An Ultra-wide Band Omnidirectional Monopole Antenna

Ultra-wide band (UWB) wireless communication occupies a bandwidth from 3.1 to 10.6 GHz to achieve high data rate over a short distance. Two competing schemes, namely multiband orthogonal frequency-division multiplexing (MB-OFDM) and direct sequence ultra-wide band (DS-UWB) are proposed to make use of the ultra-wide bandwidth. In this paper, an omnidirectional UWB monopole antenna is proposed. It was constructed by symmetrically wrapping a planar monopole antenna, to give almost omnidirectional radiation in both strength and phase delay over the UWB band. Impedance matching was kept good. The return loss of the antenna was examined numerically and verified experimentally. Antenna radiation characteristics in different azimuth angles were investigated numerically. Time-domain analysis was carried out for the monopole antenna under the content of both the DS-UWB and MB-OFDM schemes. Radiated waveforms in different directions were compared, and found to be almost independent of the azimuth angle. It demonstrated that the antenna is suitable for UWB applications where an omnidirectional property is required.