Unintentional radiation from shielded transformers

It is shown experimentally that a typical shielded broadband transformer intended for bulk current injection measurements radiates far-field electromagnetic energy. This radiation occurs in spite of the shield and is distinct from any radiation due to common mode currents on the exterior of the coaxial feed transmission line. The radiation patterns presented here taken together with previous results which showed that the flux in such a transformer can vary in the azimuthal direction indicate that the radiation is to some extent tied to the nonuniform flux. However, it is also shown that the radiation is enhanced and modified by the imperfect electrical connection of the two halves of the shield along the split line.