DIPOLE ANTENNA

ANTENNA:
                    "Antenna is a any metallic structure which is used to transmit or receive the electromagnetic signals".
From definition we come to know that antenna can be used to transmit as well as receive the electromagnetic waves , but one thing which is important  is that the impedance should be matched between source side and load side .
When we pass an electric signal through a conductor then the electric signal will be reflected back to source end . but here the point is that the amount of electric current received after bounce back will be slightly less as compared to sent electric signal . Thus the loss here will be converted into radiations or electromagnetic waves which will be travelling in space to reach the receiver to form the communication between to ends.

TYPES OF ANTENNA:

                                               There are number of antennas based on their application in specific domain some of them are as listed below

1) Patch antenna 

2) mono pole antenna 

3) Dipole antenna 

4) Parabolic reflector antenna

5) yagi uda antenna 

6) loop antenna 

7) array antenna 

                                       Out of all these antennas the most important one is the Dipole Antenna which most basic one . The patch antenna is used in small electronic devices where space is very compact like mobile phones , wireless hand sets etc . The parabolic reflector antenna is used in the TV Transmission where it is used to receive the electromagnetic signals from the satellite . The name parabolic is based on the fact that the shape of reflector is made "parabolic"such that it concentrates most of signal into the receiving part of the antenna .

                                                                                     NOW coming to yagi uda antenna it is also used in TV Transmission itself but it was used in olden days , the disadvantage with this antenna is that it has got low gain due to this its efficiency will decrease.

we will be talking about the "Dipole Antenna " in details .

MONO POLE ANTENNA:

                                                       As its name itself suggests it a type of antenna with input at its" only one end ". these are most basic ones but the required radiation cannot be obtained from these type of antenna due to their mono pole structure.
                                                                            The improved version of these type of antenna is the dipole antenna which can be used to obtain convenient radiation pattern. which is discussed below .

DIPOLE ANTENNA:

Definition : "An antenna which contains two poles which are opposite in charge.  "

                          

                                                   From definition we come to know that a dipole antenna is one which contains two poles (i e : poles means basically two ends) which are opposite in charge , Hence the name to this antenna is the "dipole " meaning "two" poles .

CONSTRUCTION:

                                      The construction of dipole antenna is very easy compared to other types of antennas as it contains only two poles which are center fed by suitable voltage .

                                      consider a metal of length L , now bend the metal in two equal parts as shown in below figure and in between these two metallic parts give source may be current or voltage depending on the application we may use either of them. and that's it our dipole antenna is ready .

"dipole antenna with center feed "

HOW IT WORKS:

                                      Until now we have seen how to construct an dipole antenna , now lets see how  it works actually.

As stated earlier the antenna contains two poles "so when we apply current between the two poles " due to difference in voltage "positive and negative charges will be stored on opposite  sides to each other ". As current varies in the metallic conductor   the charges will move in opposite direction to each other , but at one point in between they will be meeting with each where they will be moving with "maximum velocity". Thus again for other cycle of current the charges will again reverse their direction and move in opposite direction to each to other. now they will be again meeting at a point with maximum velocity and creating another wave (electromagnetic wave). 

                                                         Thus as the amount of current through the conductor (antenna) increases the back and forth motion of charges increases and amount on radiation also increases .

below figure shows the process of radiation production.

"dipole antenna radiation pattern"

APPLICATIONS:

 1)  It is used as a transmitter and receiver (Trans-receiver) in Radio frequency communication .

2)   It is used in military applications to form communication between solders and the base station(     army head quaters).

3) It is used in radio stations to transmit data either by AM or FM  techniques.

4) It can also be used to form mutual communication between trains.

5) Apart from this it can be used every where there is use of RF waves for communication.

HALF WAVE DIPOLE ANTENNA:

                                                                          As name it self suggests it is half wavelength long  (L/2) . This is the shortest length of antenna which can be used to get the convenient radiation pattern. It is most widely used type of antenna due to production of most suitable pattern of radiation 

                                       

                                           It is normally fed at a point which is equidistant from both the the ends means at a length of "quarter" from both the sides of antenna. It is to be noted that the length of the antenna will be equal to the half of wavelength of signal which is flowing through the antenna conductor or metallic tube of antenna depending on the fact that the material which is used to construct the antenna.

The below figure shows the half wave length dipole antenna ..

"half wave length dipole antenna"

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