ANALYSIS OF 2-CONDUCTOR MULTILAYER SHIELDED MICROSTRIP TRANSMISSION-LINE

The analysis of the quasi-static TEM mode of a shielded microstrip tra nsmission line is investigated in this paper using the method of momen ts. The transmission line consists of two perfect conducting co-planar strips located between two ground planes. Four different dielectric r egions are considered in this problem (two layers of substrates, a rec tangular notch below the strips, and an overlay or a superstrate). The formulation of the problem is based on the solution of Laplace's equa tion subject to certain boundary conditions, and the use of image theo ry, the free space Green's function, and the method of moments. The go al of this paper is to study the effects of the structure parameters o f the shielded multi-layer transmission line on the odd and even modes , phase velocities, and the electrical coupling. Once the odd and even phase velocities are equalized, the design of distortionless lines is achievable, It has been found that the presence of the shield allows for the reduction of the interline spacing with minimum coupling. Furt hermore, with the proper selection of the height of the shield and the separation distance between the strips, it is possible to equalize th e phase velocities at more than one combination of the substrate heigh ts. It was also found that the coupling between the strips can be sign ificantly reduced by removing the dielectric material between the stri ps or by setting the dielectric constant of the overlay equal to that of the free space.