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A dual-band balun capable of providing inherent impedance transformation required for unequal terminations at the balanced and unbalanced ports is proposed in this paper. A systematic design analysis of the proposed balun is carried out to provide closed-form design equations for quick prototyping. Design cases are included to demonstrate the effectiveness of the developed design procedure. The proposed balun is capable of achieving a high frequency ratio (1.6<; r<; 5.0) and high impedance ratio (1<; k<; 10). A prototype operating at 1/2.6GHz and port terminations of 25Ω and 75Ω is fabricated for the evaluation of both the proposed design and the design procedure. An excellent agreement between the EM simulation and measurement results verifies the effectiveness of the dual-band operation of the proposed balun structure.