COMPLEX IMPEDANCE TRANSFORMERS BASED ON BRANCH-LINE HYBRID COUPLERS

A topology, equations and design methodology for complex impedance-transforming branch-line hybrid couplers are presented. This method also allows the realization of real impedancetransforming to higher impedances. Limitations for real, imaginary and complex impedances are discussed. Test results are shown for a 3 dB 50 to 450 Ω hybrid coupler, at a 2GHz center frequency, with a 21% bandwidth, an amplitude balance of 4.35 ± 1 dB and a phase balance of 92.16◦ ± 8.8◦. To showcase the complex impedance scenario, two 3dB 50 Ω to 70 − 200j Ω are measured at a 2 GHz center frequency. One of these couplers uses a technique for reducing the chip size, yielding a 22.5% bandwidth, 4± 0.9 dB amplitude balance and 93.22◦ ± 6.74◦ phase balance, while accomplishing a 25% size reduction.