By employing the semiempirical dispersion formula for coplanar transmission lines, the mode dispersion and Cerenkov radiative attenuation characteristics in the frequency domain over a terahertz range of coplanar striplines on thick LT GaAs substrate were analyzed. The analytical result reveals that the radiative attenuation and the mode dispersion characteristics can be improved by reducing the total linewidth,and that a greater aspect ratio should be designed to reduce the conductor loss.