Electromagnetic coupling of microstrip lines and coplanar waveguides to multilayer lossy media

The spectral-domain method is used to analyze the electromagnetic surface-wave-type coupling of microstrip lines and coplanar waveguides to multilayer lossy dielectric media. Detailed analysis of these coupling characteristics and the role of a thin superstrate layer of lossless material in controlling this coupling are important in fully developing the application of microstrip circuit technology in medical and geophysical applications. Numerical results obtained for the dispersion characteristics were found to be in excellent agreement with published data in special cases of coplanar waveguides and slot lines. Results for the spatial distribution of the various field components in a lossy medium are, however, more involved. Specifically it was noticed that the presence of a superstrate of lossless dielectric medium significantly enhances the axial electric field component, thus facilitating a surface-wave type coupling with exponential decay to the lossy medium.<>