Radiation loss in open-waveguide directional couplers

The appearance of radiation in open-waveguide directional couplers is discussed, as it can modify the behavior of the coupler. Analytical and numerical examples are presented to illustrate this modification. It is determined that when the phenomenon occurs, substantial changes in the decay of the electromagnetic field against the distance from the structure occur. The numerical method used is based on a finite-infinite-element technique, and an example is given where two coupled dielectric waveguides are considered in the interior of an overdimensioned rectangular metallic waveguide. This structure is useful as it supports only a discrete spectrum of propagating modes, and the structure also may be used in practical application solutions at millimeter wavelengths. Theoretical and experimental studies are in progress to determine if a useful device with controlled radiation can be obtained.