Analysis of a Π-Model-Based Filtering Complex Impedance Transformer with Controllable FBW

In this letter, a π-model-based complex impedance transformer (CIT) with two short-circuited stubs and a coupled line (CL) is proposed. The synthesis theory is developed by the ABCD matrix and S-parameter matrix. By controlling the lower and upper cutoff frequencies and the return loss (RL) of the S 11 within the passband, the CITs with different controllable fractional bandwidths (FBWs) are discussed and compared to verify the controllable FBW. Furthermore, the influence of the imaginary part of load variation on impedance matching performance is also discussed. Finally, a filtering CIT with a 50% FBW is simulated and fabricated to verify the feasibility of the synthesis theory.