In this manuscript, a new lumped equivalent-circuit model is proposed for the simulation of the coplanar waveguide (CPW) step discontinuity within the frequency range of 0 to 150 GHz. With the computer-aided modeling and appropriate parameter extraction method, the parameters can be extracted from electromagnetic (EM) simulations without any optimization. Furthermore, we also make the model scalable. Excellent agreement is obtained between the model data and electromagnetic simulations over a considerable range of frequencies and device geometries, which also verifies the validity of our model.