Modal expansion basis for statistical estimation of maximum expected field strength in enclosures

Estimating the electromagnetic field strength in avionics boxes at high frequencies and in electrically large enclosures such as launch vehicle payload fairings is often impractical using a “full wave” numerical model. The ratio of wavelength to characteristic dimensions is such that both temporal and spatial field response is highly sensitive to small geometric details which are typically not known or not practical to model. However, the statistical distribution of such a chaotic wavefield collapses uniformly to a convenient two parameter probability distribution. This paper reduces a deterministic modal expansion of electric field in an enclosure, to show the basis for a simple statistical model which can predict both the spatio-temporal mean response and the maximum expected response, for any required statistical confidence level. The paper compares preliminary predictions of the statistical model with experimental data from reverberation chamber tests at NASA LaRC.