This paper presents a novel structure for compact dual-band balun design. The proposed structure is based on modified Marchand (with the fourth port shorted). To achieve the desired dual-band operation, two additional open-ended stubs are added to the two balanced ports of the modified Marchand balun. Explicit design equations are then derived using even-odd mode analysis. Finally, to verify the design concept, a microstrip balun operating at 0.9/2 GHz are fabricated on Duroid RO3210 printed circuit board. Measurement results are in good agreement with the theoretical predictions.
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