Hai friends in this artilce let us discuss about various definitions which comes across Antenna and Microwave Propagation and it will be very helpful for friends who study Engineering

Radiation Pattern:

#)Radiation pattern of an antenna is nothing but a graph which shows the variation in actual field strength of electromagnetic field at all points which are at equal distance from the antenna.

#)The graph of the radiation pattern will be 3-D and hence can not be represented on a plain paper.

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 #)Gain of an antenna without involving the antenna efficiency is defined as “the ratio of maximum radiation intensity in the give direction to the maximum radiation intensity from a reference antenna produced in the same direction with same power input.

#)It is expressed as

Gain(g) =                                  maximum radiation intensity from test antenna
--------------------------------------------------------------------------------------
maximum radiation intensity from a reference antenna with same power input

Power Gain:

#)Power gain in a given direction is defined as the ratio of the radiation intensity in that direction to the average total input power.
#)It is expressed as

Power gain(Gp) =               radiation intensity in a given direction
----------------------------------------------------------
average total input power
Directivity (D):

#)Directivity of an antenna is defined as the ration of maximum radiation intensity to its average radiation intensity

#)It is given by

directivity(D) =                   maximum radiation intensity of test antenna
------------------------------------------------------------------
average radiation intensity of test antenna

Antenna efficiency:

#)The efficiency of an antenna is defined as the ratio of power radiated to the total input power supplied to the antenna and is denoted by η or k.

Antenna efficiency( η) =            power radiated
------------------------
total input power
Effective length:

#)The term effective length of an antenna represents the effectiveness of an antenna as radiator or collector of an electromagnetic wave energy.

#)It is expressed as

Effective length =           open circuited voltage
----------------------------------
incident field strength( electric)

Radiation resistance (Rr):

#)This is defined as that fictitious resistance which when substituted in the series with antenna will consume same power as is actually radiated.

Bandwidth:

#)Antenna bandwidth is a width of frequency over which the antenna maintains certain required characteristics like gain, front back ration or S.W.R pattern, polarization and impedance.

Beam width:

#)It is an angular width in degrees measured on the radiation pattern between the points where the radiated power has fallen to half its maximum value.

#)This is called beam width between half power point or half power beam width (HPBW) because the power at half power points is just half.

Virtual height:

#)It may be defined as the height to which a short pulse of energy sent vertically upward and traveling with the speed of light would reach taking the same two ways travel time as does the actual pulse reflected from the layer.

Maximum usable frequency( MUF):

#)It is a reflecting frequency which can be reflected back to the earth but this time for a specific angle of incidence rather than the period.

#)It can also be defined as the frequency which makes a given receiving point corresponds to a distance from the transmitter equal to the skip distance.

Skip distance:

#)It may be defined as the the minimum distance4 from the transmitter at which a sky wave of given frequency is returned to the earth by the ionosphere.

#)It is represented as D.

Fading and its types:

#)Fading is the fluctuation in the received signal strength at the receiver or a random variation in the received signal.

#)It is caused by the variation in the heights anddensity of ionization in the different layers of the ionosphere.

#)The types of fading are :

1. Selective fading
2. Interference fading
3. Absorption fading
4. Polarization fading
5. Skip

• Written by Raaghavan Krishnamurthy.
• In category Engineering.
• 15 years ago.

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