A 2.4–3.5 GHz Broadband Analog Predistorter With Independently Tunable Gain

Abstract

This letter proposes a method for a broadband reflective analog predistorter (RAPD) with independently tunable gain. The predistorter is based on asymmetric loadings of a hybrid bridge. Constant-gain and constant-phase variation curves can be plotted in the Smith chart to analyze the amplitude-phase characteristics. Based on the constant-gain and constant-phase variation curves at different frequencies, a broadband RAPD can be designed. To validate the method, a predistorter was designed and fabricated at 2.4–3.5 GHz. The measurement results indicate that the AM-AM tuning range exceeds 2.1 dB across the entire frequency band, while the AM-PM is less than 2.8°. The predistorter was employed to linearize a broadband power amplifier. The experimental results demonstrate that under the excitation of a 20 MHz 64-QAM signal, the adjacent channel power ratio (ACPR) improves to below -45 dBc within the operating frequency.