Microwave four parameter material characterisation and its application in the design of wideband radar absorbers

It has been shown previously by Crossley, Chambers and Bennett (1988) that a proper characterisation of the microwave properties of lossy materials can enable the optimum design of broadband radar absorbers. The present article extends these principles to deal with the more general four-parameter evaluation where a material possesses both dielectric and magnetic loss mechanisms. The technique described is applicable to electrically large samples of lossy material and is based on the measurement of free-space reflectivity using an NRL arch. It is particularly attractive for dealing with composite materials whose macroscopic properties may well differ from those deduced using the small samples. Furthermore, as the technique involves only measurements of normal incidence reflection coefficient, no reconfiguration of the measurement system for transmission measurements is necessary. Finally, the technique is found to be tolerant of the errors in a typical measurement system