High-low impedance transformer using transmission line method

In this paper, a simple transmission line method is proposed to precisely predict the center frequency of the compact high-low impedance transformer. It has been shown that the center frequency of the return loss stays at 3 GHz even though the electrical length θ_T reduces greatly. Besides, the compact high-low impedance transformer with θ_T = 60° yields 35.89% area-saving and maintains the same 15-dB bandwidth as compared with the conventional quarter-wavelength transformer. In order to verify the simulation results, back-to-back transformers are fabricated and measured where the measurement results are in good agreement with the simulation results.