A Design Method for Reflective Analog Predistorter With Independently Tunable Gain

This letter proposes a design method for a reflective analog predistorter based on asymmetric loadings of a hybrid bridge. The amplitude and phase characteristics of the predistorter by tuning the two loadings can be intuitively presented on the Smith chart. By using the method, the load impedance of the two branches can be visually selected on the Smith chart to decouple the gain and phase characteristics of the predistorter. To validate the method, a predistorter is designed and fabricated at 3.4 GHz. The measurement results indicate that the tuning range of AM-AM is over 2.4 dB, and that of AM-PM is less than 0.8°. A power amplifier (PA) with a 20 MHz 64-QAM signal stimulated is linearized by the predistorter, and the adjacent channel power ratio (ACPR) can be improved by 13.4 dB.