HYBRID COUPLERS IN BILEVEL MICROSTRIP

Hybrid couplers can be built using a bilevel microstrip structure in w hich two strips are positioned broadside, one above the other. This si mple geometry provides large coupling factors without the need for rig orous manufacturing tolerances. Remarkably, if the dielectric constant of one of the layers can be freely chosen, ideal hybrid coupler perfo rmance is achievable. Even when the choice of dielectric constant is c onstrained, good results can be obtained. A technique for achieving op timal design has been developed, and design curves are shown. Experime nts confirm design predictions. The reentrant coupler may be analyzed as an interconnection of two bilevel couplers of the kind described he re. This provides a simpler analysis than methods used earlier, and in some cases yields more accurate results.