Investigation of a compact and broadband balun

Investigations indicate that the bandwidth and circuit size of a conventional branch‐line balun can be improved, where the bandwidth improvement is achieved by introducing a quarter‐wavelength short‐stub at one of the output ports and the size reduction is implemented by meandering the branches of a conventional balun. In this article, a planar balun with broadband bandwidth and compact size is proposed and confirmed, theoretically and experimentally. The results show that a circuit area is reduced to 47.4%, and when referring to a phase difference of ±10°, a flat coupling of over 30% is achieved from measurements, and within this phase difference, the magnitude imbalance is maintained within ±0.25 dB. Both simulated results and measured data are presented, and a good performance is observed. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1380–1384, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23361