High resolution ISAR radar for nondestructive testing

The FMCW radar described was developed to to explore techniques for imaging objects or flaws inside solid bodies. The system produces high resolution radar images. The system bandwidth is 7.3-10 GHz typically resolving targets about 2-3 cm apart depending on the dielectric constant of the material. FMCW radar is generally used in cases were the object being imaged is at close ranges to the radar. In this case the radar is not more than a meter from the object. At X-band high resolution is achievable, and penetration is not of prime importance. We investigate the use of the system as an ISAR radar resolving cracks, flaws, or inclusions within cylindrical bodies, such as wax and concrete pillars. The radar is able to achieve this capability without the need for quadrature mixers as used in more conventional step frequency coherent systems. We revisit the theory of the conventional FMCW radar and then move on to show the processing used to generate ISAR images in dielectric materials. We describe the construction of the radar and show test results and images indicating the resolving power and sensitivity of the system. The radar was also used to evaluate several processing techniques for improving the image quality. This work includes the use of background subtraction, Widrow's (1985) algorithm and wavelet transforms.