Wideband Bandpass Filtering Impedance Transformer with Cascaded Coupled-line Sections for Complex Terminal Loads

This letter proposes a novel impedance transformer (FIT) that offers a wideband filtering characteristic while effectively matching complex impedances. The FIT is composed of a cascaded connection of two coupled-line sections, thereby enabling the presence of two transmission poles (TPs). Through the analysis of the circuit based on the transmission line theory, mathematical constraints are derived and summarized. Several design examples are given and compared in this letter. Finally, an experimental circuit is fabricated for verification, the measured and simulated results demonstrate a high level of consistency.