Coupling Between Two Rectangular Bars Through a Finite Thickness Slot

A conformal mapping procedure is described to obtain the coupling capacitance between two rectangular bars through a finite thickness slot. Representative theoretical graphs of the coupling capacitance and even-mode fringing capacitance for the coupling geometry are presented. A comparison is made between graphs of the theoretical coupling coefficient computed from the fringing capacitances, and measured results for two sets of coupling plates. For each set the thickness was kept constant and the slot width varied. The slot coupled rectangular bar geometry finds application in the construction of interdigital and combline linear-phase filters.