  We present a model for calculating broadened Autler-Townes spectra when
probing ac electric field magnitudes by use of Rydberg atom
electromagnetically-induced transparency. This model approximates the atom
vapor as a multi-layered media and uses Beer's law to combine probe beam
absorption through many discrete thin segments, replicating the broadening seen
in experimental measurements. The methodology can be easily applied to other
non-uniform optical parameters when monitoring total spectral transmission or
phase delay. Field non-uniformity is present in standing waves of unmatched
waveguides and glass vapor cells, which are generally due to source
characteristics and environmental reflections. We present broadening and
distortion effects caused by various types of electric-field distributions, and
compare this model to results obtained from measured atomic spectra.
