Evaluation of RF power combination techniques at 800 MHz: Design, simulation, and experimental validation

Abstract

This paper explores various RF power combination techniques for a proton linear accelerator (linac) using a four-vane Radio Frequency Quadrupole (RFQ) operating at 800 MHz. The total power requirement is estimated via 3D simulations to be about 60 kW including the transmission line losses. This power is to be obtained by merging output from two independent power supplies using TH582 and TH382 tetrode tubes fed by two identical solid-state power amplifiers providing up to 2.5 kW, and triggered by a common RF source. The whole system operates with a pulse length of 10 mu s at with a repetition rate of 1 Hz. We investigated three approaches for power combination: a 3 dB hybrid coupler, a T-coupler, and a magic-Tee junction. Each method was analyzed through detailed simulations to evaluate performance metrics such as power distribution, insertion loss, and phase stability. Based on the simulation results, we selected the most efficient configuration, which was subsequently built and tested. Low-power measurements using a Vector Network Analyzer (VNA) were conducted to validate the performance of the chosen design, comparing the experimental data with the simulation outcomes. The results demonstrate effective RF power combination with minimal losses, high isolation and efficiency of close to 97%, confirming the suitability of the magic-Tee which is an original design, method for use in high-power applications within the 800 MHz proton linac system.