 myself Piyusha Shedkar, Electronics and Telecommunication Engineering Department. In this video, we will see the topics related to the antenna array types, collinear and parasitic antenna array elements. These are the learning outcomes for today's session. At the end of the session, students will be able to define collinear and parasitic antenna array whereas they will be able to explain the Yagi Uda antenna. At the end of this session, students will be able to define collinear and parasitic antenna array. They will be able to explain Yagi Uda antenna. These are the contents. Before going to start an antenna array types, you can pause video here for a second and recall that what is the meaning of an antenna array and all the types of an antenna array. Yes, array is an assembly of antenna elements arranged in an orderly fashion. Generally, these elements are identical. What are the types of an antenna array? First is the broadside array antenna, end fire array antenna, collinear array antenna and the last one is the parasitic array antenna. In the last session, we have discussed the broadside and end fire array antenna. In today's session, we will see the information related to the collinear array and the parasitic array antenna. So, what is the collinear array? The collinear array in which the elements are arranged coaxially that is along with the same axis. These antennas are either mounted end to end in a single line or these are stacked over one another and depend upon the arrangement of these elements it can be defined in two different ways. It is also like a broadside array antenna because the elements are fed equally in phase related to the currents. But the radiation pattern of a collinear array has the circular symmetry with its main loop everywhere normal to the principal axis and this type of the radiation is obtained for that it is called as the omnidirectional array. Therefore, the collinear array is also known as the broadcast or omnidirectional array. Collinear array consists of the two elements a simple collinear array having these two elements or you can increase the number of elements for the collinear antenna array. The performance characteristics of the array does not depend directly on the number of elements used to form the antenna array. The collinear array provides the maximum gain when the spacing between each element is considered in the order of 0.3 lambda to 0.5 lambda. By providing the spacing between these elements you can get a maximum gain and the directivity of an antenna. Now, the collinear array of an identical element the five control points are to be considered to get a overall pattern of the antenna is used. So, first control point is the geometrical configuration of an antenna in case of the linear or the circular polarization. Relative displacement is considered between the two elements whereas, the excitation amplitude and the phase of the individual antenna also will be considered. Relative pattern of an individual element is also considered as the control point to decide the pattern of an antenna. So, this is the figure shows for the collinear array. The first figure, figure A shows the collinear array which is arranged in the vertical manner. So, if you observe this figure these are connected vertically and in the second figure these are connected horizontally. Here it is placed one by other and these are placed one after the other one. So, this total length is denoted with the capital L and the direction of the maximum radiation will be observed which is perpendicular to the array axis. In horizontal collinear array, again it is the direction of the maximum radiation and the array axis is placed horizontally. These two are the types of the collinear array defined as vertical and horizontal collinear array. So, collinear array one in this collinear array, the length of the collinear array is increased the directivity of the array is antenna array is also increased. If the number of array elements are more that is more than 2, so this will be increased to keep the current in phase in all the elements it is essential to connect the phasing stuffs between the adjacent elements of an antenna array. A collinear array is usually mounted vertically to increase the overall gain and to increase the directivity in the horizontal direction. Also the stacking of the dipole antennas in the fashion of doubling their number with the proper phasing between them produces a 3 dB increase in the directive gain. What is the parasitic array? Parasitic array in some way it is similar to that of the broad side array antenna, but only one element is fade directly from the source and the other element are electromagnetic, coupled. These are not connected physically, but these are coupled to each other electromagnetically. Feed element is also called as the driven element while the other elements are called as the parasitic elements. So, the parasitic elements are defined as radiator or the reflector depend upon the function of each element. In a radio antenna, a passive radiator or parasitic element is a conductive element, typically it is a metal rod which is not electrically connected to anything else. So, this figure shows the parasitic array antenna. So, first one is the reflector, middle one is the driven element, driven element is placed at the center one whereas, one of the side is placed with the parasitic element that is directus. So, number of directus can be increased depend upon the applications. In this direction the maximum radiation will be possible by using the directus and this is the antenna array axis whereas, in case of the broad side antenna, the major lobe will be observed perpendicular to the antenna array axis and this is the reflector is used to reflect the signal in undesired direction. So, what is parasitic array an element is lengthened by 5 percent to the driven element which acts as a reflector. So, this is the length of the reflector will be more than the driven element, driven element is placed here. The signal will be fed to the driven element whereas, at the back side reflector is used which having the length is 5 percent longer than this driven element. Whereas, the directus are connected after this driven element these are having the length is 5 percent shorter than the driven element and the reflector makes the radiation maximum in perpendicular direction towards the driven element and the director helps in making the maximum radiation perpendicular to the next parasitic elements. Thus, you can define the working of each element for the parasitic array antenna. When the parasitic element is placed so that it radiates away from the driven element it is known as the director whereas, the parasitic element is placed so that it radiates towards the driven element then the parasitic element is a reflector and combining this reflector and the director with the driven element which causes a decrease in the back radiation and an increase in the directivity that is it is used to reduce the signal in the backward direction it is used to reflect the signal in unwanted desired direction. So, which results in a main advantages for the parasitic array it is a unidirectivity element and it will be useful to increase the gain. The directivity pattern resulting from the action of parasitic elements depends on the two factors. The first factor is the tuning factor which is determined by the length of a parasitic element and the other factor is nothing, but the spacing provided between the parasitic and the driven elements. Again one of the parameter is considered, but it is in the lesser degree that is also depends on the diameter of the parasitic element diameter is concerned to the effect of the tuning factor. Now, the example of the parasitic element parasitic array antenna is the Yagi Uda Antina. So, this figure shows the Yagi Uda Antina in the first figure you can observe the number of elements are 1 2 3 4 and 5 out of these 4 5 elements the 3 are the directors whereas, the this one is the driven element and this is nothing, but the reflector driven element is nothing, but the radiator. So, the director and the reflector in the Yagi Uda Antina are usually welded to a conducting rod this is the conducting rod or a tube at their contents. Since the driven element is at the center fed it is not welded to the supporting rod and the center impedance can be increased by using the folded dipole antenna as a driven element. So, second figure shows this is the driven element which is called as the folded dipole antenna instead of using a single simple dipole antenna you can use the folded dipole antenna to increase the center impedance. Now, the Yagi Uda Antina has suppose the 3 directors as shown in the above figure it is used to get the greater gain when the number of parasitic elements are greater. If the greater the number of such elements have a narrower frequency response as well as the narrower beam width which is used to increase the directivity of an antenna. But for this the proper adjustment of the antenna becomes critical and the gain of an Yagi Uda Antina does not increase directly with the number of elements. For example, a 3 element Yagi array is considered with the relative gain of an 5 dB adding another directors results in just 2 dB increase in the previous value. So, the additional directors have a less and very less effect on the gain of an antenna. So, Yagi Uda Antina used by the military services it operates at frequencies 12 to 50 MHz it consists of two separate arrays high frequency and the low frequency array antenna mounted on one frame Yagi whereas, the high frequency array consists of one reflector, one driven element and the two directors whereas, the low frequency array has the same arrangement with a one less director length of an element in the high frequency array are shorter than that of the low frequency array and the physical lengths of an elements is in the individual array are equal, but the electrical lengths can be varied by means of the tuning steps at the centre of the elements for this type of an antenna. And the array can be rotated in any desired direction by remotely controlled electrically driven antenna rotator. These are the references used for today's session. Thank you.