Abstract: An ultra-wideband planar antenna with a shallow cavity for the life detection radar is designed. The antenna is composed of a pair of semi-elliptical antenna arms and fed by a compact 1:2 unbalanced to balanced transmission line transformer. For the life detection radar working in pulse mode, large bandwidth and good time domain characteristics are key requirements to ensure the signal without distortion during the antenna design. In order to eliminate the reflections from the truncated edge on the antenna arm, one semicircle is digged out from the truncated edge, which improves effectively the absorption ability of the loaded resistors by forming two sharp tips at the end and enhancing the concentration of residual current on the antenna arm end. The simulated and measured results show that the designed antenna has good time domain characteristics and is suitable for the development and requirements of the life detection radar design.