Frequency-dependent characteristics of shielded broadside coupled microstrip lines on anisotropic substrates

A spectral-domain technique is applied to compute the propagation characteristics of a shielded broadside coupled microstrip line printed on homogeneous uniaxial and biaxial substrates. The formulation derives the Green´s functions for even and odd modes of the guiding structure via the transformed fourth-order differential equations. The analysis includes anisotropic substrates which are simultaneously characterized by both [ε] and [μ] tensors. This rigorous full-wave approach to the solution of the problem is shown to yield results agreeing well with the existing data. The propagation characteristics are studied with respect to different line width/thickness ratios as well as to the material substrate parameters