Assuredly Effective Filters

This paper intends to put to rest a longstanding EMC controversy. Thus far an interrelated set of unresolved problems existed for power feed line filters. One never knew whether or not they would behave as predicted; that is, would they attenuate in the stopband, as desired, and/or ring in the passband, as not desired? Successful testing, according to accepted standards, does not guarantee satisfactory performance in the real world. This problematique is solved by combining extreme-value theory (newly applied) of mismatch with application of a properly categorized statistical data base (now established) on interface impedances. The delineation of the surprisingly transparent conditions for filter dysfunction permits establishment of practical measures for design and testing of filters that must often work under indeterminate and fluctuating interface conditions.