Novel technique for performance improvement in impedance-transforming planar Marchand baluns

A new technique which significantly improves the performance of a microstrip Marchand balun is described in this paper. The technique uses a series capacitor at the unbalanced input port to improve the matching bandwidth and inductors at the ground connections to greatly improve amplitude/phase balance. The technique is demonstrated with experimental results of a 50-150 Ω balun at 900 MHz. The measured results show amplitude/phase tracking within 0.1 dB and 1 degree over a 40% operating bandwidth.