Design of dual-band coupled-line balun

This paper presents a novel structure for the implementation of compact dual-band balun for multiple-band antenna application. Two stubs tapped to the two balanced ports in a conventional Marchand balun configuration facilitate the dual-band operation. Explicit design equations are derived using even-odd mode analysis. To verify the design concept, a microstrip balun operating at 0.9/2 GHz is fabricated on printed circuit boards. Measurement results are in good agreement with the theoretical predictions.