Prediction of system-level emissions performance via equipment shelf primary power bus frequency response characteristics
This paper reports an interesting extension of the frequency response testing technique to characterize real-world EMC conditions as encountered in the Product Realization cycle. It is demonstrated that the behavior of the Primary Power Bus of a system Equipment Shelf is a reliable predictor of the system’s EMC performance. In particular, the Conducted and Radiated Emissions characteristics of the system are anticipated before the system is fully assembled, and long before System-Level formal compliance testing is done. The frequency pass-bands and resonances of the Primary Power Bus are identified and these outcomes are closely correlated with independently obtained Conducted and Radiated Emissions spectra for the populated system Equipment Shelf.
Pre-compliance testing and characterization of equipment shelf EMC behavior by empirical frequency response measurements on the primary power bus
This paper demonstrates a frequency-swept measurement technique for predicting the conducted and radiated emissions performance of equipment shelves for pre-compliance and diagnostic purposes. The technique is based on the use of a vector network analyzer to identify the frequency passbands and resonances of the inherent coupling structure(s) presented by the primary DC power bus of the equipment shelf. The outcomes are compared with independently obtained conducted and radiated emissions spectra for the same equipment. Relevant data are presented and discussed. The technique is well suited for pre-compliance and diagnostic testing. It does not require fully populating nor powering the equipment shelf. The test is easy to perform and the information it provides goes a long way in optimizing or ranking alternate designs for electromagnetic compatibility.
Coupling of apertures in enclosures to external cabling structures
In addition to the direct radiation from enclosure apertures, an indirect contribution also exists due to the coupling to external cables. Based on an inductive coupling model, a relation for the external coupling voltage is derived and combined with a resonant dipole-antenna model for worst case estimations of the radiation level. An expression for the direct-to-indirect radiation-amplitude ratio is deduced. The model is well confirmed by a numerical example for a rectangular box with a slit. The results clearly indicate that in the low-to-intermediate frequency range the indirect cable radiation exceeds by far the direct radiation from the aperture.