Modeling and Design of High-Power Non-Isolating RF Power Combiners based on Transmission Lines

• Main Authors: Zhang, Haoquan, Cassidy, Grace, Jurkov, Alexander, Luu, Ky, Kozitsky, Vladimir, Radomski, Aaron, Perreault, David J.
• Format: Conference Proceeding
• Language: English
• Subjects: Integrated circuit modeling; Loss measurement; magnetic core; Power combiners; power combining; power transformer; Power transmission lines; Propagation losses; Radio frequency; radio-frequency power amplifier; transmission line; Transmission line measurements
• ISSN: 2470-6647
• DOI: 10.1109/APEC43599.2022.9773770

Many industrial radio-frequency (rf) power applications are characterized by high power levels, narrow frequency ranges, and the need to combine rf power from multiple sources. In the HF frequency range (3-30 MHz) and above, power combiners based on coupled transmission lines are attractive due to their small form factor and high efficiency. However, most available literature on rf power combining with transmission-line structures focuses on frequency response, with little consideration regarding losses or efficiency optimization. This paper explores the design and optimization of lossless narrow-band rf combiners using transmission-line conductors. We introduce a lumped-element circuit model suited towards this application space, and further propose a tuning technique that, by adding two capacitors, minimizes impedance distortion while preserving high efficiency within a specified operating frequency range. A 1 kW combiner designed to operate around 13.56 MHz is prototyped, and a custom testbench is developed to measure its loss. The model and tuning technique are validated with both small-signal measurements and high-power tests. Improvements in impedance distortion from 1.19:1 to 1.03:1 VSWR is achieved (with 50\ \Omega load) through the proposed methods, and high combiner efficiency of >99.3% (