  We report the analysis of measurements of the complex magnetic permeability
($\mu_r$) and dielectric permittivity ($\epsilon_r$) spectra of a rubber radar
absorbing material (RAM) with various MnZn ferrite volume fractions. The
transmission/reflection measurements were carried out in a vector network
analyzer. Optimum conditions for the maximum microwave absorption were
determined by substituting the complex permeability and permittivity in the
impedance matching equation. Both the MnZn ferrite content and the RAM
thickness effects on the microwave absorption properties, in the frequency
range of 2 to 18 GHz, were evaluated. The results show that the complex
permeability and permittivity spectra of the RAM increase directly with the
ferrite volume fraction. Reflection loss calculations by the impedance matching
degree (reflection coefficient) show the dependence of this parameter on both
thickness and composition of RAM.
