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Radiation Characteristics of a Side Fire Helical Antenna
Radiation characteristics are presented for a side fire helical antenna. The antenna consists of a vertical conducting cylinder, 5 wavelengths long, and two conducting helices, of larger diameter, wrapped around it, with opposite pitches, starting at half of the cylinder length, the feed point, and progressing toward the ends. It radiates mostly a horizontal polarized field. The horizontal pattern is approximately circular and the vertical forms a beam of 12 degrees (gain 5). The bandwidth is over 10%. It has only one feed point on the 5 wavelength aperture. It is very easy to build, self supporting, easily stacked to form an array and can also be used as self-diplexing. An exponentially decaying traveling current is assumed on the helices. The Fourier transform method for reducing the problem to a two dimensional one was used successfully. Computed and experimental data are presented showing good agreement.
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