A 16:1 Bandwidth Planar Balun with Low Common Mode Impedance

This paper presents a wideband planar balun with a low common mode impedance. In differential mode, the balun has a return loss better than 10 dB from 0.7 GHz to 11.5 GHz, and an amplitude and phase imbalance better than 0.2 dB and 2°, respectively. The common mode impedance is close to a short circuit from DC up to 12 GHz, and the common mode suppression is better than 38 dB from DC up to 10 GHz. These features make the presented balun a promising candidate for push-pull power amplifiers.