Fringing capacitance in thick-strip transmission-line filters

To evaluate the odd-mode fringing capacitance against strip gap width in a parallel-coupled thick-strip transmission-line filter, Cohn has proposed two equations, one valid for the narrow-gap region and the other for the wide-gap region. A simple technique to combine these equations into a single one valid for the entire range of gap widths is presented. It is shown that the results are similar to those obtained by Getsinger from a different approach, and are satisfactory for filter design, since they lead to good agreement with experiment.