  We investigate the structure of the meson Regge trajectories based on the
quadratic form of the spinless Salpeter-type equation. It is found that the
forms of the Regge trajectories depend on the energy region. As the employed
Regge trajectory formula does not match the energy region, the fitted
parameters neither have explicit physical meanings nor obey the constraints
although the fitted Regge trajectory can give the satisfactory predictions if
the employed formula is appropriate mathematically. Moreover, the consistency
of the Regge trajectories obtained from different approaches is discussed. And
the Regge trajectories for different mesons are presented. Finally, we show
that the masses of the constituents will come into the slope and explain why
the slopes of the fitted linear Regge trajectories vary with different kinds of
mesons.
