On the Dual-Frequency Impedance/Admittance Characteristic of Multisection Commensurate Transmission Line

In this brief, first an interesting dual-frequency feature of a section commensurate transmission line (TL) is reported. The property concerns the impedance (or admittance) looking into a multisection TL terminated with real impedance. A rigorous mathematical analysis is provided to prove the existence of the property. Second, as an application, a novel multisection dual-frequency impedance transformer for the real impedance is presented. The proposed transformer can be used to provide matching over a much wider transformation ratio that is otherwise impossible to realize using the current state-of-the-art of dual-frequency transformers. The electromagnetic (EM) simulated and measured results exhibit good performance.