Analysis of broadside-coupled strip lines with anisotropic substrate

Two analytical approaches are presented for broadside-coupled strip lines with anisotropic substrates. One is based on the quasi-static approximation which uses the Fourier transformation and the Ritz procedure. The other is based on the rigorous hybrid-mode formulation, and the frequency dependent solutions are obtained by using the network analytical methods of electromagnetic fields and Galerkin's procedure. Some numerical results are presented for sapphire and Epsilam-10 substrates. The effect of the inclination of the optical axis is not so large, and the effect of the shift of central axes of strip lines S/W in the odd modes is larger than that in the even modes. The rigorous frequency dependent solutions converge to quasi-static values at lower frequencies, and the dispersion of the even modes, which cannot be neglected at higher frequencies.