CAD formula of a microstrip on a grounded substrate of two layers by synthetic asymptote

This paper gives simple CAD formulas of the characteristic impedance and propagation constant for a microstrip on a grounded substrate of two layers by synthetic asymptote. Similar to the one-layer case, based on the derived formula, the equivalent circuit is a fringe capacitor in parallel with an ideal parallel-plate capacitor of the two-layer substrate. The average error is less than 2%. The top layer is assumed thin, at 30% or less of the width W of the microstrip. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 584–588, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21237