Novel Dual-Band Matching Network for Effective Design of Concurrent Dual-Band Power Amplifiers

In this paper, a systematic approach to the synthesis of a novel dual-band matching network is proposed and applied to design a dual-band power amplifier (PA) capable of maintaining high power efficiency at two arbitrary, widely spaced frequencies. The proposed network incorporates two different stages. The first one transforms the targeted complex impedances, at the two operating frequencies, to a real one. The second stage is a dual band filter that ensures the matching of the former real impedance to the termination impedance. An additional transmission line is incorporated between the two stages to adjust the impedances at the second and third harmonics without altering the impedances seen at the fundamental frequencies. The harmonic termination control is very effective in enhancing the efficiency of radio frequency transistors, especially when exploiting the Class J design space. The proposed dual-band matching network synthesis methodology was applied to design a dual band PA using a packaged 45 W Gallium Nitride (GaN) transistor. The PA prototype maintained a peak power efficiency of about 68% at operating frequencies of 800 MHz and 1.9 GHz. In addition, a Volterra based digital pre-distortion technique was successfully applied to linearize the PA response around the two operating frequencies.