An omnidirectional and low-VSWR antenna for ultra-wideband wireless systems

This paper proposes an omnidirectional-in-azimuth, low voltage-standing-wave-ratio (VSWR), and easy-to-construct antenna for ultra-wideband (UWB) systems. Most wideband antennas do not simultaneously meet omnidirectional and low-VSWR requirements, essential for applications such as UWB channel sounding. The proposed antenna consists of a circular ground plane and a teardrop that is defined as a combination of a finite cone and a sphere to be inscribed inside the cone at lite cone base. This antenna can be considered either as a rounded finite monocone antenna or as a simplified volcano smoke antenna. Assuming 50-Ω excitation, the optimum half-cone angle is 48° which gives the lowest maximum VSWR between 2 and 10 GHz. A prototype antenna was constructed and its VSWR and radiation characteristics were measured. The proposed antenna shows lower VSWR than a finite monocone of the equivalent size across most of the bandwidth. There was a good correlation between the measured and the calculated radiation patterns observed.