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

R. Tong1, O. Bengtsson2, J. Olsson3, A. Bäcklund4, and D. Dancila1

Published in:

IEEE Trans. Microwave Theory Tech., vol. 70, no. 2, pp. 1401-1409 (2022).


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.

1 Division of Solid State Electronics, Department of Electrical Engineering, Ångström Laboratory, Uppsala University, 75236 Uppsala, Sweden
2 Ferdinand-Braun-Institut gGmbH, Leibniz-Institut für Höchstfrequenztechnik, 12489 Berlin, Germany
3 Department of Materials Science and Engineering, Uppsala University, 75103 Uppsala, Sweden
4 GEMS PET Systems AB (General Electric Company: GE Healthcare), 75228 Uppsala, Sweden

Index Terms:

Drain supply control, high efficiency, kilowatt, laterally-diffused metal-oxide semiconductor (LDMOS), power amplifier, RF energy.

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