A lumped equivalent circuit model for both series and double-shunt (butterfly) connected radial stub has been developed. The model-simple and effective-not only includes conductor and dielectric losses but also radiation ones, which play an important role in microstrip circuit elements. Experiments widely demonstrate its suitability for implementation in available CAD (computer-aided design) programs. Furthermore, a synthesis procedure for using radial stubs in circuit design is described. An application of the proposed design procedure and simulation tools in the development of very broadband nongrounded termination is also presented.