Seeing through walls with a self-injection-locked radar to detect hidden people

This paper presents the use of a self-injection-locked (SIL) radar operating in the 2.4-GHz ISM band for seeing through walls to detect hidden people. This goal is achieved for a subject standing still, breathing normally, and located between a wood board and wood wall with glass windows. In the experiment, the SIL radar scans using its carrier frequency to obtain position information about various objects based on the echo signals. As a result, the standing subject was identified owing to the respiration signal that can be fast extracted from subtracted spectra.