A 50–67-GHz Transformer-Based Six-Port Balanced-to-Unbalanced Quadrature Hybrid Coupler

This letter presents the first on-chip transformer-based six-port balanced-to-unbalanced quadrature hybrid coupler (QHBC). The proposed six-port QHBC employs three transformers to replace eight inductors design in conventional LC-based couplers for miniaturization. Fabricated in CMOS 28 nm, the overall size of the proposed coupler is 0.23 mm $\times0.17$ mm, which is equivalent to $0.046\cdot \lambda _{0} \times 0.034\cdot \lambda _{0}$ , around 20 times smaller compared to the state-of-the-art six-port QHBC. Operating from 48 to 67 GHz, the measured differential and common mode return loss are <−8 dB and >−2.2 dB, respectively. The measured output phase and magnitude imbalance are within 10° and 2 dB, respectively. The measured voltage gain varies from −5.8 to −2.8 dB.