Compact and Highly Efficient Kilowatt Lumped Push–Pull Power Amplifier for Cyclotron in Radioisotopes Production

Abstract

This article presents a very compact highly efficient solid-state power amplifier (SSPA) module at kilowatt level in a push-pull architecture. This SSPA is intended to be used as a modular RF source for a 20 kW cyclotron that operates in the low VHF band for radioisotopes production. For a compact design, a lumped LC balun is adopted instead of a traditional ferrite transformer for the 180° phase shift requirement of the push-pull architecture. Lumped harmonic traps are employed as harmonic tuning to achieve higher efficiency. This implementation enables an ultracompact design realized on a 90 mm x 70 mm circuit board. Improved efficiency at reduced output power is achieved through a static supply voltage variation, which gives more than 90% efficiency over a 5 dB output power range. This approach enables considerable energy saving when applied to the whole cyclotron system. The achieved results show that the proposed SSPA with drain supply modulation is a very promising architecture for very high-power RF sources in cyclotrons for radioisotope production.