A 2-kW High-Efficiency and Broadband GaN Linear RF Power Amplifier for Multinuclear Magnetic Resonance Imaging

Multinuclear magnetic resonance imaging (MRI) requires high-power, broadband radio frequency (RF) amplification to transmit signals efficiently and linearly. In this study, we propose an innovative 2-kW highly efficient broadband gallium nitride (GaN) linear power amplifier designed for multinuclear MRI at 5.0 T, showing its first application in multinuclear MRI. The amplifier design is optimized through a multiobjective optimization load–pull analysis, enabling optimal impedance matching across a wideband range (30–300 MHz) to achieve high power, efficiency, and gain flatness. In addition, a broadband high-power combiner with compensation inductors was developed to enhance phase and amplitude consistency while optimizing return loss, insertion loss, and isolation. Furthermore, an adaptive frequency-based pre-compensation linearization technique was implemented to improve amplitude linearity. Experimental validations were performed for <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup>H and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>H spectroscopy and imaging at 5.0T MRI. The amplifier achieves 2-kW output power across 30–300 MHz with efficiencies of 68.1% (<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup>H), 70.3% (<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>H), 63.7% (<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">23</sup>Na), and 64.8% (<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup>P). Furthermore, gain variation and phase changes remain within ±0.9 dB and 10° over a 40-dB dynamic range. The proposed GaN amplifier offers broadband amplification and high efficiency, making it a suitable candidate for multinuclear MRI.