Methodology for accurate free-space characterisation of radar absorbing materials

Although it is now some 50 years since the first practical application of radar absorbing materials (RAM), there does not seem to have been a comprehensive discussion in the literature of the optimum methodology for characterising such materials using free-space methods, the sources of error that arise in a typical laboratory measurement facility and, perhaps most important of all, an estimate of the measurement uncertainties. A previous paper started to address these problems by discussing calibration techniques for a vector network analyser system used for making complex reflectivity measurements on RAM. It is the aim of this paper to extend the discussion to include the use of a scalar measurement system (since these are still in common use), the factors affecting the design of a free-space reflectivity arch and the verification of measured reflectivity data