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