Practical definition of interface barrier effective shielding

In the traditional definitions of electric and electromagnetic shielding effectiveness, externally radiated electric fields are sampled at a point inside an enclosure with and without a shielding interface. In this investigation, conductors cross the lower and upper sections of a radio telescope pedestal through galvanic interface barriers. The barriers are partially compromised by apertures. Shielding level predictions based on traditional definitions are not practically informative in this cable/interface system. We propose that the levels of shielding are given by the reduction in common-mode (CM) current measured either side of the interface on the same conductor. Computational analysis is used to compare the decrease in CM current with shielding effectiveness calculations based on electric field values in the centre of the pedestal. Simulations and measurements on the actual telescope are compared.