A quad-band impedance transformer using two-section stubbed coupled line

Based on the stubbed coupled line for matching a load, we design an impedance transformer matched the load of ZL = 100Ω , working at four frequencies in this paper. This proposed transformer comprises two sections of coupled line constructed from parallel-coupled transmission lines. Two different types of the proposed transformer are given and analyzed, and we derive carefully about the open-circuit form equations for impedance transformer. We fabricate an impedance transformer to certify the validity of design equations theoretically, and the frequency is measured at 0.7/2.4/3.6/5.3 GHz. The measured results are in good agreement with the simulated results at each frequency.