions in a localized area which results in an immense increase in network throughput However the optimum scheduling of concurrent transmission is an NP Hard problem 4 Gallery Edit An early example 1922 of a directional AM radio transmitter using a long wire antenna built for WOR then in New Jersey and targeting both New York City and Philadelphia Karl Jansky and his rotating directional radio antenna 1932 in Holmdel New Jersey which was the world s first radio telescope discovering radio emissions from the Milky Way Grote Reber s homemade antenna in Wheaton Illinois 1937 world s second radio telescope and first parabolic radio telescope Holmdel Horn Antenna in Holmdel New Jersey 1960s Built to support the Echo satellite communication program 5 it was later used in experiments that revealed the cosmic background radiation permeating the universe 6 Parabolic antenna the 70 m antenna at Goldstone Deep Space Communications Complex in the Mojave Desert California Voyager 2 spacecraft The HGA a parabolic antenna is the large bowl shaped object A giant phased array radar in Alaska A Yagi Uda antenna 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 longer 5 or more than all the other elements and the director s a bit shorter 5 or more See also EditAmateur radio direction finding Antenna gain Cantenna Cardioid Cassegrain antenna Cassegrain reflector Loop antenna Omnidirectional antenna Parabolic antenna Phased array Radio direction finder Radio propagation model Antenna subsection Radiation patternReferences Edit Zainah Md Zain Hamzah Ahmad Dwi Pebrianti Mahfuzah Mustafa Nor Rul Hasma Abdullah Rosdiyana Samad Maziyah Mat Noh 2020 Proceedings of the 11th National Technical Seminar on Unmanned System Technology 2019 NUSYS 19 Springer Nature p 535 ISBN 978 981 15 5281 6 Extract of page 535 Joseph A Angelo 2014 Encyclopedia of Space and Astronomy Infobase Publishing p 364 ISBN 978 1 4381 1018 9 Extract of page 364 Low gain antenna Oxford Reference a href Template Cite journal html title Template Cite journal cite journal a Cite journal requires journal help Bilal Muhammad et al 2014 Time Slotted Scheduling Schemes for Multi hop Concurrent Transmission in WPANs with Directional Antenna ETRI Journal 36 3 374 384 arXiv 1801 06018 doi 10 4218 etrij 14 0113 0703 S2CID 2285688 Crawford A B D C Hogg and L E Hunt July 1961 Project Echo A Horn Reflector Antenna for Space Communication The Bell System Technical Journal 1095 1099 doi 10 1002 j 1538 7305 1961 tb01639 x a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link National Park Service Astronomy and Astrophysics Horn Antenna 2001 11 05 Archived from the original on 2008 05 12 Retrieved 2008 05 23 External links EditWhat are high and low gain Retrieved from https en wikipedia org w index php title Directional antenna amp oldid 1134682426, wikipedia, wiki, book, books, library,
