An equivalent circuit model for the coplanar waveguide step discontinuity

An approximate analytical model for the CPW (coplanar waveguide) step discontinuity is presented which includes a lumped shunt capacitance as the dominant effect. Good agreement is obtained with data from extensive 3-D field simulations, and verified by a limited number of measurements on alumina. The magnitude of the discontinuity is found to be smaller than indicated in previous work, but it is nevertheless of the same order as a microstrip step in a comparable situation. These effects need to be taken into account in any serious design, and the model presented, when incorporated into CAD (computer-aided design) circuit analysis programs, will allow rapid evaluation of performance.<>