A reduced branch-line coupler with eight stubs

A branch-line coupler using eight stubs is proposed for size reduction. As for the stubs, a structure consisting of two sections of high and low impedance transmission lines is presented in order to connect a low impedance stub to a signal line. According to transmission line theory, no practical differences are found in the frequency characteristics between the normal hybrid and an experimental circuit, except for slight differences in higher frequency region over the center frequency. The experimental circuit was reduced to 25% in area, and showed good agreement with theory.