Nonlinear correction of terahertz FMCW based on time-domain phase compensation

Terahertz frequency-modulated continuous-wave (THz FMCW) technology has become a widely used nondestructive testing tool due to its imaging and detection advantages. Nonlinearity is one of the most common problems with FMCW technology. This is due to the inability to maintain strict linearity during the high-frequency sweep process, resulting in multiple frequencies in the calculated intermediate frequency (IF) signal. This reduces the detection capability of the system, as the effective frequencies are swamped. This paper proposes a nonlinear correction method based on the time-domain phase compensation technique. The causes of nonlinear distortion are analyzed, and the corrected signal is obtained after phase compensation of the instantaneous time-domain signal. Experimental results obtained from an actual terahertz imaging system proved the effectiveness of the proposed method, achieving precise positioning of three-dimensional objects. The range resolution was improved by an order of magnitude, reaching the theoretical resolution of the experimental system. The method improves the detection accuracy of the system without the need for additional equipment.