Metamaterial-based Wilkinson balun using asymmetrical T-structure power divider for improving phase response flatness

In this paper, a new Wilkinson balun is proposed using the asymmetrical T-structure power divider connected with the metamaterial and conventional transmission lines at outputs to improve the phase response flatness. Since the asymmetrical T-structure power divider can be designed to provide a output phase difference, it can be applied to compensate the nonlinear phase difference between the metamaterial and conventional transmission lines. The Wilkinson balun is designed at the center frequency 1.5 GHz. Over the frequency range of 1.15-2.45 GHz, namely a 72.2% relative bandwidth, the phase difference of the developed Wilkinson balun is within 180±3°, and the amplitude imbalance is less than 0.6 dB.