SUMMARYWith 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.
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