The imaging problem of low signal to noise ratio （SNR）echo is very important for ultra-wide band （UWB） through-wall radar. An improved multi-channel blind image restoration algorithm based on sub-space and constrained least square （CLS） is presented and applied to UWB radar system to deal with this issue. The high resolution of radar image is equivalent to multi-channel blind image restoration based on the improved model of the through-wall radar echo. And a new cost function is proposed to the multi-channel blind image restoration by considering the concept of sub-space as the limitation of blur identification. The proposed algorithm has all advantages of CLS and sub-space, and converts the image estimation to alternating-minimizing the two cost functions. Experimental results prove that the proposed algorithm is effective at improving the resolution of radar image even at low SNR.
