Different Parameters Of Antenna

7/30/2019 Different Parameters Of Antenna

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Antenna Parameters

By

Shahbaz Ali KhidriB.E-VI (E.E)


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Outline

Antenna Beamwidth

Antenna Bandwidth

Q-function and Bandwidth Relationship

Antenna Beam Area or Beam Solid Angle

Antenna Beam Efficiency


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Antenna

A device used to efficiently transmitand/or receive electromagnetic waves.

An impedance matching device.

The transitional structure between freespace and a guiding device.


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Antenna


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Antenna Beamwidth

Beamwidth is associated with the lobes inthe radiation pattern of antenna.

The angular separation or angular distancebetween two identical points on theopposite sides of the main lobe.

It is measured in radians or degrees.

It defines the ability of the system toseparate two adjacent points or targets.

It is inversely proportional to the

Directivity.


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Half Power Beamwidth (HPBW)

The most common type of Beamwidth isHalf Power Beamwidth (HPBW).

The angular distance between the halfpower points.

The half power expressed in decibels (dB)is -3dB, so the HPBW is sometimes

referred to as the 3dB Beamwidth. The voltage at half power points is 70.7%.


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First Null Beamwidth (FNBW)

Another frequently used measure ofBeamwidth is the First Null Beamwidth(FNBW).

The angular separation or angular distancebetween two identical first null points on

the opposite sides of the main lobe.


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Antenna Beamwidth


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Antenna Bandwidth

The range of frequencies over which theantenna can properly radiate or receiveenergy.

It is typically quoted in terms of VoltageStanding Wave Ratio (VSWR).

The VSWR is a measure that numerically

describes how well the antenna isimpedance matched to the radio or thetransmission line it is connected to.


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Antenna Bandwidth

The smaller the VSWR is; the better theantenna is matched to the transmission lineand the more power is delivered to the

antenna.


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Antenna Bandwidth


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Q-function and BandwidthRelationship

The concept of Q-factor is used todescribe the antenna as resonator.

A high Q-factor means a sharp resonance

and narrow bandwidth.

fr= Resonant Frequency, f= Bandwidth


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Q-factor depends upon the applications.

In Circuit Design we want elements to havea high Q-factor in order to reduce the

circuit loss. In Antenna we want a low Q-factor

because a low Q-factor antenna is easier

to match and tune, and have a widerbandwidth.

The smaller the bandwidth of antenna, the

higher value of Q-factor.


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There is a theoretical limit for theminimum Q-value of antenna.

If the antenna is placed inside a sphere of

radius a, then the minimum Q-value is:

Qmin=1/(ka)


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Antenna Beam Area or BeamSolid Angle

Angle: Transverse distance at a distance.

Solid Angle: Transverse area at a distance.


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The two dimensional angle or area of themain beam of antenna through which all ofthe antenna power would flow with the

maximum radiation intensity.


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The total beam area or beam solid angleAconsists of the main beam area or solidangleMplus the minor-lobe area or solid

anglem. A =M +m.

The ratio of the main beam areaMto the

total beam areaAis called as main beamefficiency or beam efficiencyM.

M =M/A.


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The ratio of the minor-lobe areamto thetotal beam areaA is called as strayfactor.

m=m/A.

M+ m= 1.


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It is also defined as the ratio between theenergy received through the main beamand the total energy received by the

antenna.


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Different Parameters Of Antenna