Design and development of 40-port coaxial line based radial RF power combiner at 325 MHz

Development of pulsed Solid State RF Power amplifier (SSPA) of the order of few hundreds of KW at 325 MHz is under progress at RRCAT for Indian Spallation Neutron Source (ISNS) program. As output power of solid state RF MOSFET devices is moderate, design of efficient RF power combining structures is a mandatory requirement for SSPA. As a part of this system, 40-port radial power combiner have been successfully designed, developed and characterized at 325 MHz with power handling capability of 80 kW pulsed RF (Pulse width 1-5 ms, repetition rate-50 Hz). This 40 port power combiner has output at 3 1/8 inch rigid coaxial line and 40 inputs at Ntype connector. More than 50 kW of pulsed RF output is very much feasible from single SSPA unit by combining 40 nos. of previously developed pulsed RF 1.8 kW solid state RF amplifier modules in a single step with this 40 port power combiner. Amplitude and phase symmetry better than ± 0.1 dB and ± 1 deg respectively, have been achieved among 40 input ports successfully. This paper discusses detailed RF design aspects, low power and high power RF measurements for this 80kW pulsed RF, 40- port RF power combiner. (author)