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 band-width 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°, aflat 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.