In this paper, scattering and radiation from scalable planar bodies are investigated in a wide frequency band. Characteristic basis functions (CBFs) are utilized for this purpose with a different approach. The CBFs for the body are calculated at the highest frequency of interest and reused at other frequencies. As the frequency decreases, the unnecessary CBFs are removed from the basis set. The reduced impedance matrices generated at lower frequencies are also used for the calculation of the ones at higher frequencies. As a result, a significant reduction in CPU time is obtained with the proposed method. Numerical results for the problems of scattering from a square plate and radiation from a bowtie antenna are presented to demonstrate the accuracy and efficiency of the proposed method.