An Isophase-Based Life Signal Extraction in Through-the-Wall Radar
In this letter, we propose an isophase-based method for human life signal extraction using a stepped-frequency continuous-wave through-the-wall radar. Isophase is the line connected by points of the same phase value in the slow time range map and is a key feature to distinguish a stationary human from mechanical vibrating targets. First, the isophase is introduced and associated linearly with human life signal, and the linear coefficient is greater than 1. Then the limitation of the isophase is discussed. Finally, the isophase is extracted by the edge detection method. The isophase expands the micromotion range and therefore robust to noise. Due to the sudden change from <inline-formula> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">$- \pi $ </tex-math></inline-formula>, the isophase can remove outliers effectively. The simulation results verify its advantages over the amplitude peak locus. The experiments done with a stationary human and a rotating fan behind a wall show that the proposed method can extract human life signal effectively and precisely.