A TEM horn antenna applied to ultra-wideband radar for human being detection is designed. The proposed TEM horn antenna is simulated by CST MICROWAVE STUDIO software. And the influences of antenna structural parameters on antenna pass band are discussed and analyzed. Finally, the prototype of the proposed antenna is manufactured and measured in the microwave anechoic chamber. The simulation and experimental results show that the working frequency of the proposed antenna is from 0.71 GHz to 3.25 GHz with reflection coefficient less than -10 dB (bandwidth ratio 4.6∶1). The antenna front-to-back ratio is greater than 14.0 dB at 2.4 GHz, and the antenna gain is greater than 9.0 dBi within the pass band. So the proposed antenna has characteristics of ultra-band, high gain, and strong directional radiation.