Design of Fully Integrated Impedance Transforming Multi-Winding 90° Coupler

In this paper, a design methodology for a fully integrated impedance-transforming multi-winding 90° coupler is proposed. The operation of the proposed coupler was verified using measurement results. These couplers were fabricated using the WIN semiconductor InGaP/GaAs heterojunction bipolar transistor (HBT) process. To provide an impedance transformation, the proposed couplers were designed with 3, 4 and 5 turn coils for 50-, 75-, and 100-Ω impedance transformations, respectively. The center frequencies of each coupler were 5.5, 3.33, and 2.47 GHz. Two copper metal layers were combined together with a via to attain a high Q factor, and its improvement was analyzed. The measurement results show that the insertion losses of the proposed couplers are less than 0.37 dB and phase imbalances are less than 2.74°.