| Summary: | 碩士 === 國立彰化師範大學 === 電信工程研究所 === 97 === Abstract
In this thesis, we will study the characteristics and mechanics of the circular polarization for the helical antenna. Helical antenna can be a broadband circular polarized antenna under some specific design parameters. The characteristics of circular polarization are significantly affected by pitch size and turn number. For a right-handed circular polarized (RHCP) helix antenna with less turn number and smaller pitch size, the axial ratio of circular polarization is poor and larger than 3dB. For this kind of helix antenna, we propose a method to improve the axial ratio. Due to the traveling-wave characteristics, we add an isolated metal patch to the helix at the first turn height to suppress the LHCP with very small effects on the RHCP. Then we can improve the axial ratio of the circular polarization. When we use this method to improve circular polarization, the impedance bandwidth may be shifted because of the antenna input impedance is changed by the additional patch. Some solutions are also presented to shift back the impedance bandwidth.
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