Design Equations for an Interdigitated Directional Coupler (Short Papers)

General design equations for an interdigitated directional coupler are derived. The design equations are written in terms of even- and odd-mode admittances for a pair of coupled lines which are identical to any pair of adjacent lines in the coupler. The calculated values of even- and odd-mode admittances can be translated into a physical configuration from published data on coupled lines.