Design of Filtering Power Amplifier Based on a Novel Band-pass Impedance Transformer

This article presents a novel band-pass filtering impedance transformer (BFIT) with the transformer ratio from 0.1 to 10. This BFIT is composed of two stepped impedance resonators (SIRs) which are cascaded and electric coupled. The analytical formulas and design steps of BFIT are given, and the impedance transformer (IT) is used in the design of a band-pass filtering power amplifier (PA). Finally, a 2.31-2.36 GHz band-pass filtering PA with measured drain efficiency of 54%-64% and large-signal gain of 11.2-11.5 dB is designed, fabricated and measured. Besides, the designed PA shows a good band-pass filtering characteristic, and achieves out-of-band suppression of 25 dB and 53 dB in the upper and lower sidebands.