AN ANALYSIS OF ENCLOSED COPLANAR STRIPS
Abstract:
With the increasing use of high speed digital circuits in modern electronic devices, coplanar stripline (CPS) transmission lines are of major importance as interconnecting lines. For example, the high speed digital circuits used in differential receivers operate best when fed using CPS balanced transmission lines. However, the theoretical CPS geometry and associated current design equations do not take into account the presence of a bottom ground conductor, which is often present in printed circuit board MIC or MMIC configurations. When a bottom ground conductor is inserted below a CPS, the resulting structure is a conductor-backed coplanar strip (CBCPS). Such a configuration is often encountered in microwave mixers as well. In addition, until today no simulation model in CAD tools existed for these CBCPS transmission lines. Using current quasistatic analysis, this article develops simple closed-form equations for characteristic impedance and effective dielectric constant for CBCPSs and considers the effect of a top ground cover. These equations are well suited for implementation in CAD simulations tools.