Full-wave iterative variational formulation for multiple coupled microstrip lines

A novel variational formulation in terms of two formally decoupled potentials is derived for the full wave propagation constants of multiple coupled microstrip lines. At very low frequency limits, the present formulation is reduced directly to the conventional quasi-static formulation. The quasi-static solutions are then used as an initial guess to solve the high-frequency problem for each coupled mode by a generalized Newton-Raphson iterative scheme. Numerical results are presented for two and three coupled microstrip lines of identical or nonidentical widths with various spacings and frequencies