 Myself Piyusha Shedgarh in this session will see the information related to the horn antenna. These are the learning outcomes. At the end of this session, students will be able to explain horn antenna with suitable diagram. They will be able to write the design equations for horn antenna. These are the contents. So, before going to start the introduction part of the horn antenna, you can pause video here for a second and recall that what is the meaning of directivity and efficiency of an antenna? Yes, the directivity is the major of the concentration of an antenna's radiation pattern in a particular direction that is in which direction you are getting the maximum radiation can be defined with this directivity and antenna efficiency is defined as the ratio of radiated power to the input power. Let us introduce the horn antenna. So, to improve the radiation efficiency and the directivity of the beam, the waveguide should be provided with an extended aperture to radiate all the energy in the forward direction which is termed as a flaring of the antenna. So, flaring is provided to get the directivity is more and thus you can get the proper signal at the receiver side. So, mainly the horn antennas are constructed by flaring of the waveguide. Frequency range used for the horn antenna is around 300 MHz to 30 GHz. So, let us recall some points of the horn antennas. So, antennas which are constructed by the flaring of the waveguide, this is the horn antenna. Horn antenna is used to increases the directivity. It also used to improves the impedance matching with the free space. It is a directional antenna so can be utilized for a long distance communication purpose also. Let us discuss the construction of horn antenna. So, whenever the energy of the beam is transformed into the radiation in that case the losses are reduced and the focusing of the beam will be improved. Horn antenna may be considered as a fled out waveguide. The directivity is improved and the diffraction is reduced by using horn antenna and therefore you are getting the antenna efficiency is more. So, what is the use of the flaring used in horn antenna? So, flaring helps to match the antenna impedance with the free space impedance for better radiation. That means there are less chances of the reflection of the signal towards the transmitter side and therefore it improves the directivity of the signal. It is also used to avoids standing wave ratio. Flaring is also used to provide the greater directivity and the beam width is narrower. The flared waveguide can be technically termed as electromagnetic horn reflector. So, the flaring is provided with an angle which is denoted with the phi letter phi of the horn antenna. It plays an important factor, it plays important role in case of the horn antenna. If this flaring angle is too small, then the resulting wave will be spherical instead of you are getting the plane wave front and the radiated beam will not be directive. Therefore, there is the condition that the flare angle should have an optimum value and is closely related to its length. So, this looks like a horn antenna. So, initially there is a waveguide is used and after that you can give the flared construction for the waveguide to form the horn antenna. There are the different types of the horn antenna. So, the sectoral horn antenna, pyramidal horn antenna and the conical horn antenna. So, this figure shows the different types of the horn antenna in sectoral. This figure is sectoral E-plane horn and this figure is shown by the sectoral H-plane horn. These two are the types of the sectoral horn antenna whereas the second type is the pyramidal horn antenna and the third one is the conical horn antenna. So, these are nothing but the flaring construction is used after some part of the rectangular waveguide. It looks like a horn shape and therefore the name given as a horn antenna. So, how to define the sectoral and the other types of the horn antenna? So, sectoral horn antenna which is flared out in only one direction. So, again the sectoral horn antenna is divided into two types, sectoral E-plane horn and the sectoral H-plane horn. How to define the sectoral E-plane horn? In that case the flaring is in the direction of the electric vector that is the flaring is provided in parallel with the electric field whereas in case of the sectoral H-plane horn the flaring is in the direction of the magnetic vector. What is the pyramidal horn? It is defined as in which the flaring is done on both the E and H walls of the rectangular waveguide whereas in case of the pyramidal horn the shape of the antenna is somewhat like a truncated pyramid. In case of the conical horn antenna the walls of a circular waveguides are flared out. Some important properties of the horn antenna, so to have higher antenna gain horn antenna must have the large antenna aperture. For the given aperture size it should have the high gain and when the tappering is significantly long. So, generally the gain of the horn antenna is around 20 decibel. Now, how to define the design equations of horn antenna? So, to get the better efficiency and the directivity horn antenna can be defined. To design horn antenna the two equations are required. So, for that consider this is the horn antenna. In that case if you refer this figure this is nothing but the flared waveguide is used which having the length is equal to L denoted with the letter L and this total length is nothing but L plus delta where delta shows the face difference between these two points and center point is denoted with the O letter. Center point for this total height of the antenna is X and at the one of the end is denoted with the letter Y. Horn antenna gives rise to the uniform phase wavefront having a greater aperture in comparison to the waveguide and therefore it is used to give the higher directivity. The uniform wavefronts propagates in outward direction which are cylindrical in nature. As the wave propagates in a different direction from apex to aperture thus there exists a difference in phase at the origin and aperture and this path difference is shown by the delta value. So, from the geometry of this figure you can define the different design equations for horn antenna. Now, consider this is the angle theta so you can calculate the cos theta value so you know that cos theta is a adjacent value upon the hypotenuse. So, adjacent value of the length is given by this capital L divided by L plus delta and again you can calculate the value of the theta by using the tangent ratio. So, tan theta is given by opposite upon adjacent value. So, tangent length is given by h by 2 where the adjacent is the L. So, h by 2 by L then from this equation you can write tan theta is equal to h upon 2 L. So, from these two equations you can calculate the value for the angle flare angle therefore theta is equal to tan inverse of h by 2 L is equal to cos inverse of L by L plus delta. So, you can calculate the theta value from this cos first equation and the second equation. So, theta is equal to tan inverse of h by 2 L it is always given by this equation and again it can be calculated by using this equation cos inverse of L upon L plus delta. Let us consider this is the equation number 1. Now, consider the triangle O, Y, X. So, consider this center point O, Y and X. So, if you observe this is nothing but the right angle triangle so use Pythagoras theorem here. By using Pythagoras theorem, hypotenuse square is equal to base square plus height square therefore L plus delta square is equal to L square plus h by 2 square. Now, solve this equation so that you are getting L square plus 2 L lambda plus delta square is equal to L square plus h square by 4. Now, if you refer this delta which having a very small value therefore neglect delta square so by neglecting delta square from the previous equation and cancelling this L square L square on both side just remaining 2 L delta is equal to h square by 4. So, from this equation you can calculate the length of the antenna. So, L is equal to h square by 8 delta give that equation number 2. Now, from the above equation you are getting the equation number 1 for the theta value and the equation number 2 for the L value. So, theta is equal to tan inverse of h by twice of L it can be also equated to cos inverse of L upon L plus delta and L becomes equal to h square by 8 times of the delta value. So, these 2 equations are considered as the design equations of the horn antenna. By using these 2 equations you can design the horn antenna. Let us now list the advantages of the horn antenna. Horn antenna offers easy construction as can be easily configured with the waveguide. Absence of the resonance element in the structure in horn antenna allows it to operate over a wide bandwidth. It also provides a good impedance matching it highly directional in nature thereby providing the higher directivity for the horn antenna. It offers the less reflections along with some of the disadvantages. So, the directivity of the antenna is dependent on the flare angle there should have some optimum value for the flare angle. Another disadvantage the dimensions of the flare must be sufficient large and this sometimes makes the antenna bulky. Let us now discuss the applications of the horn antenna. Horn antenna used mainly for the astronomical studies. It is also used in microwave based applications. It is applicable in speed enforcement cameras to keep away from reflections that interrupt the desired response. It also used in laboratories to measure different antenna parameters. At microwave frequencies used where as the moderate gains are required is to be adequate. The horn dimensions must be high for high gain to use in moderate gain operations. It also used as a feed elements. These are the references for today's session. Thank you.