The patterns represent far-field variation. The patterns are plotted either in polar coordinates or in linear coordinates. The power pattern is proportional to the square of the field strength pattern. The radiation patterns of an antenna are of two types: In other words, the radiation pattern of an antenna is a graphical representation of radiation as a function of direction.
#Antenna and wave propagation ou free#
They indicate the distribution of radiation power in free space in different angular regions. The directional characteristics are nothing but the radiation patterns of antennas. 4.2 DIRECTIONAL CHARACTERISTICS OF DIPOLE ANTENNAS In this chapter, analysis of array antennas is presented in view of their significance. Moreover, arrays provide a greater number of parameters and offer better flexibility for the designer. There is no aerodynamic drag as there is no movement of the antennas. In view of the above facts, array antennas are extremely useful in both airborne as well as ground-based applications. The scan rate can be as high as a fraction of a microsecond with digital phase shifters. Here, the antenna is fixed and only the beam is rotated. The electronic scanning can be with either phase control or frequency control. In such situations, array antennas are more useful as it is possible to scan the beam from the arrays electronically. When the antenna directs its beam in a direction to catch the target, the target will be in a different direction due to its velocity being greater and it will always be out of sight. This is due to the limited speed of the motor which in turn limits the scan rate of the antenna. Moreover, even when the antenna is on the ground, it is difficult to track the target if it is moving with a very high velocity. When such antennas are airborne, there is a considerable amount of aerodynamic drag. Here, the entire antenna system is rotated to change the direction of the beam. A radiation pattern or beam can be scanned by a single antenna like a parabolic dish using a motor. Arrays are also used to increase directivity and reduce beam width.Īntennas are used in both scan and unscan applications.
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Under these circumstances, use of arrays provides the answer.Īrrays are used to increase the gain just like cascaded amplifiers are used to increase the gain. The gain of a single antenna element is not sufficient for most applications. Exercise problems to develop self problem solving skills.Objective questions and solved problems useful for class tests, final examinations and also for competitive examinations.Transmission loss between transmission and receiver.Pattern calculations and effects of the earth.The pattern characteristics of uniform and linear arrays.
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The directional behaviour of dipoles and monopoles.