The design theory for a flat microwave absorber with a protective cover

Abstract

To achieve a complete absorption for a microwave absorber with a protective cover, which is a practical assembly, it is important to establish a general design theory for such an assembly. The equations that elucidate the relations of the electromagnetic parameters of the absorber and its dielectric cover for a zero reflection are established by inverse solving the equations obtained by transmission line model used to calculate the reflection of the assembly. This design theory is applied to three kinds of practical polymers (PTFE, epoxy resin and phenolic resin) at three given frequencies (2, 10, and 18 GHz) as examples. For a given cover material and a given frequency, the complex electromagnetic parameters and the thickness of an absorber are determined by solving these equations and the results are graphically represented in the loss-angle plane and the possible use of these design curves is illustrated. For a certain cover material, the required relative thickness of a magnetic absorber is thinner than that of an electric absorber and the required electromagnetic loss should be weak when the ratio of the real part of relative complex permittivity and permeability of the absorber is small. For different cover materials, the design curves show a similar tendency. For a cover with strong dielectric properties, for example, phenolic resin, to achieve a total absorption, the required dielectric loss of an electric absorber is strong, while the required magnetic loss of a magnetic absorber is weak.