Microwave techniques for measurement of radar absorbing materials-a review

Summary form only given. The transmission line approach, used in conjunction with a network analyzer to measure the complex values of epsilon and mu of homogeneous as well as heterogeneous, but isotropic and thick samples, was described. For biaxial samples, a method that uses a guided-wave structure with a preferential axis, such as coaxial line or a waveguide of rectangular cross-section, was presented. The problem of measuring the permeability of anisotropic thin films by using a loop, the extraction of mu from the knowledge of the flux variation, and the validation of these results by comparison with theoretical values of mu vs. frequency that can be computed from the static measurements was addressed. The single frequency measurement techniques, based on the cavity resonance perturbation approach, for accurate characterization of small samples were discussed. Free space techniques that are useful for the measurement of anisotropic and heterogeneous materials were described. Typically, free-space measurements are carried out in anechoic chambers, involve both the reflection and transmission measurements, and yield information on absorption and surface impedance characteristics of the sample. This information is useful for designing the shape as well as the coating of complex targets with a view to reducing their radar cross section.<>