New design for ultra-wideband hemispherical helical antennas

This study investigates a new design for the hemispherical heliacal antenna that provides significant improvement in bandwidth, while maintaining essentially the same directivity and half-power beamwidth of the basic hemispherical helical design. The proposed new design utilizes a wideband impedance matching technique and replaces the wire radiating element with a tapered metallic strip. This design provides an overall measured bandwidth of 24% at a center frequency of 3.35 GHz. Over this bandwidth, the axial ratio is les 3 dB, the VSWR is les 2 relative to a 50-ohm reference impedance, the directivity is about 9 dB, and the half-power beamwidth is about 70deg. This compact low-profile antenna is of considerable interest in ultra-wideband wireless communication systems.