A frequency-dependent basis function applied to microstrip

Spheroidal wave functions (SWF) and the spectral-domain method (SDM) are used to compute the effective dielectric constant for microstrip. The authors explore the ability of the SWF to change shape as a function of a parameter, e.g. frequency, while maintaining orthogonality, completeness, edge condition, and aperture limit. The authors introduce the SDM equations, provide a brief overview of the SWF, and study the effective dielectric constant as a function of frequency for several commonly used basis functions. A single-term expansion for the vector current density provides excellent results over a broad spectrum (1-100 GHz). Numerical results compare favorably with other commonly used techniques