Analysis of coupling characteristics of coplanar waveguides and microstrip lines to multi-layer dielectric media

The spectral domain technique is used to analyze the coupling characteristics of coplanar waveguide and microstrip lines to highly lossy multilayer dielectric media. The possibility of exciting surface waves and hence generating and coupling nontransverse electric field components is also investigated. It is shown that surface waves will not be excited in the substrate when a high-dielectric lossy media is placed on top of the coplanar structure. In the presence of a superstrate between a high-dielectric lossy medium and the coplanar waveguide, however, the quasi-static TEM and TM/sub 0/ modes may be excited. An axial electric field component can then be coupled to the loss medium. The developed solution was also utilized to optimize the coupling performance of these structures to lossy dielectric media. It is shown that to enhance the EM coupling, higher frequencies should be used, the dielectric constant of the substrate should be small, and the width of the center conductor and the air gaps in a coplanar waveguide should be as large as possible.<>