Wideband Spherical Helix Antenna with Multi-mode Excitation

An electrically small spherical helix antenna (SHA) with a transmission line structure was developed to achieve wideband characteristics using multi-mode excitation. The proposed antenna was designed using numerical simulation and was fabricated to validate the radiation characteristics, including the voltage standing wave ratio (VSWR) bandwidth VSWR $\leq 3$. It is found that the proposed antenna can achieve wideband characteristics for a SHA with a small Q factor. Good agreement of the impedance and radiation efficiency is observed between the numerical and experimental results. The relative bandwidth ratio was 26.0% when the antenna size was 0.08 of a wavelength.