Limitations in determining absorbing-material parameters

Different techniques can be used to evaluate the potential performance of radar-absorbing material (RAM). Transmission-line methods, which are based on distributed parameter measurements, are frequently used to determine its constitutive electromagnetic parameters--ε, µ and η, χ. The thin-sample and short-circuit-open-circuit (SCOC) techniques are most common in the UHF-SHF range. Although simple, the thin-sample method cannot always be used because of thickness limitations. The SCOC method, while relieving that limitation, suffers from others less understood. This paper discusses the considerations necessary in determining the parameters of RAM, and points out some limitations which must be recognized.