SAR imaging of thick composite structures using circular aperture probe

Composite materials are commonly utilized in the manufacturing of many critical aerospace components. While these composites exhibit competitive properties compared to other materials, they are prone to subsurface defects which could compromise their structural integrity and potentially lead to catastrophic failures. Therefore, monitoring the integrity of these composites during their lifecycle becomes of paramount importance. Microwave and millimeter wave non-destructive testing techniques have proven to be effective in inspection of these materials. However, inspecting thick composite structures remains a challenge for conventional near-field non-destructive testing methods. In this paper, a Teflon-loaded circular waveguide operating from 22 GHz to 26 GHz is used to produce synthetically focused image of thick five-layered dielectric composite structure. Additionally, the same composite structure is also imaged by a conventional K-band rectangular waveguide and the obtained image is compared to the one produced using the circular waveguide. Finally, the synthetically focused images are compared with the images obtained using near-field imaging. It is demonstrated that the circular waveguide produces better quality images with clear indications of the defects in the composite sample compared to the rectangular waveguide.