 Hello and welcome to a video lecture on Satellite Tracking. Myself, K.R. Biradar, Assistant Professor, Department of Electronics and Telecommunication Engineering, Wall Change Institute of Technology, Solapur. First we shall see the, what are the different learning outcomes for this video. At the end of this video, you will be able to classify different types of satellite tracking techniques. Before looking into actual topic, recall what are the different subsystems of earth station. Pass the video, memorize and write your answer. I think you might have written the answer. The different subsystems of earth stations are transmitter, receiver, antenna and last one is tracking subsystem. In this video, I am going to discuss the last one that is satellite tracking subsystem. What is satellite tracking is all about. It is a process in which the position of north of orbiting satellite is monitored. Its various uses are visual, observation, active or passive radio communication are simply follow the current location and ground track of the satellite. Architecture of satellite tracking. The figure shows the block diagram of satellite tracking system. The earth station antenna makes use of beacon signal to track itself to the desired position in both azimuth and elevation. The auto track receiver see the diagram drives the tracking correction data or in some cases the estimated position of the satellite. The estimated position is then compared with the measured position in the control subsystem whose output feeds the servomechanism. In the case manual track method, the desired position of satellite in the two orthogonal axis are set by the operator whereas in the program track method the desired position of satellite in the two orthogonal axis are set by the computer. The difference in actual and desired antenna positions produces error signal. This error signal is used to drive the antenna. Tracking techniques. The various types of tracking techniques are low switching first one, second one is sequential lobing, third one is conical scan, fourth one is mono pulse technique and last one is step track. First one we shall see now low switching. In low switching tracking technology, here antenna beam is rapidly switched between two positions around the antenna axis in a single plane as shown here. The two amplitudes that is satellite eco amplitude one and satellite eco amplitude two as shown in the diagram are compared for the two low positions, position one and position two. The difference between the two amplitudes is the indication for locating the target with respect to the antenna axis. Here target is the satellite. When the object to be tracked is on the axis the eco amplitudes for the two positions of the beam are equal and then the difference between the two amplitude that is amplitude one and amplitude two is zero. When the object is on one side of the antenna axis the amplitude and the sense of the difference signal tells how much and what side of the antenna axis the object is located. The difference signal then we use to generate correction signal with the help of servo control and the loop is used to drive the antenna to bring the object onto the antenna axis. Next one is sequential lobing. In sequential lobing the beam is slightly shifted off the antenna axis. The squinted beam is sequentially placed in four discrete angular positions around the antenna axis as shown in the figure. The angular information about the object to be tracked is determined by processing several eco signals. The error information is contained in the eco signal amplitude variations. The squinting and beam switching is done with the help of electronically controlled feed and therefore can be done very rapidly practically simulating simultaneous lobing. Next one is conical scan. This is similar to sequential lobing except for the difference that in case of conical scan the squinted beam is scanned rapidly and continuously in circular path around the axis as shown in the diagram. The object to be tracked is of the antenna axis the amplitude of the eco signals varies with antenna's scan position. The tracking system senses the amplitude variations and the phase delay as function of the scan position to determine the angular coordinates. The amplitude variation provides information on the amplitude of the angular error and the phase delay indicates direction. The angular error information is then used to steer the antenna axis to make it coincide with the object location. This technique offers good tracking accuracy and an average response time. It is however not in common use. Next one is monopulse tracking. There are two types of monopulse tracking technology. First one is amplitude comparison monopulse. Second one is phase comparison monopulse technique. In this video I am going to discuss only amplitude comparison monopulse technique. Amplitude comparison monopulse technique. In case of amplitude comparison monopulse the antennae use four fields placed symmetrically around the focal point. Figure 5A shows the wave fronts of the issued signal for to be tracked satellite being on antenna axis. Similarly, figure 5B shows the wave fronts of the issued signal for to be tracked satellite being off antenna axis. In the on antenna axis the wave front will be focused on to a spot on the antenna axis as shown in figure 6A. For off axis location of satellite the focus spot will also be off the antenna axis as shown in figure 6B. As a consequence in the case of satellite being on axis the amount of energy falling on four fields representing four quadrants quadrant A quadrant B quadrant C quadrant D will be same. When the satellite is located off axis the amount of energy falling on four fields will be different depending on which quadrant around the antenna axis the satellite is located. Figure 6A to E shows five different cases figure 6A shows satellite is on the axis figure 6B shows satellite located above antenna axis with same azimuth location figure 6C shows satellite located below antenna axis with the same azimuth location figure 6D shows satellite located towards right of antenna axis with same elevation location figure 6C shows satellite located towards left of the axis with same elevation location. Last one is step track in case of step track antenna axis are moved in small incremental positions in order to maximize received signal strength it is simple and low cost. It is best suited for small and medium earth stations this technique is susceptible to amplitude perturbations caused by signal fading. Accuracy of tracking is determined by step size and signal to nice ratio. These are the some of the references I referred to prepare above PPT. Thank you.