A compact high efficiency 8Â kW 325Â MHz power amplifier for accelerator applications

A solid state RF power amplifier (SSRFPA) has been designed and developed for 8 kW RF power at 325 MHz. The work was carried out to achieve high efficiency (over 70% efficiency), high gain and compact size for the amplifier module. The sub-components of this amplifier like a 1 kW amplifier module at 325 MHz, an 8-way RF power combiner rated for 8 kW RF power and a micro-strip based power divider have been designed and developed in-house. The size of the amplifier is miniaturized by incorporating innovative design techniques and proper selection of the substrate material in the input/output matching networks. Measured power gain and conversion efficiency of the solid state RF power amplifier module at 1.06 kW output is 21.7 dB and 73.2%, respectively. A coaxial line based 8-way Wilkinson power combiner has been designed and developed. Return loss of the combiner at the output (combined) port is 26.4 dB at 325 MHz. Transmission parameters of the combiner from each input (splitting) port to output port are 9.1 dB±0.15 dB. This amplifier uses a pre-driver of 20 W and a driver amplifier of 150 W. Total power gain and efficiency of 8 kW SSRFPA have been 92.3 dB (including the driver stages) and 68.3%, respectively. The harmonic content in the RF output is less than −50 dBc for all the harmonics. Main features of this development are high power density (kW/cm3), large value for kW/module, high efficiency (68.3%) for 8 kW SSRFPA at 325 MHz and rugged operation.