Representative Contents Design for Shielding Enclosure Qualification from 2 to 20 GHz

The electromagnetic environment inside a shielding enclosure is affected by the absorption characteristics of the contents, which should therefore be represented in shielding measurements and simulations. At frequencies up to a few gigahertz, lossy dielectric materials have previously been used as surrogates for printed circuit boards in enclosure shielding assessment, both experimentally and in simulations. However, no systematic methodology for the design of these surrogates and their calibration against real hardware at high frequencies has been elucidated. In this paper we show how both lossy dielectric material and microstrip transmission line based “representative contents” can be designed and calibrated against real printed circuit boards over the frequency range 2-20 GHz using power balance concepts. The calibration is made by matching the average absorption cross-section of the surrogate to an average value for a class of real contents measured in a reverberation chamber. The surrogates are designed using efficient power balance models for layered media and field-excited microstrip lines and verified using full-wave simulation. The fabricated surrogates are validated by shielding measurements. The methodology presented could form an important part of future standards for enclosure qualification measurements that more accurately represent the internal environment of real equipment.