A full-wave spectral-domain method with an asymptotic extraction technique is formulated for multilayer microstrip lines. This formulation provides a simple closed-form representation of the asymptotic part of the impedance matrix by using Chebyshev polynomial basis functions with the square-root edge condition and the asymptotic behavior of the Green's function. The formulation is applied to open microstrip lines. Numerical results, in the form of the effective dielectric constants, are

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... ed for the dominant mode. It is shown that the proposed method significantly reduces the computational time and improves the accuracy over the conventional spectral-domain approach (SDA). Index Terms-Accleration technique, microstrip lines, spectral-domain approach. Abstract-This paper presents for the first time a computer-aided design-oriented (CAD) analytical formula for the determination of the characteristic parameters of asymmetrical coupled lines of a conductorbacked coplanar type. Closed-form expressions are developed for evaluating the self and mutual static capacitances based on a sequence of conformal transformations. The derived formulas show excellent accuracy compared to the results produced by a spectral-domain approach.