A compact tri-band impedance transformer for frequency-dependent complex loads

A compact tri-band impedance transformer that can match the frequency-dependent complex loads is presented in this letter. The proposed transformer is cascade of a dual-band conductance transforming network, a dual-band susceptance stub network and a dual-to-tri-band transformer. There are four topologies of the transformer are available according to the different loads at the first frequency and the realizability of the transformer. All the parameters are acquired by solving the closed form design equations and a detailed design process is provided. The proposed design method is demonstrated through two examples, and a prototype is fabricated. Good agreement between the simulated and measured results is obtained. Compared with the existing works, the transformer not only can match the frequency-dependent complex loads, but also obtains wide bandwidths and has a very short electrical length. In summary, the proposed impedance transformer is very suitable for the design of tri-band active circuits and systems.