 term on the propagation constants of the modes. We find that the propagation constants of the lower order modes suffer significant modification by taking the
 term on the propagation constants of the modes. We find that the propagation constants of the lower order modes suffer significant modification by taking the  term into account, while for the higher order modes the effects are small enough to be disregarded.
 term into account, while for the higher order modes the effects are small enough to be disregarded.