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A feeding method is proposed for small helical antennas with diameters of about 1/80 to 1/20 wavelength. The present feeding method consists of excitation of a helix with a total length of about 1/4 wavelength and with its lower edge grounded by an open-ended center conductor oriented coaxially to the helix. In this paper, it is shown that matching with a 50-Ω feed system can be accomplished even when the helical diameter is varied in the same feeding method. The gain and the bandwidth characteristics of the ground plane versus diameter are discussed. As an example, a gain of -7.2 dBd (with respect to the dipole antenna) on the ground plane is obtained when the helical diameter is 1/46 wavelength and the height is 1/56 wavelength. Like the monopole antenna, the main radiation pattern is omnidirectional vertical polarization in the horizontal plane and figure-eight in the vertical plane. When this antenna is installed on a transmitter case, the gain is about -4 dBd. When installed on the transmitter case, the antenna radiates the orthogonal polarization component. The null of the main radiation pattern in the zenith direction can be compensated by this polarization. The radiation characteristics of the antenna are numerically calculated by the method of moments and are verified experimentally. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(3): 33–41, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20324 [ABSTRACT FROM AUTHOR]

A design method is presented for a uniform array made of half-wavelength dipoles placed in parallel with the mutual coupling between elements taken into account. In the design, the induced electromotive force method is used. By using the variations of the input impedance and the current due to change of the element length, the desired current value is approached. In addition, the reactance component of the input impedance is suppressed. Numerical calculations by the moment method are carried out with the obtained element length. The results are confirmed and also verified by experiment. The experimental results demonstrate that the proposed design method is useful. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(1): 1–15, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10054 [ABSTRACT FROM AUTHOR]

In this paper a simple calculation method for estimating the shielding effectiveness of a conducting spherical cell is proposed. The spherical cell has a small size compared with the wavelength. The shielding effectiveness of a conducting spherical cell with a small antenna set in it is analyzed by approximated equation using the F matrix of the distribution circuit theorem. The calculation results using the proposed approximated equation coincide with an error of a few decibels compared with the results of the rigorous solution of the spherical wave equation. Good agreement is also obtained with the experimental results. The proposed calculation method without Bessel and Hankel functions included in the rigorous solution is very easy to estimate the shielding effectiveness. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(1): 84–90, 2001 [ABSTRACT FROM AUTHOR]

The airborne antenna may be considered to be small since it is mounted on a conductor which is large compared to the wavelength and its radiation pattern has to include the diffracted fields from the conductor. Moreover, thick dielectric coating on the body, which is used as insulating material, causes a serious distortion of the radiation pattern; and this is confirmed through measurements that the effect is quite large. This paper proposes a method of analysis where the effect of dielectric material on the radiation pattern is estimated analytically using a simple plane conductor model. Analysis is based on the excitation of the surface wave which propagates inside the dielectric sheet and making assumptions about the radiation mechanism, its diffracted field is calculated by the uniform theory of diffraction (UTD) method. The availability of this method of analysis was confirmed by comparing the measured results of this model with the calculated values. From the measured and analytical results, it was confirmed that a large effect is produced in the axially back direction of the rocket due to dielectric coating on the body. [ABSTRACT FROM AUTHOR]

A radar reflector with controllable reflectivity has been proposed by one of the present authors. This reflector is capable of electrically controlling its radar cross section. By using this reflector as a target, information including an identification code at a reflector site can be sent to a radar site by the modulation of reflected echoes. Thus, we can build up a passive telemetry system consisting of radar, the reflectors and a demodulator device. Since the reflector is a passive device, it does not interfere with other communication systems. Furthermore, the system at the reflector site uses little power because it has no transmitter. Experiments on the ground and on the sea have been conducted successfully. This paper presents a method of acquiring data in the case of a rotating radar antenna, transmission codes which eliminated the inverting effect of the reflection on the sea, and a type of demodulation process. The evaluated result of this system from outdoor experiments is also presented. The reflector was put into practical use as a traffic monitoring system and tested over a tong period. From the experiment- at results it was discovered that the demodulation method using automatic threshold selection based on the probability distribution was the most successful. Hence, from the foregoing, we are able to conclude that the system using the radar reflector with controllable reflectivity is useful in passive telemetry. [ABSTRACT FROM AUTHOR]

Recently, many conducting plastic shielding materials have been retailed in connection with environmental electromagnetic problems. This paper proposes a method of measuring the shielding effectiveness using a spherical cell as a means of evaluating shielding effectiveness. The shielding effectiveness against electric and magnetic fields can be evaluated by the proposed method. The measured values provide quantitative information for practical shielding because the cell forms a practical shield housing of circuits or parts. It is easy to handle theoretically since we use a spherical shape. Favorable agreement is obtained between the results of theoretical analysis and values of experimental measurements. Gradual decreases of the shielding effectiveness occurred in the high-frequency region against the electric fields and in the low-frequency region against the magnetic fields for a material with low electrical conductivity. Sudden large decreases of the shielding effectiveness against the electric and the magnetic fields due to resonant effects were observed when the diameter of the sphere becomes close to the wave-length based on numerical calculations. It was found that in designing shielding housings, careful attention must be given to their dimensions. [ABSTRACT FROM AUTHOR]

A radar reflector with bi-directional communication capability is presented. The reflector consists of a Luneberg lens and a reflecting plate combining a microstrip antenna and a switching circuit, which is placed at the focus of the lens. The reflector is capable of transmitting information from a reflector site as well as receiving signals from a radar station. Characteristics of the reflector are analyzed by the moment method using a wire-grid model. The results are confirmed by experimental measurements. An experimental model of the reflector yields an antenna gain of 26.5 dB and a modulation ratio of reflectivity of 13 dB. A passive telemetry system covering a wide area can be built with a radar station and a group of these reflectors. Alternatively, a Luneberg lens having may reflecting plates can respond to plural radar stations simultaneously and independently. [ABSTRACT FROM AUTHOR]