Reduction of radiated emissions from apertures in resonant enclosures by the use absorptive materials

Preliminary results are presented which show that the radiation from non-resonant (i.e. electrically small) apertures in metallic enclosures is enhanced at the closure resonances. It is shown that the levels of radiation at resonance can be significantly reduced by the use of ferrite absorbing tiles or carbon loaded dielectric absorbers to damp the enclosure resonances. A simple equivalent circuit model has been developed which allows prediction of the effects of absorber and slot placement for first order waveguide modes. It is believed that the model can be extended to higher order modes