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In array antennas, sometimes the desired radiation pattern cannot be obtained due to coupling between element antennas, reflections from the surroundings, or amplitude and phase error of the power supply circuits or failures. In these cases, it is necessary to regenerate the desired radiation pattern by estimating the excitation amplitude and phase of the array antennas. Among methods of estimation of the excitation amplitude and phase, the rotation element field vector method of element antennas is used for the phased array antenna with variable phase shifters, and the planar near-field measurement method is used for the array antennas with no variable phase shifters. The former is limited to phased array antennas, and the latter requires a large-scale scanner for the measurement and results in increased measurement time with larger-scale array antennas. In this paper, we propose a method of estimation of excitation amplitude and phase using the radiation pattern of array element antennas and the measured radiation pattern of the array antennas. Two methods are proposed here; the first method of estimation is the least-squares method using the electrical field as the measured radiation pattern, and the second is the repeating calculation method using the electrical power as the measured radiation pattern. We describe here the principle and experimental results when the first method is used, and the principle and the effectiveness of selection of the initial value for the second method is confirmed by numerical results. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(9): 102–110, 2000 [ABSTRACT FROM AUTHOR]

A small antenna with a size of 1/15 to 1/5 wavelength, consisting of a toroidal coil of fixed length, is proposed. The radiation characteristics of antennas with a limited range of turn numbers and pitch angles are analyzed by the conventional method and the method of moments. The conventional method is based on the assumption of a cosinusoidal current distribution along the antenna element. The results are then compared with experimental results. It is found that the method of moments with correction for the resonant frequency expresses well the characteristics of this small-size antenna, and that fairly good agreement between the results of the conventional method and the experimental results is obtained. For the limited size range adopted in this paper, the proposed antenna offers the advantages of having the same radiation pattern as a one-wavelength loop antenna, allowing easy matching to a coaxial line, and achieving a relatively high gain despite its small size. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(9): 10–19, 2000 [ABSTRACT FROM AUTHOR]

In the present paper, a new method of selective image amplification using two photorefractive BaTiO3 crystals is proposed and the amplification characteristics of this method are investigated. The gain of beam amplification obtained using the proposed method is almost equal to the product of the gain obtained from each crystal. The rise time of the amplification output also changes when the signal beam power changes with time. The blurring of images caused by the amplification reveals a very small region. The images obtained using this method are more distinct than those obtained using single BaTiO3 crystals, and amplified images obtained by the selective image amplification are of high quality. © 2000 Scripta Technica, Electron Comm Jpn Pt 2, 83(7): 14–21, 2000 [ABSTRACT FROM AUTHOR]