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The electromagnetic properties including ac conductivity, permittivity, and permeability of percolative Fe/Al2O3 composites, which were prepared by in-situ synthesis process, are investigated in the radio frequency range. There is an obvious percolation transition with the increase of iron contents. When iron content is beyond but near the percolation threshold, the negative permittivity and permeability are simultaneously obtained from 631MHz to 1GHz in sample FA30. Further increasing iron content, the Fano-like resonances are observed, and the resonance frequency where the permittivity changes from negative to positive shifts to lower frequency. In addition, the frequency region of negative permittivity and negative permeability are not overlapped any more. Hopefully, the percolative Fe/Al2O3 composites with tunable negative permittivity and negative permeability can be used as electromagnetic wave absorber. [ABSTRACT FROM AUTHOR]