A novel dual-band balun based on the dual structure of composite   right/left handed transmission line
  Utilizing the opposite phase shifting property of a standard Composite Right/Left Handed (CRLH) transmission line (TL) and a dual structure of CRLH (D-CRLH) TL, a dual-band balun is designed. The dual-band balun is formed by a 1x2 (3-dB) splitter with a D-CRLH phase-shifting line in the top branch and a CRLH phase-shifting line in the bottom branch. The performance of the balun is verified with circuit simulation at 2.4 GHz and 5.0GHz. The balun exhibits a very wide bandwidth for differential output phase, the return loss is well below -100dB, and the insertion losses |S12| and |S13| are around -3.03dB at both frequencies. 
Hu Xin, Zhang Pu, He Sailing