Ultra-Compact Low-Loss Integrated Transformer-Based Ku-Band Quadrature Hybrid Coupler

In this paper, an ultra-compact transformer-based integrated quadrature hybrid coupler is presented. Its design, taking advantage of the transformer distributed parasitic capacitances to minimize lumped capacitors, achieves low insertion loss and high compactness. For demonstration purposes, a prototype, operating at Ku-band and based on the 130 nm BiCMOS technology from STMicroelectronics, has been fabricated. Theoretical, simulated and experimental results are reported. The demonstrated integrated coupler occupies an area as small as 0.0014 mm². In the 17.3 to 20.2 GHz frequency range (15.5% relative bandwidth) used for SATCOM applications, an insertion loss and a phase imbalance of better than 0.4 dB and 2° are experimentally obtained, respectively, with an amplitude imbalance of less than 1 dB.