Broadband wilkinson balun using pure left-handed transmission line

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 righthanded (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.