Triple‐band impedance transformers using equal‐length serial transmission lines

Abstract

A new formulation of the fundamental load impedance circuit in the z -plane is employed to study transformers. The design employs prototypes of transfer function, parametric modelling techniques, and optimisation methods; a model describing multisection transmission-line transformers is proposed to match load impedance for use in wireless and mobile communication applications. Configuration of the transformer consists of multisection serial transmission lines. This transformer was designed on a PCB FR4 substrate featuring a permittivity of 4.4, a loss tangent of 0.0245, and a thickness of 1.6 mm. Microstrip line circuits were fabricated to verify the feasibility of the technique. The simulation and measurement results show that real and complex load impedances can be matched simultaneously at three different frequency bands. The characteristic impedance values of the transmission lines synthesising the transformers were adjusted according to the autoregressive process by using optimisation algorithms. The experimental results are in agreement with theoretical values.