Fudamentals of Antenna

8/10/2019 Fudamentals of Antenna

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Fudamentals of Antenna


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Definition of Antenna

An antenna is a specialized transducer that convertsradio-frequency (RF) fields into alternating current (AC)

or vice-versa.

There are two basic types:The receiving antenna, which intercepts RF energy anddelivers AC to electronic equipment andThe transmitting antenna, which is fed with AC fromelectronic equipment and generates an RF field.


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Antenna TypesWire Antenna

Microstrip AntennaTravelling Wave AntennaOther Antenna

Reflector AntennaLog-periodic AntennaAperture Antenna


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Wire Antenna: Short Dipole Antenna

Half Dipole Antenna BroadBand Diploe Antenna Monopole Antenna Folded Dipole Antenna

Loop Antenna


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Microstrip Antenna:

Rectangular microstrip(patch)Antenna Planar Inverted-f Antenna(PIFA)

Travelling Wave Antenna: Helical Antenna

Yagi-uda Antenna

Spiral AntennaReflector Antenna: Corner Antenna

Parabolic Antenna(Dish Antenna)


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Other Antenna:

NFC Antenna

Fractal Antenna Wearable AntennaLog-periodic Antenna: Bow Tie Antenna

Log-periodic Antenna Log-periodic dipole Array


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Aperture Antenna:

Slot Antenna

Horn Antenna Telescopes Slotted Waveguide Antenna Vivaldi Antenna

Inverted-f Antenna Cavity-backed Slot Antenna


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Components of antenna

systemsAntenna feeding

Antenna tunerAntenna rotatorBlock upconverter

Coaxial cableGround SystemFeed lineLow-noise block downconverter

Passive radiatorReceiverStubTransmitter


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Antenna radiation sources and

regionsAntenna boresight

Focal cloudGround planeMain lobe

Near and far fieldSide lobeVertical plane


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Antenna characteristicsAntenna efficiency

Antenna equivalent radiusAntenna factorAntenna height considerations

Array gainDirectivityElectrical length


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Friis transmission equation

Gain

Radiation patternRadiation resistanceRadio propagation

Radio spectrum

Signal-to-noise ratio


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Radiation Pattern:

An antenna radiation pattern or antennapattern is defined as a mathematicalfunction or a graphical representation ofthe radiation properties of the antenna asa function of space coordinates.


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Radiation Pattern Lobes:

A radiation lobe is a portion of the radiation patternbounded by regions of relatively weak radiationintensity.Types of lobes:

Main lobe

Minor lobesSide lobesBack lobes


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Beamwidth:

The beamwidth of an antenna is a very importantfigure is used as a trade-off between it and the side lobelevel; as the beamwidth decreases, the side lobeincreases and vice versa.

The beamwidth of the antenna is also used to describethe resolution capabilities of the antenna to distinguishbetween two adjacent radiating sources or radar targets.


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Types of beamwidth: Half power beamwidth(HPBW)

First null beamwidth(FNBW)

Half-Power Beam Width (HPBW):

In a plane containing the direction of themaximum of a beam, the angle between the twodirections in which the radiation intensity is one-half

value of the beam.

First-Null Beamwidth (FNBW) : Angularseparation between the first nulls of the pattern.


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Radiation Intensity:

Radiation intensity in a given direction is defined asthe power radiated from an antenna per unit solid angle.The radiation intensity is a far-field parameter.It can be obtained by simply multiplying the radiation

density by the square of the distance.


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The near field and far fieldare regions of

the electromagnetic field around an object, such as atransmitting antenna, or the result of radiationscattering off an object.Non-radiative 'near-field' behaviors of electromagnetic

fields dominate close to the antenna or scattering object.

while electromagnetic radiation 'far-field' behaviorsdominate at greater distances.Near-field strength decreases with distance, whereas

far-field strength decreases with the inverse square ofthe distance.


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Directivity:

The ratio of the radiation intensity in agiven direction from the antenna to the radiationintensity averaged over all directions.The average radiation intensity: total power radiatedby the antenna divided by 4.

Stated more simply, the directivity of a nonisotropicsource is equal to the ratio of its radiation intensity in agiven direction over that of an isotropic source.


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Beam Solid angle:

The beam solid angleA is defined as thesolid angle through which all the power of the antennawould flow if its radiation intensity is constant (andequal to the maximum value of U) for all angles withinA.


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Polarisation:

Polarization is the curve traced by the end point of thearrow (vector) representing the instantaneous electricfield.

The field must be observed along the direction ofpropagation.Polarisation Types: Linear

elliptical

Circular


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Antenna Gain:

Antenna gainrelates the intensity of an antenna in agiven direction to the intensity that would be producedby a hypothetical ideal antenna that radiates equally inall directions and has no losses.Since the radiation intensity from a lossless isotropicantenna equals the power into the antenna divided by asolid angle of 4steradians.


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Antenna Factor:

In telecommunications the antennafactoris defined as the ratio ofthe electric field strength to

the voltage V(units: V or V)induced across the terminals ofa antenna.


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Antenna Efficiency:

The efficiencyof an antenna relates the powerdelivered to the antenna and the power radiated ordissipated within the antenna.A high efficiency antenna has most of the power

present at the antenna's input radiated away.

A low efficiency antenna has most of the powerabsorbed as losses within the antenna, or reflected awaydue to impedance mismatch.


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Wearable antennaWearable Antennasare essentially any antenna that is

specifically designed to function while being worn.Examples: include smartwatches (which typically have

integrated bluetooth antennas), glasses (such as GoogleGlass which has WIFI and GPS antennas).Wearable antennas are becoming increasingly commonin consumer electronics, and as such this page is

dedicated to describing the unique difficulties involvedin wearable antenna design.


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Wearable Antenna ChallengesProximity to the human body:

The human body is a lossy material for electromagneticwaves. This means the body converts Electric Fields into

heat; put another way, the body absorbs energy fromelectromagnetic waves.Consequently, when an antenna is placed near the body,the result is a large reduction of the antenna efficiency of

your wearable antenna.


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For example, if you design an antenna and measure an

efficiency of -3 dB (50%), when placed on the body theefficiency may easily drop to -13 dB (5%). This is a hugehit to the performance of the wireless system.

Wearable antenna need to be shorter by 15% to 25%from the antenna length in free space.


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Very limited Volume:Wearable devices must be as small as possible. No onewants a watch with a big dipole antenna hanging out theside.Space is at an extreme premium on wearable devices,

particularly for anything near the face (such as googleglass). As such, industrial designers and productdesigners often give very little space for the antenna,which further makes the antenna design problem more

difficult.


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Frequency(MHZ) Permittivity Elec.Cond(s/m)

300

37.1

0.36

450 33.9 0.43

835 30.3 0.59

900 30.0 0.62

1450 27.9 0.85

1575

27.5

0.9

1800 27.0 0.99

1900 26.7 1.04

1950 26.6 1.07

2000

26.5

1.09

2100 26.3 1.14

2450 25.7 1.32

3000 24.8 1.61


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Wearable antenna for Medical

application

Helix antenna for human body:In order to compare the variation of the new antennainput impedance as function of distance from the body

to other antennas a helix antenna has been designed.However, in the helix antenna area there is no groundplane.The antenna has been designed to operate on human

body.


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Wearable tunable printed antenna:It is used to control the antenna resonant

frequency at different locations on the human body.

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Fudamentals of Antenna