Broadband Microwave Interferometry for Nondestructive Evaluation

A broadband microwave interferometric technique for scanning near-field microscopy applications is proposed. The method is based on the association of a vector network analyzer, a hybrid coupler, an evanescent microwave coaxial probe and a precise impedance tuner built up with a high precision programmable delay line and a variable motor-driven attenuator. Advantages such as simplicity of operation, broad frequency band capabilities and high measurement sensitivity are achieved. In particular, the measurement sensitivity, the depth and lateral resolutions of the microwave microscope are experimentally verified to evaluate the performances of the system. The usefulness and versatility of the method make it also suited for a wide range of applications.