Multilayer microstrip directional coupler with discrete coupling

A multilayer microstrip coupler with a high directivity has been developed, involving two strips which crossover twice at a right angle. A general full-wave model has been derived. It has been simplified in a quasi-static approximation. Based on the latter, a computer-aided design has been carried out, using finite differences in a commercial package. This design has been experimented, showing good agreement with the simplified model.