Analysis of modified transmission line antenna for a portable telephone

Abstract

In previous works, the authors have developed a mobile communications antenna and a high-frequency communications antenna using the modified transmission line antenna with good results. The modified transmission line antenna is a kind of low-profile transmission line antenna of half a wavelength. It has the advantage that desirable operating characteristics can be chosen in the antenna design because it is relatively easy to control impedance and gain by modifying its shape. In this paper, for the purpose of developing an antenna for portable telephones, a modified transmission line antenna is proposed for a portable telephone with this antenna mounted on a conducting box representing the body of the portable telephone. This configuration was analyzed using the wire-grid method. As a result, impedance, gain, and directivity characteristics which make this antenna suitable for portable telephones were obtained and the results are described here. Furthermore, if the conducting body representing the telephone is 100 to 160 mm long, it has a relatively small effect on the antenna characteristics, which is useful for miniaturization of the telephone body. From the calculated results and measurement results, the effectiveness of the wire grid analysis method is verified. Finally, the case is analyzed where the modified transmission line antenna is mounted on a folding portable telephone body, which is becoming popular. It is shown that the folding angle of the telephone does not significantly affect its characteristics.