Optimized design of wideband Wilkinson balun using composite Right/Left-Handed Transmission Line

In recent years, metamaterials has become very popular, not only in microwave field but also others field, such as optical metamaterials, mechanical metamaterials etc. the popularity of metamaterials is result of special properties, which does not exist in natural materials (right-handed materials). Negative refractive index (NRI) is the most utilized property in RF field. This property is outcome of negative phase. Utilizing the opposite phase shift property of a microstrip line (MSL) and a Composite Right/Left-Handed Transmission Line (CRLH TL), the wideband Wilkinson balun is designed. The CRLH TL branch is designed using an interdigital capacitor and cross connection of the end-fingers through vias to ground. The CRLH TL gives phase-advanced response properties, when unit-cell is balanced because of negative phase velocity, whereas a conventional MSL has a phase-lag response. This property of a wideband CRLH TL branch applies to the implementation of wideband balun. The proposed balun is compared with balun implemented using Pure Left-Handed (PLH) TL [3]. The optimized balun has a good return loss below -14.09 dB and good isolation between output ports over range 2.2 GHz to 5.4 GHz. and equal-power division (−2.87 dB to -3.53 dB) the phase difference is 180±10° over range 2.34 GHz to 5.37 GHz and fractional bandwidth of 84.17% and size 28.52 mm X 20.3 mm.