Reduced branch-line coupler using eight two-step stubs

Abstract

A branch-line coupler with eight stubs is proposed for size reduction. A two-section stub consisting of high- and low-impedance transmission lines to make interconnection of low-impedance transmission lines easy is presented. According to the transmission-line theory, almost the same frequency characteristics as those of a normal branch-line coupler can be obtained, although there are slight differences in the high-frequency region over the centre frequency. The experimental circuit was reduced to 25% in area, and the frequency characteristics showed good agreement with the theoretical results except for the shift in centre frequency.