On a reduced branch‐line coupler with two‐step stubs considering a spurious notch

Abstract

SUMMARYIn a reduced branch-line coupler that is designed with two-step stubs such that the area occupancy on the substrate is 25% of the standard branch-line coupler, a sudden variation (spurious notch) occurs at a certain frequency in the frequency range higher than the center frequency. In this paper, the mechanism of generation of the spurious notch is investigated by using the eigenmode impedance obtained by mode decomposition. A circuit design that does not generate a spurious notch while maintaining the area ratio of 25% is developed. Next, by means of an experimental circuit, the effectiveness of the method is verified.