3-D Terahertz Imaging Based on Piecewise Constant Doppler Algorithm and Step- Frequency Continuous-Wave Signaling

A novel 3-D time-domain terahertz (THz) imaging system based on piecewise constant Doppler (PCD) algorithm and step-frequency continuous-wave (SFCW) signaling is proposed in this article. First, the SFCW THz imaging system configuration and the Gaussian beam propagation model are introduced. Then, the conventional time-domain correlation imaging algorithm is reviewed, and the closed-form expression of its point spread function (PSF) is derived to quantify the range and lateral resolutions. To reduce the computational complexity, a 2-D recursive imaging process based on the plane approximation of the range surface is proposed, by which the original PCD algorithm is extended for 3-D imaging with 2-D aperture synthesis. The 3-D PCD imaging principle, implementation, and complexity analysis are discussed afterward. Finally, simulation and experimental results are provided to validate the theoretical analysis of the 3-D time-domain THz imaging and demonstrate the high quality of the proposed imaging algorithm at a low computational cost.