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Gain of aperture antennas focusing in zone of near radiated field

Keywords:

Yu.E. Sedelnikov – Dr. Sc. (Eng.), Professor, Department «Radio-Electronic & Telecommunication Systems», Kazan National Research Technical University named after A.N. Tupolev. E-mail: sed@ru.kstu-kai.ru O.V. Potapova – Ph. D. (Eng.), Associate Professor, Department «Radio-Electronic & Telecommunication Systems», Kazan National Research Technical University named after A.N. Tupolev. E-mail: potapova_olga@bk.ru


Basic laws of the aperture theory of antennas became now classical. They are widely used in practice and in educational literature. Comprehensive researches of fields focused in near radiated zone weren\'t conducted. However some results of private character was received. Recently using electromagnetic fields at distance approximate equal size of aperture causes increasing interest. Therefore necessity of extending classic aperture theory of antennas on near radiated zone is appear. Gain is one of basic characteristics of classic antennas theory. In paper the common notion of gain is entered for homogeneous space. It notion is correct for for near radiation and far zones. In a number of practical applications there is dissipative object located in near radiation zone. Therefore in this paper the notion of gain extended for nonhomogeneous space. The linear antenna was used as a basic radiator like in classic theory. Focusing point (x0, y0, z0) was located on some distance symmetrically concerning a radiator. Dependence of gain from geometry\'s and aperture\'s characteristics shows a number of essential differences from case of focusing in far zone. Most important of differences are listed below. In case of constant amplitude of exciting currents focusing on distances approximately equally with aperture is characterized by limited value of gain. Extremely achievable value of gain is exists for each relative focusing distance z0/L. Extremely value of gain corresponds the optimal electric size of aperture Lopt/λ. The optimal amplitude distribution which provide the extremely value of gain is exists for each of relative focusing distance z0/L and directional pattern of elementary radiator. Possibility of focusing remains in mediums with losses (to values of αλ ~ 1…2). Value of focused gain significantly decrease in mediums with losses. Extent of decrease depends on type and polarization of an elementary source in an aperture. Focusing in any point of space of near radiation zones can be realized by means of a choice of the corresponding phase distribution. Optimal amplitude distribution providing the maximum gain exists for each focusing point and attenuation coefficient. The entered indicator – gain allows to characterize quantitatively efficiency of focusing in a zone of the near radiated field. The determined general consistent patterns in behavior of KND give the chance to carry out conscious choice of mediums parameters, of electrical size of aperture and of amplitude distribution.
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