Characteristics of Microstrip Transmission Lines

Equations are developed which accurately describe the characteristic impedance and signal propagation delay for narrow microstrip transmission lines. Differences in signal propagation delay for microstrip, strip line, and coaxial cables are compared as a function of dielectric constant. The characteristic impedance equation is verified through comparison with experimental results for impedance values from 40 to 150 ohms. The sensitivity of characteristic impedance to variations in physical parameters, such as dielectric constant, line width, and board thickness, is presented. Finally the equation is shown to yield exceptionally accurate results when the inherent inaccuracies of the physical measurements are considered.