Compact Branch-line Coupler using Radial stubs

This manuscript shows a novel compact branch-line coupler with radial stubs installed on each branch. The proposed implementation is only 10 mm by 10 mm and it achieved a size decrease of 70% compared with a traditional one. Measured S
₁₁
, S
₂₁
, S
₃₁
and S
₄₁
of the proposed coupler are better than -23, -3.6, -3.6 and -27 dB at 3 GHz, respectively. Moreover, the phase difference between coupling and through ports is within 0.9°.