A simple, efficient CAD-oriented equivalent circuit modeling approach of frequency-dependent behavior of substrate noise coupling is presented. It is shown that the substrate exhibits significant frequency-dependent characteristics for high frequency applications using epitaxial layers on a highly doped substrate. Using the proposed modeling approach, circuit topographies consisting of only ideal lumped circuit elements can be synthesized to accurately represent the frequency response using y-parameters. The proposed model is well-suited for use in standard circuit simulators. The extracted model is shown to be in good agreement with rigorous 3D device simulation results.