Miniaturized Branch-Line Coupler with Harmonic Suppression

This paper presents a miniaturized branch-line coupler with harmonic suppression. By using a combination of a 45° open stub and a 45° short stub instead of using a 90° short stub, we can achieve harmonic suppression while maintaining good RF bandwidth. We compare the proposed design with the conventional design. The measurement results of the fabricated branch-line coupler designed at 1 GHz exhibit good harmonic suppression at the frequency of 2GHz.