A compact and harmonic-suppressed 3-dB 90° hybrid coupler using coupled-line section

In this paper, a compact and harmonic-suppressed 3-dB 90° hybrid coupler is proposed. A coupled line is inserted into the low impedance section in conventional branch-line coupler. With slightly increased design complexity, the proposed structure can be designed to have compact size and comparable electrical performance to the conventional one with excellent structural flexibility. The fabricated structure occupies 10.4% area compared to the conventional branch-line coupler, and prevents degradation in operation bandwidth. Furthermore, the proposed structure demonstrates the harmonic suppression property due to the structural asymmetry at odd order harmonics.