To obtain wideband radar cross-section (RCS) frequency response of multiple perfectly electric conducting (PEC) objects, the frequency sweeping by reusing the ultra-wide band characteristic basis functions (UCBFs) is applied. This method, based on the Characteristic Basis Function Method (CBFM), maintains all the benefit of CBFM, especially accelerating the solution of matrix equations generated by the method of moments (MoM) applied to the scatting problems in electromagnetics. Compared with conventional CBFM procedure, reusing the UCBFs without repeating the calculations of them at different frequency points leads to a significant reduction of computational time. Generating UCBFs for highest frequency, reusing UCBFs for lower frequencies and constructing reduced matrix for each frequency are the three keys of this method. Numerical results demonstrated the efficiency of this method.