Problems related to the use of coupled mode equations in directional coupler design for millimeter wave open structures

Millimeter wave waveguides are characterized by open conductive surfaces and a discontinuity in the dielectric media. The application of coupled mode equations to the design of directional couplers involves the introduction of losses that may affect severely the mathematical model used for the design. Examples of a coupler anomalous performance are presented. A qualitative modification of the mathematical models is suggested and a procedure consisting of simultaneous discretization and introduction of losses is presented to bypass the design problem.