Dual-band rat-race coupler with arbitrary power-split ratios

This study presents a dual-band rat-race coupler featuring two controllable center frequencies with arbitrary power-split ratios. Novel dual-band stub-loaded 90° lines were used to replace the conventional single-band 90° lines according to the required branch impedances for specific power-split ratios. The proposed structure has two degrees of freedom, providing more design flexibility and obtaining short lengths and realizable impedances. This research successfully synthesized a 2.4/5.2 GHz rat-race coupler with a 1:2 power-split ratio at dual bands. The measured results were well-correlated with simulation results.