An exact controllability approach is used for the calcuation of time periodic solutions of the wave equation, which is proved to be equivalent to the Maxwell equation in two dimensions for the T.M.mode. The numerical results of scattered fields and Radar cross sections(RCS) are presented for complicated aerodynamic shapes with cavity, external obstacle or a slender body. The method presented has the ability to deal with more complicated aerodynamic shapes due to the use of unstructure triangulations.