Basic Statistical Concepts forAnalysis ofRandomCable Coupling Problems

The analysis of electromagnetic pulse(EMP)internal coupling tocritical electronic components andsubsystems is complicated by thepresence ofmanyseemingly random parameters, suchastherelative positions ofbunched cables nearpoints ofentry(POE)andtherandompositions of conductors inN-wire lines. Theserandomparameters preclude thestrictly deterministic solution forEMP induced excitations atparticular loadpoints. Onecan,ofcourse, choose to analyze asingle deterministic "average model"ofthesystem inthehopethattheexcitations obtained will indicate expected excitations on anyofseveral randomly different actual systems.Iftherandomparameters strongly affect thecoupling tocertain critical systempoints, theactual excitations may differ vastly fromthedeterministic modelpredictions. Atthis point, astatistical analysis should beperformed toobtain a valid range ofexpected excitations. Thediscussion herewillconcernabasic methodforthe statistical analysis ofloadexcitations on anunshielded Nwirerandomcable illuminated byanincident monochromatic field. Thetechnique utilizes theconcepts oftime-harmonic electromagnetic field reciprocity andstatistical representation ofanensemble byasubset. Although thediscussion hereis restricted toa limited class ofstructures (e.g., unshielded unbranched N-wire cables), themethodshould beextendable toshielded andbranched cables aswell. Inaddition, itmay be possible toconducta direct time-domain analysis via Welch's reciprocity theorem [1].