A Design Method for Analog Predistortion Linearizers With Independently Tunable Gain and Phase Conversions

In this paper, a design method for an independently tunable analog predistortion linearizer is proposed, which transforms the design of nonlinear circuits into the design of a load impedance network. First, inspired by the load-pull technique from power amplifier design, a systematic approach is introduced to determine the load impedance that achieves the required gain and phase conversion characteristics for a reflective analog predistortion (RAPD) linearizer. Then, two load curves are derived to determine the required load impedance enabling independent gain and phase conversions in the RAPD linearizer. Finally, a varactor-based variable load impedance matching network (VLMN) is designed,whose impedance varies with voltage in accordance with the calculated load curve. Using the proposed method, two RAPD linearizers for traveling wave tube amplifiers (TWTAs) have been designed and fabricated in the Ka-band (30-31 GHz) with independently tunable gain and phase conversions, respectively. The measured results demonstrate that the two linearizers exhibit independent tuning ranges of 3.9 dB and 28.6° for gain and phase conversions at 30.5 GHz, respectively.