A Dual-Band Impedance Transformer Using Pi-Section Structure for Frequency-Dependent Complex Loads

In this paper, a new approach to build a dual-band impedance transformer is presented. The transformer can handle impedances that are complex and vary with frequency. This transformer contains a Pi-section structure, which can be equivalent to having two different electrical lengths at the two operating frequencies. One of the electrical lengths serves as complementary angle of the other. In this way, the conjugate impedances obtained through previous process are transformed to real impedance concurrently. All parameters are derived from closed-form equations. In addition, several simulations as well as a fabricated power amplifier (PA) are presented to verify the proposed transformer. The measured result performs a good agreement with the simulated one in return loss and gain. This transformer may find use in different stages of a transceiver such as power amplifiers which operate at two independent frequencies.