Abstract: In order to improve the radiation gain of the traditional Vivaldi antenna in low frequency band to meet the needs of microwave detection of brain activity, an antipode-type Vivaldi antenna with dimension of 100 mm× 120 mm× 2 mm is designed. The radiation characteristics of the antenna is improved by adopting the method of loading a circular reflector on the ground layer,while the size of the original antenna is not changed. The results show that the VSWR of the antenna in the 1-3 GHz band is lower than 2, the gain is higher than 4 dB which is increased by a maximum of 3 dB compared to the gain without the reflector in the frequency band. The antipode-type Vivaldi antenna is fabricated and measured, the measured results agree well with the simulated, so that the antenna can be applied to human brain activity detection and other fields.