 Hello everyone, today I will be explaining you about the antenna subsystems. So what are all the different types of antennas which are used in satellite communication. So those different types of antennas will see it in this session. Now what is the learning outcome of this? So at the end of this session, the student will be able to explain and identify different types of antennas used in the satellites. Now before going to the next slide, let us recall the different types of subsystems which are used in the satellites as well as a basic knowledge of electromagnetic wave propagation, then types of polarization are needed. So electromagnetic wave propagation in the sense the propagation of the wave that is the electromagnetic characteristics of the wave that we have to know then what are the different types of polarization. So basically there may be horizontal polarization or there may be a vertical polarization or there may be an orthogonal polarization. So it depends upon the types of polarization. So now let us look at the basic antenna parameters. So if at all if you consider an antenna, so what are all the basic parameters that an antenna should have or in order to study the properties of an antenna, so what are all the basic parameters that one has to know about antenna. So those are radiation pattern, then second one that is beam width, then antenna aperture, then antenna gain, directivity as well as polarization. So now let us know what is radiation pattern. So radiation pattern is nothing but it is the plot of the electromagnetic field with respect to the frequency of observation or you can say that different fields that will be emitted by the antenna. So they are plotted in a graph with respect to the frequency of operation. So that is nothing but the radiation pattern. So radiation pattern it depends upon the physical structure of the antenna. So the physical structure of the antenna it may be circular or it may be rectangular one or it may be some cross-sectional one. So it depends. So that is what we call it as the physical aperture of the antenna. So that is what aperture in the sense the physical appearance. So basically the antenna aperture is classified into two types that is effective aperture then physical aperture. So physical aperture in the sense the physical appearance of the antenna whereas the effective aperture, effective aperture in the sense the area of the antenna which is responsible for the radiation pattern in a particular direction. So that is nothing but the effective aperture. Now let us look at the beam width. So what do you mean by the beam width? Basically the beam width is nothing but the radiation pattern that is sometimes the radiation pattern it may appear like a circle or it may appear like a random structure. So it may take different forms. So that is nothing but the beam width. So antenna aperture as I told you antenna aperture is nothing but the physical appearance that is physical aperture as well as the effective aperture. Now let us look at the antenna gain. So what do you mean by the antenna gain? So antenna gain is nothing but the property of the antenna which has the capability to produce radiation pattern in an effective way. So basically the gain of the antenna is measured in decibels. Now directivity. So what do you mean by the directivity of an antenna? Directivity of an antenna is nothing but it is the property of the antenna which will speak about the radiation pattern how directional it is. In the sense in what direction does the radiation pattern is large or you can say that the beam width with respect to a particular direction is nothing but the directivity. Again directivity is measured in decibels. So I have already told about the polarization that is polarization is nothing but it is the property of the electromagnetic wave where it is going to propagate in the medium. So if at all if the electromagnetic field or you can say the electric field if it is perpendicular to the surface of the earth then it is orthogonal polarization. So basically polarization is being spoken with respect to the angle of electric field or the magnetic field with respect to the surface of the earth. So at what angle does the electric field propagates with respect to the surface of the earth. So that is nothing but the polarization. So polarization plays a very much important role while deciding the important factor of the antenna that is directivity of the antenna. So if at all if we have the polarization in a particular direction. So suppose if you have the antenna with respect to the surface of the earth. So if it is straight or if it is mounted somewhere then the polarization will speak you about the electromagnetic propagation in a particular direction. So these are the important antenna parameters. Now let us move to the satellite antennas. So basically which types of antennas are used in satellites. So what are the different types of antennas which are used in satellites. Now there are mainly four basic types are there. So those are wire antennas again wire antennas can be divided into monopoles and dipoles then horn antenna then reflector antenna. So in the reflector antenna we are going to have two types that is the parabolic reflector antenna then hyperbolic reflector antenna. So it depends. So it mainly depends upon the radiation pattern or you can say the beam width. So the reflector antennas they play a very much important role especially in communication systems. Now the last one is array antennas. So what are these array antennas array antennas are nothing but the antennas which are arranged in a specific pattern. So specific pattern in the sense suppose if we have a TV antenna like Agi Uda antenna it is going to have the arrays of antennas. So that is nothing but the antenna array. So again the beam width or you can say that the radiation pattern. So it constitutes the different radiation patterns produced by all those antennas. So that is nothing but the array antenna. In array antenna again we are going to have phase array antenna. So I will be speaking about what are these different phase array antenna as well as array antenna in the next slide. Now let us look at the antennas how they are going to appear. So you can see in the slide that is H plane sectoral horn antenna then pyramidal horn antenna so E plane sectoral horn in the sense. So these E plane or the H plane so they are nothing but the polarization of the electromagnetic wave. So suppose if it is a orthogonal polarization or if it is a horizontal polarization then what type of antenna should be used so that depends upon the polarization. So that is what horn antennas are available in different forms. So you can also see the canonical horn antenna. So usually these types of antennas you can find it on the mobile towers. Now let us look at the reflector antennas. So these reflector antennas you can see it in the slide. So it basically consists of the parabolic reflector antenna and then cascane antenna. So the parabolic reflector antenna it is going to be the primary radiator which consists of the primary radiator and then the cascane antenna you can see the sub reflector antenna. So these are all the umbrella like structures which have the capability of getting or which have the capability of directing you can say. So directing the radiation pattern in a particular pattern. Now let us look at the array antennas. So you can have a look at the array antennas in the slide. So array along y axis you can see that then array along x axis you can see there then array along the z axis. It means that the antennas can be arranged in all the dimension that is in one dimension you can arrange two dimension as well as the three dimension. Now you can see the two dimensional array. So how does the arrays of antenna so they are arranged in the y plane as well as in the x plane. Now you can have a look at the typical antenna subsystem on the satellite. So different types of antennas you can see there that is the receiving antenna which is of 30 gigahertz so which has been mounted on the satellite. You can also see the sterable antenna means it has the property of staring in all directions. So then you can also have a look over the solar arrays that is the power subsystem. Then you can also see about the range of frequency that these types of antennas are able to handle the frequency that is 30 gigahertz or you can say suppose if the satellite link if it if at all if it's been designed then always there will be the uplink frequency is always greater than the downlink frequency. So these are the references I have referred so you can refer the textbook by Timothy Pratt that is satellite communication textbook by Timothy Pratt that is second edition. Then I have also referred to the NPTEL courses. Then the best book that you can refer is antennas and wave propagation textbook by John D. Cross thank you.