An improved planar UWB antenna based on hexagonal structure is designed. By introducing the defect structure to the ground plane of the regular hexagonal antenna, the -10dB impedance bandwidth of the antenna is 3.0-19.2GHz, covering the frequency range of UWB communication and higher frequency range. The antenna has a simple structure and a size of 26mm*31mm*1.6mm. The pattern and impedance matching in the whole bandwidth range meet the requirements of UWB communication.