Abstract
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. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(12): 37–44, 1998
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