Upper and lower bounds on capacitances of coupled microstrip lines with anisotropic substrates

The Fourier transform has been used to obtain stationary expressions for the even- and odd-mode capacitances of coupled microstrip lines on anisotropic substrates. Expressions for calculating the upper and lower bounds on true values have been found using variational techniques; so the margins of error in the calculation can be estimated. The method is used to compute the even- and odd-mode characteristics of coupled microstrip lines on sapphire, and to study the effect of substrate anisotropy on the line characteristics.