The feature of the narrow-pulse transmission on conventional coplanar waveguides when power leakage is present

The authors report a new feature of wave-form deformation and unexpected crosstalk when a narrow pulse is transmitted on the conventional coplanar waveguide (CPW). The causes of such a new feature are that the standard, well-known dominant mode on a conventional CPW becomes leaky above a certain critical frequency, and also that the CPW possesses another type of dominant mode below that frequency. Especially, the leakage effect appears on most printed-circuit waveguides. The authors have calculated the properties associated with the narrow-pulse transmission, for several different structures, by means of the finite-difference time-domain method. Numerical examples for conventional coplanar waveguides prove that such a feature has a serious influence on high-speed circuit design.<>