Miniaturized 60 GHz Branch-Line Coupler Using Dual Slow-Wave Techniques in 22-nm FDSOI

This paper presents a compact 60 GHz branch-line coupler designed in 22-nm FDSOI technology, leveraging dual slow-wave techniques for miniaturization. The design integrates meandered transmission lines with alternate floating shields for the 50-Ohm sections and a bed-of-nails structure with open-ended stubs for the 35-Ohm sections. The coupler occupies an area of 0.049 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> $\left( {1.9\lambda _0^2 \times {{10}^{ - 3}}} \right)$ and a fractional bandwidth of 49% as shown by measurements and simulations. It demonstrates a return loss of 26 dB, isolation of -13.3 dB, and insertion loss of -2.7 dB at 56 GHz, with an amplitude imbalance of 1.2 dB and phase imbalance of 3°.