A compact low-loss Ku-Band 90° Hybrid Coupler for Front-End Modules in 45 nm SOI CMOS

This paper presents an integrated 90° hybrid coupler chip designed for the frequency range of $12-16 \mathrm{GHz}$, intended for high-power backhaul applications. We show that a simplified equivalent circuit model can be used for accurate dimensioning of the coupler. The analytical model demonstrates a very good correlation with an electromagnetic field simulation and 4-port measurement results. The measured amplitude and phase imbalances in the desired frequency range are $\mathbf{0. 7 5} \mathrm{dB}$ and $89.5^{\circ} \pm 0.5^{\circ}$, respectively. The chip is implemented using GlobalFoundries 45RFE technology and occupies an area of $0.34 \mathrm{~mm}^{2}$, including pads.