New approach to analyse strip-and microstrip-like transmission lines with anisotropic substrates having a tilted optical axis

Generalised expressions are evolved for the line capacitance of single as well as edge-coupled strip and microstrip-like transmission lines with anisotropic substrates having a tilted optical axis. An example of a two-layered strip line with anisotropic dielectrics having a tilted optical axis is first analysed using the spectral-domain method under a quasistatic approximation. The only parameter that is dependent on the transmission line media in the expression for the capacitance is identified as the admittance at the charge plane of the structure. Since the admittance parameter for any multilayer structure can be easily and independently determined using a two-wire transmission line equivalent, the capacitance expression serves as a general formula. Numerical results on the isolated strip line and the coupled microstrip lines compare well with those reported in the literature. Computed impedance and effective dielectric constant characteristics of single and coupled inverted and suspended microstrip lines are presented as a function of the tilt angle of the optical axis of the anisotropic substrate.