I. Introduction
It is difficult to detect human targets hidden in buildings or behind walls in the process of urban warfare, antiterrorist, and rescue after disasters. Compared with other penetrating detection technologies [1]–[3], there are four obvious advantages of impulse through-wall radar (ITWR) [4]–[7]: 1) it is quite simple for the transmitters and receivers with no such complex modulation and demodulation modules; 2) signal attenuation is small when penetrating walls or other media; 3) detection blind area is small because emitting impulse signal takes a very short time; and 4) signal processing is simple without pulse compression and other operations. With these advantages, the ITWR technology has become a research hotspot [8]–[11].