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.

A new approach using radiation mode expansions is presented for calculating radiated fields from arbitrary distribution of electromagnetic sources in the half space region partitioned by a dielectric layer with a ground conductor. This method is applied to the calculation of radiation from microstrip-type antennas with a dielectric substrate of theoretically infinite extent. To be able to use this method, it is necessary to obtain first the field distribution around antenna patches, which is accomplished rather easily by using the FD-TD method. Radiation pattern calculations are presented for a rectangular patch antenna to verify the feasibility of this approach.