The authors have developed a Doppler-type ground penetrating radar (GPR) unit to find survivors buried in houses that have collapsed in an earthquake or other disaster. The purpose of this study is to improve the dynamic range of radar consisting of an array antenna so that it can quickly identify far-off survivors under rubble. The authors focused on time-variable elements from the respiration of a survivor awaiting rescue in order to remove clutter components, such as the rubble. A healthy individual's respiratory frequency varies from 0.2 Hz to 0.5 Hz, so the authors propose a signal processing method to extract these frequency elements in an effective manner. The authors also examine the effectiveness of this method experimentally.