FDTD simulation of signal degradation in lossy and dispersive coplanar waveguides for high-speed digital circuits

The signal degradation stemming from the conductor loss and the substrate dispersion of coplanar waveguides for the high-speed digital circuits is analyzed by a combination of the original and frequency-dependent versions of the FDTD method. The metallic strips with the finite thickness are described by the equivalent Z-parameters. The backed conductor, if any, is modelled by the surface impedance. The dispersive property of the GaAs substrate is formulated by using the Kronig-Kramers relationship. The simulation results demonstrate the signal degradation due to modal dispersion, conductor loss, substrate dispersion and leakage effects in a conductor backed CPW structure.