  We study the electronic band structures of massless Dirac fermions in
symmetrical graphene superlattice with cells of three regions. Using the
transfer matrix method, we explicitly determine the dispersion relation in
terms of different physical parameters. We numerically analyze such relation
and show that there exist three zones: bound, unbound and forbidden states. In
the central zone of the band structures, we determine and enumerate the
vertical Dirac points, opening gaps and additional Dirac points. Finally, we
inspect the potential effect on minibands, the anisotropy of group velocity and
the energy bands contours near Dirac points. We also discuss the evolution of
gap edges and cutoff region near the vertical Dirac points.
