Chebyshev multi-layer microwave absorber design

Abstract

This paper presents the use of Chebychev transformer in the design of multi-layer microwave absorbers constructed of coconut shells. The two, three and four multi-layer absorbers were modelled based on measured permittivity. The permittivity were obtained using microwave non-destructive testing (MNDT) from previous experiment. Then the permittivity of each layer was calculated using Chebychev multi-section transformer to provide a proper transition impedance. These microwave absorbers were modelled and simulated in MATLAB. The simulations were carried out from 1 GHz to 15 GHz to analyse the absorbers performance. The two-layer absorbers showed the multiple resonant frequencies. The permittivity of back layer influences the resonant frequency. A higher permittivity reduces the resonant frequency to a lower value. The two and three-layer absorbers showed an excellent bandwidth up to 110% and 120% respectively. The bandwidth can be improved by adding more layers to provide a smooth transition impedance between layers.