  We study the step meandering instability on a surface characterized by the
alternation of terraces with different properties, as in the case of Si(001).
The interplay between diffusion anisotropy and step stiffness induces a finite
wavelength instability corresponding to a meandering mode. The instability sets
in beyond a threshold value which depends on the relative magnitudes of the
destabilizing flux and the stabilizing stiffness difference. The meander
dynamics is governed by the conserved Kuramoto-Sivashinsky equation, which
display spatiotemporal coarsening.
