Multilevel delay lock loop approach for wall clutter mitigation in through-the-wall radar imaging

Wall clutter mitigation is important in through-the-wall imaging (TWI) because the target information is often buried in the wall's reflections, especially when the target is located close to the wall. A new wall clutter mitigation method is proposed based on the multilevel delay lock loop (M-DLL) technique. The M-DLL structure uses the M-sequences' phase information sequentially remove the direct wave, wall's primary echo and the multiple echoes, then the rest part of the signal is used to probe and estimate the position of the target. The M-DLL can obtain the precise correlation of the signal, and the rest target echo has an enhanced signal-to-noise ratio. This method is used in TWI as a new technique, and the results compared with other methods show that it has an excellent detectability and a good anti-jamming performance.