  We study two-dimensional frustrated Josephson arrays driven by a combined DC
plus AC current. We propose {\it ansatz} solutions that are a generalization of
the solutions obtained in the DC case by Marino and Halsey (PRB {\bf 50}, 6289
(1994)). Using these solutions we derive expressions for the Shapiro step
widths for $f=1/2$ and $f=1/3$ for the first few winding numbers. We show that
the qualitative difference in the behaviors of the fractional and integer steps
is related to the relative size of the vertical supercurrent with respect to
the normal current.
