Full wave analysis of transmission lines above a perforated ground plane.

摘要

Planar transmission lines embedded in a dielectric sandwiched between conductive ground planes are used in high-speed microelectronic packaging to carry signals between integrated circuit chips. Ground planes may be perforated to allow signal connections between transmission lines on different layers through vias and also for structural integrity. In some cases of ceramic-based multilayer circuits composed of Low Temperature Cofired Ceramic (LTCC), fabrication technology requires the metal area in the interface be below 50% to maintain enough tape-to-tape contact during lamination to achieve a good bond between adjacent layers. Also, due to the different shrinkage and expansion behavior of glass and metal during firing and cooling, the metal area between two dielectrics should remain at a low value compared to the total dielectric area. Thus perforated ground planes are prevalent in modern electronic packaging.;Apertures on ground planes can definitely influence the characteristic impedance, propagation constant and signal velocity of a transmission line, and, also, coupling between transmission lines. Furthermore, transmission lines with perforated ground are not precisely planar transmission lines, which require uninterrupted ground planes; therefore traditional analytic approaches using Transverse Electric and Magnetic fields (TEM) or quasi-TEM methods of electromagnetic analysis for transmission lines fail to yield sufficiently accurate results. At high frequencies when coupling, radiation loss and surface waves become important, full-wave analysis must be used to take these effects into account.;An approach based on solution of mixed field integral equations using the Method of Moments and Green's functions derived for both electric and magnetic currents is proposed. The method of moments using the derived spectral domain formulation was implemented in the FORTRAN and the program has been used to analyze a multi-layer transmission line structure above a perforated ground plane problem. Dispersion and cut-off effects in the two-dimensional periodic structure have been discussed. The influences of line location and aperture geometries on the characteristics of transmission lines have been analyzed. The coupling effects of odd and even modes are also analyzed and discussed.