A Novel Compact LC-Based Balun Combiner with 2nd and 3rd Harmonic Suppression

This paper presents a novel compact balun combiner based on lumped inductors and capacitors. In addition to the functions of harmonic reducing, power combining, and impedance matching, the new structure accomplishes both the 2^nd and the 3^rd harmonic suppression by constructing band-stop filters and cancellation pathways. The proposed topology is studied theoretically and demonstrated on an FR4 printed circuit board with the size of 2 cm×4 cm. Experiment results show that differential power combination is achieved with around 0.7-dB loss for each path when all three ports are loaded to 50 ohms at 1 GHz. The 2^nd harmonic suppression is more than 28-dB at 2 GHz and the 3^rd harmonic can be largely canceled out with equal amplitudes while opposite phase at 3 GHz. Furthermore, the topology can be applied in not only printed circuit boards but also monolithic microwave integrated circuits.