Kilowatt Power Amplifier With Improved Power Back-Off Efficiency for Cyclotron Application

This article presents a highly efficient solid-state kilowatt level power amplifier implemented in laterally-diffused metal-oxide semiconductor (LDMOS) technology in a single-ended architecture. It is designed for power-combining systems of radioisotope production cyclotrons. To achieve high efficiency at high power as well as output power back-off (OPBO), waveform engineering is adopted to evaluate the performance of alternative efficient narrowband modes of operation in saturation with various drain supply voltages. Based on a large signal model, a multimode with Class-J/Class-F
⁻¹
properties is found to enable a flat 10 dB OPBO-range exceeding 90% drain efficiency. The implemented solid-state RF power amplifier (SSPA) module based on this waveforms analysis achieves 93% efficiency at 980 W output power and more than 90% efficiency over a measured 5 dB OPBO-range. Drain supply-controlled OPBO is shown to improve the efficiency by 15%-points at a 75% full power rating of the system, which is the estimated long-term average output power. The proposed operational mode will enable considerable energy saving for 24–7 cyclotron operation and is a very promising approach for other kilowatt narrowband applications with the need for efficient OPBO operation.