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MAIN CONCEPT ANTENNA GAINWITH IRRADIANCE

Abstract : In electromagnetic, an antenna'spower gain or simply gain is a key

performance figure which combines theantenna's directivity and electrical efficiency.This paper describe affect an antenna gainwith irradiance. The larger an antenna's is, themore power it can collect from a given field ofelectromagnetic. Antenna pattern type is alsoinfluence electromagnetic field collection.

1. Introduction

An antenna is a device that transmits and/orreceives electromagnetic waves.

Electromagnetic waves are often referred to asradio waves. Most antennas are resonantdevices, which operate efficiently over arelatively narrow frequency band. Irradiancemeans the power of electromagnetic radiationper unit area (radiative flux) incident on asurface. Radiant emittance or radiant exitanceis the power per unit area radiated by asurface.

2. Directivity and Gain

Directivity is the ability of an antenna to focusenergy in a particular direction whentransmitting or to receive energy better from aparticular direction when receiving. Therelationship between gain and directivity: Gain= efficiency/Directivity. The decibel (dB) is alogarithmic unit of measurement thatexpresses the magnitude of a physical quantity(usually power or intensity) relative to aspecified or implied reference level.

An antenna with increased directivity ishopefully implemented efficiently, is low loss,

and therefore exhibits both increaseddirectivity and gain. Power gain (or simplygain) is a unitless measure that combines anantenna's efficiency, E antenna and directivity, D:

G = E antenna D

3. Radiation Patterns

The radiation or antenna pattern describes therelative strength of the radiated field in variousdirections from the antenna, at a fixed or

constant distance. The radiation pattern is a"reception pattern" as well, since it also

describes the receiving properties of theantenna. The radiation pattern is three-dimensional, but it is difficult to display thethree-dimensional radiation pattern in ameaningful manner, it is also time consumingto measure a three-dimensional radiation

pattern. There is two type of radiation patterns,absolute and relative patterns means andnear-field and far-field patterns.

4. Antenna Pattern Types

4.1. Omnidirectional Antennas

For mobile, portable, and some base stationapplications the type of antenna needed hasan omnidirectional radiation pattern. Theomnidirectional antenna radiates and receivesequally well in all horizontal directions.

4.2. Directional Antennas

Directional antennas focus energy in aparticular direction. Directional antennas areused in some base station applications wherecoverage over a sector by separate antennasis desired. Point to point links also benefit fromdirectional antennas

4.3. Antenna Polarization

Polarization is defined as the orientation of theelectric field of an electromagnetic wave.Polarization is in general described by anellipse. Two often used special cases ofelliptical polarization are linear polarization andcircular polarization. The initial polarization of aradio wave is determined by the antenna thatlaunches the waves into space

5. Conclusion

Antenna Gain is given in reference to astandard antenna. The two most commonreference antennas are the isotropic antennaand the resonant half-wave dipole antenna.The isotropic antenna radiates equally well in"all" directions. Real isotropic antennas do notexist, but they provide useful and simpletheoretical antenna patterns with which tocompare real antennas