 Hello, Namaste. Welcome to the session of Spiral Antenna. Myself Rohini Mirgo working as associate professor at Walchin Institute of Sulapu. Learning outcomes at the end of this video you will be able to explain spiral antenna and its types. You will be able to list the applications of spiral antenna. So before I move further let us just discuss what is made by an antenna. Just think of what is an antenna. Antenna or aerial is sometimes also called as aerial. It is a means for radiating or receiving radio waves. It is a linking component of guided wave and free space wave. It is a source or radiator of electromagnetic waves. When I am saying source in that case I am talking about transmitting antenna. It is a sensor of electromagnetic waves. When I am saying sensor then it is the receiving antenna. Antenna acts as a transducer between the transmission line that is the guided wave and the free space wave. Spiral antenna has came into picture. So let us see its history. In 1954 Edwin Turner started messing with the dipole antenna. Instead of leaving the arms as open as a straight arms he wrapped them around each other. He wrapped these arms around each other. So like this forming a spiral. So here you can see this is a lambda by 2 dipole antenna whose arms are straight. But here this arm is rotated like this. This arm is rotated like this. So you can see this type of structure forms which is nothing but a spiral antenna. Let us see the characteristics of spiral antenna. Spiral antennas belong to the class of frequency independent antennas FI frequency independent antennas. So frequency independent antennas are characterized by a very large bandwidth. So the antennas which are frequency independent they have their parameters constant over a very large frequency range that is the large bandwidth. Antennas which theoretically have no limitation on bandwidth are called frequency independent antennas. In practice lower frequency limit is determined by the size of the antenna and upper frequency limit is determined with a precision of construction. So F low is C upon 2 pi r2. C is the free space velocity which is 3 to 10 raised to 8 m per second and F high is C upon 2 pi r1. The fractional bandwidth for this frequency independent antenna which I am talking today is the spiral antenna is as high as 30 s to 1. It means that the lower frequency is 1 gigahertz and the antenna still can efficiently be used up to 30 gigahertz. That means its parameters will remain same still if I use up to 30 gigahertz and every frequency in between 1 to 30 gigahertz. Half for bandwidth that is HPBW is approximately 70 to 90 degrees. What about polarization of spiral antenna? So when I talk about the polarization of spiral antenna let us first discuss what is polarization and what are types of polarizations. Polarization it refers to the path traced by the tip of the electric field vector as a function of time. There are three forms of polarizations linear circular and elliptic. So here we can see this way the tip of the electric field intensity vector will scan a straight line. So it is called as a linear polarization. In this case you can see the tip of the electric field intensity vector is scanning a circle. So it is called as a circular polarization and in the last case if you see the tip is forming a ellipse. So it is called as a elliptical polarization. What type of polarization is there in case of spiral antenna? Spiral antenna usually are circularly polarized. Spiral antenna's radiation pattern has a peak radiation in the direction perpendicular to the plane of the spiral. So we are going to talk about the radiation pattern also further and in the broad side direction the radiation happens but its polarization is circular polarization. Like you can see here the tip is forming a circle so that it is a circularly polarized antenna. So radiation pattern of the spiral antenna. So if I see this spiral antenna maybe airborne if I consider. So in that case here you can see the radiation pattern is a figurate pattern like this. So it is a bi-directional radiation pattern I can see here. But in case if the same spiral antenna is backed by some cavity as shown in the figure B. If the spiral antenna is backed by cavity the lower lobe is suppressed and will get only unidirectional radiation lobe like this. There are different types of spiral antennas. Out of that the first one is Archimedean spiral antenna. It is a popular frequency independent antenna. We have talked about the frequency independent antenna in previous slides. It has two arms. Each arm of Archimedean spiral is linearly proportional to the angle psi. It has two arms and each arms are proportional to the angle psi and which is described by the equation r is equal to r0 psi plus r1 and r is equal to r0 psi minus pi plus r1 where r1 is the inner radius of the spiral. r2 is the outermost radius of the spiral. W is the width of the spiral and s is the spacing between the spirals. So spacing s can also be given as r2 minus r1 upon 4n where n is the number of turns of this spiral. So here it is shown diagrammatically whereas its actual spiral antenna is shown here. So Archimedean spiral antenna is one of the popular spiral antennas. Another type of spiral antenna is a log periodic spiral antenna. The log periodic spiral antenna also known as equi-angular spiral antenna. Each arm defined by the pole equation that is r equal to r0 e raise to a5. r0 is a constant which controls the initial radius of the spiral and a is a parameter which controls the rate at which the spiral antenna grows with angle. So a is the rate with which the spiral antenna grows with the angle. So here you can see in the log periodic spiral the spiral antenna's width is increasing like this. The width is increasing. So this is the actual antenna. This is diagrammatically it is shown. Another type of spiral antenna is cavity-backed spiral antenna. They are commonly used in aircraft and other metallic backed object. As such it is desirable to design the antenna to be cavity-backed. So why it is needed to be cavity-backed antenna is it is backed by some metal. So due to this it isolates the spiral antenna from what is behind it. So it is mounted on the objects without worrying about returning antenna. So if it is cavity-backed we can mount it anywhere. Then it comes to the applications of spiral antenna. Spiral antennas are widely used in defense industry for sensing applications where very wideband antennas that do not take up much space are needed. That means small size where it is needed in that case when for wideband applications spiral antennas are used in the defense and sensing. Other applications of spiral antenna include GPS Global Positioning of Satellite where it is advantageous to have right-handed circular polarized antenna RHCP. Spiral array systems are typically used in high-gain applications such as high data rate satellite and terrestrial communication networks also in ultra wideband communication technology. So for high data rate satellite and terrestrial communication networks for ultra wideband communication technology the spiral antenna array systems are used. Spiral antenna arrays are also used in military aircraft for the frequency range of 1 to 18 gigahertz. Spiral antennas are useful for microwave direction finding. So here pictorially some applications are shown like spiral antenna array. See here you can see this is a spiral antenna. So number of such spiral antennas are kept and which forms the array of spiral antenna which is used in missiles. Also here you can see the spiral antenna is mounted which is used for identification of friend or foe IFF warning system. In that case also the spiral antennas are used. So these are the references used. Thank you.