NEC-LIST: RF voltage levels involving dielectric layers and structures

Extending this discussion to dielectric layers and structures attached to
the conductor, is there a way in NEC or NEC4 to model the voltage gradients
within these dielectrics? Two examples: with a glass wall penetration
window, I've seen voltage breakdown in rain sheeting on the glass due to
fields in the glass. How would these fields be modeled? In the second
example, a teflon bushing about 4 inches wide and 3 inches thick on a 2 inch
diameter tube was damaged from corona due to a tapered air gap between the
bushing and a wall feed-through tube. A corona ring finally solved this
problem, but how could this be modeled in NEC -- or is there a better
solution? At the time, and at our lower frequencies of operation, we made
assumptions of a simple capacitive division, but a better model technique is
needed.

Regards,
Paul Lynas

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