Yoshihisa Okumura

Increasing the bandwidth of a meander line antenna consisting of two strips

Small antennas for handsets in personal communication systems are required. A meander line antenna (MLA) can be used in such systems. The input impedance of the MLA can be easily matched by use of impedance step-up and balance mode impedance loading. But increasing the bandwidth of an MLA through the use of a two-strip geometry has not been accomplished so far. A method for increasing the bandwidth of the 2-strip MLA is described. An equivalent circuit of the MLA is represented by use of the balance mode impedance as an open- or short-circuited shunt stub. On the basis of the equivalent circuit, a numerical analysis of the impedance characteristics of the 2-strip MLA is carried out. In the analysis, the contribution of the parameters of the 2-strip MLA towards increasing the bandwidth are discussed.

Numerical analysis of the radiation characteristics of the meander line antennas consisting of two strips

With the development of mobile terminal equipment, the demand for smaller handsets has increased. The size of many devices are decreasing, however, it is difficult to reduce the size of an antenna, that is, there are problems of impedance matching, bandwidth and radiation efficiency with down sizing. Currently, in a personal radio system, a whip antenna, a planar inverted F antenna (PIFA) and a helical antenna in the normal mode are used. The PIFA and helical antenna satisfying the condition that their sizes are smaller than /spl lambda//2/spl pi/ (1 radiansphere) are well known as a reference of a small antenna. The PIFA is not thin, while the normal mode helical antenna needs a matching circuit because of the small radiation resistance. The radiation characteristics of a meander line antenna are described and a method of improving the matching by using two strips are shown. The impedance matching is considered on the basis of its equivalent circuit and an analysis of the current distributions of the meander line antennas is carried out.

Increasing the bandwidth of a normal mode helical antenna consisting of two strips

A normal mode helical antenna (NMHA) is usually used for handsets in personal communication systems. As the small NMHA has low radiation resistance, it requires a matching circuit. The matching circuit has loss and the radiation efficiency decreases. An NMHA consisting of two wires (the 2-wire NMHA) has been suggested (Noguchi et al., 1997). The radiation impedance of the 2-wire NMHA can be matched by itself to the characteristic impedance of the feed line. The impedance matching is carried out by use of current modes that include balance and unbalance modes. However, it is difficult to increase the bandwidth of the 2-wire NMHA because reactance components of the antenna can not be eliminated by reactance in the balance mode of two wires. A small meander-line antenna of two strips has been suggested to increase the bandwidth of the antenna without a matching circuit (Noguchi et al., 1997). The reactance component of the antenna can be eliminated by reactance in the balance mode over a wide frequency range. In this paper, a small NMHA consisting of two strips (the 2-strip NMHA) is presented. The method of increasing the bandwidth is applied to this antenna.

Impedance characteristics of two‐wire helical antenna in normal mode

A helical antenna in normal mode is used as a small antenna for handsets in personal communication systems. When the diameter and axial length of the helical antenna is small compared with the wavelength of the operating frequency, the antenna works in normal mode and has a radiation pattern and linear polarization the same as a monopole antenna. Because the radiation resistance of the antenna is low and the Q-factor is high, the impedance characteristic is a problem. In this paper, a normal-mode helical antenna consisting of two wires is treated and the impedance characteristics of the antenna are analyzed. It is possible to use currents on the helical antenna in balanced and unbalanced modes by use of two wires of the antenna. The analytical results show that the radiation resistance in the unbalanced mode as the radiation mode can be stepped up, and the reactance in the balance mode as transmission-line mode can be used for impedance matching.

Analysis of aperture fields for shaped beam antennas by use of Gaussian beams

The authors present the analysis of the aperture distributions corresponding to a desired shaped beam by the synthesis of Gaussian beams. An advantage of Gaussian beams is that the field distribution in the beam waist and its near plane can be easily obtained. Numerical results on the aperture fields for shaped beam antennas are shown.<<ETX>>

Reflection and transmission characteristics at the ground surface by the electromagnetic plane waves from under ground

In recent years, observations of anomalous electromagnetic emissions possibly related to earthquakes have been carried out with the aim of earthquake prediction. The observation points are almost near the ground surface, and the receiving frequencies are less than several megahertz. As the attenuation is strong in the ground, and as the observed data are few as yet, these data are not entirely acceptable. Some basic data are presented which may help to clarify this situation. Numerical results on the reflection and transmission coefficients are reported. The planes of constant phase and constant amplitude, the phase velocities, and the propagation directions are discussed.<<ETX>>