A two‐wire spiral antenna backed by a plane reflector with an unbalanced feed system

Abstract

AbstractA novel unbalanced feed system, which achieves quasi‐antiphase excitation without a balun circuit, is proposed for a two‐wire spiral antenna backed by a conducting plane reflector. An inner spiral‐wire end is fed from a coaxial line and the other inner spiral‐wire end is short‐circuited to the reflector. The antenna is analyzed using the method of moments. The radiation characteristics are found to be comparable to those of a conventional spiral antenna with antiphase excitation. The frequency bandwidth for a 3‐dB axial‐ratio criterion is 18% (20% for antiphase excitation), with a gain of approximately 8 dBi (8 dBi for antiphase excitation). The input impedance is almost constant at 170–j30 ohms. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(4): 1–9, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10079