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This paper presents a planar 90° branch-line coupler designed by replacing the quarter-wavelength transformers with coupled lines, which provides the proposed circuit with the ability to operate at two arbitrary frequencies. Explicit design formulas are also included. To validate the proposed design methodology, a branch-line coupler operated at 2.4 GHz and 4.9 GHz was designed and fabricated. The simulated and measured results are presented and show a good agreement with each other. In addition, area of the fabricated circuit is only 40% of the area of a conventional 90° branch-line coupler at 2.4 GHz.