[en] The vane shapes of RFQ have been designed based on a shape prescribed with so-called two-term potential and realized through simplifications by modifying cross-sections constant and/or approximations for smooth connection between the cells. Among the simplifications, simple trapezoidal modulations instead of elaborate wave modulations in the longitudinal direction has become reconsidered for its better acceleration efficiencies. However, the mixture of the higher order harmonics components to the electric field would increase nonlinearity on the beam optics. The less nonlinear vane shapes with higher acceleration efficiencies that include the trapezoidal shape can be generated by adding only the less nonlinear terms to the two-term potential. (author)