Precise characterization and design of composite absorbers for wideband microwave applications

This paper presents a novel measurement, characterization, and design procedure for practical broadband absorbers. A multi-layer absorber ideally suited to broadband communication applications has been designed, optimized and analyzed. A newly developed and precise transmission-reflection (T/R) based waveguide measurement technique has been used to determine the frequency dependent complex permeability and permittivity of a variety of dielectric and magnetic absorbers in the microwave spectra. These materials have been accurately characterized for the first time across eight frequency bands from 2 to 40 GHz. The constitutive parameters have then been analyzed to design a 2-18 GHz multi-layer composite structure that offers minimum specular reflection and maximum absorption of electromagnetic energy across the bandwidth. To verify the absorption performance in wideband applications, the multi-layer structure has been inserted in the lossy cavity of a 2-arm Archimedean spiral antenna and simulated for its radiation patterns. The optimal thicknesses of each absorbing layer have been determined for this specific broadband application. Finally, the reflection properties of the composite structure have been experimentally verified using the T/R measurement technique.