An analysis method based on the FD-TD and radiation mode expansion methods and its simulation tool are developed for calculating circuit characteristics and parameter values of passive MMIC (Monolithic Microwave Integrated Circuits) elements having multilayer structure. For straight multilayer microstrip lines and coplanar waveguides, it is possible to calculate characteristic impedance, effective permittivity, transverse field distribution of guided modes, etc. For various multilayer microstrip and coplanar waveguide elements, it is possible to calculate scattering parameters, radiated power, radiation patterns, etc. As an example of application of the present technique, effects of inclusion of lower permittivity layer in the substrate on transmission and radiation characteristics are investigated for right-angled microstrip bends.