Abstract: A miniaturized ultra-wideband extension Vivaldi antenna for brain imaging system is proposed in this paper.The Vivaldi antenna with sidelobe suppressor, has the performance of low frequency, ultra-wideband and high gain, which meets the demand of antenna in microwave brain detection system. The antenna size is 0.2λ×0.25λ×0.003λ, and the measured impedance bandwidth is 0.5-4 GHz, the frequency multiplier is up to 8 times, and the measured peak gain can reach 8.5 dBi at 3 GHz. The antenna shows directional radiation effect in the main operating frequency band (1-4 GHz), and the measured results are consistent with the simulation results. The antenna can be used in the medical field such as microwave brain detection system.