SYSTEMATIC COMPUTATION OF THE MODAL SPECTRUM OF BOXED MICROSTRIP, FINLINE, AND COPLANAR WAVE-GUIDES VIA AN EFFICIENT SDA

This work reports an efficient and systematic procedure to obtain the complete modal spectrum of multilayer boxed planar lines. The complex propagation constants are obtained by computing the zeros of a properl y built analytic complex function. This function is the product of two factors. One of them is the determinant function provided by the spec tral domain-Galerkin analysis (SDA). The other factor is a function wh ich cancels out the poles of the former factor without introducing add itional poles nor zeros. The elimination of the poles overcomes numeri cal difficulties usually found in the zero searching process. In addit ion, powerful zero-searching integral techniques can be applied withou t problems, The numerical aspects involved in the computation of the s pectral series are considered to speed up the computations. The featur es of an arbitrary number of propagating, evanescent, backward or comp lex modes of three important boxed structures (microstrip, finline, an d coplanar waveguide) can be systematically studied with our method.