Broadband Wilkinson balun using pure left-handed transmission line

Abstract

Utilizing the opposite phase shift property of a microstrip line (MSL) and a pure left-handed transmission line (PLH TL), the broadband Wilkinson balun is designed.The PLH TL without a right-handed (RH) branch is designed using effectively negative elements obtained by a cross connection of vias to ground. The PLH TL gives inherently phase-advanced response properties because of negative phase velocity, whereas a conventional MSL has a phase-lag response. The property of a broadband left-handed branch of a PLH TL applies to the implementation of broadband balun. The proposed balun has a good return loss, a good isolation between output ports, an equal-power division, and a 180° ± 10° phase difference in a wide fractional bandwidth of ∼71%. Furthermore, the wideband balun that has the fractional bandwidth of 107.8% is theoretically designed with the modified PLH TL having four unit cells. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1665–1668, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25242