 As their focal lengths depend on frequencies, samples can be imaged at various locations along the propagation path to the imaging plane.In 2000, Igor V. Minin and Oleg V. Minin in Russia used continuous sub-terahertz solid-state generator with frequency of 75 GHz to conduct TS imaging on 3D objects and two letters "C", and "R" at different depths , which can be applied to tomographic imaging.Synthetic aperture processing (SA) differs from traditional imaging systems when collecting data.