Characteristics of Lumped Element Branch Line Couplers

Lumped element orthogonal couplers are analyzed using the eigenvalue approach. A wide range of different designs is compared and tabulated. Parallel branch and series branch circuits are shown to fall into four classes with different output phase characteristics. Within each class, three different kinds of amplitude behavior exist. Experimental results are given as examples and compared with theory. The eigenvalue approach is also helpful in the explanation of the measurements. Special features in the application of the couplers are discussed and "orthogonal baluns" are suggested as special cases of some of the series branch couplers.