Significance of the Higher-order Modes to the Near-field Calculation of the Spherical Helix Antennas

The radiation characteristics of spherical helix antennas (SHAs) such as the Q factor and the radiation efficiency were analyzed by both numerical [1] and analytical [2] method such as the vector spherical harmonics (VSH). The VSH enables one to derive theoretical results. However, previous study with the VSH were restricted to the current distribution of the lowest TM and/or TE modes on the whole spherical surface. The effect of the higher-order modes was, thus, ignored in the conventional theoretical model. In this summary, the significance of the higher-order modes is demonstrated by calculating the near-electric field of the SHA with the VSH.