  Spanner construction is a well-studied problem and Delaunay triangulations
are among the most popular spanners. Tight bounds are known if the Delaunay
triangulation is constructed using an equilateral triangle, a square, or a
regular hexagon. However, all other shapes have remained elusive. In this paper
we extend the restricted class of spanners for which tight bounds are known. We
prove that Delaunay triangulations constructed using rectangles with aspect
ratio $\A$ have spanning ratio at most $\sqrt{2} \sqrt{1+\A^2 + \A \sqrt{\A^2 +
1}}$, which matches the known lower bound.
