Estimation of radiation limit from a Huygens' box under non-free-space conditions

The recently studied Huygens' box method has difficulties when radiation of an electronic module is to be determined under non-free-space conditions, i.e. with an enclosure. We propose an estimate on radiation limit under such conditions based only on the Huygens' box data from free-space measurements. Numerical experiment shows that the limit is valid everywhere except the resonance frequencies. Consequently, it is argued that knowledge of the inner structure of the module is in fact necessary also for the limit estimation.