Broadband Balun Using Fully Artificial Fractal-Shaped Composite Right/Left Handed Transmission Line

In this letter, a compact balun with bandwidth enhancement is firstly proposed based on fully artificial fractal-shaped composite right/left handed transmission line (CRLH TL). It consists of three -90° CRLH branches and one +90° CRLH branch. The left handed contribution is realized by chip components while the right handed part is exploited by fractal microstriplines in terms of miniaturization. For verification, a balun operating at 1.5 GHz is designed, fabricated, and measured. Numerical and measured results agree well, which has confirmed the design concept and the derived formulae. The fabricated balun exhibits a bandwidth of 83.3% from 1 to 2.25 GHz, characterized by return loss better than 10 dB, amplitude and phase imbalance varied within ±1 dB and ±3.4°. Moreover, the circuit footprint is only 24.5% of the area that its conventional counterpart occupies.