Quad-Band Impedance Transformer for Extremely High Load Impedance Matching with Out-of-Band Spurious Response Suppression

A novel approach to design a quad-band impedance transformer (QBIT) is presented. The primary purpose of this transformer is to match an extremely high load impedance to a source impedance of 50Ω at four distinct frequency bands with suppression of the spurious passband. The proposed QBIT is constructed using a π-shaped topology and two series microstrip-lines. The ABCD matrix method is employed to derive closed-form design formulas. The latter are employed to obtain the circuit parameters that allow for matching extremely high load impedances. For validation, two prototypes of QBIT realized to match 500Ω and 1500Ω loads are fabricated and measured. The simulated and measured transformer characteristics are in good agreement.