Dual-frequency impedance transformer with a transmission zero

This work presents a shunt-stub dual-frequency transformer with a controllable transmission zero. The transformer is used to connect two circuit modules. The output circuit module has different input complex impedances at two uncorrelated frequencies. The proposed transformer not only provides a good match between the two circuit modules, but also generates an additional transmission zero such that some unwanted signal can be suppressed. The proposed impedance transformer has two configurations. Both configurations consist of cascaded transmission lines and shunt open stub that is the cause of the additional transmission zero. The numerical simulation shows a good performance satisfying the desired specifications.