High-speed coplanar transmission lines

The authors present measurements of picosecond pulse propagation on coplanar strip transmission lines for which speed (i.e., group velocity), as well as phase and amplitude information are measured. Electrode effects are studied using transmission line loops 1 mm in diameter with cumulative propagation distances as long as 6 cm. The intrinsically low dielectric constant of coplanar-air transmission lines is shown to result in high signal speed and low attenuation. The authors use the data to verify the applicability of a model based largely on empirical formulae for radiation loss (geometry) and conductor absorption. The model is then used to identify optimal design criteria (for a given bandwidth) and is extended to the case of small dimensions.<>