Closely wound small helical antennas

• Published in: Electronics & communications in Japan. Part 1, Communications Communications, 2005-06, Vol.88 (6), p.11-22
• Main Authors: Mitsugi, Shinichi, Takikawa, Michio, Ozaki, Kouji, Suzuki, Atsushi, Sakaguchi, Satoshi, Nogawa, Mariko, Hasebe, Nozomu
• Format: Article
• Language: English
• Subjects: helical antenna; mobile communications; normal mode; small antenna
• ISSN: 8756-6621; 1520-6424
• DOI: 10.1002/ecja.20170

With a view to applications to base stations for mobile communication, the results of experimental and conventional analysis of a small antenna are reported. The present antenna consists of a closely wound coil‐shaped external conductor and a coaxially placed inner linear conductor. The bottom of the linear conductor is connected to the center conductor of the coaxial feed and the lower part of the coil‐shaped conductor is connected to the outer conductor of the coaxial conductor. In this paper, a method of shorting the upper part of the coil‐shaped conductor with the inner conductor and of opening this part are proposed as feed methods. The antenna height of the former is about 1/26 wavelength and that of the latter is 1/80 wavelength. Both structures can be matched to a 50‐Ω feed line without any matching circuit. The present antenna attached to a small metallic case has a vertically polarized omnidirectional pattern in the horizontal plane and a figure‐8 shape in the vertical plane, similar to those of a usual monopole antenna. The measured gain is about –15 dBd relative to the dipole. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(6): 11–22, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20170