Abstract: For an ultra-wideband(UWB) system,the antenna with wide bandwidth to operate from 3.1 to 10.6 GHz is required.In this paper,four types of wideband planar monopole antennas are presented:planar circular monopole antenna,orthogonal planar monopole antenna,planar monopole antenna with dual frequencies and orthogonal planar monopole antenna with dual frequencies.The second antenna gives omni directional radiation pattern with wide bandwidth,the third and fourth ones have dual frequencies and broad bandwidth at both resonant frequencies.The,radiation patterns of the fourth antenna over all frequency range are almost omni-directional in the horizontal plane.