Hybrid Branchline Couplers -- A Useful New Class of Directional Couplers

The hybrid branchline coupler consists of two transmission lines connected alternately by /spl lambda//4 shunt and series branches. The analysis of this structure leads to a class of directional couplers of which the parallel transmission-line and the de Ronde strip-slot types may be regarded as special cases. From the precise design data thus available, a number of 3-dB strip-slot couplers have been built in C band and X band with a performance close to the predicted one.