YAGI-UDA ANTENNA

Yagi-Uda Antenna:

                                       It's the most simple type of antenna which basically uses the dipole antenna as its fundamental working element . It's an directional beam creating antenna which is mostly used in TV channel operations in olden days and even today in some parts of India.

Why The Name Yagi-Uda:

                                                   Basically this antenna was designed and developed by two scientists of japan named "Yagi and Uda " so in the honor of them it was named so . Here it should be noted that it has not got any technical meaning in it . most of antenna's were named on the basis of its inventor .

What is Use Of Yagi - Uda Antenna :

                                                                      AS we know that "dipole "  antenna is roughly an Omni directional antenna which radiate the electromagnetic waves in nearly 360 degree except at some points as illustrated in the below figure .

"dipole antenna "

                                                                   But the question here is that what is the necessary of this Yagi - uda  antenna to understand this we should first know some basic things about antenna Directivity . The problem with the dipole antenna is that as stated earlier it generates the radiation in all directions but it will cover a very small distance , which can't be tolerated in far distance communications like TV transmissions. 

                                                                Here the yagi-uda antenna came into picture which is capable of generating such an "radiation pattern which will cover a large distance ". That means the Directivity of the antenna is more .

Why the reflectors and directors are used in it :

                                                                                                Before we come to this point why these are used . we should know that a "inductor" basically "lag's the current in it " and the "capacitor lead's the current through it ". 

                                                 Now as we can see in figure that a dipole antenna is placed at the middle point . and an reflector is placed on left side of dipole and an directors are placed on right side of dipole antenna . here it is to be noted that we want to create the directive radiation on right hand side of the dipole . 

"Yagi-Uda Antenna "

             The" size of the reflector is made a little longer as compared to dipole antenna and that of director is made a little shorter why ?????.

                                                                             The reason behind is that "When an electromagnetic wave is created in both the directions we want the waves on right side only so we will keep an element longer than the length of dipole antenna which will be acting as the "inductor " and it will lag the current through it . so here when wave travel from dipole slit to reflector slit there will be change in the phase of electromagnetic wave so in order to correct that one the reflector acts as an inductor . 

                                                                                

                                           NOW coming to the directors as their name itself indicates "They are used to provide the direction to the electromagnetic waves " . as we know a smaller element will act as capacitor and the property of capacitor is that it tends to "lead the current through it " thus it will confine the radiation in one direction and also gives more strength to the radiation thus covering a larger distance . Here it should be noted that the length of directors could be kept in their decreasing order or as a same length as shown in figure . 

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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WIRELESS ANTENNA

WHAT IS ANTENNA :

                                             "It's a electromechanical structure which is used to transmit and receive  electromagnetic signals into space" .

HOW THE NAME ANTENNA COINED:

                              We know that in communication we require a electrical signal to be transmitted in the wire. But we cannot link long distances due to requirement of high infrastructure . And maintaing of these electrical cables is very difficult or we can say almost impossible .

                     So avoid this problem the scientists decided to use free space as the medium . But we all know that free space cannot be used to transmit electrical signals .

         NOW Scientists thought of something which will convert the electrical signal to electromagnetic signals and radiate it in free space 

And this is how "Antenna" was come into picture.

HOW ANTENNA WORKS:

                                             According to source theorem we know that "Maximum power will be transfered between source and destination if there is equal load on both sides or there should be matching in impedance ".

                        So what if there is mismatch in impedances , Suppose we have sent 1 watt power and the power reached to destination is 0.9 watt . 

          The question arises that where that 0.1 watt of power has gone. The Answer to this question is that " LEAKAGE CURRENT" .

The 0.1 watt will be converted to leakage power and it will be in terms of "RADIATION". Which is basically a electromagnetic waves.

The below figure shows "reflection signal and radiation"

"Production of Radiation by using waveguide "

                                                                                 

But the problem is that it is only small amount of radiation which can cover very small distance of about 100 meters .

CHALLENGES:

1) The radiation cover very small distance .

2) To increase radiation we may think of increasing power but it should be kept in mind that the human and other living cells will be affected due to more powerful radiation so we can no more increase power level.

USE OF ANTENNA TO SOLVE THIS:

Now the concept of antenna came that , If we increase the width of waveguide at destination side we can get more radiation's  with the same input power of 1 watt ( just for example purpose) .

HOW RADIATION INCREASE WITH INCREASE IN WIDTH OF WAVEGUIDES END:

                                   Basically radiation is nothing but leakage current . so as conducting medium increase the amount of leakage current will increase and automatically the amount of radiation will increase.

The below figures shows amount of radiation for various antenna widths .

Note: It is to be pointed that the width is increased in small amounts for comparison purpose.

"small amount of radiation for small antenna width"

"Amount of radiation increase with increase in antenna width"

"Radiation further increase with antenna width"

  BUT up to what extent we can increase the width of antenna .

The limit for that is " not more than 90 degree".

                    Because anything beyond this will lead to same results as original width of waveguide . it is shown in below figure .

                                          

"It is maximum amount of tapering limit for antenna beyond which the results will be similar to original waveguide".

ALSO READ HAND OFF IN WIRELESS COMMUNICATION
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