Two novel spherical helical antennas are designed by projecting the planar equiangular spiral antenna onto hemisphere and partial sphere surfaces. Their radiation properties are analyzed by the moment method with curved basis and test function, and the curves of the voltage standing wave ratio (VSWR), gain, polarization and pattern that change with frequency are also given, respectively. It can be seen that the circular polarization band of the novel hemispherical helical antenna is broader. The gain curve of the partial spherical helical antenna is flatter and the structure is simpler.
A novel ellipsoidal helical antenna is proposed and studied in this letter. As a special instance, the hemispherical helical antennas are analyzed firstly, which indicates that the characteristics of a two-arm unit are better than that of a single-arm unit. Based on this, the ellipsoidal helical antenna, formed by changing the axial direction's dimension of the two-arm hemispherical helical antenna, is analyzed by the moment method with curved basic and testing function. The effects to VSWR (Voltage Standing Wave Ratio), gain, polarization and patterns by the axial direction's dimensions are investigated. The study results provide dependable gist to the choice of antenna format according to the practical requirements.
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