Design of Ku-Band Broadband Compact Branch-line Coupler

In this paper, a novel design of a broadband compact branch-line coupler for Ku-Band applications is proposed and verified using simulation. Specifically, the conventional transmission lines used in broadband branch-line coupler are replaced by coupled-line, T-shaped, and cross-shaped structures to overcome the size limitations imposed by fixed electrical phase conditions, thereby achieving miniaturization. Furthermore, the coupled-line, T-shaped, and cross-shaped networks are mathematically validated and represented by closed-form equations. The proposed Ku-Band broadband compact branch-line coupler exhibits S11 and S41 bandwidths below - 15 dB of 9.1 GHz ∼ 14.7 GHz and 8.95 GHz ∼ 14.85 GHz, respectively, while the maximum insertion loss for S21 and S31 is 3.61 dB, and the bandwidth maintaining a phase difference within ±5° spans from 8.85 GHz to 15.25 GHz. The overall dimensions of the broadband compact branch-line coupler are theoretically reduced by more than 41 %, measuring 7.6 × 5.5 ㎟ .