Abstract: In this paper an ultra-wideband Quasi-Yagi antenna is designed. According to the characteristic mode theory, the traditional Quasi-Yagi antenna is analyzed. Combined with the antenna theory, the current path is increased and the working bandwidth of low frequency is widened by using bending and grooving techniques without changing the original antenna size. The antenna size is 0.256 λ0 ×0.256 λ0 ×0.002 λ0 (where λ0 is the wavelength corresponding to the minimum operating frequency), and the operating bandwidth is 0.78 GHz ~1.58 GHz. Compared with the initial antenna, the relative bandwidth is increased from 30.0% to 67.8%. It can be seen from the front to back ratio that the antenna has good directional performance, which can meet the needs of human brain detection activities.