Impedance and crosstalk of stripline and microstrip transmission lines

Signal conductors between two ground planes (i.e.. stripline transmission lines) and signal conductors above one ground plane (i.e., microstrip transmission line) serve as the means for propagating high-speed digital and analog signals on printed wiring boards (PWBs), and multichip modules (MCMs). For many important applications (e.g., wireless and other high speed technologies), the need for miniaturization requires that these high-speed electrical interconnections be provided on relatively dense PWBs and MCMs. This leads to design uncertainties concerning characteristic impedance and especially crosstalk. The purpose of this paper is to develop relatively simple formulas for computing the characteristic impedances and crosstalk of coupled stripline and microstrip transmission lines. Both unbalanced and balanced transmission lines are treated. The new formulas apply to both rectangular and circular conductors and are expressed in terms of the physical dimensions of the conductors and the effective dielectric constant of the medium. The formulas yield results which agree well with known results and experimental results.