Impedance-Transforming 3-dB 90° Hybrids

Design techniques and performance results for impedance-transforming branch-line and coupled-line 3-dB 90° hybrids are discussed, and designs equations for a single-section impedance-transforming branch-Iine coupler are presented. Test results for a 50- to 25-Omega branch-line hybrid show approximately 20-percent bandwidth at a 5.4-GHz center frequency with 3.15+-0.25-dB amplitude balance. A. broad-band hybrid with 50- to 20-Omega impedance transformation has also been realized by tandem connection of coupled-line sections. Measured results show an amplitude balance of 3.7+-0.68 dB over the 3-5-GHz range for a section coupling of 11.44 dB. The amplitude balance is improved to +-0.2 dB for a design with section coupling of 12.1 dB. Test results for a 50-Omega tandem hybrid are also presented.