Design of compact and broadband Wilkinson baluns using metamaterial phase shifting transmission lines

Abstract

A compact and broadband Wilkinson balun design incorporating three metamaterial phase shifting transmission lines (MTM-PSTLs) is proposed in this study. The two quarter wavelength lines generally used in a Wilkinson divider are replaced by -90° and +90° MTM-PSTLs for the broadband balun (balun #1) and by +90° and +270° MTM-PSTLs for the compact balun (balun #2). The characteristic impedance of the MTM-PSTLs is 70.7Ω. To improve isolation characteristics at output ports, a +180° MTM-PSTL with a characteristic impedance of 50Ω is connected in series with two 50Ω resistors between the two output ports. The designed baluns have the same size. The measured differential output phase bandwidths (180°± 10°) are 340MHz (55%) (445 - 785MHz) for balun #1 and 62MHz (30%) (174 - 236MHz) for balun #2.