A super-compact wideband balun composed of multi-layered CRLH transmission line

This paper proposes a super-compact wideband balun configured by a combination of a multi-layered (ML) composite right/left-handed (CRLH) transmission line (TL) and a conventional right-handed meander line. Quasi left-handed property of the ML CRLH TL is fully utilized for the phase design, leading to significant size reduction of the balun. The balun, with dimensions of 7.5 × 5.0 × 1.8 mm³, has been demonstrated theoretically in the frequency range from 5.0 GHz to 11 GHz (corresponding fractional bandwidth of 75 %). An amplitude imbalance was less than 2.0 dB (at 9.0 GHz) and a phase error was -7 to +5 degrees in this range.